32371011 Nov 09

8/13/2019 32371011 Nov 09

http://slidepdf.com/reader/full/32371011-nov-09 1/41

PETRONAS TECHNICAL STANDARDS

DESIGN AND ENGINEERING PRACTICE

MANUALS

INSTALLATION OF ON-LINE INSTRUMENTS

PTS 32.37.10.11

NOVEMBER 2009

2010 PETROLIAM NASIONAL BERHAD (PETRONAS) All rights reserved. No part of this document may be reproduced, stored in a retrieval system or transmitted in any form or by any means

(electronic, mechanical, photocopying, recording or otherwise) without the permission of the copyright owner.

8/13/2019 32371011 Nov 09


PTS Circular

This revision of PTS 32.37.10.11 – Installation of On-Line Instruments has been updatedincorporating PETRONAS Lessons Learnt, Best Practice and new information issued by relevantindustry code and standards. All updates in the document are highlighted in italic font.

The previous version of this PTS (December 2007) will be removed from PTS binder/ e-repository

from herein onwards.

Document Approval

Revision HistoryDate Version Description of Updates Author

2009 - SKG14-006

PTS No: 32.37.10.11

Publication Title: Installation of On-Line Instruments

Base PTS Version: <Release 13>

8/13/2019 32371011 Nov 09


SUMMARY OF CHANGES

Section Description of Changes

1.1.1 Following abbreviations were added:1.3.2 Abbreviations MTBF Mean Time Between Failure

MVC Measurement Validation and Comparison

TCoO Total Cost of Ownership

2.2.1 RemoteMountingConcepts

MESC reference were removed as follows (bold and strikethrough)

The remote mounting concept has proven to be very valuable and covers allfrequently applied hook-up arrangements. Typical hook-up arrangements withMESC-coded component listings are available for liquid, gas and steamapplications as given in standard drawings S 37.001 (metric version) andS 37.002 (imperial version).

2.2.3.7 Designaspects

Rephrase as follows (bold):

For the direct mounting concept, the following aspects need specific attention:

• To prevent too high stresses on the process nozzle, the length and weight ofthe instrument with its accessories need to be reviewed, especially invibrating service and on small bore process piping and very hightemperature service. Co-ordination with Mechanical Engineering isrequired.

• Direct mounting is less suitable for applications that require rodding out ofprocess connections. However, if auto-rodder is used, direct mounting ispreferred.

Rephrase as follows (bold):

If a liquid contains vapours, dissolved gas or low temperature (below ambienttemperatures) liquids e.g. LNG, LPG, etc , the process connection should beinstalled in a vertical line. If a process connection can only be made availablefrom a horizontal line, the tapping should be either at the side or pointingdownwards at an angle of up to 45 degrees from the horizontal axis except forlow temperature liquids where the process connection shall remainhorizontal or pointing upwards. The impulse lines shall slope downwards tothe instrument so that gas is automatically vented back into the process, asshown in Figure 7. Downward-pointing tappings in horizontal lines arevulnerable to fouling and may only be used if approved by the Principal. Ifdownward-pointing tapping is used, provide proper flushing facility as

shown in Figure 7a; further consideration on this conf iguration in 4.3.

3.1 General

Following figure were added

Figure 7a (new) Downward-pointing tapping with flushing facility

Instrument Flush line

4.1 Specification Para 3 (adding in bold)

8/13/2019 32371011 Nov 09


Section Description of Changes

of Components For applications where AISI 316 stainless steel is not suitable, other materialssuch as Duplex, Super Duplex, Incoloy, Monel, Hastelloy, Tantalum orTitanium should be applied.

Para 4 (adding new list and rephrase notes - bold)

UNS S32750 Alloy 2507 e.g. Super Dup lex 2507

NOTES: 1. However for super duplex tubing, only s uper duplex fitting shall be used, thethree groups of tubing materials, listed above, may be used in conjunction with AISI316 type stainless steel compression fittings.

2. The hardness of the high nickel alloy tubing shall be within the range of 77 HRB to83 HRB, hardness of super duplex tubing shall be within 30 HRC.

Para 5 (rephrase - bold)

Stainless steel impulse line components may be selected on the basis of theMESC numbers given on standard drawings S 37.001 (Instrument impulselines, metric version) or S 37.002 (Instrument impulse lines, imperial version).Gauge blocks shall be provided with a 1/2 inch female threaded gauge adapter (not applicable when gauges integral with tube adapter are used). The typeof thread for the pressure gauge (tapered 1/2 inch NPT or parallel G 1/2 inch)shall be specified by the Principal. To reference PTS 32.31.09.31 forcalculation on TCoO.

4.2.1 General Additional notes added:

Note: The protective shade should be installed for exposed instrumentation intropical and desert environment

4.2.2.3Instrumentlocation androuting ofimpulse linetubing

1.1.1.1 Para 2 rephrase as follows (bold):For straight lengths up to a maximum of 1 m the tubing is self-supporting, forlonger lengths the tubing shall be supported up to maximum of 1 m intervalswith proper tube supports/clamps.

8/13/2019 32371011 Nov 09


PREFACE

PETRONAS Technical Standards (PTS) publications reflect the views, at the time of publication, ofPETRONAS OPUs/Divisions.

They are based on the experience acquired during the involvement with the design, construction,operation and maintenance of processing units and facilities. Where appropriate they are based on,or reference is made to, national and international standards and codes of practice.

The objective is to set the recommended standard for good technical practice to be applied byPETRONAS' OPUs in oil and gas production facilities, refineries, gas processing plants, chemicalplants, marketing facilities or any other such facility, and thereby to achieve maximum technical andeconomic benefit from standardisation.

The information set forth in these publications is provided to users for their consideration and decisionto implement. This is of particular importance where PTS may not cover every requirement ordiversity of condition at each locality. The system of PTS is expected to be sufficiently flexible to

allow individual operating units to adapt the information set forth in PTS to their own environment andrequirements.

When Contractors or Manufacturers/Suppliers use PTS they shall be solely responsible for the qualityof work and the attainment of the required design and engineering standards. In particular, for thoserequirements not specifically covered, the Principal will expect them to follow those design andengineering practices which will achieve the same level of integrity as reflected in the PTS. If in doubt,the Contractor or Manufacturer/Supplier shall, without detracting from his own responsibility, consultthe Principal or its technical advisor.

The right to use PTS rests with three categories of users:

1) PETRONAS and its affiliates.

2) Other parties who are authorised to use PTS subject to appropriate contractual arrangements.3) Contractors/subcontractors and Manufacturers/Suppliers under a contract with users referred to

under 1) and 2) which requires that tenders for projects, materials supplied or - generally - workperformed on behalf of the said users comply with the relevant standards.

Subject to any particular terms and conditions as may be set forth in specific agreements with users,PETRONAS disclaims any liability of whatsoever nature for any damage (including injury or death)suffered by any company or person whomsoever as a result of or in connection with the use,application or implementation of any PTS, combination of PTS or any part thereof. The benefit of thisdisclaimer shall inure in all respects to PETRONAS and/or any company affiliated to PETRONAS thatmay issue PTS or require the use of PTS.

Without prejudice to any specific terms in respect of confidentiality under relevant contractual

arrangements, PTS shall not, without the prior written consent of PETRONAS, be disclosed by usersto any company or person whomsoever and the PTS shall be used exclusively for the purpose theyhave been provided to the user. They shall be returned after use, including any copies which shallonly be made by users with the express prior written consent of PETRONAS.

The copyright of PTS vests in PETRONAS. Users shall arrange for PTS to be held in safe custodyand PETRONAS may at any time require information satisfactory to PETRONAS in order to ascertainhow users implement this requirement.

8/13/2019 32371011 Nov 09


TABLE OF CONTENTS

1. INTRODUCTION ........................................................................................................1 1.1 SCOPE........................................................................................................................1 1.2 DISTRIBUTION, INTENDED USE AND REGULATORY CONSIDERATIONS .........1

1.3 DEFINITIONS .............................................................................................................1 1.4 CROSS-REFERENCES .............................................................................................3

2. GENERAL...................................................................................................................4 2.1 INTRODUCTION ........................................................................................................4 2.2 DESIGN CONCEPTS .................................................................................................4

3. INSTRUMENT PROCESS CONNECTIONS FOR ON-LINE INSTRUMENTS ..........8 3.1 GENERAL...................................................................................................................9 3.2 INSTRUMENT PROCESS CONNECTIONS FOR THE REMOTE MOUNTING

CONCEPT.................................................................................................................11 3.3 INSTRUMENT PROCESS CONNECTIONS FOR THE DIRECT MOUNTING

CONCEPT.................................................................................................................11

4.

GENERAL SPECIFICATION FOR IMPULSE LINES ..............................................12

4.1 SPECIFICATION OF COMPONENTS .....................................................................12 4.2 MOUNTING ARRANGEMENTS...............................................................................13 4.3 FILLING, FLUSHING, VENTING AND DRAINING...................................................14 4.4 PAINTING AND COATING.......................................................................................15 4.5 TESTING...................................................................................................................15

5. SPECIAL APPLICATIONS AND CONSIDERATIONS FOR IMPULSE LINES ......16 5.1 STEAM SERVICE.....................................................................................................16 5.2 OXYGEN SERVICE..................................................................................................16 5.3 HYDROGEN FLUORIDE (HF) SERVICE.................................................................16 5.4 FLUIDS WITH HIGH POUR POINTS OR HYDRATE FORMATION RISK..............17 5.5 FLUIDS CONTAINING SUSPENDED SOLIDS........................................................17 5.6 FOULING AND WAXY SERVICE.............................................................................17

5.7 SUSCEPTIBILITY OF LOW RANGE GAS MEASUREMENTS TO LIQUIDSLUGS......................................................................................................................17

5.8 LOW TEMPERATURE SERVICE.............................................................................18 5.9 VERY TOXIC SERVICE ...........................................................................................18 5.10 ‘SOUR’ OR ‘WET H2S’ SERVICE ............................................................................19

6. SEALING AND PURGING .......................................................................................20 6.1 LIQUID SEAL............................................................................................................20 6.2 LIQUID SEAL AND HOOK-UP OF WET LEG LEVEL APPLICATIONS ..................21 6.3 DIAPHRAGM SEALS................................................................................................25 6.4 EXTERNAL PURGING .............................................................................................27 6.5 SELF-PURGING.......................................................................................................28

7. HEATING AND INSULATION ..................................................................................29 7.1 GENERAL.................................................................................................................29 7.2 STEAM HEATING.....................................................................................................29 7.3 ELECTRICAL TRACING...........................................................................................30 7.4 INSULATION ............................................................................................................30

8. REFERENCES .........................................................................................................31

APPENDICES

APPENDIX 1 PRESSURE AND TEMPERATURE LIMITATIONS OF SS TUBING ANDPACKINGS ......................................................................................................0

APPENDIX 2 EXAMPLE OF CALCULATIONS OF THE EFFECT OF PROCESS

VARIABLE CHANGES ON dP LEVEL MEASUREMENTS...............................1

8/13/2019 32371011 Nov 09


PTS 32.37.10.11November 2009

Page 1

1. INTRODUCTION

1.1 SCOPE

This PTS specifies requirements and gives recommendations for installation of on-line

instruments.

This PTS is a revision of the PTS of the same number, dated December 2007.

1.2 DISTRIBUTION, INTENDED USE AND REGULATORY CONSIDERATIONS

Unless otherwise authorised by PETRONAS, the distribution of this document is confined tocompanies forming part of or managed by PETRONAS, and to Contractors nominated bythem.

This PTS is intended for use in oil refineries, chemical plants, gas plants, supply/marketinginstallations and in exploration and production facilities.

If national and/or local regulations exist in which some of the requirements may be morestringent than in this PTS, the Contractor shall determine by careful scrutiny which of therequirements are the more stringent and which combination of requirements will beacceptable as regards safety, environmental, economic and legal aspects. In all cases theContractor shall inform the Principal of any deviation from the requirements of this PTSwhich is considered to be necessary in order to comply with national and/or localregulations. The Principal may then negotiate with the Authorities concerned with the objectof obtaining agreement to follow this PTS as closely as possible.

1.3 DEFINITIONS

The Contractor is the party which carries out all or part of the design, engineering,procurement, construction, commissioning or management of a project or operation of afacility. The Principal may undertake all or part of the duties of the Contractor.

The Manufacturer/Supplier is the party which manufactures or supplies equipment andservices to perform the duties specified by the Contractor.

The Principal is the party which initiates the project and ultimately pays for its design andconstruction. The Principal will generally specify the technical requirements. The Principalmay also include an agent or consultant authorised to act for, and on behalf of, thePrincipal.

The word shall indicate a requirement.

The word should indicate a recommendation.

8/13/2019 32371011 Nov 09


PTS 32.37.10.11November 2009

Page 2

1.3.1 Specific defini tions

Direct mounting A mounting concept, whereby an on-line instrument (with orwithout manifold) is mounted directly on and supported by theprocess connection(s).

NOTE: This mounting concept is sometimes referred to as‘close coupled’. This term is however also used in the literal sensefor instruments mounted on a separate stand in the direct vicinityof the process connection(s). To avoid confusion, the term‘close coupled’ is no longer used in this PTS.

ElectricalEngineering

Term used in this PTS to identify activities ordevices/components which are considered outside theresponsibility of the typical Instrument Engineering disciplineserving a project. It is not intended to preclude a particularproject from reassigning responsibilities, but primarily toidentify areas which may otherwise be overlooked.

Impulse line(s) Components used to connect an on-line instrument to itsprocess connection. It includes but is not limited to tubing,fittings and manifold blocks plus components for filling,flushing, sealing, purging, heating, insulation, venting,draining, mounting and supporting.

MechanicalEngineering

Term used in various parts of this PTS to identify activities ordevices/components which are considered outside theresponsibility of the typical Instrument Engineering disciplineserving a project. It is not intended to preclude a particularproject from reassigning responsibilities, but primarily toidentify areas which may otherwise be overlooked.

On-line instrument Instruments connected to process and utility lines orequipment via small (maximum DN 50) block valves. They aresubjected to the pressures of the piping systems or equipmenton which they are installed. The block valves are referred toas primary isolation valves in the context of this PTS.

Instruments with diaphragm seals are also considered to beon-line instruments, if they are connected to process and utilitylines or equipment via primary isolation valves of any size.

For more detailed definition, refer to: PTS 32.31.00.32:Instruments for Measurement and Control.

Remote mounting A modular mounting concept, whereby an on-line instrument(with or without manifold) is installed on a dedicatedinstrument mounting support and connected with the processconnection via tubing, capillary or pipe.

Very tox ic See definition in PTS 00.00.01.30

8/13/2019 32371011 Nov 09


PTS 32.37.10.11November 2009

Page 3

1.3.2 Abbreviations

LRV Lower Range Value; the lowest quantity that a device is adjusted tomeasure

MTBF Mean Time Between Failure

MVC Measurement Validation and Comparison

TCoO Total Cost of Ownership

URV Upper Range Value; the highest quantity that a device is adjusted tomeasure

1.4 CROSS-REFERENCES

Where cross-references are made, the number of the section or sub-section referred to is

shown in brackets. All publications referred to in this document are listed in (8).

8/13/2019 32371011 Nov 09


PTS 32.37.10.11November 2009

Page 4

2. GENERAL

2.1 INTRODUCTION

The best hook-up arrangement for each on-line instrument shall be determined on the basis

of the specifications given in Sections (4) and (5) and the additional requirements ofsections (6) and (7) on sealing, purging, heating and insulation. The selected hook-up shallguarantee proper measurement at all normal and abnormal process operating and climaticconditions. Instrument sealing and purging shall only be used if alternative hook-upsarrangements are less attractive from a TCoO, measurement accuracy or maintenancepoint of view.

To obtain acceptable response times, the kinematic viscosity of liquids in impulse lines shall

be kept below 200 mm2/s under all normal and abnormal conditions.

In locations where freezing may occur, the water-filled parts of sensing lines and theinstrument shall be winterised (i.e. heated and insulated), see (7).

For access requirements and guidance on selecting the location of instruments andinstrument process connections, refer to PTS 32.31.00.32.

Impulse lines for sample take-off and transport for on-line process stream analysis arecovered by PTS 32.31.50.10.

Installation drawings for instrument impulse lines shall be prepared in accordance with therequirements of PTS 32.31.00.10.

2.2 DESIGN CONCEPTS

This PTS covers the requirements for two distinct design concepts:

- Remote mounting concept, as example given in Figure 1;- Direct mounting concept, as example given in Figure 2.

Figure 1 Example of remote mount ing concept.

8/13/2019 32371011 Nov 09


PTS 32.37.10.11November 2009

Page 5

Figure 2 Example of direct mounting concept

2.2.1 Remote mounting concept

In the early 1980s, a modular mounting concept was developed for transmitters mountedremotely from the process connection(s): a mounting plate, attached to a dedicatedinstrument mounting support, accommodates the transmitter, manifold, heating elementwith terminal box, insulation covers, nameplate and protective shade, as required. Tubingwith compression fittings interconnects manifold and process connection(s).

Maintenance requirements have dominated the design of the remote mounting concept.

The concept is based on a need for permanent access and includes facilities for in situtesting and calibration.

The remote mounting concept has proven to be very valuable and covers all frequentlyapplied hook-up arrangements. Typical hook-up arrangements with component listings areavailable for liquid, gas and steam applications as given in standard drawings S 37.001(metric version) and S 37.002 (imperial version).

Metric tubing (12 mm OD) and compression fittings should be used for new projects. Theapplication of imperial sized tubing (1/2 inch OD) and related compression fittings should berestricted to locations which have standardized on imperial sizes and requires approval bythe Principal.

The reliable and proven use of compression fittings requires that:

- all compression fittings in a plant, including those supplied with equipment packages,shall be of the same size, make, type and suitable material composition as the tubing.Mixing of fittings of different size (e.g. metric with imperial) or different make/type willresult in unreliable joints and might consequently result in loss of containment; the makeis subject to Principal’s approval.

- the fittings and tubing shall be installed by skilled personnel, strictly in accordance withManufacturer's instructions; e.g. avoidance of over-tightening, use of correctly sizedtubing, etc.

- the impulse lines shall be pressure-tested after installation, see (4.5).

8/13/2019 32371011 Nov 09


PTS 32.37.10.11November 2009

Page 6

2.2.2 Direct mount ing concept

Reduced access needs for modern instrumentation, the increased TCoO awareness andproduct developments have paved the way for alternative mounting concepts, such asdirect mounting.

In the direct mounting concept, the on-line instrument and its manifold are mounted directlyon and supported by the process connection(s). Some designs combine the primaryisolation valve and instrument manifold in one component, for instance in amonoflange-type device.

This concept is characterised by a small number of components, forming a compact design.This concept is not standardized (no standard forms), but leaves the market forces to findeconomically attractive and technically sound solutions within the constraints specified inthis PTS. Consequently, the solutions offered by the various Manufacturers will be differentand the role of the Manufacturer will be that of a solution-provider rather than just a materialSupplier.

2.2.3 Comparison of design concepts

2.2.3.1 General

It is essential to make the selection between the remote mounting and the direct mountingconcept in an early project stage. This Section lists aspects to be considered.

2.2.3.2 Accessibility

The remote mounting concept provides some freedom regarding instrument location andthe resulting accessibility. For maintenance purposes, permanent and easy access used tobe the dominant factor in selecting the physical location of remote mounted instruments.Long impulse lines and additional ladders/platforms were the result.

The location of a direct mounted instrument is fully determined by the physical location ofthe process connection, which typically provides limited freedom for positioning.

Major improvements in MTBF, MVC techniques and remote diagnostics via ‘intelligent’communication have drastically reduced the need for on-the-spot maintenance of modernfield instruments. Minimum accessibility requirements are specified in PTS 32.31.00.32

2.2.3.3 TCoO

The cost involved with the remote mounting concept is high due to the large number ofcomponents, the need for an instrument mounting support and the labour intensiveinstallation and testing. Furthermore, tubing and fittings are vulnerable to

damage, particularly in the construction phase of a project.

These disadvantages do not apply to the direct mounting concept. Furthermore, the use offewer components and connections can be a major cost saver.

When the direct mounting concept is chosen, extra cost may be involved to meet theminimum access requirements for specific field instruments (e.g. instruments thatrequire regular in situ testing and/or calibration).

2.2.3.4 Performance and maintenance aspects

The compactness of the direct mounting concept brings the sensor closer to the processwhich improves the measurement accuracy and makes the measurement less susceptible

to the proper functioning of heating and insulation. Shorter runs and fewer fittings reducevulnerability to damage and leaks.

8/13/2019 32371011 Nov 09


PTS 32.37.10.11November 2009

Page 7

2.2.3.5 Responsibilities, risks and construction timing

The remote mounting concept entails a clear demarcation of scope between theMechanical and Instrument Engineering disciplines. The design is proven and thecomponents are available as commodity items.

The installation of a remote mounted transmitter (material delivery/erection/wiring/looptesting) is hardly affected by the progress of piping installation activities and therefore nottime critical.

Most direct mounting concepts include the primary isolation valve (e.g. by usingmonoflanges), which requires additional co-ordination between the Mechanical andInstrument Engineering disciplines, as the concept should satisfy the requirements of bothdisciplines. The Manufacturer should be selected in an early project phase, as proprietarydesign details affect plant design. Furthermore, the primary isolation valve should beinstalled before pressure testing of equipment and process piping, which might not be theappropriate time for transmitter installation and associated instrumentation activities.

2.2.3.6 Variety control

If the direct mounting concept is selected, it will not be suitable for all applications, so bothconcepts will be mixed on a specific project. This will increase the variety of componentsand Engineering effort.

2.2.3.7 Design aspects

For the direct mounting concept, the following aspects need specific attention:

• To prevent too high stresses on the process nozzle, the length and weight of theinstrument with its accessories need to be reviewed, especially in vibrating service andon small bore process piping and very high temperature service. Co-ordination with

Mechanical Engineering is required.

• Direct mounting is less suitable for applications that require rodding out of processconnections. However, if auto-rodder is used, direct mounting is preferred.

• The compactness of most direct mounting designs causes the instrument housing tooperate close to the process operating temperature. The upper and lower temperaturelimits of sensor fill fluids/electronics of instruments restrict the use of the directmounting concept in low and high temperature applications.

• When the direct mounting of a differential pressure type flow meter is considered, thetransmitter/manifold shall be supported by only one of the tappings and connected by

tubing to the second tapping. If the transmitter is supported by two tappings pointing inthe same direction, as shown in Figure 3, a slight misalignment of the tapping pointscauses leakage and undue stress at the mounting bolts. Furthermore, the thickness ofan orifice plate depends on the plate type and its nominal pipe size.

8/13/2019 32371011 Nov 09


PTS 32.37.10.11November 2009

Page 8

Figure 3 Incorrect direct mounting of a DP flow transmitter/manifold by supporting itfrom both tapping

8/13/2019 32371011 Nov 09


PTS 32.37.10.11November 2009

Page 9

3. INSTRUMENT PROCESS CONNECTIONS FOR ON-LINE INSTRUMENTS

3.1 GENERAL

Process connections for on-line instruments shall have dedicated primary isolation valvesto allow disconnection from the process. Only if a loop requires multiple instruments tocover the full operating range may the primary isolation valve(s) be shared, providing thatsecondary isolation is available for each instrument.

NOTE: In certain applications, a straight-through type primary isolation valve, e.g. gate, ball or plug valve, maybe required to allow rodding out of plugged connections.

The flange facing finish of direct mounting components (e.g. gauge blocks) and lap jointtube adapters shall be in accordance with ASME B16.5.

The number of connections shall be minimised. Where required, compression fittingsand/or flanged connections are preferred. For certain applications, the Principal mayspecify threaded connections. Parallel threaded connections with soft annealed metalsealing rings, as shown in Standard Drawings S 37.808 and S 37.809, have preferenceover tapered sealing connections for their leak tightness.

Appendix 1NOTE: Tapered threaded connections such as NPT require a thread sealant such as PTFE. Seefor temperature limitations.

Figure 4 Top tappings

Instrument process connections on horizontal process lines shall be located at the top(vertically up or pointing upwards at an angle of up to 45 degrees from the vertical axis) tolimit the blocking risk by solids, dirt or pipe scale, as shown in Figure 4.

For liquid measurements on horizontal process lines, however, this arrangement can causegas to collect in the impulse lines. In such cases, side tappings are preferred but if this isnot feasible, the effect on the measurement accuracy should be limited by installing sealpots to allow regular venting and/or by minimising the difference in elevation between thetop of the impulse line and the instrument process connection, as shown in Figure 5 andFigure 6.

If a liquid contains vapours, dissolved gas or low temperature (below ambienttemperatures) liquids e.g. LNG, LPG, etc, the process connection should be installed in avertical line. If a process connection can only be made available from a horizontal line, thetapping should be either at the side or pointing downwards at an angle of up to 45 degreesfrom the horizontal axis except for low temperature liquids where the process connectionshall remain horizontal or pointing upwards. The impulse lines shall slope downwards to theinstrument so that gas is automatically vented back into the process, as shown in Figure 7.

Downward-pointing tapping in horizontal lines are vulnerable to fouling and may only beused if approved by the Principal. If downward-pointing tapping is used, provide properflushing facility as shown in Figure 7a; further consideration on this configuration in 4.3.

8/13/2019 32371011 Nov 09


8/13/2019 32371011 Nov 09


PTS 32.37.10.11November 2009

Page 11

3.2 INSTRUMENT PROCESS CONNECTIONS FOR THE REMOTE MOUNTING CONCEPT

Process connections for on-line instruments shall, wherever possible, terminate in a DN 15lap joint flange with lap joint tube adaptor. Primary isolation valves, lap joint flanges,gaskets and bolts, including their heating/insulation, are the responsibility of Mechanical

Engineering. The responsibility of Instrument Engineering starts at the lap joint tubeadaptor.

3.3 INSTRUMENT PROCESS CONNECTIONS FOR THE DIRECT MOUNTING CONCEPT

Flanged gauge blocks shall be used for direct mounted pressure gauges. Similar blocksmay be used for process connections of other instrument types.

Some Manufacturers offer components that combine the primary isolation valve andinstrument manifold in one housing, for instance in a monoflange style. Such designs maybe considered in consultation with Mechanical Engineering in the light of the issuesidentified in (2.2.3).

8/13/2019 32371011 Nov 09


PTS 32.37.10.11November 2009

Page 12

4. GENERAL SPECIFICATION FOR IMPULSE LINES

4.1 SPECIFICATION OF COMPONENTS

The general rules for material selection of impulse line components are similar to those for

wetted parts of instruments, as detailed in PTS 32.31.00.32 Material selection is subject toPrincipal's approval.

Where process conditions allow, the wetted instrument impulse line components (i.e.tubing, compression fittings, manifolds etc.) shall be made of AISI 316 type stainless steel.Stainless steel tubing and compression fittings shall be suitable for a maximum allowableworking pressure of at least 413 bar (ga) at temperatures between -200 °C and +38 °C. Formaximum allowable working pressures at higher temperatures, see Appendix 1.

NOTES: 1. The maximum allowable working pressure of at least 413 bar (ga) applies to SS fittings only Lowermaximum allowable working pressures apply to CS or brass fittings.

2. The maximum allowable working pressure of the impulse line components shall equal or exceedthe upper design pressure of the process it serves.

For applications where AISI 316 stainless steel is not suitable, other materials such asDuplex, Super Duplex, Incoloy, Monel, Hastelloy, Tantalum or Titanium should be applied.Components of such materials may however be very costly and may at a later stage beinadvertently interchanged with unsuitable stainless steel components. Alternative ‘hook-up’arrangements (e.g. diaphragm seals) or alternative measurement principles (e.g. in-lineflow instruments or internal level measurements) should be considered as a first choice.

Austenitic stainless steel tubing (including insulated tubing) is vulnerable to chloride stresscorrosion if exposed to temperatures above 60 °C. Impulse and steam tracer tubinginstalled under such conditions shall be constructed from any of the following materials:

- ASTM B 423 alloy (UNS N08825) tubing, e.g. Incoloy 825 or Nicrofer 4221;- ASTM B 668 alloy (UNS N08028) tubing, e.g. Sanicro 28;

- UNS S 312 254 SMO.- UNS S32750 Alloy 2507 e.g. Super Duplex 2507

NOTES: 1. However for super duplex tubing, only super duplex fitting shall be used, the three groups of tubingmaterials, listed above, may be used in conjunction with AISI 316 type stainless steel compressionfittings.

2. The hardness of the high nickel alloy tubing shall be within the range of 77 HRB to 83 HRB,hardness of super duplex tubing shall be within 30 HRC.

3. Chloride stress corrosion on the outside of the tubing may be caused by chlorides present in rainwater (especially in marine and coastal locations) and by water-soluble chlorides in insulationmaterial.

4. Some Manufacturers offer pre-insulated tubing or tubing bundles (impulse and tracer tubing plusinsulation), including a wide range of dedicated sealing and installation accessories. If theManufacturer’s instructions regarding installation and sealing are followed, such products may beconsidered in view of their commercial attractiveness and better ingress protection than field

fabricated insulated bundles. If such products are chlorides free (e.g. not containing any PVC) andif water tightness can be guaranteed during construction and plant operation, chloride stresscorrosion will not occur and austenitic stainless steel may be used.

Stainless steel impulse line components may be selected on the basis of the given onstandard drawings S 37.001 (Instrument impulse lines, metric version) or S 37.002(Instrument impulse lines, imperial version). Gauge blocks shall be provided with a 1/2 inchfemale threaded gauge adapter (not applicable when gauges integral with tube adapter areused). The type of thread for the pressure gauge (tapered 1/2 inch NPT or parallelG 1/2 inch) shall be specified by the Principal.

NOTE: Gauge blocks are provided with adapters to allow dial positioning.

8/13/2019 32371011 Nov 09


PTS 32.37.10.11November 2009

Page 13

4.2 MOUNTING ARRANGEMENTS

4.2.1 General

Subject to environmental conditions, instruments may require protective shades; see

PTS 32.31.00.32. The shade shall be fixed in a way allowing quick installation andremoval.

Note: The protective shade should be installed for exposed instrumentation in tropical and desert environment

4.2.2 Mounting aspects of the remote mounting system

4.2.2.1 Instrument mounting supports

In the remote mounting concept, instruments are installed on dedicated mounting supports.The use of instrument mounting supports mounted on the process line requires theapproval of the Principal. They shall not be applied on:

- process line sizes smaller than DN 100;- insulated process piping;- vibrating service.

If instrument mounting supports are clamped around process piping of a different material,insulating barriers (e.g. tape or gasket material) shall be applied to prevent galvaniccorrosion.

Instrument mounting supports shall not be fixed to grating, as this does not providesufficient stiffness and does not allow the grating to be removed for painting.

If instrument mounting supports have to be fixed to fireproofed plant structures, thesesupports should be welded to the steel structure before the fireproofing is applied.

Typical examples of instrument mounting supports are shown on standard drawingS 37.004.

4.2.2.2 Standardized mounting plates

In the remote mounting concept, the instrument with its manifold is mounted on astandardized mounting plate. If required, the heating element with terminal box, insulatingcovers and protective shade are also installed on this plate.

See standard drawings S 37.815 and S 37.816 for standardized mounting plates with andwithout protective shades respectively. These plates have facilities for installing nameplatesin accordance with PTS 32.31.00.32

4.2.2.3 Instrument location and routing of impulse line tubing

Impulse line tubing shall be as short as possible and the number of joints shall be kept to aminimum. ‘Horizontal’ lines shall slope at a ratio of approximately 1:5.

For straight lengths up to a maximum of 1 m the tubing is self-supporting, for longer lengthsthe tubing shall be supported up to maximum of 1 m intervals with proper tubesupports/clamps. Insulating spacer material shall be applied to separate the tubing from itssupports to prevent galvanic corrosion. Impulse lines shall be grouped closely together.Heavy components such as seal pots shall be properly supported to prevent stress on ordamage of compression fittings and tubing.

8/13/2019 32371011 Nov 09


PTS 32.37.10.11November 2009

Page 14

For remote mounted instruments the impulse lines shall be so arranged that any movementwill not exert excessive force on any connection. Such movement may be caused bythermal expansion (e.g. in steam or LNG service) or vibration of process pipes. Thermalexpansion can be absorbed by expansion loops. Instruments connected to vibratingprocess pipes shall be installed on dedicated instrument mounting supports, with the tubing

arranged sufficiently flexibly to take up the vibration and to prevent the tubing from vibratingexcessively.

Typical examples of hook-ups for thermal expansion or vibrating service are shown onstandard drawings S 37.001 (Instrument impulse lines, metric version) and S 37.002(Instrument impulse lines, imperial version).

NOTES: 1. Special attention shall be given to long impulse lines running horizontally. This type of installationshall be avoided to prevent mechanical damage or the formation of "pockets" which may result infalse readings.

2. Where fittings are used in parallel tubing runs, their locations may require staggering to provideproper access.

3. Flexible components shall not be used to absorb movement by thermal expansion or vibration.

4.2.2.4 Connections between differential pressure measuring instruments and manifolds

For connections between differential pressure type measuring instruments and manifolds,one of the following connection types should be selected:

− Connections with standardized mating dimensions as specified in IEC 61518, type A(with an extended spigot) for a maximum allowable working pressure of 413 bar (ga) at38 °C, with O-ring dimensions according to ISO 3601-1.

− Connections not standardized by an international body, such as coplanar typeconnections. The design is vendor dependent.

4.3 FILLING, FLUSHING, VENTING AND DRAINING

The Principal should be contacted about his policy on venting, draining and removal of(contaminated) seal and process fluids from impulse lines. Draining/venting is one option;disposal into the process by means of a mobile seal liquid refill pump unit is anotherfrequently used option. The impulse line hook-up should include the necessary connectionsto connect such a pump unit.

NOTES: 1. The design of the mobile seal liquid refill pump unit requires the approval of the Principal.2. The practice of ‘venting and draining’ fluids is no longer recommended, as it leads to a large

number of small and vulnerable connections to flare and drain systems. Furthermore, thecost involved with such fixed connections is high.

Vent and drain valves shall be provided with a device to prevent tampering. Approximately500 mm tubing shall be fitted to vent or drain connections and directed downwards.

Filling/flushing connection(s) are at least required for the following cases:

− Handling of the process fluid and/or seal liquid poses a danger to human beings or tothe environment. Flushing and neutralising of the instrument and manifold is necessarybefore disconnecting the instrument.

− Process liquids or seal liquids in impulse lines need regular replacement.

Filling/flushing connectors consist of a non-return valve with a capped off compressionfitting. When the connectors are not in use, a compression-type plug shall be fitted andsecured by a bead-type chain to the non-return valve.

The connector shall be selected for:

- d/p cells applied for measurements with a seal liquid for ease of filling;- d/p cells in use for toxic & corrosive applications which require flushing before removing

the instrument.

8/13/2019 32371011 Nov 09


PTS 32.37.10.11November 2009

Page 15

Figure 7b Typical Connector

4.4 PAINTING AND COATING

All supports, brackets etc., shall be protected by a corrosion resistant paint or coating(e.g. galvanising) in accordance with the requirements of PTS 30.48.00.31. Surfaces whichwill be inaccessible after installation shall be treated before installation. Instruments andstainless steel components shall not be painted or coated.

Painting shall not foul threaded connections or jeopardise the proper operation of movingparts such as valve handles.

4.5 TESTING

All on-line instruments and impulse line components shall be pressure-tested to the designpressure limit of the instrument or to a pressure of 1.5 times the upper design pressure ofthe process, whichever is lower.

NOTES: 1. Local regulations may specify a higher test pressure, e.g. twice the intended operating pressure.2. Primary isolation valves shall be closed during flushing of process equipment and piping.

Instrument air, nitrogen or demineralised water shall be used for pressure testing. Afterpressure testing with water, the instrument and the impulse lines shall be carefully drainedand blown out.

Impulse line pressure testing may be integrated with pressure testing of process equipmentand piping, depending on the flushing medium, scope demarcations and timing aspects. Ifthe process equipment or piping is tested with another medium than specified above, theprimary isolation valves shall be closed to prevent it from entering the impulse lines.

8/13/2019 32371011 Nov 09


PTS 32.37.10.11November 2009

Page 16

5. SPECIAL APPLICATIONS AND CONSIDERATIONS FOR IMPULSE LINES

5.1 STEAM SERVICE

Steam entering the impulse line(s) shall condense before reaching the instrument to

prevent damage by overheating. In freezing climates, steam/condensate impulse lines shallbe winterised by tracing and insulation.

For remote mounted instruments, seal pot(s) shall be provided to establish a firmcondensate reference point(s). The impulse line(s) shall slope downwards from the sealpot(s) to instrument process connection and to the instrument. For differential pressure typeinstruments, these condensate reference points shall be at the same elevation, as shown inFigure 8.

For direct mounted pressure instruments, a gauge block with integral siphon should beapplied.

Manufacturer’s solutions for direct mounted, differential pressure type instruments may be

acceptable, if a firm condensate reference point can be established.

Figure 8 Steam flow measurement

5.2 OXYGEN SERVICE

All components in oxygen service shall meet the requirements of PTS 31.10.11.31

NOTE: Any medium containing more than 21% oxygen by volume or a system with air at a pressure above50 bar (ga) is to be considered as oxygen service.

5.3 HYDROGEN FLUORIDE (HF) SERVICE

The material selection for wetted parts of instruments and components shall meet therequirements of PTS 31.38.01.11

Stainless steel type AISI 316 may, under certain conditions, be subject to pitting and/orstress cracking if exposed to process fluids containing HF.

8/13/2019 32371011 Nov 09


PTS 32.37.10.11November 2009

Page 17

Impulse line tubing in HF service shall be constructed from ASTM B 165 UNS NO4400(Monel) with Monel compression fittings. Alternatively, Monel or carbon steel welded pipesmay be applied (see PTS 31.38.01.11). All valves shall be of Monel.

NOTES: 1. Cold deformation shall be minimised by the application of the largest possible bending radius,limiting the extreme fibre deformation to 5% maximum. In practice, this amounts to a minimumbending radius of 10 to 15 times the diameter for small bore piping (less than DN 25).

2. Before HF is put into the system, a careful check of the tightness of compression joints andscrewed connections is required. Fluorides formed upon leakage will produce a very hard metalsurface which will make re-tightening of the joint practically impossible.

3. The Principal shall be consulted for the selection of impulse line material for HF service.4. PTFE seals may be used in valves in HF service.

5.4 FLUIDS WITH HIGH POUR POINTS OR HYDRATE FORMATION RISK

Liquids which solidify at ambient temperatures shall be prevented from entering processtappings, primary isolation valves and impulse lines to prevent malfunctioning, blockageand/or damage.

Special attention shall also be given to those gas services where hydrates may form at lowtemperatures.

A liquid seal (6.1), diaphragm seal (6.3), external purging (6.4) or heating (7) may beapplied to prevent solidification and hydrate formation.

5.5 FLUIDS CONTAINING SUSPENDED SOLIDS

If process fluids contain suspended solids, these solids may settle in process tappings,primary isolation valves and impulse lines, and may ultimately cause complete blockage.

If the concentration of the suspended solids is relatively low, blockage may be prevented bysloping the process connections and (short) impulse lines downwards to the process atan angle of approximately 45°.

If the concentration of suspended solids is high, a liquid seal (6.1) or external purging (6.4)should be applied.

5.6 FOULING AND WAXY SERVICE

Impulse lines in fouling/waxy service are likely to become plugged, even if heating isapplied. In such cases, instruments with extended diaphragms or with remote diaphragmseals should be considered. In the latter case, additional purging may still be required to

prevent plugging between the equipment/pipe wall and the remote seal.

NOTE: Vacuum Flashed Cracked Residue (VFCR) is known to be a non-stable liquid: delayed cracking willform coke, which plugs impulse lines. In such situations, remote seals with external purging have beensuccessfully applied.

5.7 SUSCEPTIBILITY OF LOW RANGE GAS MEASUREMENTS TO LIQUID SLUGS

Experience shows that standard 10 mm OD impulse line tubing with an internal diameter of7 mm has a limited self-draining capability. If used in gas or vapour service, condensateformed may not flow back into the process, not even in vertical lines. Droplets tend tocluster and slugs of liquids ‘hang’ in the impulse line. ‘Hanging slugs’ have a considerableimpact on pressure or differential pressure sensing instruments with a relatively low

adjusted range.

8/13/2019 32371011 Nov 09


PTS 32.37.10.11November 2009

Page 18

For pressure and differential pressure sensing instruments with an adjusted range of 2 baror below, one or more of the following remedial measures should be considered:

− apply heat tracing to keep the process fluid in the impulse lines in the vapour phase;

− apply wet legs;− mount pressure sensing instruments in the direct vicinity of the process connection, if

feasible, to limit the tubing length and elevation difference between instrument andprocess connection;

− apply wide bore tubing/piping (DN 15 or DN 20) instead of standard 10 mm OD tubing torestore the self-draining capabilities.

NOTE: If very long impulse lines are required for differential pressure sensing (e.g. differential pressuremeasurement across a high column or between columns), two independent pressure sensinginstruments may be installed, whereby the differential is determined by subtraction. For details andlimitations of this alternative, see PTS 32.31.00.32

5.8 LOW TEMPERATURE SERVICE

Process liquids operating at temperatures below ambient that vaporise at ambienttemperatures will evaporate upon entering the impulse lines before reaching the remotemounted instruments. The vapours so formed will push the liquid back towards the processuntil an equilibrium is established.

This self-purging phenomenon occurs for instance in cryogenic processes operatingtypically between -100 °C to -170 °C. Where required, heating shall be considered to assistself-purging (e.g. LPG applications). For details, see (6.4) and (6.5).

Low temperature services require expansion loops in their impulse line tubing,see (4.2.2.3).

5.9 VERY TOXIC SERVICE

For personnel protection and for environmental reasons, facilities should be provided todispel very toxic liquids from instrument impulse lines into the process equipment so thatmaintenance can be performed safely. A mobile seal liquid refill pump unit should be usedto displace very toxic liquids by safe liquids during operation. See also (4.3).

For sites where the ‘vent and drain’ concept is still applied, the following shall apply to verytoxic fluids:

• Manifold valves shall be provided with an interlocking system.

• All vents from instruments/manifolds and seal pots shall be connected to flare.• All drains shall be connected to a drain vessel or covered pit which is allocated for very

toxic products and for which adequate disposal should be arranged.

• The required length of tubing for the vent and drain lines shall be added on the relevanthook-up drawing.

• The instrument or the manifold shall be provided with filling/ flushing connector(s), ifflushing and neutralising of the instrument and manifold is necessary before theinstrument is disconnected. For details see (4.3).

• The maximum allowable concentration of very toxic components in fluids which may bevented to atmosphere shall be approved by the Principal.

8/13/2019 32371011 Nov 09


PTS 32.37.10.11November 2009

Page 19

5.10 ‘SOUR’ OR ‘WET H2S’ SERVICE

‘Sour’ or ‘Wet H2S’ service is defined in PTS 31.38.01.11

Materials which, under any process condition, are in contact with process water or aqueous

condensate shall comply with ISO 15156 or NACE MR0103, as applicable, and the relevantpiping class.

If impulse line components cannot be obtained in accordance with these standards (e.g. therolled thread of some male compression fittings), the Principal shall be consulted.

Valve head spindles and/or parts of them in contact with sour fluids shall be constructedfrom 17-4 PH stainless steel, stellite-coated stainless steel, stellite or Hastelloy-C,complying with ISO 15156 or NACE MR0103, as applicable.

NOTES: 1. ISO 15156 shall apply to oil and gas production facilities and natural gas sweetening plants.NACE MR0175 is equivalent to ISO 15156.

2. NACE MR0103 shall apply to other applications (e.g. oil refineries, LNG plants and chemicalplants).

3. The front ferrules of compression fittings are the second or third sealing in the fitting and, sincethey need to have higher hardness in order to function properly, they may be exempted from thehardness limitations.

8/13/2019 32371011 Nov 09


PTS 32.37.10.11November 2009

Page 20

6. SEALING AND PURGING

6.1 LIQUID SEAL

Seal liquids for use in impulse lines shall be selected in consultation with the party

responsible for the process design, considering the following aspects:

- effect of process fluid on seal liquid, i.e. the resistance/stability of the seal liquid incontact with the process fluids (polymerisation, disintegration, solubility of processfluid);Example: Some sealing liquids decay in sour service. H2S reacts for instance with

silicon oil and causes polymerisation.

- effect of seal liquid on process fluid (process fluid contamination, poisoning of catalyst);

- maintenance: the seal liquid and the selected hook-up shall guarantee a lowmaintenance effort. A seal liquid that needs frequent replacement or replenishment forinstance is not acceptable;

- seal liquid properties (temperature expansion coefficient, evaporation and freezing point,kinematic viscosity, handling safety, cost of purchase, tracing, disposal etc.).

This includes the following aspects:

• the seal liquid density in the (traced) impulse line shall be higher than the density ofany of the process fluid components to prevent gradual replacement of sealing liquidby components from the process fluid;

• the kinematic viscosity in the impulse line shall not exceed 200 mm2/s to obtain an

acceptable response time;

•the seal liquid shall not evaporate under any operating condition at local ambientconditions;

• the seal liquid shall not freeze or shall be protected against freezing at local ambientconditions;

• the seal liquid shall not be very toxic or flammable.

Three groups of seal liquids are listed below in order of preference:

− ‘Familiar’ seal liquid: One of the heavy components, present in the process fluid, isselected as sealing liquid. If the process fluid contains water, water should beconsidered as a first choice, as it is attractive for its chemical and physical properties

(non-toxic, non-flammable, non-viscous, immune to H2S, density higher thanhydrocarbons, low temperature expansion coefficient), low cost, high availability, easeand safety of handling and disposal.

− ‘Foreign’ seal liquid: A fluid not present in the process fluid. It shall not harm nor beharmed by the process fluid.

− Process liquid: The process liquid is used as seal liquid.

8/13/2019 32371011 Nov 09


PTS 32.37.10.11November 2009

Page 21

Frequently used low-cost seal liquids are water, glycol, glycerine and silicon oil (e.g. usedsilicon oil, drained from transformers).

NOTES: 1. The process liquid is only suitable as sealing liquid, if it is self-condensing under any normal andabnormal operating pressure at the highest ambient temperature.

2. If the process liquid is a mixture of for instance hydrocarbons, the density of process fluids in wet

legs may gradually drift away from the density in the associated equipment as a result of‘stripping’.

3. If the composition of a process liquid mixture in the equipment changes gradually from light toheavy, self-condensing will replace the light components of the process fluid in the reference legby heavier components, such as water. This will for instance happen in hydro-conversion plants,that are started up with a light feedstock and subsequently converted to heavier feedstock with acomposition that change gradually as a result of decaying catalyst activity.

4. Applications using ‘familiar’ and ‘foreign’ seal liquids have the advantage that the wet leg(s) can befilled prior to start-up and eventually zero checked. This will give a reasonable instrument readingat initial plant start.

5. Level applications using process liquid in the wet reference leg require a liquid level in theequipment above the lower nozzle elevation and sufficient pressure to fill the legs with processfluid at initial plant start.

Where the above considerations do not result in a satisfactory solution, the use of remote

seals or another measurement principle should be considered.

Where seal liquids are used in impulse lines, a nameplate shall be installed near theinstrument with information about the seal liquid, such as the seal liquid name. Additionally,the seal liquid density and the height of the wet leg(s) in mm shall be mentioned forpressure and dP type level/pressure measurements.

6.2 LIQUID SEAL AND HOOK-UP OF WET LEG LEVEL APPLICATIONS

6.2.1 Introduction

The selection of seal liquids and the hook-up arrangement for differential pressure type

level instruments with wet legs is defined in global terms in PTS 32.31.00.32 ThisPTS section provides further guidance.

NOTES: 1. Seal liquid selection for the reference leg applications requires special attention, since the LRVcalculation includes a term for elevation difference (upper nozzle < > transmitter) times density ofthe reference leg. The LRV shifts if the actual density in the reference leg differs from the oneused for LRV calculation.

2. For transmitters mounted just below the lower equipment nozzle (i.e. transmitters located less than150 mm below the lower equipment nozzle), only density changes in the reference leg affect theLRV. For transmitters mounted well below the lower equipment nozzle (i.e. transmitters locatedmore than 150 mm below the lower equipment nozzle), changes in density in the measurementleg will also affect the LRV and may justify the use of seal liquids in the measurement leg.

3. For transmitters mounted well below the lower equipment nozzle, changes in densities in the legswill partially counteract each other in their effect on LRV. The density drift in the measurement leg

may however differ from the density change in the reference leg and even if they are equal, adensity drift in the reference leg is only partially compensated by the same density drift in themeasurement leg.

4. Apart from LRV errors resulting from liquid density changes, the operating pressure affects themeasurement accuracy in two ways:

− The transmitter accuracy is affected by variations in operating pressure. This effect is howeverminor compared to other measurement errors;

− The LRV calculation includes a term for elevation difference (upper nozzle < > 0% level) timesvapour density, which varies with operating pressure. This effect of vapour density on the LRVmay be considerable for high pressure applications, as shown in Appendix 2.

5. Appendix 2 provides examples for the effect of changes in process variables on themeasurements.

8/13/2019 32371011 Nov 09


PTS 32.37.10.11November 2009

Page 22

Apart from general seal liquid selection aspects discussed in (6.1), the following additionalaspects are specifically relevant for wet leg level measurements, as they may causemeasurement errors:

− If the selected seal liquid dissolves gases such as hydrogen, a (sudden) pressure dropwill cause the liquid in the reference level to rise (a phenomenon comparable with theopening of a ‘coca-cola’ bottle) and overflow into the equipment. The loss of referenceleg liquid will cause a zero error.

− The density of some seal liquids (e.g. silicon oil) varies considerably with temperature.To limit the effect of changing densities, it should be considered to keep seal liquids inwet legs at a constant temperature by the use of tracing and insulation.

− If dry inert gas is continuously fed into the vapour space of equipment (e.g. blanketinggas), the process liquid and the wet leg seal liquid will gradually evaporate. Wetreference legs (i.e. without remote seals) are unsuitable for such applications.

6.2.2 In situ calibration

The accuracy tolerance class for each measurement shall be defined in accordance withthe requirements of PTS 32.31.00.32 In situ calibration may be required to mitigatemeasurement errors caused by liquid density variations and operating pressure.

Two types of hook-ups can be distinguished:

− A hook-up that allows in situ zero and span check at the actual operating pressure.If the liquid density in the wet leg(s) varies considerably over time, the resultingmeasurement error might become unacceptable. Similarly, if the instrument is zerochecked at atmospheric pressure, the measurement error caused by a (high) gas

density might become unacceptable.

This type of hook-up should be selected if calculations show that the measurementerror caused by variations in wet leg liquid density and/or actual gas density isunacceptable.

− A hook-up that does not allow in situ zero and span check. This hook-up may beselected in all other cases.

In situ zero and span checks require an equalising line between the lower and upperequipment connections.

NOTES: 1. Some examples of measurement errors caused by liquid or gas density variations are given in Appendix 2.

2. One of the cases in Appendix 2 reflects the measurement error caused by transmitter calibrationat atmospheric pressure. The resulting measurement error for this high pressure application isextremely high and would thus require a hook-up that allows in situ calibration.

3. If the lower nozzle elevation corresponds with the LRV (0% level), in situ zero calibration isperformed with an empty but pressurised equalising line. Similarly, if the upper nozzle elevationcorresponds with the URV (100% level), in situ span calibration is performed with a full andpressurised equalising line.

4. If nozzle elevations do not correspond with the LRV and URV, in situ calibration with a standardhook-up arrangement is still possible for ‘intelligent’ measuring devices. As a first step, the LRVand URV are determined with an empty and full equalising line respectively. This provides theactual density figures required to calculate the final LRV and URV settings. As a second step, thefinal LRV and URV are entered into the transmitter by remote communication.

5. If nozzle elevations do not correspond with the LRV and URV, in situ calibration of ‘non-intelligent’measuring devices is only possible if the hook-up is modified so that the equalising line can befilled to the levels corresponding with the 0% and 100% readings.

8/13/2019 32371011 Nov 09


PTS 32.37.10.11November 2009

Page 23

6.2.3 Hook-up selection

The table below should be used for hook-up selection of wet leg level measurements.

Table 1 Hook-up selection table for wet leg level measurements (see notes 1 and 2)Transmitterelevation

Less than 150 mm below the lowerequipment nozzle

More than 150 mm below the lower equipment nozzle(see Figure 10)

(note 1) (see Figure 9)

↓ ↓ ↓

Liquid inmeasurementleg(see note 2)

Process liquid Process liquid The same‘familiar’ or

‘foreign’ seal

liquid↓ ↓ ↓ ↓

Liquid inreference leg(see note 2)

Process liquid ‘Familiar’ or‘foreign’ seal

liquid

Process liquid ‘Familiar’ or‘foreign’ seal

liquid

in both legs

↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓

Zero & spancalibration atoperatingpressure

Yes No Yes No Yes No Yes No Yes No

Resulting installation requirements (see note 6)

↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓

Seal pot inreference leg

Yes

Seal pot inmeasuring leg

No Yes No Yes No Yes

Equalising line Yes No Yes No Yes No Yes No Yes No

Manifoldvalves(see note 5)

I-I-V-V I-I-E-V I-I-V-V I-I-V-V I-I-V-V I-I-E-V I-I-V-V I-I-V-V I-I-V-V I-I-V-V

Figure 9 Typical hook-up for transmitter, mounted less than 150 mm below the lowerequipment nozzle

8/13/2019 32371011 Nov 09


PTS 32.37.10.11November 2009

Page 24

Figure 10 Typical hook-up for transmi tter, mounted more than 150 mm below the lower

equipment nozzle

NOTES: 1. If ‘familiar’ or ‘foreign’ seal liquid is used for the measurement leg, the transmitter shall be mountedmore than 150 mm below the equipment nozzle to permit seal pot installation.

6.12. For the definition of ‘familiar’ and ‘foreign’ seal liquids, see ( ).3. For process equipment operating under partial or full vacuum conditions, filling of wet legs is

cumbersome. For such applications, diaphragm seals or another level measurement principleshould be considered as a first choice.

4. For standardization reasons, the Principal may decide to use only a limited number of the hook-uptypes presented in Table 1 for all applications.

5. Manifold valves ‘I-I-V-V’ means Isolate/Isolate/Vent/Vent and ‘I-I-E-V’ meansIsolate/Isolate/Equalise/Vent, see Figure 11 and Figure 12.

6. Hook-up requirements are based on the following rationale:

a) Seal pots with vent valves are provided as buffer volume for all wet reference legs.

b) Seal pots with vent valves are provided as buffer volume in measurement legs if:

• the transmitter is mounted more than 150 mm below the lower equipment nozzle and zeroand span calibration is required

or

• the transmitter is mounted more than 150 mm below the lower equipment nozzle and themeasurement leg contains ‘familiar or ‘foreign’ liquid.

c) The vent valves on the seal pots are required for zero & span calibration at operating pressureand/or for filling of the wet leg with process fluid.

d) An equalising line between the upper and lower equipment nozzle is needed for allapplications, where zero and span calibration at operating pressure is required, see Figure 9 and Figure 10.

e) Manifolds for wet leg level measurements shall only be provided with an equalising valve (seeFigure 12) if required to fill the reference leg with process liquid, i.e. both legs contain processliquid and no equalising line is installed between the upper and lower equipment nozzle(Figures 9 and Figure 10). In all other cases, the manifold shall be provided without equalisingvalve (Figure 11) to prevent mixture of measurement and reference leg liquids and/or partialloss of the wet reference leg.

8/13/2019 32371011 Nov 09


PTS 32.37.10.11November 2009

Page 25

Figure 11 Double iso late/vent typemanifold

Figure 12 Double isolate/equalise/vent type

manifold

Valves provided I-I-V-VValves provided I-I-E-V

6.3 DIAPHRAGM SEALS

6.3.1 Introduction

Remote diaphragm seal applications and their installation (tracing/insulation) is covered byPTS 32.31.00.32 This PTS Section provides additional requirements for installation andcalibration of diaphragm seal type level transmitters.

6.3.2 Remote seals for level applications

6.3.2.1 Reducers

For new installations, the equipment nozzle shall match the flange size of the diaphragmseal.

If reducers are required to match the nozzle size of existing equipment (e.g. DN 50) withthe diaphragm seal size (e.g. DN 80), eccentric reducers shall be used and the bottom ofthe reducer shall be flush with the bottom of the primary isolation valve to prevent dirt fromcollecting/settling.

6.3.2.2 In situ calibration

If the remote seal was selected to prevent impulse line plugging in fouling or waxy service,an equalising line would also become plugged and shall therefore not be installed. Hencein situ zero and span calibration at the actual operating pressure is not possible. Apart fromflushing/purge connections, vent connections are required for in situ zero calibration atatmospheric pressure (see Figure 13).

For remote seals, used in applications where no plugging risk exists and where the liquid

kinematic viscosity can be kept below 200 mm2/s, an equalising line may be installed

between the lower and upper nozzle to allow in situ zero/span calibration at the actualoperating pressure (see Figure 14). Drain/vent or flushing/purge connections shall beinstalled as required.

8/13/2019 32371011 Nov 09


PTS 32.37.10.11November 2009

Page 26

Figure 13 Hook-up without equalising line

Figure 14 Hook-up with equalising line

Flushing rings may be ordered with the diaphragm seals. Alternatively, butt-welded primaryisolation valves may be used provided with orifice flanges on the diaphragm seal side. Theinstallation details and scope split shall be agreed with Mechanical Engineering.

8/13/2019 32371011 Nov 09


PTS 32.37.10.11November 2009

Page 27

6.4 EXTERNAL PURGING

External purging may be considered only if other methods to eliminate problems caused bycondensation, vaporisation or plugging are not practicable. Its use however, should beavoided whenever possible since it could cause false differentials, the installation costs are

higher and more frequent maintenance is required.

Since the process fluid may enter part of the impulse line on purge failure, the selectedimpulse line materials shall be suitable for the process fluid. The purge fluid shall be freefrom solids, non-corrosive and in single phase at all operating temperatures and pressures.The purge fluid shall not interfere with the process nor react with the process fluid. Purgesystems shall have a guaranteed source of supply at a pressure which is permanentlyhigher than the maximum process pressure, but lower than the design pressure of theprocess equipment or piping. A low but constant flow rate shall be maintained. The fluidvelocity at the process connection shall be approximately 0.06 m/s for liquid purge and0.6 m/s for gas or steam purge.

The purge injection point should be close to the process connection(s) to limit the effect of

pressure drop caused by the purge flow in the impulse line(s).

NOTES: 1. Purge gas injection near the instrument may cause considerable measurement errors in lowpressure and vacuum applications due to relatively high pressure drop in the impulse lines.

2. The purge injection point may be located close to the instrument, if calculations show that thepressure loss in the impulse line(s) has a negligible effect on the measurement accuracy.

A purge assembly should be used, consisting of a filter, soft seated non-return valve(s) andvent valve with anti-tamper facilities.

A constant purge flow can be reached by one of the following methods:

− A restriction orifice in the form of a purge orifice nipple.

A restriction orifice may be used, if the purge supply pressure is constant and highenough to guarantee a stable purge flow under all operating conditions. For gas andsteam service, this is reached at critical flow across the restriction orifice, i.e. the purgeflow rate is independent of variations in process operating pressure.For details on purge orifice nipples, see standard drawing S 37.805.

− A constant flow device.

For side mounted purge pipes in equipment, see Standard Drawings S 38.047 andS 38.048. Top or side mounted purge pipes and primary isolation valves are theresponsibility of Mechanical Engineering.

Instruments with gas purging shall be mounted above the maximum liquid level and theimpulse lines shall slope downwards from the instrument/manifold to the processconnection(s).

8/13/2019 32371011 Nov 09


PTS 32.37.10.11November 2009

Page 28

6.5 SELF-PURGING

6.5.1 Remote mounted instruments

Where self-purging is applied, process connections should be located on the top or side of

the equipment/process piping.

For process connections at the side of the equipment/process piping, the impulse line(s)shall drop vertically downwards from the instrument and then continue horizontally with aslope of approximately 1:5 down to the primary isolating valve(s) at the processconnection(s). To prevent measurement errors due to liquid static head if the self-purging isnot operating properly, the vertical drop from the instrument shall be as short as possible,see also (5.7).

The first part of the impulse line(s) at the primary isolation valve side shall be insulated overa length of at least 300 mm to reduce heat influx into the process. The remaining part shallhave either:

− an exposed, bare length of at least 300 mm to enable evaporation of the process fluidby heat influx from the surrounding atmosphere. This arrangement shall be used if allprocess liquid components evaporate under all normal and abnormal operatingpressures at the lowest ambient temperature;

or

− a heated and insulated length of at least 300 mm to assist evaporation. Thisarrangement shall be used, if the liquid contains heavy components which will notevaporate under any of the normal or abnormal operating pressures at the lowestambient temperature.

6.5.2 Direct mounted inst ruments

The currently available direct mounting products are less suitable for instruments in lowtemperature service, due to the requirement to reduce heat influx into the process and lowtemperature limits of instruments, see also (2.2.3).

NOTE: The lower temperature limit of instruments depends on the applied sensor fluid and on limits for theelectronics. The temperature drop between the process and a direct mounted instrument depends onthe properties of the direct mount components, such as dimensions/exposed area/number and type of

joints and materials of construction.

8/13/2019 32371011 Nov 09


PTS 32.37.10.11November 2009

Page 29

7. HEATING AND INSULATION

7.1 GENERAL

The type of heating (steam heating, electrical tracing or other means) of instruments and

impulse lines shall be established in consultation with the Principal. Tracing temperaturesshall be carefully selected to prevent overheating, resulting in boiling impulse line liquid.

7.1.1 Remote mounted instruments

If transmitters require heating, pre-assembled instrument housings with heating facilitiesand insulation shall be provided around the manifold and transmitter housing.

7.1.2 Direct mounted inst ruments

If direct mounting of heated instruments is considered, the following aspects need specificattention:

− interface with heating and insulation of the process piping or equipment;

− availability of prefabricated and readily removable enclosures with heating facilitiesand insulation for instruments within the selected direct mounting concept;

− length and additional weight resulting from heating and insulation to prevent too highstress on process nozzles.

7.2 STEAM HEATING

Steam heating systems shall comply with PTS 31.38.30.11.

The steam supply and condensate return piping shall be short. The steam supply andcondensate return piping (including steam trap) are the responsibility of MechanicalEngineering.

The manifold and instrument body shall be heated by means of a tracer block. Specialtubing (see 4.1) should be used to heat instrument impulse lines. Special tubing should alsobe used if impulse lines are winterised by steam heating. To prevent overheating,non-conducting spacers shall be fitted between the impulse and heater tubing at 400 mmintervals. The arrangement shall be such that the instrument can be removed withoutdisconnecting the tracer tubing and/or tracer block.

If steam heating is applied for reasons of high fluid pour point, the heater tubing and theimpulse line shall be clamped together. Clamping material shall be stainless steel.

The total number of joints in the tracer tubing shall be kept to a minimum.

NOTES: 1. Steam heating of in-line instruments (e.g. control valves, vortex meters, turbine meters, positivedisplacement meters, etc.) is the responsibility of Mechanical Engineering.

2. Hollow bolts shall not be applied for heating of instruments.

Each instrument shall have a dedicated steam supply and condensate return line withisolating valves, labelled with the instrument tag number. The steam supply to oneinstrument shall not be divided into parallel sections, i.e. for each instrument a singlecontinuous path is required from the steam supply point up to the steam trap.

The steam flow in the tracer tubing shall be downwards and pockets in the tubing shall be

avoided because build-up of condensate will prevent a continuous steam flow.

Each tracer line shall terminate in a condensate return line via a steam trap.

8/13/2019 32371011 Nov 09


PTS 32.37.10.11November 2009

Page 30

7.3 ELECTRICAL TRACING

The heating equipment shall satisfy the requirements for electrical safety in accordancewith the area classification.

NOTE: Certain elements are certified only when installed in the manifold block. In such cases, power to theheating elements shall be switched on only when the elements are inserted in the manifold block.

The arrangement of the electric tracing shall be such that transmitters can be removedwithout disconnecting the electrical heating block.

All electrical trace heating components (except the electrical heating block and/or electricalheater attached to the manifold) are the responsibility of Electrical Engineering and arecovered in PTS 33.68.30.32

Electrical tracing shall not be applied in processes where the upper design temperatureexceeds the temperature limit of the selected heating tape. If self-regulating tracing tape isused (e.g. for winterising), its ‘power off’ point shall be below the temperature at which theimpulse line liquid starts to strip/evaporate.

7.4 INSULATION

Traced impulse lines, traced instrument parts and all steam supply and condensate returnlines shall be insulated. All couplings in the tracer tubing and the impulse lines shall beaccessible without removing the complete insulation. Insulation of impulse lines, seal pots,steam supply lines and condensate return lines is part of the scope of MechanicalEngineering.

For insulating the instrument bodies, manifold blocks and tracer blocks, prefabricatedenclosures shall be applied fitting closely around the parts which are to be heated. These

are part of the scope of Instrument Engineering.

The body enclosure shall be constructed so that it can easily be removed in the event thatthe instrument needs maintenance.

NOTES: 1. The electronic parts of instruments should not be installed within an enclosure in order to preventoverheating and downgrading of the area classification around that part.

2. Winterising shall not be provided for impulse lines in freezing climates when they are installed intemperature-controlled buildings, such as demineralised water plants.

8/13/2019 32371011 Nov 09


PTS 32.37.10.11November 2009

Page 31

8. REFERENCES

In this PTS reference is made to the following publications:

NOTE: Unless specifically designated by date, the latest edition of each publication shall be used, togetherwith any amendments/supplements/revisions thereto.

PETRONAS STANDARDS

Index to PTS publications and standardspecifications

PTS 00.00.05.05

Definition of temperature, pressure and toxicitylevels

PTS 01.00.01.30

Painting and coating of new equipment PTS 30.48.00.31

Gaseous oxygen systems PTS 31.10.11.31

Piping - general requirements PTS 31.38.01.11

Protective steam heating of piping systems PTS 31.38.30.11

Instrument engineering procedures PTS 32.31.00.10

Instruments for measurement and control PTS 32.31.00.32

On-line process stream analysis - sample take-offand transportation

PTS 32.31.50.10

Electrical trace heating PTS 33.68.30.32

STANDARD DRAWINGS

Instrument impulse lines - metric version S 37.001

Instrument impulse lines - imperial version S 37.002

Instrument mounting supports S 37.004Purge orifice nipple S 37.805

Parallel threaded connections S 37.808

Details of parallel threaded pressure transducers S 37.809

Mounting plate type A2 S 37.815

Mounting plate type B2 S 37.816

Purge pipe for carbon steel and low-alloy steelequipment

S 38.047

Purge pipe for stainless steel and non-ferrousequipment

S 38.048

AMERICAN STANDARDS

Pipe flanges and flanged fittings, NPS 1/2 through

NPS 24

ASME B16.5

Issued by: American Society of Mechanical Engineers345 East 47th StreetNew York NY 10017, USA

Standard specification for seamless and weldedaustenitic stainless steel tubing for general service

ASTM A 269

Standard specification of nickel-copper alloy ASTM B 165

Standard specification for seamless and electric

welded low-alloy steel tubes

ASTM B 423

8/13/2019 32371011 Nov 09


PTS 32.37.10.11November 2009

Page 32

Standard specification for UNS N08028 seamlesspipe and tube

ASTM B 668

Issued by: American Society for Testing and Materials100 Barr Harbor Drive, West Conshohocken,PA 19428-2959USA

Materials resistant to sulfide stress cracking in corrosivepetroleum refining environments

NACE MR0103

Petroleum and natural gas industries — Materialsfor use in H2S-containing environments in oil andgas production

NACE MR0175

Issued by:NACE International1440 South Creek Dr.Houston, TX 77084-4906,USA

INTERNATIONAL STANDARDS

Mating dimensions between differential pressure(type) measuring instruments and flanged-onshut-off devices up to 413 bar

IEC 61518

Issued by:Central Office of IEC (Sales Dept)3, Rue de VarembéP.O. Box 131Geneva CH-1211SwitzerlandCopies can also be obtained from national standards organisations.

Fluid systems - Sealing devices – O-rings

Part 1: Inside diameters, tolerances and sizeidentification code

ISO 3601-1

Plain end steel tubes, welded and seamless -General tables of dimensions and masses per unitlength

ISO 4200

Petroleum and natural gas industries — Materials for use inH2S-containing environments in oil and gas production

ISO 15156

Issued by:International Organisation for Standardization1, rue de Varembé CH-1211 Geneve 20Switzerland

Copies can also be obtained from national standards organizations

SHELL DOCUMENTS

Measurement Validation and Comparison – Issue 2.0 OP 98-30219

8/13/2019 32371011 Nov 09


PTS 32.37.10.11November 2009

Appendix 1

APPENDIX 1 PRESSURE AND TEMPERATURE LIMITATIONS OF SS TUBING ANDPACKINGS

Table 2 Pressure and temperature limitations of SS tubing and packing

Design

temperature, °C

Maximum allowable working pressure, bar (ga)

SS tubing12 mm OD

wall thickness2.0 mm

SS tubing1/2” OD

wall thickness0.083”

SS componentswith grafoil

packing

SS componentswith PTFE

packing andPTFE tape

- 200 470 462 413 -- 150 470 462 413 -- 100 470 462 413 400

-50 470 462 413 400+38 470 462 413 400+50 470 462 399 400

+100 470 462 351 350+150 - - 320 300

+200 450 443 297 200+250 - - 276 -+300 400 392 260 -+350 - - 245 -+400 370 365 235 -+450 - - 200 -+500 - - - -+538 357 350 - -

NOTES : 1. The maximum allowable working pressures P for 10 mm OD x 1.5 mm wall thickness stainlesssteel tubing as per MESC specification 74/051 have been calculated using the formula:

min

min

8.0

2

max

t D

t S P

o

m

×−××=

in which:P = maximum allowable working pressure;Sm = the maximum allowable stress in the material caused by internal pressure

at the design temperature;tmin = the minimum standard wall thickness;

Domax = the standard maximum outside diameter.

2. The tolerances for metric sized tubing are in accordance with ISO 4200 and those for imperialsized tubing are in accordance with ASTM A 269.

8/13/2019 32371011 Nov 09


PTS 32.37.10.11November 2009

Appendix 2

APPENDIX 2 EXAMPLE OF CALCULATIONS OF THE EFFECT OF PROCESS VARIABLECHANGES ON dP LEVEL MEASUREMENTS

Figure 15 Effect of process variable changes on dP level measurement

Appl icable formulae:

( )( )[ ] Z t

P MW d U

16.273

03.12

+

××=

8/13/2019 32371011 Nov 09


PTS 32.37.10.11November 2009

Appendix 2

Table 3 Effect of process variable changes on dP level measurements

Scenarios for process variable changes

Ref.

case

HigherP

Calibrationat atm.

Pressure

LowerMW

Highert

HigherdL

LowerdTH

Combined

Process data

Pressure 190 1 190

P bar (abs) 181 181 181 181181

Molecular Weight MW g/mol 28 28 28 22 2228 28 28

Gas temperature t °C 20 20 20 20 35 3520 20

Compressibility Z - 1 1 1 1 1 1 11Process liquid density dL kg/m3 820 820 820 820 820 861 861820

990 990Measured leg density dTX-H kg/m3 1000 1000 1000 1000 10001000

990 990Reference leg density dTX-L kg/m3 1000 1000 1000 1000 10001000

Calculated resultsGas density dU kg/m3 218.3 1.1 163.4 197.8 208.0 208.0 163.2208.0

Lower Range value LRV mbar -177.0 -224.9 -189.1 -185.5 -178.2 -176.8 -185.7-179.2Upper Range Value URV mbar -58.9 -64.2 -60.2 -59.4 -50.1 -56.7 -48.8-59.2

Measurement errorsShift in LRV % 1.3 -25.5 -5.5 -1.2 0.6 1.4 -3.6-Shift in URV % 0.4 -8.6 -1.8 -0.4 15.3 4.1 17.6-

32371011 Nov 09

Documents