Pyrometry Guide 20 Nov 12

Pyrometry Reference Guide Revision: 17-OCT-12

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Heat Treating Task Group

Pyrometry Reference Guide

PERFORMANCE REVIEW INSTITUTE 161 THORNHILL ROAD

WARRENDALE, PA 15086-7527 724-772-1616


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UTABLE OF CONTENTS

Contents

BACKGROUND .............................................................................................................. 3

OUTLINE ........................................................................................................................ 3

INTRODUCTION ............................................................................................................. 4

SECTION I – TEMPERATURE SENSORS (AKA T/C’S) ............................................... 6

Thermocouples........................................................................................................... 6

Correction Factors ..................................................................................................... 6

Guidelines for Temperature Sensors/Thermocouples ............................................ 8

Terminology for Temperature Sensors/Thermocouples ......................................... 8

Thermocouples and Their Usage .............................................................................. 9

SECTION II - INSTRUMENTATION .............................................................................. 11

SECTION III – THERMAL PROCESSING EQUIPMENT .............................................. 13

Other Issues – Parts vs. Raw Material .................................................................... 15 Nadcap INTERPRETATION ...................................................................................... 15

Use of Outside Calibration Sources ....................................................................... 16 Type A Instrumentation ........................................................................................... 17 Type B Instrumentation ........................................................................................... 18

Type C Instrumentation ........................................................................................... 19

Type D Instrumentation ........................................................................................... 20

Type E Instrumentation ........................................................................................... 21

SECTION IV – SYSTEM ACCURACY TESTS (SAT) ................................................... 22

Errors and Correction Factors ................................................................................ 22

SECTION V – TEMPERATURE UNIFORMITY SURVEYS (TUS) ................................ 25

Temperature Uniformity Requirements .................................................................. 25

SECTION VI – QUALITY ASSURANCE PROVISIONS ............................................... 30

SECTION VII - TABLES ............................................................................................... 31

SECTION VIII - DEFINITIONS ...................................................................................... 32

SECTION IX – FREQUENTLY ASKED QUESTIONS (FAQ) ....................................... 33


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PYROMETRY REFERENCE GUIDE

BACKGROUND

During the period that the Nadcap Heat Treat Task Group has been reviewing audits, we have found Pyrometry to be the least understood and the causes of the most problems and confusion. A recent study indicated aside from job audit NCRs, 8 of the top 10 NCR causes are related to Pyrometry.

However, Pyrometry is also the core and basis of all heat treatment practice.

We have prepared this guide to improve the understanding of Pyrometry and the performance of Pyrometric functions. It provides guidance and interpretations of AMS2750E, as well as fundamental Pyrometry principles and tells you what a Nadcap auditor will expect to see during an audit.

SCOPE: This guide is not intended to replace AMS2750E or waive any of its requirements or those imposed by customers. The following are Nadcap interpretations of the specification and these interpretations must be used only as guidance to the specification. Customer requirements may exceed those discussed here. It is the responsibility of the supplier to understand and comply with all customer requirements.

OUTLINE

This guide parallels the structure of AMS2750E by direct reference to its paragraph numbers. The Section headings are:

Temperature Sensors (usually Thermocouples, but also others)

Instrumentation

Thermal Processing Equipment

System Accuracy Tests (SATs)

Furnace Temperature Uniformity Surveys (TUS)

Quality Assurance Provisions

Definitions

FAQs

REMEMBER

You, the heat treaters, are ultimately responsible for the product and service you supply. Many heat treaters rely on outside sources to perform Pyrometry. While many of these sources are competent, the heat treater is still responsible for properly documenting the scope of the outside source’s work including specification references, and reviewing their work (and procedures) to determine that customer requirements are being met.


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INTRODUCTION

If you are a heat treater, you need to know what you need to know.

A furnace

Certain heat treating work to do for your customer

In order to be a successful aerospace heat treater, you may need to obtain….

Nadcap approval

Specific prime approvals

So then you will need…..

A contract review (flow down) process to understand and account for what your customer requires

A quality system, including calibration, control of product, inspection, etc. to ensure that you supply it. Nadcap requires AC7004 or AS9100 3rd party accreditation.

That’s all outside our scope in this document.

So….what IS in this Guide?

As a heat treater, you have special calibration requirements and – you need to know how to control your furnace temperature by Pyrometry.

What am I going to heat treat?

What temperatures will I be using?

What temperature tolerance does my customer require?

That determines your furnace classification

What type of temperature sensors will I need?

What kind of errors must be compensated for (correction factors)?

Will I elect to or be required to use load sensors/thermocouples?

That determines what thermocouples to use

How do I know that the temperature on my instruments is correct?

How is the accuracy of my temperature control and recording changing over time?

How often do I have to check it?

That determines the system accuracy of your furnace


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How large is my qualified working zone?

What is the variation of temperature around the set point in my qualified working zone?

How many test sensors (thermocouples) are required to check it and where are they to be placed?

How often do I have to check it?

That determines the temperature uniformity of your furnace

In addition, we will tell you what the Nadcap auditor will be looking for during the audit. You, as the supplier, must have a detailed procedure covering your means of compliance with customer requirements, including documentation. This is required whether you perform these calibrations (tests) yourself or subcontract it to an outside source.


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SECTION I – TEMPERATURE SENSORS (AKA T/C’S)

WHAT IS A THERMOCOUPLE?

WHAT IS A CORRECTION FACTOR?

Paragraph 3.1 of AMS2750E discusses Temperature Sensors. Tables 1 & 2 of AMS2750E summarize the entire subject.

Thermocouples

Thermocouples are the sensors that convey information about what temperature the furnace is operating at and/or what temperature the parts are experiencing. By their very nature, thermocouples have errors associated with them that must be corrected if you want to know the true temperature.

Correction factors are used to adjust the readings of thermocouples, which have some degree of error, to the actual (true) temperature. Your procedures must clearly state when and how you determine and use correction factors.

Correction factors are supplied with your thermocouple or thermocouple wire certification. You must be sure that you understand whether the certification is reporting error deviation or correction factor. Ask for the report in tabular format.

Correction Factors

Used in Temperature Uniformity Surveys and System Accuracy Tests

All certification and documentation must be completely clear and unambiguous, e.g. (for a wire roll calibration)

ACTUAL TEMP

Location INDICATED READING

ERROR Correction Factor

Average

1500°F

Front End/ Lead End /Outside

End

1502°F +2°F -2°F

-1.5°F average

Back End/ Lag End/

Inside End

1501°F +1°F -1°F

Otherwise deviation, correction, and error terminology gets mixed.

Documentation should always be set up so that you algebraically add the Correction Factor to the indicated reading to get the actual (true) reading.


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Interpolation (estimating between known points) is allowed, but extrapolation (estimating UbeyondU known points) is not allowed.

1500°F actual

← → 1700°F actual

← → 1900°F actual

→

Not allowed extrapolation

below

Interpolation allowed between

Interpolation allowed between

Not allowed extrapolation

above

Paragraph 3.1.2.5.1 of AMS2750E covers calibration temperature intervals for thermocouples. At which temperatures and at how many temperatures do the error or correction factor of my thermocouples need to be known.

Calibration of thermocouples (furnace, test, and load) is required by this paragraph to be performed at 250°F maximum temperature intervals. Calibration at smaller temperature intervals is allowed and may be advantageous in some circumstances.

When correction factors are used:

They may be calculated:

A) Using a mathematical ratio (interpolation) between documented values on the thermocouple calibration report (250°F maximum intervals).

B) Graphically by plotting the correction factor versus the temperature and reading the correction factor from the corresponding graph.

In both cases, the assumption made is that there is a straight line (correction factor varies linearly with temperature) between each calibration point, though this is not always the case – particularly with base metal thermocouples such as type K.

Alternatively, it is allowable to assume that the correction factor is that for the closest temperature of the 250°F range. The supplier must be consistent and the procedure must clearly define the method for choosing the correction factor. AMS2750 Udoes not require interpolationU of correction factors and suppliers are Unot required to interpolate for correction factors. Rounding per ASTM E29 to a whole degree is allowed to be applied at the final result only.

Correction factors may not be extrapolated above or below calibration data listed on the certifications. (i.e.: If the highest calibration temperature on a certification is 1800°F, correction factors for higher temperatures may not be extrapolated and the wire may not be used at higher temperatures).

The use of correction factors Uon load thermocouples U is optional (except where required by a specific customer). However, you must be consistent.

If you USE correction factors, then ALWAYS use correction factors!

If you DON’T USE correction factors, then NEVER use correction factors!


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Note: Load thermocouples are subject to System Accuracy Test (SAT) requirements using a method defined in AMS2750E section 3.4.4.

Guidelines for Temperature Sensors/Thermocouples

When ordering wire or thermocouples, be sure that:

Any prime specific requirements are known and incorporated into the P.O.

The end use is known (i.e., primary, secondary, test, furnace or load)

The desired thermocouple material type is known

The maximum range of use is known

The test point schedule is specified to the supplier.

Upon receipt, review the certification for compliance to P.O. requirements, especially the test point schedule. The Quality Assurance System requires that Quality Assurance reviews the certification report and documents the review.

The user must determine the thermocouple material type, construction (expendable/nonexpendable) & the end use before purchase.

Terminology for Temperature Sensors/Thermocouples

You should be familiar with the following terms. See AMS2750E section 2.2 for their definitions:

Base Metal Thermocouple

Expendable Thermocouple

Load Sensor

Noble Metal Thermocouple

Nonexpendable Thermocouple

Primary Test Sensor

Secondary Test Sensor

Test Sensors

REMEMBER: The user must determine the intervals between calibration temperature test points based on end use.

Acceptable practice may be defined as follows:

Calibration test points must be at temperatures and intervals determined by the end use. The lower test point must be equal to or less than the lowest value of the range of use. The upper test point must be equal to or greater than the highest value of the range of use. No interval between any two test points may be greater than 250°F, unless the thermocouples are to be only used at fixed points.


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Unacceptable practice may be defined as follows:

The lowest temperature calibration test point is greater than the lowest value of the range of use, or the highest temperature calibration test point is lower than the highest value of the range of use, or where any interval between calibration test points is greater than 250°F.

Remember: No Extrapolation!

Thermocouples and Their Usage

Paragraph 3.1 of AMS2750E covers UTemperature Sensors U and should be reviewed closely for the detailed requirements. Some of the key areas that should be studied include, but are not limited to:

Paragraph 3.1.1.4 - States thermocouple type selection with respect to temperature range usage.

FAQ3&4 Paragraph 3.1.1.5 - States that extension wire in new installations after

September 1, 2006 shall conform to ASTM E230 or national equivalent, and that connectors, plugs, jacks and terminal strips are permitted if they are the compatible type.

FAQ5-7 Paragraph 3.1.2 – Covers the calibration of sensors.

Paragraph 3.1.2.6 - States requirements for length and calibration of roll thermocouple wire and what to do if the roll does not meet the accuracy limits.

Paragraph 3.1.2.6.1 - States requirements for maximum length of a roll of thermocouple wire.

Figure 1, footnote 1 - IMPORTANT – In order to re-use Types K and E thermocouples

above 500°F (260°C) the depth of insertion shall be equal to, or greater than, depth of insertion of any previous use.

Paragraph 3.1.3 addresses requirements for reuse of thermocouples.

NOTE– This requires appropriate record keeping establishing that limits are maintained.

REMEMBER: Recalibration of Types K and E thermocouples that have been exposed to temperatures above 500°F (260°C) is UALWAYS U prohibited (Table 1, footnote 11).

Paragraph 3.1.3.5 - Reuse of base metal nonexpendable TUS T/Cs.

Paragraph 3.1.4 - States the requirements for Control, Monitoring, and Recording Sensors.

Paragraph 3.1.4.2.1 – When a Load Sensor is used as a Control Sensor, an expendable load thermocouple is limited to one use.


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FAQ8-10 Paragraph 3.1.5 - States the requirements for Load Sensors.

Paragraph 3.1.5.1 - Load sensors may be used as control sensors in accordance with 3.1.4.2. When a load sensor is used as a control sensor, no control, monitoring, or recording sensor shall exceed the maximum allowed processing temperature.

Paragraph 3.1.5.3 - The life of nonexpendable base metal load thermocouples shall be determined by the operating temperature(s). Records shall be maintained of the accumulated thermocouple use (furnace load cycle).


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SECTION II - INSTRUMENTATION

HOW DOES THERMOCOUPLE DATA GET USED FOR RECORDING AND CONTROL?

WHAT ARE THE REQUIREMENTS FOR INSTRUMENTS?

The instrumentation takes the electrical impulses (millivolt, emf) supplied by the thermocouples and converts them into a readable format.

Table 3 of AMS2750E details the requirements for Test and Furnace Instrumentation, and their Calibration Standards, including their use, calibration interval and accuracy, and what type of standard is required to calibrate the instrument.

Table 4 of AMS2750E lists the resolution (readability) requirements for furnace chart recorders. (See 3.2.1 for further clarification)

Table 5 of AMS2750E gives the requirements for printing and chart speeds for furnace recorders. (See 3.2.1 and 3.2.2 for further clarification)

Paragraph 3.2 of AMS2750E covers Instrumentation and should be reviewed closely for the detailed requirements. Some of the key areas that should be studied include, but are not limited to:

Paragraph 3.2.1 - Users shall review all instrument requirements in AMS 2750E as not all instruments approved for use in AMS 2750C will meet the requirements of AMS2750D and this revision.

FAQ11 Paragraph 3.2.1.1 - The following requirements (3.2.1.1.1 and 3.2.1.1.2) apply

to control, monitoring, or recording instruments purchased 1 year after September 2005, the issue date of AMS 2750D. Control, monitoring, or recording instruments purchased prior to September 2006 may meet the requirements of AMS 2750C until 3 years after the issue date of AMS2750E (until July 2015).

Paragraph 3.2.2 - Test instruments shall be digital and have a minimum readability of 1°F or 1°C.

Note: This also means that where test recordings are required such as with a Temperature Uniformity Survey (TUS) that the recordings and printings must also be digital and automatically recorded.

Paragraph 3.2.3.1 - At least one recording and/or controlling instrument for each zone shall have a minimum readability of 1°F or 1°C.

Paragraph 3.2.4 - deals with Offsets. Please study this paragraph and the sub-paragraph carefully if you are using offsets. Either manual or electronic offsets may be used as long as the method is detailed in a documented procedure and the offsets do not exceed the limits allowed in Tables 6 and 7, as applicable.


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Paragraph 3.2.5 – Deals with Instrument Calibration.

FAQ12 Paragraph 3.2.5.3 – All instruments must be checked for sensitivity.

Paragraph 3.2.5.5.1 - States to check the As-Found condition for calibration of controlling, monitoring and recording instruments shall be performed at a minimum of three simulated sensor inputs, minimum, maximum and the middle 1/3rd of the furnace Qualified Operating Temperature Range.

Paragraph 3.2.5.5.1.1 – States to report the As-Left condition following any adjustment and re-test.

Paragraph 3.2.5.5.2 - Calibration of each separate channel in instruments.

FAQ13&14 Paragraph 3.2.5.5.3 - States the requirement for annual verification of

recorder speeds.

Paragraph 3.2.5.6 – NEW – Deals with Wireless Equipment.

FAQ15 Paragraphs 3.2.6.1 and 3.2.6.2 - State explicitly that A) The calibration sticker

be affixed to the furnace instruments (or in close proximity), and B) the calibration report include the complete list of detail items included there.

Paragraph 3.2.7 - States the requirements for Electronic Records. If you utilize computer data acquisition type or recording equipment, this is a paragraph you should review carefully.


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SECTION III – THERMAL PROCESSING EQUIPMENT

DOES MY FURNACE HAVE THE PROPER UNIFORMITY AND INSTRUMENTATION FOR THE JOBS I WANT TO PROCESS?

FAQ16 Paragraph 3.3 of AMS2750E covers UThermal Processing Equipment U and

should be reviewed closely for the detailed requirements. Some of the key areas that should be studied include, but are not limited to:

FAQ17&18 Paragraph 3.3.1 – States that Furnace classes are defined in Figure 2 and

are based on the minimum requirements for temperature uniformity. Instrumentation types are based on the level of instrumentation used to control, record, or indicate the desired temperature. Frequencies for system accuracy tests, temperature uniformity surveys, and controlling, monitoring, and recording instrument calibrations are based on the furnace class and instrumentation type, and are summarized in (Table 3, 6, 7, 8, or 9).

Furnace Class Temperature

Uniformity Range (Degrees F)

Temperature Uniformity Range (Degrees C)

1 5 3

2 10 6

3 15 8

4 20 10

5 25 14

6 50 28

&FIGURE 2 - Furnace Classes

FAQ19 Paragraph 3.3.2 and Figure 3 describe what comprises the various

Instrumentation Types A, B, C, D, and E, respectively. The required instrumentation is for UeachU Control Zone in the furnace. Therefore, multi-zone furnaces will require multiple sets of the required instrumentation.

NOTE to EUROPEAN SUPPLIERS AND OTHERS WORKING TO CELSIUS (±5°C) most closely match Class 2, but the furnace must still meet the ±5°C uniformity requirement if required by a material or processing specification.

It should be noted that AMS2750E does not require any particular Instrumentation Type for any specific heat treatment application or use. These minimum requirements, if any, are driven by the applicable heat treatment or processing specification that references AMS2750 for Pyrometry requirements.

There are incentives for having higher Instrument Types namely longer intervals for System Accuracy Test (SAT) and Temperature Uniformity Surveys (TUS)


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It should also be noted that all Instrumentation Types, except for Type E require each furnace control zone to have over-temperature protection.

FAQ20 Paragraph 3.3.3 - Instrumentation - Refrigeration Equipment and Quench

Systems

This is changed from AMS 2750D, as there are new requirements for instrumentation of refrigeration equipment and quench systems.

Paragraph 3.3.3.2 – Existing quench systems installed prior to September 2005 do not require recording instruments until July 2015.

Unique Consideration for Vacuum Furnaces – Due to the unique heating considerations and instrumentation configurations of vacuum furnaces the following policy has been adopted by the Task Group in coordination with the AMEC AMS 2750 sub-team.

Paragraph 3.3.6 - For vacuum furnaces with 225 cubic feet or less in working volume that are instrumented with Types A, B, or C instrumentation per AMS 2750, it is acceptable to treat the furnace working volume as a single work zone for the purpose of locating high and low temperature recording thermocouples and determining the number of load thermocouples required regardless of the number of control thermocouples or instruments within the vacuum furnace. The minimum requirement is summarized in Figure 4:

Instrumentation Type

High Temperature T/C

Low Temperature T/C

Load T/C

A 1 1 1

B N/A N/A 1

C 1 1 N/A

Notes:

1. For the purpose of this Guide, a Vacuum Furnace is defined as a furnace capable of operating at any pressures lower than the atmospheric pressure (760 mm Hg).

2. SAT tests are required on all process sensors that input temperature information for control or recording purposes.


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Other Issues – Parts vs. Raw Material

Nadcap INTERPRETATION

The differentiation between “Part Heat treatment” and “Raw Material Heat Treatment” is a very controversial subject. It is the prerogative of each prime OEM to designate whether they consider certain material forms as either “Parts” or “Raw Material”. This controversy is most common with, but may not be limited to, castings and forgings.

There is a difference in the SAT and TUS testing frequencies IAW AMS 2750 between Part Furnaces and Raw Material Furnaces. It is the responsibility of the Supplier to be knowledgeable of the Parts vs. Raw Materials policy for each of their prime customers and be able to document this policy to the Nadcap Auditor. Some furnaces may be designated as “Part Furnaces” and other as “Raw Material Furnaces” as long as they are identified as such. If a Supplier wishes to designate all of its furnaces as “Raw Material”, then it must have concurrence on this interpretation from ALL of its prime OEM customers.

To ease the process of identifying what prime customers consider in general, the Task Group put together the following table which is a guide and is for information only:

UDoes your company consider Castings and Forgings parts or raw material?

COMPANY

CASTINGS AND FORGINGS

PARTS (When assigned a P/N or the hardware is subjected to

a final heat treatment) RAW MATERIAL

Alenia X

BAE Systems X Boeing

X

Cessna X

Eurocopter X

GE Aviation X

Hamilton Sundstrand X

Hawker Beechcraft X

Honeywell X

MTU X Parker X

Raytheon X Rolls-Royce Corporation X Sikorsky X Sonaca X Turbomeca X Vought X

Use the definitions from AMS2750E.


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Use of Outside Calibration Sources

You, the heat treater, must inform the outside Calibration source which of these Definitions apply to the heat treating you are to perform.

From this the calibration source can determine your requirements from the specifications invoked and the size of the furnace. You, the heat treater, will need to be able to supply evidence that you reviewed and approved the calibration source’s procedures, and that you also reviewed their certifications.


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Control Instrument Control Sensor Temperature Display Recording Instrument(s) High and Low Temperature Work Zone Sensors Minimum of One Recording Load Sensor

Over Temperature Protection

Control Instrument

Control Sensor

Over-Temp Sensor &

High Temp Monitor Part or

Raw Material

Load Sensor

Furnace Work Zone

Instrument Chart Recorder

Furnace Wall

Multipoint Chart Recorder or Separate Channel(s) in Instrument Chart

Recorder

Low Temp Sensor

Type A Instrumentation

High Limit Device (Required)

Note: May be used with the high temp sensor as shown.


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Control Instrument Control Sensor Temperature Display Recording Instrument(s) Minimum of One Recording Load Sensor


Control Instrument

Control Sensor

Over-Temp Sensor

Part or Raw

Material

Load Sensor

Furnace

Work Zone


Furnace Wall

Multipoint Chart Recorder or Separate

Channel(s) in Instrument Chart Recorder

Type B Instrumentation

High Limit Device

(Required)


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Control Instrument Control Sensor Temperature Display Recording Instrument(s) High and Low Temperature Work Zone Sensors


Control Instrument

Control Sensor

Over-Temp Sensor &

High Temp Monitor

Part or Raw

Material

Furnace

Work Zone


Furnace Wall

Multipoint Chart Recorder or Separate

Channel(s) in Instrument Chart Recorder

Low Temp Sensor

Type C Instrumentation

High Limit Device (Required)

Note: May be used with the high temp

sensor as shown.


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Control Instrument Control Sensor Temperature Display Recording Instrument


Control Instrument

Control Sensor

Over-Temp Sensor

Part or Raw

Material

Furnace

Work Zone


Over Temp Protection

(Required)

Furnace Wall

Type D Instrumentation


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Control Instrument Control Sensor

Temperature Display

Control Instrument

Zone

Control Sensor

Part or Raw

Material

Furnace

Work Zone

Furnace Wall

Type E Instrumentation


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SECTION IV – SYSTEM ACCURACY TESTS (SAT)

IS MY TEMPERATURE INFORMATION CORRECT?

This is simply an on-site comparison test performed to determine that the thermocouples, lead wire, and instruments are giving an accurate depiction of temperature. It also provides information as to changes in accuracy of the system over time. It works by comparing the control and/or recording thermocouples in each furnace control zone with a test thermocouple placed near the furnace thermocouple (control and/or recording). If all is well, the same result is obtained (within allowable error limits). If not, something is wrong and corrective action must be taken if the error exceeds allowable limits.

Definition from AMS 2750E:

Paragraph 2.2.62 - “System Accuracy Test (SAT) or Probe Check”: An on-site comparison of the instrument/lead wire/sensor readings or values, with the readings or values of a calibrated test instrument/lead wire/sensor to determine if the measured temperature deviations are within applicable requirements. Performed to assure the accuracy of the furnace control and recorder system in each control zone.

Errors and Correction Factors

Error is the deviation of the indicated reading of an instrument or sensor under test from the true value.

Example1: If the indicated temperature is 1000°F and the true temperature is 1002°F, the error is -2°F. To correct the error, you must reverse the sign of the error to make it the correction factor. Then you algebraically add the correction factor to the indicated treading. To correct the indicated temperature, you must add +2°F to 1000°F to get 1002°F.

Example 2: A Test Instrument reading a Test Sensor has an indicated reading of 1000.4°F. The calibration error for the Test Instrument is +0.1°F, and the calibration error for the Test Sensor is -0.3°F The corresponding correction factors are -0.1°F for the test instrument and +0.3°F for the test sensor.

To obtain the true temperature, you must add the correction factors to the indicated reading of the Test Instrument/Test Sensor combination in this way.

This is: 1000.4 + (-0.1) + (+0.3) = 1000.6°F.

NOTE: Some may choose to also correct for the furnace instrument and furnace sensor. This is not required and not recommended. However, if correction factors other than test sensor data are used, these correction factors must be used when reading all temperatures during production.


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NOTE: It is NEVER acceptable to use the same recorder for system accuracy tests as is used to record furnace data. The only exception would be if totally separate channels are used in the same instrument and they are independently calibrated with a field test instrument that meets the accuracy requirement of a secondary standard instrument. See Table 3 of AMS2750E.

The requirements for SAT frequency are listed in Tables 6 and 7.

Paragraph 3.4 of AMS2750E covers USystem Accuracy Tests (SAT) and should be reviewed closely for the detailed requirements. Some of the key areas that should be studied include, but are not limited to:

FAQ21 Paragraph 3.4.1 - States that SATs are performed on the temperature control

and recording systems in each control zone of each piece of thermal processing equipment. It further requires that SATs are performed on the additional recording systems (furnace and/or load) that qualify the furnace for Types A, B, or C, instrumentation.

FAQ22 Paragraph 3.4.2.1 – States that a new SAT shall be performed after any

maintenance that could affect the SAT accuracy. Examples include replacement of the thermocouple, replacement of controlling, monitoring and recording instrument, and recalibration of the instrument when any adjustment has been made. Quality Assurance shall be consulted for direction on whether specific maintenance requires a new SAT.

Paragraph 3.4.2.2 – States that a SAT is not required for:

A) sensors whose only function is over-temperature control; B) sensors not used for acceptance as part of production heat treatment.

Paragraph 3.4.3 and Table 6 or 7, as applicable - States the conditions where SAT frequency may be reduced within the limitations allowed.

FAQ23 Paragraphs 3.4.3.1 and 3.4.3.2 - Provisions for SAT frequency reduction:

FAQ24 Paragraph 3.4.3.2 – Weekly readings show that the relationship between the

control sensor and an additional monitoring or recording sensor in each control zone remains within 2°F (1°C) of their relationship at the time of the last Temperature Uniformity Survey.

Paragraph 3.4.5 – Describes the procedure/practice of SAT.

Para 3.4.5.1 - The displayed temperature indication and/or recording of the sensor being tested as used in production, with appropriate offsets or correction factors, at any operating temperature, shall be compared with the corrected temperature indication of the test sensor on a test instrument.


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Paragraph 3.4.5.2 – States that the tip (measuring junction) of the SAT sensor shall be as close as practical to the tip (measuring junction) of the controlling, monitoring, or recording sensor, but the tip to tip distance shall not exceed 3 inches (76 mm). Subsequent SATs shall utilize test thermocouple(s) placed in the same locations/positions/depth as the initial test. The SAT sensor may be inserted temporarily for the test or may be a resident test sensor, subject to the limitations of 3.4.5.2.1.

FAQ25 Paragraph 3.4.5.2.1 - Addresses the use of Resident SAT Thermocouples.

FAQ26 Paragraph 3.4.5.3 – The difference calculated between the reading of the

furnace sensor system being tested (sensor, lead wire, and instrument) and the corrected reading of the test sensor system (after test sensor and test instrument correction factors are applied) shall be recorded as the system accuracy test difference. Applicable correction factors shall be applied algebraically.

Examples in Paragraph 3.4.5.3.1 – Details the use of correction factors including when and how they may be applied depending on whether any electronic offsets have been introduced into the instruments. There are also several very good examples in Figure 6 that show how to calculate the SAT result.

Paragraph 3.4.5.4 – SAT tolerances listed in Tables 6 and 7 are requirements and these values must be met. There is no more of the “greater than 2°F, but less than 5°F” gray area. If the SAT does not meet the tolerance, the test is failed, corrective action must be taken, and a new SAT must pass before processing may continue in the furnace.

NOTE: The allowable SAT differences are now expressed as x°F or 0.x% of reading, whichever is greater. Example: 5°F or 0.5% of reading for a Class 5 furnace; at 1700°F, the allowable SAT difference is 0.5% of 1700°F or 8.5°F.

Paragraph 3.4.6 - States an alternative method for performing an SAT for sensors used only once (single use) or for multiple use sensors replaced at an interval shorter than the appropriate SAT interval.

FAQ27-29 Paragraph 3.4.7 - States the conditions where the SAT may be waived.

Note that all subparagraphs of 3.4.7 must be met to exercise the SAT waiver.

Note: Some Primes (i.e. SAFRAN Group) do not allow SAT Waiver.

Paragraph 3.4.8 - States an explicit list of items to be documented for the SAT test.


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SECTION V – TEMPERATURE UNIFORMITY SURVEYS (TUS)

IS MY TEMPERATURE OK THROUGHOUT THE ENTIRE FURNACE?

These tests are to ensure that there are no temperature variations outside acceptable limits from place to place within the Qualified Work Zone of the furnace.

Temperature Uniformity Requirements

UCalculation of the actual temperature uniformity is required for each test performed. The calculation is determined by taking the deviation of the corrected test sensor reading from the specified test temperature. It is not necessary to re-record the data from the digital charts data onto a table for each data point. It is sufficient to identify the highest and lowest temperature point on the actual digital chart data and apply the correction factors to those two data points, not the entire table. It is not necessary to re-type all the data points from the survey charts data.

It is allowable to offset the furnace control set point to center the uniformity as long as it does not exceed the limits of Table 6 or 7. Offset data from the uniformity survey can be used to “center” the temperature of parts being heat treated.

The requirements for TUS frequency are listed in Tables 8 and 9.

Paragraph 3.5 of AMS2750E covers UTemperature Uniformity Surveys (TUS) and should be reviewed closely for the detailed requirements. Some of the key areas that should be studied include, but are not limited to:

Paragraph 3.5.2 - States the concept of the Multiple Qualified Operating Temperature Ranges that may therefore have multiple, different Furnace Classes based on TUS.

Paragraphs 3.5.3 and 3.5.4 – Furnace Modifications and Furnace Repairs:

A) Furnace Modifications, where a new initial TUS must be performed; and B) Furnace Repairs, where a new initial TUS need not be performed.

The important feature of this paragraph is: “All furnace modifications shall be documented and the responsible Quality Assurance organization shall make the determination whether an initial TUS is required based on the modifications made and the particular furnace configuration.”

Paragraph 3.5.5 - Requires that the initial TUS is performed at the minimum and maximum temperatures of the Qualified Operating Temperature Range(s), and at intervals of no more than 600°F (335°C) in between.

FAQ30 Paragraph 3.5.6 – States that periodic survey temperatures shall be any

temperature within each Qualified Temperature Operating Range(s).


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Paragraph 3.5.6.1 – NEW – For single operating ranges greater than 600°F (335°C), TUS temperatures shall be selected so that one temperature is within 300°F (170°C) of the maximum and another temperature is within 300°F (170°C) of the minimum qualified operating range and there are no more than 600°F (335°C) increments in between. Additionally, at least once within each calendar year periodic tests shall be performed at the minimum and maximum temperatures of each Qualified Operating Temperature Range.

Paragraph 3.5.7 –States that survey frequency shall be in accordance with Table 8 or Table 9

Paragraph 3.5.7.1- States that extended TUS intervals are based on both instrument type and history of the required number of successful surveys. In addition, a documented preventive maintenance program shall be in effect.

Paragraph 3.5.8 - States that all parameters used during TUS, except as outlined in 3.5.9, 3.5.10, 3.5.11 and 3.5.12 shall reflect the normal operation of the furnace and equipment in production.

Paragraph 3.5.10 - States that a TUS may be performed with an actual production load, simulated production load, a rack, or empty. Once a method of surveying a furnace is established during an initial TUS, subsequent surveys shall be conducted using the same method. If changes are made to the established method, an initial TUS shall be performed to validate the revised method.

Paragraph 3.5.10.1- States that if the TUS is performed empty or with a rack, and if TUS sensors are attached to or inserted into heat sinks, the side-to-side thickness or the diameter of the heat sink shall:

A) Not exceed 0.5 inch (13 mm), and B) Not exceed the thickness of Uthe thinnest material being processed in that

furnaceU. Heat sink material shall be the material with the highest room temperature thermal conductivity consistent with the predominant material processed in the furnace.

FAQ31 Paragraph 3.5.10.2 - When the TUS is performed with a load, and the TUS

sensors are attached to simulated product or parts, the load shall represent the thickness of the material normally processed.

Paragraph 3.5.11 – States that the furnace atmosphere during a TUS shall be the normal atmosphere used for production. Furnaces used for those processes whose required atmospheres could contaminate the test sensors (i.e., carburizing, Nitriding, endothermic, and exothermic) or atmospheres that could pose a safety hazard (i.e. hydrogen or ammonia containing) may be tested with an atmosphere of air or inert gas.

Paragraph 3.5.12 - States that the furnace vacuum level during TUS on vacuum furnaces shall be run at the lowest vacuum level used in production, but need not be less than 1 micron Hg (1 × 10-3 Torr, or 1.3 × 10-3 millibar).


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FAQ32 Paragraph 3.5.13.3 TUS Data Collection: Please review carefully.

Paragraph 3.5.13.3.1 - States that data collection shall begin before the first furnace or TUS sensor reaches the lower tolerance limit of each test temperature so that any furnace or TUS sensor exceeding the upper temperature uniformity tolerance is clearly detected. If the furnace is prestabilized, data collection shall begin as soon as the test load or rack is loaded in the furnace.

FAQ33&34 Paragraph 3.5.13.3.2 – States that once data collection begins,

temperature data shall be recorded from all TUS sensors at a frequency of at least one set of all readings every 2 minutes Ufor the duration of the survey. Data from furnace sensors required by the applicable instrumentation type (see 3.3) shall be recorded as follows: (Sensors whose only function is over temperature protection do not need to be recorded).

a) If the normal interval of temperature data recording in production is 2 minutes or less, or is continuous as in the case of analog recorders, the data shall be documented in the normal production format.

b) If the normal interval of temperature data recording in production is greater than 2 minutes, the recording frequency interval during TUS shall not exceed 6 minutes.

Note: Since paragraph 3.2.2 requires Digital Test Instrumentation, this also implies that Recording Test Instrumentation such as used for the performance of Temperature Uniformity Surveys (TUS) must also be digital.

FAQ35 Paragraph 3.5.13.4 – Describes the alternative probing method for performing

a TUS in Salt Baths, etc.

Paragraph 3.5.14 – States the requirements for performing a TUS on Continuous and Semi-Continuous Furnaces, by either the Volumetric Method, or the Plane Method, and the data collection requirements associated with these methods.

Paragraph 3.5.15 – Describes the alternative test methods for performing a TUS on Continuous, Semi-Continuous Furnaces or Furnaces with Retorts and Muffles including the Probing Method and the use of Property Surveys in lieu of performing a TUS.


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FAQ36 Paragraph 3.5.16 - States provisions for Temperature Uniformity Survey

Sensor Failures: No TUS sensor failures at the corner locations of the work zone are permitted. A temporary condition such as a short or loose connection where normal temperature readout is restored shall not be considered a failed survey thermocouple. Failure (see 2.2.19) of a TUS sensor (except at a corner location) during a TUS need not be cause for survey failure unless:

A) 2 adjacent TUS sensors fail or B) The number of TUS sensor failures exceeds the following:

• Survey with 3 to 9 sensors: No failures • Survey with 10 to 16 sensors: 1 failure • Survey with 17 to 23 sensors: 2 failures • Survey with 24 to 39 sensors: 3 failures • Survey with 40 or more sensors: No more than 10% failures

For test temperatures of 2000°F (1093°C) and above:

• Survey with 3 to 5 sensors: No failures • Survey with 6 to 9 sensors: 1 failure • Survey with 10 to 16 sensors: 2 failures • Survey with 17 to 23 sensors: 3 failures • Survey with 24 to 39 sensors: 4 failures • Survey with 40 or more sensors: No more than 10% failures

Paragraph 3.5.18 – States that when the hottest and coldest temperature locations change within the furnace (based on the final readings from the most recent Temperature Uniformity Survey), the monitoring sensors locations for types A and C instrumentation may need to be moved within the furnace to reflect the new hottest and coldest locations within the work zone. These sensors do not require relocation if the overall temperature uniformity does not exceed one half of the maximum temperature uniformity tolerance for the applicable furnace class at all temperatures surveyed, or if the difference between the measured temperature at the current recording locations and the actual respective hottest and coldest measured areas is less than the system accuracy test (SAT) tolerance for the applicable furnace class.

FAQ37 Paragraph 3.5.19U - Failure of a TUS.

Paragraph 3.5.19.1.1 - States that for equipment tested at extended interval, failure of a temperature uniformity survey shall cause the test frequency to revert to the initial test frequency specified in Table 8 or 9. Interval shall not be extended until the specified number of successful consecutive tests in Table 8 or 9 have been completed.

FAQ38 Paragraph 3.5.19.1.2 - States what must be done if the form of corrective

action for a failed survey is adjusting (offsetting) the control instrument.

Paragraph 3.5.20.2 – The TUS instrument correction factors must be incorporated in the final TUS calculation.


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Paragraph 3.5.21.1 - States that a Temperature Uniformity Survey Report must contains an explicit list of items, and states additional information that must be accessible to supplement the TUS report.

Paragraph 3.5.22 – States that surveys performed prior to the issue date of this revision, in accordance with previous AMS 2750 revisions, may be considered equivalent to tests performed in accordance with this revision for the purpose of qualifying furnaces for (1) waiving initial temperature uniformity tests or (2) reducing frequency of periodic temperature uniformity tests.

Paragraph 3.5.23.1 – Radiation test sensors(s), when performing a radiation test, shall be added to the normal survey sensors.

Paragraph 3.6 - States unique requirements for Laboratory Furnaces used for “response to heat treating testing” per material specifications.

Paragraph 3.7.1 – States that all calibration and test records including sensors, standard cells and instruments, system accuracy tests, and temperature uniformity surveys, including any test or survey failures shall be available for inspection and maintained for not less than 5 years (or in accordance with customer requirements, whichever is greater).

Paragraph 3.7.2 – States that calibration records of sensors, standard cells, and instruments shall include traceability to the NIST or equivalent National Standard.


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SECTION VI – QUALITY ASSURANCE PROVISIONS

What are my obligations to my Quality Assurance System?

Paragraph 4.1 - States that the processor shall be responsible for the performance of all required tests and for conformance to all requirements specified herein. The purchaser reserves the right to witness any of the tests or calibrations specified herein to ensure that processing conforms to the prescribed requirements, but such witnessing shall not hinder operation of the facility.

Paragraph 4.1.1 - States that any instrument/sensor/test failing to meet these requirements, or that has exceeded its test interval including any applicable permissible extension period (see Table 10), shall be taken out of service.

Paragraph 4.1.1.1 - States that corrective action shall be documented including the actions taken to bring the instrument/sensor/test into compliance.

Paragraph 4.2 - States that in the event of any test failure or out-of-tolerance condition, an evaluation of the possible effects of the non-conformance on product processed since the last successful corresponding test shall be performed and documented. The evaluation shall be documented per established material review procedures. Appropriate corrective action shall be taken, documented and maintained on file. When material processing conditions deviate from specification requirement affected purchaser(s) shall be notified.

Para 4.2.1 - States that a conforming corresponding tests shall be required as evidence of adequate corrective action.


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SECTION VII - TABLES

TABLE 1 – SENSORS AND SENSOR CALIBRATION TABLE 2 – THERMOCOUPLES AND EXTENSION WIRE

TABLE 3 – INSTRUMENTS AND INSTRUMENT CALIBRATION FAQ39&40

FAQ43

TABLE 4 – RESOLUTION REQUIREMENTS FOR CHART RECORDERS

(ANALOG CHART RECORDING INSTRUMENTS)

TABLE 5 – PROCESS RECORDER PRINT AND CHART SPEEDS FAQ41&42

TABLE 6 – PARTS FURNACE CLASS, INSTRUMENT TYPE, AND SYSTEM

ACCURACY TEST (SAT) INTERVAL FAQ43 FAQ44 FAQ45

TABLE 7 – RAW MATERIAL FURNACE CLASS, INSTRUMENT TYPE, AND

SYSTEM ACCURACY TEST (SAT) INTERVAL FAQ43 FAQ44 FAQ45

TABLE 8 – PARTS FURNACE CLASS, INSTRUMENT TYPE, AND

TEMPERATURE UNIFORMITY SURVEY INTERVAL FAQ43

TABLE 9 – RAW MATERIAL FURNACE CLASS, INSTRUMENT TYPE, AND

TEMPERATURE UNIFORMITY SURVEY INTERVAL FAQ43

TABLE 10 – PERMITTED CALIBRATION/TEST INTERVAL EXTENSION FAQ46

TABLE 11 – NUMBER OF TUS SENSORS REQUIRED FOR BATCH FURNACES,

SALT BATHS, CONTROLLED TEMPERATURE LIQUID BATHS, FLUIDIZED BED FURNACES, OR CONTINUOUS FURNACES TESTED USING THE VOLUMETRIC METHOD


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SECTION VIII - DEFINITIONS 9B

What do all of these terms mean?

FAQ1 Section 2.2 of AMS 2750E has a list of 79 Pyrometry terms and their definitions

that are used in that Specification and in Pyrometry in general.

FAQ2 Paragraph 2.2.30 - “Measuring Junction”: That area of a thermocouple joined

together to complete a measurement circuit, which is used to measure an unknown temperature. Also it is called the hot junction.

Paragraph 2.2.34 - “Nonexpendable Thermocouples”: Thermocouples that are not covered with fabric or plastic insulations. One type consists of ceramic insulators over bare thermocouple wire, sometimes inserted in a tube for stability and protection. A second type consists of a combination of thermocouple wires, mineral insulation, and a protecting metal sheath compacted into a small diameter. The thermocouple thus constructed is protected, flexible and, within the temperature limits of the sheath material, may be used many times without insulation breakdown.

Paragraph 2.2.45 - “Raw Material Heat Treatment (e.g., sheet, plate, bar, extrusions, forgings, castings)”: Heat treatment performed by or for the raw material producer and product is tested as required by a material specification.

Paragraph 2.2.46 - “Raw Material Furnaces”: Equipment used by or for a material producer (or an approved supplier of a material producer) in accordance with a material specification which may require by reference conformance to a heat treating specification.


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SECTION IX – FREQUENTLY ASKED QUESTIONS (FAQ)

Reference AMS 2750E

Disclaimer note:

The following FAQs represent solely the PRI/Nadcap interpretation of AMS 2750E until any future revision will be made available by the SAE. The actual interpretations do not intend to override the specification’s requirements. For a proper interpretation of the specification’s requirements, please address your inquires to the AMEC committee who wrote the specification. 1) Paragraph 2.2.18 - Basically, an expendable thermocouple has plastic or woven insulation and a nonexpendable has the thermocouple wire protected inside of a metal or ceramic sheath. How does the task group categorize an expendable thermocouple protected inside of a metal sheath tube? Response: A thermocouple user could arrange thermocouples and/or thermocouple wire in a variety of different configurations. It is best to avoid any potential for misinterpretation or confusion incurred by attempting to redefine expendable vs. nonexpendable based on specific user configurations. For AMS 2750 applications, the condition in which a thermocouple is purchased shall dictate whether the thermocouple

is expendable or nonexpendable. Back

2) Paragraph 2.2.30 - Revision E does not provide any guidance (or requirements) on the allowable methods to make the “measuring junction” (expendable thermocouples). A number of methods are employed, i.e., twisting only, twisting and welding, twisting and banding, etc. Are there any specific recommendations or requirements? Response: AMS 2750E is silent on the subject of making the measuring junction. It is incumbent upon the supplier to use a method that is suited for the application of the

thermocouple. Back

3) Paragraph 3.1.1.5 - For connecting thermocouple wire to lead wire or splicing lead wire, it is designated that: “Connectors, plugs, jacks and terminal strips are permitted if they are the compatible type, i.e. they have thermoelectric properties conforming to the characteristics of the corresponding thermocouple type.” Is it acceptable to use silver solder to make thermocouple wire joint connections, or thermocouple wire to lead wire joint connections? Response: AMS 2750E referenced publications controlling use of thermocouples and extension wire do not include provisions that would allow the use of silver solder as a wire joint connection method.


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4) Paragraph 3.1.1.5 - We use thermocouple wire as extension wire with our furnace systems. Is it necessary to have the calibration certification for thermocouple wire used as extension wire? Response: It is not required that calibration certificates be maintained for thermocouple wire that is used solely as extension wire in furnace control, recording, and monitoring systems. In this application thermocouple wire serves as a conductor. Acceptable function of thermocouple extension wire will be verified during system accuracy testing

of furnace control, monitoring, and recording systems. Back

5) Paragraph 3.1.2.4 - Paragraph 3.1.2.4 states: “Users shall have supporting data such as, but not limited to, SAT, TUS, and re-calibration data and written procedures controlling the replacement of sensors including limits on maximum life and/or number of uses, as applicable.” Does this declaration imply that the heat treater must have a replacement schedule for controlling, monitoring, and recording thermocouples in a furnace? Response: AMS 2750E does not place any restrictions on the length of time that a controlling, monitoring, or recording thermocouple may be used (with the exception of applying provisions for implementing a SAT waiver as presented in Paragraph 3.4.7). However, the heat treater is reminded that AC 7102 requires that a preventative maintenance plan be in place for each item of heat treat processing equipment. The primary purpose of preventative maintenance is to avoid or mitigate the consequences of failure of equipment or equipment components. Therefore, to preclude failure (excessive drift, etc.) of controlling, monitoring, and recording sensors, the heat treater shall have a schedule for replacement of those sensors. The replacement frequency is determined by the heat treater based on historical data that supports the replacement

frequency (i.e., a replacement time interval that precludes failure of the sensor). Back

6) Paragraph 3.1.2.5 - What is considered acceptable for use of thermocouple sensors with respect to the bottom and top of the calibration range? For example, is it

allowed to use thermocouple wire calibrated at 1000°F, 1250°F, 1500°F, 1750°F, and

2000°F (542°C, 682°C, 822°C, 962°C, 1102°C) to perform a TUS at 1000°F (542°C) or

2000°F (1102°C)? It would be expected that a TUS at 1000°F (542°C) would include

some TUS test temperature values below the lower sensor calibration temperature of

1000°F (542°C) and that a TUS at 2000°F (1102°C) would include some test

temperature values above the upper sensor calibration temperature of 2000⁰F (1102°C).

Response: It is acceptable to apply the minimum and maximum of the sensor calibration range as nominal values relative to furnace “set point” temperatures. To illustrate with examples from the question: It is acceptable to use thermocouples with a lower calibration temperature of 1000°F (542°C) for conducting a TUS on a furnace with a set point of 1000°F (542°C) and a temperature tolerance requirement of ±25°F (±14°C). Likewise it would be acceptable to use thermocouples with an upper calibration temperature of 2000°F (1102°C) to perform a TUS with a set point of 2000°F (1102°C) and a temperature tolerance requirement of ±25°F (±14°C).


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7) Paragraph 3.1.2.5.1 – What is the definition of the term “calibrated at fixed points?” Response: Fixed point calibration as referenced in ASTM MNL 12, UUse of Thermocouples in Temperature Measurement, is a method for calibration of thermocouples using the freezing point (or sometimes melting point) of various materials as temperature standards. The method is more commonly used in the calibration of noble metal standard thermocouples. Most base metal thermocouples are calibrated using comparison methods. 8) Paragraph 3.1.5.1 - It is stated that, “Load sensors may be used as control sensors in accordance with 3.1.4.2. When a load sensor is used as a control sensor, no monitoring or recording sensor in or representing the work zone shall exceed the maximum allowed processing temperature.” It is assumed that this paragraph is not applicable to retort furnaces. When using a load thermocouple to control temperature in the retort it would not be uncommon to have sensors outside of the retort that showed temperatures exceeding the upper limit of the process temperature tolerance range. Response: That assumption is correct. The sensors referenced in 3.1.5.1 are intended to be sensors that measure work zone temperature (with the work zone obviously inside of the retort). Paragraph 3.5.13.3.4 provides additional clarification by stating, “When a retort is used, the temperature of the furnace in which the retort is inserted shall be controlled so that the specified heat treating temperature is maintained within the retort.” AMS 2750E recognizes retort furnaces and related considerations in multiple paragraphs. 9) Paragraph 3.1.5.2 - Paragraph 3.1.5.2 limits the life of expendable base metal load

thermocouples to a single use at temperatures above 1200°F (650°C). However, the

same nonexpendable wire types could be used up to 15 times at temperatures between

1200°F (650°C) and 1800°F (980°C) for conducting temperature uniformity surveys.

Why is there so much disparity in reuse provisions between the two applications? Some individuals reason that the more restrictive reuse provisions should apply to TUS thermocouples instead of load thermocouples. Response: Based on an individual’s specific background, there are numerous approaches to interpretation of general requirements relating to heat treating. AMS 2750E was written by Aerospace Materials Engineering Committee, Materials Group Committee B. AMS 2750E has been accepted and approved by the aerospace heat treating community. Therefore, the aerospace heat treating community is compelled to comply with the requirements without attempting to rationalize why certain requirements exist.


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10) Paragraph 3.1.5.2 - We reuse expendable base metal load thermocouples that have been subjected to temperatures above 1200°F by trimming off the portion exposed to temperature and remaking the hot junction. For one example, the furnace requires a load thermocouple with a total length of 20 feet (10 feet of wire inside the furnace and 10 feet of wire from the furnace door to the recording instrument connection. Our approach is to cut a length of thermocouple wire 100 feet in length. After each load, the used portion is trimmed off (10 feet) and the next 10 feet is inserted, etc. Is this cost saving approach to load thermocouple use acceptable? Response: In accordance with AMS 2750E requirements, this method of load thermocouple application is not acceptable. This type of usage would be categorized as salvage of load thermocouples. Paragraph 3.1.3.1.2, states that, “The number of uses prior to salvage shall be included in the total number of uses of the thermocouple.” Expendable base metal thermocouples subjected to temperatures in excess of 1200°F are limited to one use. As written, this limitation on reuse applies to the full length of the load thermocouple (both the section of wire inside of the furnace and the section of wire

outside of the furnace). Back

11) UParagraph 3.2.1.1.2 - The only reference to maximum intervals for temperature data collection during production processing appears to be presented in Table 5. It is interpreted that for a 60 minute soak cycle, it would be required to record process temperatures only at 15 minute intervals throughout the soak period. Response: The above interpretation is correct. However, most heat treaters would likely opt to print or record temperature data at a more frequent interval. In many cases, collection of temperature data at the maximum allowed time interval of 10 minutes would make it difficult or impossible to determine precise start of soak times and to demonstrate compliance with ramp-up requirements (to include verification of the absence of overshoot). It is considered that Footnote (4) to Table 5 is applicable to both

heat-up and cooling. Back

12) UParagraph 3.2.5.3 - This paragraph reference notes that “sensitivity shall be checked during calibration.” For a multichannel instrument, is it required that the sensitivity check be performed on each individual channel? Response: A wide variety of instrumentation exists for performing aerospace heat treating. To preclude individual interpretation of specific instrument configurations, it is considered that each channel in use that can be altered or adjusted requires sensitivity

testing as a component of the calibration effort. Back

13) Paragraph 3.2.5.5.3 - Is the requirement to perform annual verification of chart recorder (circular and strip) speed applicable to refrigeration and quench bath temperature recording instrumentation?


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Response: Paragraph 3.2.5.5.3 does not distinguish between different types of equipment related to thermal processing. Annual verification is required for all circular

and strip chart recorders, regardless of the application. Back

14) Paragraph 3.2.5.5.3 - It is stated that, “Chart recorder (circular and strip) speed(s) shall be verified annually and shall be accurate within ±3 minutes per hour.” Will I need to use a calibrated stop watch to perform the annual verification of recorder chart speed? Additionally, does this requirement also apply to chart recorders that print the scale? With these types of recorders, printing of the time line is integral with printing of the chart and is not dependent on following preprinted chart paper. Response: Basic QA and calibration principles would require that the device used to verify (measurement standard) the accuracy of the recorder is calibrated. Otherwise, there is no way to demonstrate the accuracy of the measurement. The verification process applies to all recorders, regardless of how the scale, temperature, and times

are printed. This would also apply to the device used to measure quench delay. Back

15) UParagraph 3.2.6.1 - It notes that “Any limitations or restrictions of the calibration shall be indicated on the sticker.” What are some examples of limitations or restrictions that might represent the intent of this requirement? Response: Examples could include a limited temperature range, or limited channels of a data logger, or multi-point recorder because of calibration issues. If space on the sticker does not permit listing of the limitations or restrictions, a notation such as “See

Report” on the sticker is acceptable. Back

16) UParagraph 3.3 - Categorization of furnace equipment for Class and Instrumentation Type: AMS 2750E designates a method to categorize furnaces with Class and Instrumentation Type. Some primes utilize a different method of categorizing furnaces (for example Boeing specification, BAC5621). What is the position of the Heat Treating Task Group on categorization of furnaces and how should that categorization be documented and/or displayed by the heat treater? Response: The basic consideration is to ensure that the furnace meets the customer specification requirements for the type of processing performed. Internal procedure must identify the furnace categorization in accordance with applicable customer specifications. This may require multiple methods of categorization to comply with the requirements of multiple customers. It is desirable, but not mandatory, that the categorization (i.e., AMS 2750E, Class 2, Instrumentation Type D; and/or BAC5621, Class 2, Instrumentation Type B) be displayed on the furnace or the furnace instrument panel. Note: Categorization of furnaces in accordance with customer requirements must be

specified in the internal procedure. Back


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17) Paragraph 3.3.1 - Paragraph 3.3.1 indicates that the furnace class used for a heat treatment shall be as designated by the customer or as specified in the controlling heat treat specification. What do I use for a furnace class (or temperature tolerance range) if that requirement is not stated in the heat treat specification? Response: The heat treater would contact the customer or prime as applicable for clarification. It is required that confirmation of all process parameters associated with a job be identified prior to performing the job. This should be an integral part of the

contract review process and a basic quality system concept. Back

18) UParagraphs 3.3.1 and Figure 3 - Requires that for Instrumentation Types A, B, C, and D, the temperature indicated by the control sensor in each control zone shall be recorded by a recording instrument. Is it permissible to use a video camera to record the display temperature on the control instrument as a means to accomplish this requirement? Response: Use of a video camera as described is not included in the provisions allowed by AMS 2750E for temperature recording. While a video camera may be able to record the visual output from the controller, there are no provisions in AMS 2750 which establish readability or discrimination requirements for the recording, how to control the signal and recording, how to link it to time/date through a controlled process, or how to maintain the file as a tamper-resistant record. While it may serve as a very short term measure to record displayed temperatures during the replacement of a failed recorder, it

is not acceptable for use as the temperature recording instrument. Back


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19) UParagraph 3.3.2 - Instrumentation Type A and Instrumentation Type C. What method is to be used in identifying locations for the high and low temperature sensors in furnace equipment with multiple controlling zones and a smaller size work zone volume?

Example: Consider a furnace with less than 225 cubic feet of work zone volume and

three control zones. A TUS for a furnace of this work zone size would require nine test sensors. To qualify the furnace for Instrumentation Type C, it is required that each control zone be equipped with a temperature monitoring sensor installed at the high and low temperature locations in each of the three control zones as determined by the results of the most recent TUS. In this example, the center control zone would contain only one TUS sensor (at the center of the overall work zone).

Response: The method of determining locations for high and low temperature monitoring sensors relative to Instrumentation Type A and Instrumentation Type C is not specifically addressed in AMS 2750E. The above example would require six temperature monitoring sensors - one high temperature and one low temperature sensor in each of the three control zones within the overall qualified work zone of less than 225 cubic feet. Some might consider this requirement to be “overkill” in order to configure a furnace for Type A or Type C Instrumentation. However, except the vacuum furnaces, at this time that is the requirement. If a heat treater chooses to configure a furnace for Type A or C instrumentation in order to take advantage of SAT and/or TUS frequency reductions, it is suggested that an “initial” TUS be performed with sufficient additional test sensors to adequately evaluate the temperature extremes of each control zone. The heat treater is reminded that currently there are no consensus specifications that require configuration of a furnace with Instrumentation Type A or Instrumentation Type C.

Note: This issue is addressed in Revision E, Paragraph 3.3.6, for vacuum furnaces

where the question is most relevant. Back


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20) UParagraph 3.3.4 - Additional sensor in a furnace work zone: Is it acceptable for a heat treater to configure a furnace with additional sensors for internal use only? For example, internal procedure might require the use of a load sensor with each load. Per AMS 2750E, the furnace configuration could be Instrumentation Type B. However, the supplier chooses to classify and maintain the furnace as Instrumentation Type D. Internal procedure would state that the load sensor was for internal use only and would state that the furnace was Instrumentation Type D. Therefore, AMS 2750D requirements for the additional load sensor (SAT, usage limitations, etc.) would not be applicable. Response: The heat treating Task Group considers this to be acceptable practice providing internal procedure is written to adequately address the purpose of the additional sensor. Internal procedure must clearly identify that the additional sensor is for “information only” and the readings are not used for start of soak, process acceptance, or any other metallurgical decisions.

Note: A furnace could be identified as Instrumentation Type D, but occasionally a load

sensor is used for compliance with customer requirements (part temperature, determination of start of soak, etc.). If the load sensor is used for process control or product acceptance, an SAT on the load sensor recording system is required.

Back

21) Paragraph 3.4.1 - Paragraph 3.4.1 states that “SATs shall be performed on the temperature control and recording systems in each control zone of each piece of thermal processing equipment . . . .” In a furnace with multiple sensors, the increased number of control and/or recording systems that require SATs may be offset by a reduction in SAT frequency. But, the procedure is more complicated and time consuming than inserting one test sensor in one position. Is it acceptable for the supplier to designate a furnace with multiple sensors as Instrumentation Type D and carry out a weekly SAT only on the main control and recording systems? Response: It has always been the requirement to perform system accuracy testing on all control and recording systems in the furnace that are used for temperature control or product acceptance. It is acceptable for the supplier to categorize a furnace as Instrumentation Type D while having additional sensors in each control zone. However, internal procedure must specify the additional sensors are for reference only and are not used for temperature control or product acceptance purposes. Paragraph 3.4.1 clearly implies that any additional control and/or recording sensors in each control zone that are used for temperature control or product acceptance shall have system accuracy

testing performed at the designated frequency. Back


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22) Paragraph 3.4.2 - We have a furnace that is used only on an infrequent basis. Is it necessary to start the furnace and perform system accuracy testing at the required frequency, or is it acceptable to wait until the furnace is put back in use and perform testing prior to production heat treatment? Response: It is acceptable to remove the furnace from service (red tag, etc.) at the expiration of the SAT calibration period. Then, prior to use for aerospace applications

the SAT (and any other due calibration testing) must be performed. Back

23) Paragraph 3.4.3.1 – Paragraph 3.4.3.1 states that SAT frequency may be reduced one step if “Two sensors in each control zone are Type B, N, R, or S.” If the over-temperature sensor is B, N, R, or S, is an SAT required for qualification of the over-temperature sensor as the additional B, N, R, or S sensor for this purpose? Response: Yes, if the sensors are to be used for the basis of frequency reduction, then

an SAT will be require on both sensors at the specified frequency. Back

24) Paragraph 3.4.3.2 - Requirements of the noted paragraph do not appear to be clearly defined. It is stated that “Weekly readings show that the relationship between the control sensor and an additional monitoring sensor in each control zone remains within 2°F of their relationship at the time of the last temperature uniformity survey.” How is that relationship to be defined? During the last TUS, normal cyclic temperature patterns within the work zone could easily result in a varying temperature relationship between the control sensor and an additional monitoring sensor. That relationship could also be influenced by load distribution within the work zone. Furthermore, it is assumed that the “additional monitoring sensor” could be the over- temperature sensor in an Instrumentation Type D furnace. Paragraph 3.4.3.2 does not appear to require that the additional monitoring sensor be recorded; therefore it would appear that some sort of a log could be developed to record the weekly reading comparison once the issue with relationship is resolved. Response: Wording of referenced Paragraph 3.4.3.2 provides the heat treater with some flexibility in compliance with the noted provision. Within that flexibility afforded, the heat treater that chooses to employ this option should determine the specific method to demonstrate compliance with Paragraph 3.4.3.2, and then implement that method through internal procedure. Note that some furnaces may not be capable of compliance without special consideration for the monitoring sensor relationship and sensor location relative to the control thermocouple. It would be required that the established procedure be appropriately documented and that monitoring results be recorded and maintained (form, log, etc.) to verify compliance. The over-temperature

sensor could be a likely candidate for the additional sensor in many applications. Back


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25) Paragraph 3.4.5.2.1 - Recalibration frequencies for resident SAT sensors. What are the replacement and/or recalibration frequencies for resident SAT nonexpendable base metal and noble metal thermocouples? Response: Replacement and/or recalibration requirements for resident SAT sensors are the same as for nonresident SAT sensors.

Note: See Figure E, Figure A, and Table 1. Back

26) Paragraph 3.4.5.3.1 and Figure 6 - What is considered to be appropriate and/or acceptable for decimal place recording of temperatures during a SAT and TUS? Table 3 does not require a readability that exceeds ±1°F for a field test instrument. The example of SAT temperatures in the Pyrometry Reference Guide shows readings to the tenth of a degree. Response: Most field test instruments in use today will read to the nearest tenth of a degree. Additionally, most certificates of calibration for sensors and sensor wire provide correction factors (or error/deviation) to the nearest tenth of a degree. An approach that is widely used and considered acceptable is to conduct the SAT and TUS with calculations to the tenth of a degree (when possible with consideration to the calibration certificate on the sensor and the field test instrument). For the final test result value(s), it is acceptable to round off in accordance with ASTM E29 to the nearest whole number. The method employed should be included in internal procedure and should be

consistent in the manner applied. Back

27) Paragraph 3.4.7.1 - To qualify for waiver from system accuracy testing with Instrumentation Types A, B, C, and D furnaces, Paragraph 3.4.7.1 requires that “there are always at least two recording load sensors in each control zone, one monitoring and one controlling.” It is further stated that “the controlling load sensor, in this context, does not need to be physically connected to the furnace controller.” Many times load thermocouples are used to trigger the start of soak (but do not control the temperature). Do these counts as controlling thermocouples? How are these requirements interpreted by the heat treat task group? Response: Within the context of this paragraph, the “controlling” load sensor does not need to be physically connected to the furnace control instrument. Paragraph 3.4.7.1.2 states that: “Manual adjustments to the controller set point, based on observed load sensor readings provide acceptable control.” It may be that the observed load sensor readings do not require manual adjustment of the controller; however, the load sensor is serving the same purpose (monitoring of the load temperature to determine if manual adjustment of the set-point temperature is required). As noted in the question, the controlling load sensor, in this context, does not need to be physically connected to the

furnace controller. Back


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28) Paragraph 3.4.7.6 - Our facility is not clear on the interpretation of: “Weekly readings must also show that the relationship between the control sensor and an additional monitoring sensor in each control zone remains within 2°F (1°C) of their relationship at the time of the last Temperature Uniformity Survey.” Would the task group provide an example of how the 2°F (1°C) relationship might be applied? Response: As an example, let us say that the additional monitoring sensor to be used for this purpose is the over temperature sensor connected to the over temperature instrument. Note that when used for this purpose, the over temperature instrument must be calibrated. During the most recent temperature uniformity survey the control maintained a temperature of 1000°F (542°C) and the over temperature instrument displayed a temperature of 1004°F (544°C). Therefore, the difference between the two readings is 4°F (2°C). Subsequently, during the weekly (seven day period) observations and recordings of the difference between the compared temperature values must not exceed 2°F (1°C) of their relationship at the time of the last temperature uniformity survey. In this example, if the controller read 1000°F (542°C) during weekly readings, acceptable readings for the monitoring sensor would be 1002°F (543°C) to

1006°F (544°C). Back

29) Paragraph 3.4.7.6 - A requirement for compliance with provisions for an SAT waiver states, “The load sensors are recalibrated or replaced anytime that observations, made and recorded at least weekly, reveal any unexplainable difference between their readings and the readings of other control, monitoring and recording sensors.” I use expendable load sensors and replace the sensors after each load. Is this requirement applicable when expendable load sensors are used? Response: Yes. Wording of referenced Paragraph 3.4.7.6 provides the heat treater with some flexibility in compliance with the noted provision. Within that flexibility afforded, the heat treater that chooses to employ provisions for SAT waiver should determine the specific method(s) to demonstrate compliance with Paragraph 3.4.7.6, and then implement that method through internal procedure. Remember that the purpose of applying SAT waiver provisions is to provide for monitoring the instrument systems for conditions that might be indicative of changes that could affect compliant

operation of the furnace. Back


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30) Paragraph 3.5.6.2 - It is stated that “For multiple qualified operating ranges, TUS shall be performed within each operating range during each test period and at the maximum and minimum of each operating range at least once each year.” What are the TUS test temperature requirements for a furnace that has multiple qualified temperature ranges to different furnace class requirements, with one intermediate range that exceeds 600°F (335°C)? Is the requirement in Paragraph 3.5.6.1 applicable to that intermediate range because the range exceeds 600°F (335°C)? Or, is just one temperature within that operating range acceptable? Response: The 600°F (335°C) rule applies to both a furnace with only a single qualified operating temperature range and a furnace with multiple qualified operating temperature ranges. Any intermediate range of a furnace that exceeds 600°F (335°C) requires testing within that range at temperatures that comply with the 600°F (335°C) maximum test temperature interval and the requirement in 3.5.6.1 that test temperatures be within

300°F (170°C) of the minimum and maximum of the range. Back

31) Paragraph 3.5.10.2 - “When the TUS is performed with a load, and the TUS sensors are attached to simulated product or parts, the load shall represent the thickness of the material normally processed.”

Example: Where a producer of aluminum coiled sheet uses actual 6000 pound coils of

sheet material to perform temperature uniformity surveys on a large Class 2, Instrumentation Type D, furnace that functions only for aging of coiled sheet to the final temper. Aluminum sheet coils are dedicated to conducting the TUS and include holes drilled for insertion of the TUS sensors (some at mid radius of a 48 inch diameter coil). In this example, “load sensors” are used for the TUS, but the load “represents the thickness of the material normally processed.” It appears that this method of performing a TUS would be acceptable iaw Revision E, providing that the stipulations of Paragraph 3.5.13.3.3 “At no time shall any test, control or recording sensor exceed the upper temperature uniformity tolerance,” and other applicable requirements are in compliance.

Response: It is assumed that in addition to “buried” TUS thermocouples, there are additional thermocouples attached to (or very close to) the surface of the coil. There is a requirement (paragraph 3.5.13.2.3) that states: “The work zone volume tested shall be such that no material heat treated extends beyond the defined work zone boundaries.” The TUS sensors define the extremes of the work zone. In this example, it would be logical to include test thermocouples at the surface at the outside of the load to detect

any overshoot and to define the extremes of the work zone. Back


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32) Paragraph 3.5.13.3 - Computer controlled TUS data collection. When using computer controlled data collection during a TUS, is it acceptable practice to run lead wire from the control instrument to the data collection device if the control instrument already has a connection between it and the furnace recording instrument? Response: There is no restriction against the described procedure, but the intent is that the data documented on the furnace recorder be representative of the data documented on the TUS instrument. The above would not meet that requirement; therefore, it would

be in addition to and not in place of the requirement specified in 3.5.13.3.2. Back

33) Paragraph 3.5.13.3.2 – It states: “Once data collection begins, temperature data shall be recorded from all TUS sensors at a frequency of at least one set of all readings every two minutes for the duration of the survey. Data from furnace sensors required by the applicable instrumentation type (see 3.3) shall be recorded as follows:” Does this imply that for Instrumentation Type A and Instrumentation Type B furnaces, some type of representative load is always required for a TUS in order to provide load sensor temperature data? Response: Load thermocouples are required for configuration of a furnace to Instrumentation Type A or Instrumentation Type B. Load thermocouples measure metal temperature. If the TUS is performed without a load, the load thermocouples may be inserted in heat sinks that meet the requirements of Paragraph 3.5.10.1 so that metal

temperature is measured during the TUS. Back

34) Paragraph 3.5.13.3.2 - The reference states that “If the normal frequency of temperature data recording in production is 2 minutes or less, or is continuous as in the case of analog recorders, the data shall be documented in the normal production format. If the normal frequency of temperature data recording in production is greater than 2 minutes, the recording frequency interval during the TUS shall not exceed 6 minutes”. Some Pyrometry technicians are wrapping a second sensor around the furnace system sensor (i.e., control sensor) to obtain a record on their survey report. Is this acceptable? Response: This approach does not meet requirements for recording of furnace sensor data. The requirement is to obtain data from the recording instrument used with the furnace system. Including a copy of the furnace process temperature record (as recorded on the production process recorder) for the TUS period is the acceptable method to comply with the requirements of Paragraph 3.5.13.3.2 for recording of “data from furnace sensors.” It is required that the furnace chart recording be in the same format as a production load, and meet the readability and resolution requirements of Figure 4. An analog trace (trend line) is acceptable if used in production. All furnace sensors used in production for the designated instrumentation type shall be included

(i.e., control, high/low monitoring, load, etc.). Back


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35) Paragraph 3.5.13.3.4 - Our facility utilizes a large retort furnace with multiple control zones. Internal procedure designates a recording load sensor for each control zone. The noted paragraph states: “When a retort is used, the temperature of the furnace in which the retort is inserted shall be controlled so that the specified heat treating temperature is maintained within the retort. TUS sensors shall be within the retort; at least one TUS sensor shall align within 2 inches (50 mm) of the sensor used to record temperature within the retort during operation.” Is the interpretation such that during a TUS it is required that a TUS sensor be located within 2 inches (50 mm) of each of the multiple control zone sensors used to record temperature within the retort during operation? Response: It is the interpretation of the heat treat task group that during a retort furnace TUS, sensors be located within 2 inches (50 mm) of each recording sensor inside of the retort. In some cases furnace configuration and/or work zone geometry may require that additional sensors be included with the TUS to ensure coverage of the work zone.

Back

36) Paragraph 3.5.16 - It states: “No TUS sensor failures at the corner locations of the work zone are permitted.” To some, the use of the word “corners” implies a square or rectangular work zone. Does the restriction on sensor “corner” failures also apply to failures in the end planes of a cylindrical work zone? Response: It is interpreted that the word “corners” applies to the three sensors around

the circumference of each end plane with a cylindrical work zone. Back

37) Paragraph 3.5.19 - Failure of a TUS at one temperature, but pass at another temperature: Consider an example of a temperature uniformity survey that fails (out of the temperature tolerance range) at one temperature, but passes at another temperature. Is it permissible to use the furnace for processing product at the temperature that passed the survey? Response: This situation would require a temporary redefinition of the qualified operating temperature range to document the temperature range where the furnace meets the required tolerance. There would also be consideration for qualification of the furnace for that temperature range with respect to the requirements applicable to an initial TUS (i.e., the new or temporary qualified operating range would require a TUS at

the top and bottom of each qualified operating range). Back

38) Paragraph 3.5.19.1.2 - If I run a TUS at intervals that do not exceed 300°F (165°C), and my TUS can be corrected in one of those ranges that do not exceed 300°F (165°C) by using an appropriate offset only in that range, does that satisfy the requirement of 3.5.19.1.2 and not require a new TUS?


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Response: No, you must divide the operating range into separate qualified operating ranges, even if all have the same tolerance requirements, and then can correct any one

of those ranges by using the appropriate offset. Back

39) TABLE 3, Note 7 - This question concerns calibration of test instruments. Note 7 states: “Field Test instruments meeting accuracy requirements of secondary standards may be used to calibrate SAT and TUS test instruments in the field.” What are the requirements for calibration of a field test instrument meeting accuracy requirements of a secondary standard? Response: A field test instrument meeting the accuracy requirements of a secondary standard must be calibrated against a primary standard at a frequency that does not

exceed three months. Back

40) TABLE 3, Note 8 - Calibration of digital over-temperature instruments. Note 8 states that over-temperature instruments used solely for furnace over-temperature protection do not need to be calibrated. If calibration is performed and it is a digital instrument, do the accuracy requirements for a digital instrument apply (i.e., ±2°F)? Response: As stated, calibration is not required unless the over-temperature instrument is used for purposes other than over-temperature protection. An example of other purposes would include a dual function of the instrument as over-temperature protection and for monitoring of the high temperature location in each control zone (i.e., Instrumentation Types A and C). A second example would include use of the over-temperature instrument to qualify for SAT reduced frequency (Paragraph 3.4.2.2) or SAT waiver (Paragraph 3.4.3.6). When calibration is performed, accuracy requirements

of Table 3 apply for the type of instrument (digital, electro-mechanical, etc.). Back

41) TABLE 5 - We use a circle chart recorder for aluminum aging cycles that encompass a total time of 24 to 25 hours. With ramp-up and ramp-down, the total cycle time exceeds 24 hours. It is not always feasible to change the chart paper due to shift schedules. Is it permissible to have more than 24 hours’ worth of data on a circle chart recorder by programming the recorder to change scale so that the trend line does not cover the previous line? Response: It is not considered acceptable to have more than 24 hours recorded on a furnace temperature circle chart recorder. Time/date data on the outer circumference of the chart paper would be overwritten and a portion of the circle chart would be “reused.” It is acceptable to change the chart paper at any time during the soak cycle with

appropriate annotation. Back


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42) TABLE 5 - Note 2 for Table 5 requires that the “recorder shall be operating during the entire time that product is in the furnace.” Our facility operates a day shift only. If we have a load end soak and begin furnace cool down on Friday after the end of first shift, it would be required for the recorder to continue in operation until the beginning of first shift on Monday morning. The circle chart recorder would be recording over previously recorded temperature data which is not allowed. Are there provisions to accommodate for this type of situation? Response: The referenced Note 2 clearly states that “recorder shall be operated during the entire time that product is in the furnace.” The Heat Treat Task Group requires

compliance with Note 2. Back

43) TABLE 3, TABLE 6, TABLE 7, TABLE 8 and TABLE 9 - Clarification on °C equivalents. Many European companies work to a ±5°C tolerance for thermal processing. As presented in AMS 2750E, it appears that a furnace with a ±5°C uniformity tolerance would be categorized as a Class 1 furnace. This could entail an increase in the frequency for performing instrument calibration, system accuracy testing and temperature uniformity testing as compared to a Class 2 furnace. What action is being taken by the heat treat task group to address this problem? Response: It is the interpretation of the heat treat task group that a ±5°C uniformity equates to a Class 2 furnace. Frequency of instrument calibration for a ±5°C furnace would be in accordance with Table 3. Frequency of system accuracy testing and temperature uniformity testing would be in accordance with Table 6 and Table 8 for the

applicable instrumentation type. Back

44) TABLE 6 and TABLE 7 - SAT frequency for furnaces with multiple classifications - When a furnace is qualified for multiple operating ranges, is the SAT frequency applicable to the furnace class with the most stringent SAT frequency requirement even if the furnace is not routinely used in that temperature range? For example, consider a vacuum furnace that is configured as Class 2, Instrumentation Type D, at 1000–1400°F; and Class 5, Instrumentation Type D, at 1400–2000°F. Is a weekly SAT (vs. biweekly) required even though use of the furnace at temperatures below 1400°F is infrequent? Response: System accuracy testing would be performed at the most stringent frequency unless provisions are established to restrict Class 2 (using the example above) heat treatments until an SAT is performed to the Class 2 requirements. If the noted approach is used, internal procedures must provide adequate control to preclude

use within the Class 2 range until SAT requirements are accomplished. Back


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45) TABLE 6 and TABLE 7 - Maximum SAT and TUS offset that may be applied to furnace instruments is listed in Tables 6 and 7. Manufacturer’s instructions for some furnace instruments state that calibration is accomplished by applying offset to the instrument. Is there a limit on offset that may be applied to furnace instruments as bias for the purpose of instrument calibration? Response: AMS 2750 does not include restrictions on the amount of offset that may be applied to furnace control, monitoring, or recording instruments for the purpose of

calibrating the instrument. Back

46) TABLE 10 - Calibration intervals - Table 10 is entitled “Permitted Calibration/Test Interval Extension.” Does this terminology include instrument calibrations? Response: Yes. Table 10 refers to test interval extension allowed for any calibration or

test interval listed in AMS 2750E. Back


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REVISION RECORD

REV DATE Description of Changes

A 3-Apr-06 Complete revision including update to AMS2750D requirements

18-Jul-06 Section VIII – Most frequently asked questions added

2-Feb-07 Added Table FAQ’s Added additional frequently asked questions Paragraph 3.1.5.2 and Table 1 Paragraph 3.2.5.3.3 Paragraph 3.2.6.1 Paragraph 3.3 Paragraph 3.3.1.1 through 3.3.1.4 Paragraph 3.3.1.2 & 3.3.1.4 Paragraph 3.3.1.2.3 Paragraph 3.3.1.3 Paragraph 3.4.1 Paragraph 3.4.2.1 Paragraph 3.4.3.1 Paragraph 3.4.4.2.1 Paragraph 3.4.4.3.1 Paragraph 3.5 Paragraph 3.5.19 Paragraph 3.5.13.3 Paragraphs 3.5.5 and 3.5.6 Paragraph 3.5.7.1 Tables 8/9 Paragraph 3.5.13.3.2 Table 3, Table 6, and Table 8 Disclaimer Note

30-Mar-09 Added additional questions to Section VIII

Paragraph 3.1.1.1 Paragraph 3.2.5.4


Paragraph 3.1.1.4.1 Paragraph 3.3.1.1.4 and Paragraph 3.3.1.2.3


Paragraph 3.1.8.4 Paragraph 3.4.4.3.1


Paragraph 3.1.1.9 Paragraph 3.5.13.3.4

Paragraph 3.2.2 Table 3, Note 5

01-Nov-10

Paragraph 3.2.5.3.2 Added clarification for Vacuum furnaces for one work zone and necessary number/type of thermocouples for various instrumentation types Added table Parts vs. Raw Material Added a 4th note for

Table 3, Note 7 Page 14 Page 15 & 16 Page 35 (Matrix)


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expendable test thermocouples Added 20 new FAQs.

From Page 32 to Page 58

20-Apr-11 Clarification of FAQ 38 Page 46

2-Sept-11 We removed the following text from FAQ #65:

The TUS report must show objective evidence that the furnace sensor temperature values were compared to TUS sensor values for the TUS period to evaluate the relationship between the two sets of data. Objective evidence could be comparison of maximum temperatures recorded during furnace temperature recovery, and high/low temperatures recorded during the TUS period for both the TUS sensors and the furnace system sensors.

Page 57

21-Oct-11 The text “and system accuracy testing must be performed on the over temperature system” was removed from the FAQ #51.

Page 50

17-Oct-12 Update for AMS 2750 Rev. E Multiple

Pyrometry Guide 20 Nov 12

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