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EVALUATION OF HTHA EFFECT ON CARBONSTEEL & CARBON 0.5M0 EXCHANGER USINGVARIOUS NDE TECHNIQUES FOR REFORMER

WASTE HEAT BOILER GAS EXCHANGER INHYDROGEN UNIT

By

Musaed Mohammed Al-Aradah

Mr. Mefleh Al- Otaibi

Mr. Mohmoud E. Mohd

INSPECTION&CORROSIONDIVISION

MINA

ABDULLA

REFINERY

KUWAITNATIONALPETROLEUMCOMPANY

STATEOFKUWAIT

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Contents

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Inspection Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Inspection Narrative . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Detection of HTHA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Inspection Plan & Use of Advanced NDT . . . . . . . . . . . . . . . . . . . . . . . . . 6

Schematic Process Flow Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Schematic Diagram of E-18-205 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

LPT Photographs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

The Advanced Ultrasonic Backscatter Technique . . . . . . . . . . . . . . . . . . . 14

Traditional Inspection Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

High Temperature Inspection Approach and Method Validation . . . . . . . 14

Schematic diagram of Inspection Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Data Acquired during TOFD Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Radiography Reports during Fabrication . . . . . . . . . . . . . . . . . . . . . . . . . 28

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INTRODUCTION

HTHA has been observed in petroleum refining andpetrochemical equipment used in the environment with highhydrogen pressures at elevated temperatures. This attack iscaused by the ingress of hydrogen into steel. Hydrogen atomsreact with dissolved carbons or carbides in steel and formmethane gas in accordance with the following chemicalreaction.

4H + C CH4 or 4H + MC CH4 + 3M (M: metals)

This gaseous methane forms voids mainly on grain boundariesor inclusions, and the increase of gaseous methane pressurein the voids may result in the formation of micro fissure,blistering or cracking. The attacked material significantlydeteriorates its mechanical properties in tensile strength andductility, and finally causes catastrophic failures.

Depending on the combination and number of the abovevariables, the hydrogen damage may be classified as shownbelow:

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ABSTRACT:

Existing C-0.5Mo steel in hydrogen service is still our concernin industries. High Temperature Hydrogen Attack (HTHA) hasbeen one of the major problems in petroleum andpetrochemical industry because of its effect. Since the originalNelson Curves was suggested in 1949 to define the operating

limits for steels used in hydrogen service to avoid HTHA, anumber of research and investigation activities on HTHA havebeen carried out around the world.

In USA, API summarized these data as Publication 941 Steels for Hydrogen Service at Elevated Temperatures andPressures in Petroleum Refineries and Petrochemical Plants

in 1970 and, since then, it has been widely used for materialselection in hydrogen service, operation and maintenance inpetroleum and petrochemical plants.

After completing the NDT activities the inspection results was

revealed that some difference between the original NDT resultreport and onsite report

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InspectionOutline

During hydrogen unit shut down E18205 (Waste Heat BoilerExchanger) was opened for Maintenance & Inspection.

This heat exchanger operates at high temperature in hydrogen service.

The 10 bypass flue gas pipe made of C0.5Mo in this reformer wasteheat exchanger in hydrogen unit was found leaking while hydrotestof

the equipment during plant shutdown (Jan 2009). Subsequently, variousNDE techniques were used to determine the location and extent of thecrack on the base metal of the center pipe.

The dish end of the inlet chamber (Hot End) of the waste heat gasexchanger is made of C0.5Mo material having refractory lining on theinternal surface. Due to high temperature operation in the presence of

hydrogen service, this material is subjected to HTHA (High TemperatureHydrogen Attack). Hence to investigate that no more damage has beendone to the equipment & to conform the equipment is fit for the serviceit is meant to be, the mechanical integrity of the equipment wasestablished by using various NDE techniques like TOFD, Phased Array,InSitu Metallography and Hardness etc.

Key Words : NDE Non Destructive Examination, HTHA High

Temperature Hydrogen Attack, TOFD Time of Flight Diffraction.

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Inspection Narrative

E-18-205 (Waste Heat Boiler Gas Exchanger)

While carrying out shell side Hydrotest, heavy leak wasobserved from the wide open crack occurred on base metal of

10 by pass flue gas pipe at location near to the its west sideend between 4 and 5 O Clock position. Subsequent, visualinspection and Liquid Penetrant Examination showed a 3long wide open crack 2 away from the west end of pipe andalso multiple cracks originating from the west end of pipewhich were extending inside the pipe over area of 2 sq in.

All the circumferential and longitudinal welds of exchangershell were subjected to TOFD (Time of Flight Diffraction)additional advance ultrasonic technique is applied . DuringTOFD inspection Phased Array Technique was applied , somelinear indications were reported in BFW shell circumferentialweld joint CS-3 having a approximate length of 1 meter.

Subsequent to Hydrotest of the shell side, this section of theabove mentioned circumferential weld was again subjected toTOFD NDE in order to reassess its condition with respect toany further deterioration due to high stress encountered

during Hydrotest. However, no significant deterioration to itsoriginal condition was reported.

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DETECTION OF HTHA

Material degradation caused by high temperature hydrogen damage

occurs in three distinct stages. During the first stage hydrogen reacts

with carbides located in the material leading to decarburization and the

formation of methane bubbles located at the grain boundaries.

With time the methane bubbles will lead to micro-cracks, stage two,

which, affect the mechanical properties of the material, these micro-

cracks can propagate, stage 3 and may lead to failure.

Detection of HTHA is reliably performed non-destructively using

advanced back scatter ultrasonic techniques early during the stage 2degradation.

The most cost-effective and often specified approach involves the

advanced backscatter ultrasonic technique which includes the following

and is appropriate for detection and assessment:

Backscattering

Velocity Ratio

Ultrasonic Spectrum Analysis

The advanced ultrasonic back scatter technique is based on the detection

and subsequent analysis of the backscattered ultrasonic signal. Clearly

as the size of the micro-cracks increase the amount of energy reflected

increases and the amplitude of the reflected signal increases

proportionally. As the micro-cracks develop deeper into the material thedepth of penetration can be measured and monitored. Interpretation

must however rely on the pattern rather than the absolute

backscattering amplitude in order to differentiate between HTHA and

inclusions and impurities

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The purpose of the inspection technique is to reliably detect the presence

of micro-cracking as well as accurately and effectively measure and

report the depth of penetration such that this information can be used to

determine fitness for service and remaining life.

The exact technique deployed as the primary detection technique is

dependent on whether the parent material or welds are to be inspected.

None the less the primary detection tool is the advanced backscatter

ultrasonic technique supported by the velocity ratio and Fast Fourier

Transformation techniques both of which are used to support the

backscattering technique.

Inspection Planning and the use of Advanced NDT

Before putting the equipment back into service it was necessary to make

sure that no more damage has been done to the equipment & to

confirming the equipment is fit for the service it is meant to be, the

mechanical integrity of the equipment was established by using variousNDE techniques like TOFD, Phased Array, In-Situ Metallography and

Hardness etc.

An initial assessment of the vessel was carried out to identify susceptible

regions of equipment for inspection. It was decided to inspect a band

50mm wide on either side of all longitudinal, circumferential or nozzle to

shell welds, as well 6 locations with area of 1m x 1m subjected for

inspection by back scatter technique. Further to the above alllongitudinal and circumferential welds would also be inspected using the

Time of Flight Diffraction ultrasonic technique & Phased Array

Technique.

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Flow Diagram for

R-18-201

TUBE BYEPASS

EXCHANGER TUBES

24"

MW

24"

MW

8" 16"

2"

2"4"

REFORMER EFFLUENT TO R-18-203

P-18-2312-CHC1-20"

CONTROL

CONNECTIONS

10" 10"

14"

STEAM & WATER

TO STEAM DRUM

V-18-206

BY

VENDOR

GAS INLET FROM

REFORMERTHROUGH

TRANSITION CONE(VENDOR SUPPLY)

E-18-205

REFORMER

WASTE HEAT

EXCHANGER

2" 2"

INTERMITTENT BLOWDOWN TO V-18-208

BB-18-2304-S1-3"

14"

14"

1

SM-18-2303-C1-1

BOILER FEED WATER

FROM STEAM DRUM V-18-206

FOR INSPECTION

V-18-206

STEAM DRUM

H-18-201

REFORMER

P-18-2305-CH1-6'

FROM SULFINOL UNITP-18-2308-CH1-6'

FED GAS TO R-18-201

R-18-20

2A

R-18-20

2B

P-18-2309-CHC1-8'

P-18-2311-CHC1-8'

V-18-208

INTERMITTENT

BLOW

DOWN

DRUM

SULFUR ABSORBER

HYDROGENERATOR

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Schematic Process Flow Diagram

Schematic Diagram for Waste Heat Boiler (E-18-205)

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Crack indications observed During Liquid Penetrant Test

Cracks observed on Tube sheet to internal sleeve pipe weld of a Waste HeatExchanger of Hydrogen Reformer Unit

E-18-205

E-18-205

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Cracks observed on Tube sheet to sleeve weld fusion area & face edges of

the sleeve as well as internal surface of the sleeve

E-18-205

E-18-205

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E-18-205

Cracks observed on Tube sheet to sleeve weld fusion area

E-18-205

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E-18-205

Cracks observed on face edges of the sleeve

E-18-205

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Multiple transverse cracks observed on the sleeve

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THE ADVANCED ULTRASONIC BACK SCATTER TECHNIQUE

The advanced ultrasonic back scatter technique is based on the detection and subsequent analysis of thebackscattered ultrasonic signal. Clearly as the size of the micro-cracks increase the amount of energy

reflected increases and the amplitude of the reflected signal increases proportionally. As the micro-

cracks develop deeper into the material the depth of penetration can be measured and monitored.Interpretation must however rely on the pattern rather than the absolute backscattering amplitude in

order to differentiate between HTHA and inclusions and impurities

TRADITIONAL INSPECTION APPROACH

The inspection options and approaches available to assess C-0.5Mo equipment susceptible to HTHAhave been documented in many areas, including API 5816. API 581 outlines several levels of

inspection effectiveness options for base metal and weld inspection. Base metal is often inspected

using ultrasonic back scatter (with 0 Degree compression wave) or by utilizing a suite of methodssometime referred to as AUBT (Advanced Ultrasonic Backscatter Techniques). These methods have

been extremely difficult to implement at high temperatures because they depend on the detection of

micro-fissures and high frequency attenuation. Both of these parameters can be difficult to assessduring high temperature UT.

Welds may be inspected for HTHA using shear wave, TOFD, or radiography. Shear wave inspection

may be done with conventional pulse echo methods, or the more specialized approach known as ABSA(Angle Beam Spectrum Analysis). In either case, working at 750oF (400oC) is considered to be

impractical. Radiography can be performed at elevated temperatures; however significant precautions

must be taken (e.g., insulating the film and/or large stand-off) to avoid heat damage to the film. Since

radiography is not ideally suited for detecting the early stages of HTHA, it becomes even less attractivewith these precautions that tend to degrade performance. TOFD has been used for elevated temperature

crack inspection. However, neither the ability of TOFD to detect initial HTHA, nor its ability to detectsmall defects associated with HTHA has been widely published.

HIGH TEMPERATURE INSPECTION APPROACH AND METHOD VALIDATION

Based on the anticipated challenges of performing an HTHA inspection at 700F (370 C), Backscatter

spectrum analysis was utilized for the base metal inspection and TOFD used for the weld and HAZ

(heat affected zone) inspection. The ambient temperature application of the backscatter spectrumanalysis method is based on the attenuation increase of a backwall (ID) reflection7. It has been shown

that attenuation increase with increasing frequency is a function of scattering associated with HTHA

damage (e.g., micro-voids, micro-fissuring, etc.).

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Data acquired from TOFD Inspection

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Indication Showingin 54.8mm

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Indicationshowing from44.8mm up tothe Back

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Indication

showing from44.8mm up tothe Back surface

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Indicationshowing from44.8mm up tothe Back surface(linear

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THE FINDING

The Internal 10 Inch Diameter internal pipe found to having different cracks at different locations.

WeldIdent.

TotalLength

Scanned

DefectIdnt.

Defect Size in mmType

WelderNo.

Assessmentl d H a/t A/l Criteria

CS-03 5600mm

1 153 47.1 11.2 .088 .037 .020

SlagMixedwith

Porosity

WN/A

To be rejectedaccording to

ASME section8 Division 1

2 542 47.9 18.1 .141 .017 .020

SlagMixedwith

Porosity

To be rejectedaccording to

ASME section8 Division 1

Scan with 52 Degree TOFD probes with 125mm Space mainly focus on the half T and below

and 45 degree Phased array 128 Element Probe. Both TOFD and PH Reports attached.

Inspectors Comments / Remarks /Attachments (If any)Total 2 scan covered 100% of the weld Length.L- Length of the defect,d- Depth, h- Height of the defect, a= height of the defect for surface flaws and2a height of the defect for subsurface flaws.

Channels and Transducers settings

Channel 01 -52-5 MHz 10mm -48 dB-- TOFD1stDefect starting from 3045mm to 3198mm2nddefect starting from 3341mm to 3883mm

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4. CONCLUSIONS

1. Hydrogen attack is caused by exposure of steel to a hydrogen environment. The severity of the damagedepends on the time of exposure, temperature, hydrogen partial pressure, stress level, steel composition and

structure.2. Hydrogen undamaged and damaged samples of steel used in plant equipment should be available for the

hydrogen attack testing purposes.3. Recommended methods for detection of hydrogen damage are AUBT - Advanced Ultrasonic BackscatterTechniques, methods based on TOFD, thickness mapping, backscatter and velocity ratio and in-situmetallography - replicas. Results of methods like AUBT Phased Array can be used for estimation of life ofhydrogen attacked equipment.

4. Non-destructive methods based on ultrasonics are able to quantify the hydrogen attack and estimatemechanical properties of hydrogen-damaged steels. The results of such tests can be used in life assessmentcalculations.

5. It would be recommended to review all NDT reports before receiving any new equipment specially whichdesigned for hydrogen Environment.

6. Spot NDT activity 1%-10% internal testing is recommended7. Most of the sleeve cracking because cement refractory was damaged