EVALUATION OF HTHA EFFECT ON CARBON STEEL & CARBON 0.5M0 EXCHANGER USING VARIOUS NDE TECHNIQUES FOR REFORMER WASTE HEAT BOILER GAS EXCHANGER IN 

HYDROGEN UNIT By

Musaed Mohammed Al-Aradah Mr. Mefleh Al- Otaibi

Mr. Mohmoud E. Moh’d

INSPECTION & CORROSION DIVISION MINA ABDULLA REFINERY 

KUWAIT NATIONAL PETROLEUM COMPANY STATE OF KUWAIT 

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 Findings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

INTRODUCTION HTHA has been observed in petroleum refining and petrochemical equipment used in the environment with high hydrogen pressures at elevated temperatures. This attack is caused by the ingress of hydrogen into steel. Hydrogen atoms react with dissolved carbons or carbides in steel and form methane gas in accordance with the following chemical reaction. 4H + C → CH4 or 4H + MC → CH4 + 3M (M: metals)

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

Depending on the combination and number of the above variables, the hydrogen damage may be classified as shown below:

• Hydrogen Embrittlement • Hydride Embrittlement • Solid Solution Hardening • Producing Internal Defects (Cracks)

ABSTRACT:

Existing C-0.5Mo steel in hydrogen service is still our concern in industries. High Temperature Hydrogen Attack (HTHA) has been one of the major problems in petroleum and petrochemical industry because of its effect. Since the original Nelson Curves was suggested in 1949 to define the operating limits for steels used in hydrogen service to avoid HTHA, a number of research and investigation activities on HTHA have been carried out around the world.

In USA, API summarized these data as Publication 941 – “Steels for Hydrogen Service at Elevated Temperatures and Pressures in Petroleum Refineries and Petrochemical Plants” in 1970 and, since then, it has been widely used for material selection in hydrogen service, operation and maintenance in petroleum and petrochemical plants.

After completing the NDT activities the inspection results was revealed that some difference between the original NDT result report and onsite report

Inspection Outline 

During  hydrogen  unit  shut  down  E‐18‐205  (Waste  Heat  Boiler Exchanger) was opened for Maintenance & Inspection. 

This heat exchanger operates at high temperature in hydrogen service.  

The 10” Ø bypass flue gas pipe made of C‐0.5Mo in this reformer waste heat exchanger  in hydrogen unit was  found  leaking while hydrotest of the equipment during plant shutdown (Jan 2009). Subsequently, various NDE techniques were used to determine  the  location and extent of  the crack on the base metal of the center pipe.  

The  dish  end  of  the  inlet  chamber  (Hot  End)  of  the  waste  heat  gas exchanger  is made of C‐0.5Mo material having refractory  lining on  the internal surface. Due to high temperature operation  in the presence of hydrogen service, this material is subjected to HTHA (High Temperature Hydrogen Attack).  Hence to investigate that no more damage has been done to the equipment & to conform the equipment is fit for the service it  is  meant  to  be,  the mechanical  integrity  of  the  equipment    was  established  by using various NDE techniques like TOFD, Phased Array, In‐Situ Metallography and Hardness etc.

Key Words : NDE – Non Destructive Examination, HTHA – High Temperature Hydrogen Attack, TOFD – Time of Flight Diffraction.

Inspection Narrative

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

While carrying out shell side Hydrotest, heavy leak was observed from the wide open crack occurred on base metal of 10” Ø by pass flue gas pipe at location near to the its west side end between 4 and 5 O’ Clock position. Subsequent, visual inspection and Liquid Penetrant Examination showed a 3” long wide open crack 2” away from the west end of pipe and also multiple cracks originating from the west end of pipe which were extending inside the pipe over area of 2 sq in.

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

Subsequent to Hydrotest of the shell side, this section of the above mentioned circumferential weld was again subjected to TOFD NDE in order to reassess its condition with respect to any further deterioration due to high stress encountered during Hydrotest. However, no significant deterioration to its original condition was reported.

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 various NDE 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 all longitudinal and circumferential welds would also be inspected using the Time of Flight Diffraction ultrasonic technique & Phased Array Technique.

Flow Diagram for

R-1

8-20

1

TUBE BYEPASS

EXCHANGER TUBES

24" MW

24" MW

8" 16"

2"2"4"

REFORMER EFFLUENT TO R-18-203P-18-2312-CHC1-20"

CONTROL CONNECTIONS

10" 10"

14"

STEAM & WATERTO STEAM DRUM

V-18-206

BYVENDOR

GAS INLET FROM REFORMERTHROUGH TRANSITION CONE (VENDOR SUPPLY)

E-18-205REFORMER

WASTE HEAT EXCHANGER

2" 2"

INTERMITTENT BLOWDOWN TO V-18-208

BB-18-2304-S1-3"

14"

14"

1½”SM-18-2303-C1-1½”

BOILER FEED WATERFROM STEAM DRUM V-18-206

FOR INSPECTION

V-18-206STEAM DRUM

H-18-201REFORMER

P-18-2305-CH1-6'’FROM SULFINOL UNITP-18-2308-CH1-6'’

FED GAS TO R-18-201

R-1

8-20

2A

R-1

8-20

2B

P-18-2309-CHC1-8'’

P-18-2311-CHC1-8'’

V-18-208INTERMITTENT

BLOWDOWN DRUM

SULFUR ABSORBER

HYDROGENERATOR

Schematic Process Flow Diagram

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

Crack indications observed During Liquid Penetrant Test

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

E-18-205

`

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

E-18-205

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

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

Cracks observed on Tube sheet to sleeve weld fusion area

E-18-205

Cracks observed on Tube sheet to sleeve weld fusion area

E-18-205

Cracks observed on face edges of the sleeve

E-18-205

Cracks observed on internal surface of the sleeve

Multiple transverse cracks observed on the sleeve

THE ADVANCED ULTRASONIC BACK SCATTER TECHNIQUE 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 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 HTHA have 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 methods sometime 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 assess during 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 attractive with 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 detect small 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 spectrum analysis 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.).

Data acquired from TOFD Inspection

Indication Showing in 54.8mm

Indication showing from 44.8mm up to the Back

Indication showing from 44.8mm up to the Back surface

Indication showing from 44.8mm up to the Back surface (linear

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

Weld Ident.

Total Length

Scanned

Defect Idnt.

Defect Size in mm Type Welder

No. Assessment l d H a/t A/l Criteria

CS-03 5600mm

1 153 47.1 11.2 .088 .037 .020

Slag Mixed with

Porosity

W N/A

To be rejected according to

ASME section 8 Division 1

2 542 47.9 18.1 .141 .017 .020

Slag Mixed with

Porosity

To be rejected according to

ASME section 8 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 and ‘2a’ height of the defect for subsurface flaws.

Channels and Transducers settings Channel –01 -52° -5 MHz 10mm -48 dB-- TOFD

1st Defect starting from 3045mm to 3198mm 2nd defect starting from 3341mm to 3883mm

4. CONCLUSIONS

1. Hydrogen attack is caused by exposure of steel to a hydrogen environment. The severity of the damage depends 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 Backscatter Techniques, methods based on TOFD, thickness mapping, backscatter and velocity ratio and in-situ metallography - replicas. Results of methods like AUBT – Phased Array can be used for estimation of life of hydrogen attacked equipment.

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

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

6. Spot NDT activity 1%-10% internal testing is recommended 7. Most of the sleeve cracking because cement refractory was damaged