Paper No.
13326
High Temperature Hydrogen Attack Life Assessment Modeling and Inspection
James Johnson, Brian Olson, Michael Swindeman, Mark Carte
Stress Engineering Services, Inc.
13800 Westfair East Dr.
Houston, TX 77041
Jeffrey Browning
Riccardelli Consulting Services, Inc.
3347 Mayflower Ave.
Lehi, UT 84043
ABSTRACT
Key elements of a technology initiative aimed at developing high temperature hydrogen attack
(HTHA) assessment methodologies for equipment and piping operating in hot hydrogen service
are presented. Two assessment methodologies have been developed: (1) a Screening
Assessment and (2) an Advanced Assessment, both of which predict the development of HTHA
damage with time. The HTHA assessment methodologies utilize fitness-for-service (FFS)
frameworks and are in good agreement with reported HTHA incidents in API RP 941 and API
TR 941 for carbon steel and C-0.5Mo materials. The Screening Assessment provides an
improved decision basis by classifying and ranking equipment operating in hot hydrogen
service. The Advanced Assessment predicts through-wall damage progression. An inspection
philosophy and the use of inspection findings as a means of risk mitigation are also discussed.
Application of the assessment methods and utilization of advanced inspection methods are
reviewed through an illustrative case study. The developed methodologies provide an improved
link between HTHA damage assessment and progression, inspection and detection limits,
damage tolerance, and operation severity.
Key words: high temperature hydrogen attack, HTHA, modeling, inspection, life assessment,
FFS, MT, HSWFMT, PAUT, FMC, TOFD, AET
INTRODUCTION
High temperature hydrogen attack (HTHA) has been a challenging damage mechanism for the
petroleum refining and petrochemical industry to address since the industry first became aware
of it in the early 1900’s. The earliest attempts to design for HTHA relied on a time-independent
basis commonly referred to as the Nelson Curves. 1 The Nelson curves are lines drawn below
operating conditions (combination of temperature and hydrogen partial pressure) that caused an
HTHA incident for a given material class, e.g. post-weld heat treated (PWHT) carbon steel,
carbon-0.5 molybdenum (C-0.5Mo) steel, etc… Recent industry experiences with HTHA have
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1
reduced acceptable temperature and hydrogen partial pressure combinations by removing the
C-0.5Mo Nelson curve and the addition of an even lower non-PWHT carbon steel Nelson curve
to the American Petroleum Institute (API) (1) Recommended Practice (RP) 941. 2, 3
LIFE ASSESSMENT METHODOLOGIES
Several time-dependent HTHA models have been developed to provide an owner/user an
improved understanding of their likelihood of HTHA damage and remaining life: 4-6
Model 1.
Model 2.
Model 3.
Provides prioritization and likelihood of damage based on hot hydrogen exposure
and material class.
Provides through-wall volumetric HTHA damage progression by integrating
Model 1 as a function of through-wall position and methane partial pressure.
Provides through-wall HTHA crack growth by correlating the effect of methane
pressure at a crack tip to crack growth.
Model 1 is used in the Screening Assessments; while Models 2 and 3 are implemented in the
Advanced Assessment methods.
Screening Assessments
Screening Assessments use Model 1 to calculate a Damage Index (DI) that represents a
subject asset’s hot hydrogen exposure relative to the average hot hydrogen exposure for a
specific material class that resulted in HTHA damage, as reported in API RP 941, API TR 941,
and select literature. 3, 7 To prioritize equipment, a DI is calculated below. The DI at a given time,
t, is calculated by integrating the damage rate, 𝑑𝑑̇, over the service history, s, as shown in
Equation 1:
𝑡𝑡
𝐷𝐷(𝑡𝑡) = � 𝑑𝑑̇ (𝑑𝑑𝑑𝑑)
(1)
0
The modifications were influenced by a number of bubble nucleation and growth models. 8-18
Parthasarathy developed an expression that described grain boundary diffusion controlled void
growth, which the authors have fitted into the modified Orr-Sherby-Dorn interpretation for Model
1 (Equation 2):
𝑑𝑑̇ =
𝐵𝐵
𝑛𝑛
�𝑃𝑃𝐶𝐶𝐶𝐶4 � 𝑒𝑒 (𝑄𝑄⁄𝑅𝑅𝑅𝑅 )
𝑇𝑇
(2)
The Model 1 damage rate equation is considered to be an empirical expression with the B, n,
and Q constants developed for each material class. The effect of methane pressure, PCH4, is
assumed to be much larger than the effect of surface energy over most of the life. The sintering
term of the nucleation and growth models has been neglected, similar to the procedure outlined
in API Technical Resource (TR) 941 Annex G. 7 All of the other terms are assumed to be
constant.
1
American Petroleum Institute, 1220 L Street, NW, Washington, DC, 20005.
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2
The methane partial pressure is calculated using the procedure developed by Odette and
Vagarali and is dependent on the hydrogen partial pressure and the temperature. 19 A
smoothing function has been implemented to address the discontinuous nature of the C(T)
function, which has been fitted to the original data. 6
Equation 2 was preliminarily validated against laboratory test data and appeared reasonable. 9,
A representative validation case takes data from Weiner’s study that exposed tensile test
specimens to hot hydrogen for various temperatures, hydrogen partial pressures, and times.
The time to measurable ductility loss, as characterized by reduction in area, was labeled the
incubation time and is plotted as a function of temperature in Figure 1a. For hydrogen partial
pressures of 700 psi (4.83 MPa) and temperatures greater than 1000 °F (538 °C), the time to
degraded mechanical properties increases with increasing temperature.
20-28
Model 1 can be presented in a form analogous to a Larson-miller creep formulation and fitted to
the data. Figure 1b shows the test data set regressed using Model 1, which captures the
incubation conditions resulting in an R2 value of 0.98. The diagram in Figure 1b can be nonintuitive as each axis is a function of multiple variables, as demonstrated in Figure 2a.
Model 1 was then optimized to assess likelihood of HTHA damage for in-service equipment by
fitting it to the API RP 941 incident data and select laboratory data already in API RP 941.
Constants for the following material classes have been determined:
•
•
•
Carbon steel including base metal, PWHT, and non-PWHT material
C-0.5Mo with low HTHA resistance, e.g. non-PWHT or annealed microstructures
C-0.5Mo with high HTHA resistance, e.g. PWHT material and normalized
microstructures
Alternative models have been developed for modeling HTHA damage in low-alloy steels.
These data sets include reported HTHA incidents that resulted in damage being found from
inspection, leaks, ruptures, or fires. Application of Model 1 is relatively simple as factors such as
applied loads are not considered at this stage. Stainless steel cladding/ weld overlay can reduce
the effective hydrogen partial pressures and can be addressed by modeling a temperature
dependent steady state hydrogen concentration profile. 29
Using this approach, a DI of 1 represents the average hot hydrogen exposure that resulted in
damage in the incident data set. Margins on DI have been developed and are applied to set
categories as outlined in Table 1. Application of the margins expressed graphically is shown in
Figure 2b.
DI categories have been linked to upper bound expected HTHA damage using full immersion
literature data and the Advanced Assessment (higher level methods). The lower bound DI (0.1)
is related to the initiation of HTHA damage in full immersion laboratory testing data. The upper
bound DI (0.4) was set to mark the approximate start of the incident data for all material classes.
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3
Advanced Assessments
The Advanced Assessment is not a fitness-for-service (FFS) assessment in the truest sense per
API 579-1/ASME (2) FFS-1 (API 579), as the current API 579 does not include HTHA damage
assessment options. 30 However, it does use accepted FFS methods and principles to assist in
understanding remaining life/likelihood of failure. Multiple FFS approaches have been
considered for guidance in developing the Advanced Assessment. 30-33 Three methods to model
through-wall damage progression are utilized:
1. Volumetric HTHA damage progression using Model 2, which is usually applicable to low
or compressive stress conditions.
2. HTHA crack-growth using Model 3, appropriate for higher stress conditions, e.g. nonPWHT assets or assets with relatively low design margins.
3. Combined damage progression considering crack growth through volumetric HTHA
damage.
All procedures rely on the establishment of the minimum detection limit and the critical flaw size
for the component, both of which are detailed in the following sections.
A threshold for damaged material has been developed based on the through-wall mechanical
properties of HTHA damaged components. 26, 34 Material considered to be "damaged” has a
measurable loss in ductility and, for conservatism, is assumed to have no tearing resistance.
This assumption appears consistent with the work from Dauskardt, Pendse, and Ritchie, which
measured markedly reduced tearing resistance for even early stage damage. 35 Leak-beforebreak scenarios are not considered.
Minimum Detection Limit
The minimum detection limit is an estimate of the maximum flaw size that may go undetected in
an inspection. This value depends on the type of flaw, the method of inspection, the geometry of
the sample, and other factors. The recommended inspection intervals for a range of minimum
detection limits can be generated and provides guidance for inspection planning activities.
Critical Flaw Size
The critical flaw size is established by use of either API 579-1/ASME FFS-1, June, 2016 Part 9
Level 2 or 3 assessments for a hypothetical flaw in the wall of the component or 50% of the wall
thickness, whichever is less. Two important and conservative assumptions are used in
establishing the critical flaw size:
•
•
Bending stresses whether resulting from thermal expansion or sustained loads are
treated as primary membrane stresses. The maximum stress is always used.
The flaw length (2c) is assumed to be very long compared to its depth (a).
The fracture toughness of the material ahead of the crack-tip is considered to be 100 ksi√in,
which is the lower bound KIR curve for high-sulfur steels with unknown chemistry (see API 5791/ASME FFS-1 Annex 9F). Residual stress fields for PWHT and non-PWHT are estimated in
accordance with API 579-1/ASME FFS-1 Annex 9D.
2
The American Society of Mechanical Engineers (ASME), Two Park Avenue, New York, NY, 10016.
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4
Volumetric HTHA Damage Modelling
Due to a through thickness hydrogen concentration gradient, damage is modeled initiating at or
near the inner surface. At this location, the hydrogen concentration in the steel is expected to be
the highest. This allows for the through-wall integration of Model 1 and results in an effective
damage gradient from the inner surface (highest level of damage) to the outer surface (lowest
level of damage). For the Advanced Assessment, the evolution of the damage gradient with
time is considered to model volumetric or classical HTHA damage.
The volumetric damage model (Model 2) is based on the observation that HTHA damage
progression at any point through the thickness and at constant service conditions (temperature
and hydrogen partial pressure) progresses linearly in time. Here we must be careful in regards
to what the term “Damage” refers to. Recall that the DI determined in the Screening
Assessment refers primarily to the relationship between the conditions seen in service and the
known incident data such that a DI of 1 can be said to correspond to conditions that fall along
the mean line of the incident data.
For the level 2 assessment the calculated level of damage has been linked to a metallurgical
interpretation of damage, as characterized by the percentage of damaged grain boundaries. A
Damage Tolerance has been established, such that calculated damage less than the Damage
Tolerance is considered to have no measureable loss of properties. Conversely, ductility is
considered to be completely degraded if the calculated damage is greater than the Damage
Tolerance. The depth of degraded material increases with hot hydrogen exposure time.
HTHA Crack-Growth Modelling
Model 3 is intended for establishing a reasonable inspection interval based on the time to grow
a crack from a detection threshold to the critical flaw size. The crack growth rate has a form
similar to Model 1, but incorporates the through-wall stress intensity and was fitted to data from
Shewmon and Xue’s work. 25 Due to the limited HTHA crack growth data, an inherent HTHA
resistance factor was applied to allow for consideration of alternative material classes. The
differences between the Model 1 material classes were used to provide the inherent HTHA
resistance factor for a given material class.
Combined HTHA Damage Growth Approach
Since the two damage growth approaches have different behaviors, the combined approach
considered them each independently. Typically, volumetric damage progression initiates with a
high growth rate, but slows with increasing amount of damaged wall fraction (damage depth).
Conversely, crack growth initiates with a low growth rate and increases velocity with increasing
crack size.
INSPECTION PHILOSOPHY
An inspection philosophy has been developed for HTHA damage that centers around
progressive validation of damage. 5 Currently, industry does not have a singular, mature, and
easily deployable non-destructive testing (NDT) technology that can detect all HTHA damage
types with well-established minimum detection limits. As such, the authors have found utilization
of multiple inspection techniques for the detection of HTHA damage to be beneficial. The main
inspection methods utilized for the detection of HTHA damage are as follows:
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5
•
•
•
•
•
Acoustic emission testing (AET) pre-turnaround (either continuous monitoring or during
shutdown) as a way to prioritize inspection locations and/or provide a layer of protection
against an end of life type event
Visual testing (VT) inspection of the internal surface for late stage HTHA damage
(bulges and severe cracking) with oblique white lighting resulting in shadows from
surface discontinuities
High-sensitivity wet florescent magnetic particle testing (HSWFMT) optimized for the
detection of HTHA damage
Emerging advanced UT techniques:
o Advanced methods of external time-of-flight diffraction (TOFD),
o External phased array ultrasonic testing (PAUT) using full matrix capture (FMC)
inspection with the total focusing method post-processing,
o Beam forming PAUT
Metallurgical extraction and examination (scoop sampling, boat sampling, full thickness
sampling) to confirm the damage mechanism and validate NDT findings
The first portion of the above inspection philosophy is centered around 1) high coverage NDT
detection techniques, 2) sizing, and 3) validation with metallurgical examination. High coverage
NDT techniques allow for inspection of a large percentage of the equipment and address the
localized nature of the HTHA damage mechanism. Coverage extent is typically handled by
qualitative discussions on risk and prioritizing high consequence locations (longitudinal welds)
and high likelihood locations for vessels (nozzles, closure welds, weld repairs) and piping
(flanges and highly stressed locations).
If detected, indication depths are sized using FMC. Metallurgical extraction from the internal
surface (scoop, boat, or full thickness window) is always recommended. If no damage is
detected, metallurgical extraction and examination is still recommended and provides improved
confidence that there is no damage in the equipment. If indications are detected, metallographic
examination will confirm the damage mechanism and reduce the likelihood of a false positive.
Additionally, the examination can qualify the sized FMC indications to a level of microstructural
damage. Qualifying or bounding the edge of damage can be critical when trying to size damage
as HTHA damage does not abruptly end, but rather gradually reduces in severity with volumetric
damage or has discontinuous crack tips.
HSWFMT for HTHA
The authors’ experience and research performing WFMT for HTHA has determined surface
preparation, application method, and interpretation are critical for delivering a HSWFMT
inspection for HTHA. Surface preparation starts with abrasive blasting with garnet followed by
smooth blending of welds, heat affected zone, and base material. Metal is then removed using
rubber backed fiber discs with a final grind grit of 80 to 100. The surface roughness should not
impair particle mobility. At minimum, 2 inches on either side of welds should be prepared. A
depth of 0.030 inch (0.76 mm) to 0.090 inch (2.29 mm) of the wall thickness within the area to
be inspected is removed during the surface preparations while ensuring the corrosion allowance
is not exceeded. The final surface preparation step is to macro-etch the ground surfaces using
three applications of 5% Nital in 3 minute intervals.
Application of the HSWFMT method calls for extended durations of applied magnetic fluxes
using an AC yoke and WFMT solution, typically 30 to 45 seconds. Multiple directions are utilized
for both magnetic flux lines and WFMT solution flow. Non-aerosol based deployments of
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6
HSWFMT solution as there is more particle control with the deployment. Prepared florescent
particle to carrier solution ratios are in accordance with ASTM International (3) guidelines. It is
important to ensure the ultraviolet (UV) light source intensity and wave length is correct. The
background light limits should be checked and managed in the area of inspection. AC yoke
strength should be checked frequently as long durations of use can cause overheating and lack
of magnetic flux line strength. Finally, acute vision is essential for this inspection as indications
can often be relatively fine. The inspector should be mindful of the clarity of their personal
protective equipment (PPE) as smudged or dirty glasses and face masks can hinder visual
detection of fine indications.
The last portion of a HSWFMT inspection is interpretation and is considered to be the most
challenging. HSWFMT indications can appear as indications consistent with macro-cracking.
However, they can also appear as clusters of very fine indications with indication density and
shape varying from cluster to cluster. Fine indication clusters have been detected in base metal,
heat affected zones, and weld metal. Often, these indications appear as linear clusters in the
heat affected zone adjacent to welds. Fine indication clusters should be verified with multiple
HSWFMT solution flow directions. Indications should be removed between each solution flow
direction application.
CASE STUDY
In 2016, a refinery from the Western US initiated a revamp of their HTHA program and began
re-assessing the potential for HTHA damage in all of their assets. The process started with a
review of equipment using process flow diagrams (PFD) and piping and instrumentation
diagrams (P&ID) to identify carbon steel and C-0.5Mo steel equipment in hydrogen service.
Maximum operating temperatures and maximum hydrogen partial pressures were determined.
The beneficial effects of cladding were not considered. If the maximum temperature and
maximum hydrogen partial pressure were within 100 °F (56 °C) of the appropriate carbon steel
API RP 941 curve, the equipment priority was elevated and a Screening Assessment was
performed.
Hydrocracker Feed-Effluent Exchanger Background
The review identified a Hydrocracker feed-effluent exchanger that operated as shown in Figure
3. The exchanger was PWHT C-0.5Mo steel with no cladding, which was in-service since 1966.
In 2011 it was inspected using multiple NDT inspection techniques including: external advanced
ultrasonic backscatter and spectrum analysis (AUBT/ABSA), external conventional PAUT, and
internal WFMT. No damage was detected in the exchanger.
Screening Assessment
The Screening Assessment’s Model 1 was integrated using a Robinson rule approach over the
exchanger’s shell side outlet (reactor feed inlet) operating conditions (Figure 3). The
Instantaneous DI rate and cumulative DI are graphed over the provided data and the entire
service in Figures 4 and 5. The average damage rate calculated over the data was then
extrapolated over the service history resulting in a calculated DI of 5.4. The effective conditions
are plotted relative to the C-0.5Mo PWHT HTHA incident data set in Figure 6a. Given the
calculated DI was relatively high; it was considered that the equipment had a high likelihood of
HTHA damage.
3
ASTM International, 100 Barr Harbor Drive, PO Box C700 West Conshococken, PA, 19328.
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7
Advanced Assessment
An Advanced Assessment of the vessel was performed to determine the degree of damage
progression since the last inspection. HTHA crack growth based on a minimum detection limit of
20% of the wall to the critical flaw size is shown in Figure 6b. A preliminary critical flaw size of
0.78 inches (19.8 mm) was determined based on internal pressure in a cylindrical geometry with
a long longitudinal crack. Sensitivity analyses using the most optimistic material properties
(slowest crack growth) resulted in potential crack growth from below the detection limit to critical
flaw size within 5 years – with a maximum recommend inspection interval of 2.5 years.
To demonstrate continued safe operation of the equipment, on-line AET was immediately
applied. AET detected signals on the long seam and inlet nozzle that were near or below typical
minimum signal thresholds. No other reportable signals were detected. All detected signals
were relatively low energy and were not consistent with a near end of life type scenario. On-line
AET was then applied for the remaining 4 months until the next scheduled shutdown.
HTHA Inspection Results and Exchanger Path Forward
An extensive HTHA inspection was performed in 2017 on the exchanger and included the
inspection techniques summarized in Table 2. NDT techniques that detected indications were
the on-line AET, internal HSWFMT, FMC, and metallurgical extraction via scoop sampling. Initial
inspections with AUBT/ABSA, conventional PAUT, and WFMT did not detect HTHA damage.
The high-sensitive WFMT inspection detected indications on the long seam, multiple
circumferential welds, inlet nozzle, and outlet nozzle. Indications appeared random along the
long seam welds and almost continuous around the outlet nozzle. Indications were sized using
FMC to be up to 0.5 inch (6.4 mm) deep on both the long seam and inlet nozzle. FMC screen
capture of the long seam is shown in Figure 7.
To confirm the damage mechanism and qualify the degree of damage relative to the output
FMC signal, metal scoop sampling was performed. Scoop sampling involves removing a lens
shaped volume of metal from the wall. API 579-1/ASME FFS-1 Part 4 local thin area (LTA)
calculations were performed to determine acceptable scoop sampling depths that would not
need to be repaired.
Metallographic examination of the scoop samples confirmed the presence of HTHA damage in
the long seam (Figure 8) and outlet nozzle (Figure 9). The long seam exhibited decarburization,
grain boundary fissuring, and was relatively uniform in appearance for a given depth. This form
of HTHA damage is considered to be volumetric HTHA damage. The nozzle damage exhibited
crack-like HTHA damage that was dominated by fissuring, and cracking in the weld metal and
heat affected zone (HAZ). Isolated slight decarburization was also observed. Cracking could be
described as aligned fissures, branched cracking, and discontinuous in nature.
An API 579-1/ASME FFS-1 Part 9 Level 3 was performed on the damage at the outlet nozzle.
The damage was modeled as 0.5 inch (12.7 mm) deep cracking completely around the nozzle.
The size of damage was larger than the critical flaw size and the vessel was retired from
service.
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8
SUMMARY
Two assessment methodologies have been developed and provide owner/user’s a more
detailed understanding of likelihood of HTHA damage and remaining life: 1) the Screening
Assessment to determine the potential for HTHA damage based on equipment life cycle; and 2)
the Advanced Assessment to better predict damage depth, damage manifestation type (crack
versus volumetric), and rate of damage propagation. These methodologies address the time
and stress dependency of HTHA damage, which are currently not explicitly addressed in API
RP 941. Due to the historic challenges in detecting HTHA damage, the authors advocate
utilization of multiple high-sensitivity inspection techniques to provide improved detection of
HTHA damage.
(a)
(b)
Figure 1: Graph (a) is reproduced from Weiner’s study and shows the effect of temperature on
the incubation time, which represents the hot hydrogen exposure time to degraded mechanical
properties. 2 Graph (b) plots the data from Figure 1a regressed using Model 1.
(a)
(b)
Figure 2: Model 1 (a) assessment variables affect plotted points. Example graph (b) shows a
new hypothetical component (red circle) with a DI < 0.0001. The red arrow indicates direction
the equipment will follow as time increases at a constant temperature and hydrogen partial
pressure.
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9
Table 1
HTHA Damage Index Categories
Category
A
B
C
D
Damage Index
Upper Bound HTHA Stage Description
D=1
• Average hot hydrogen exposure that resulted in damage.
D > 0.4
• Advanced HTHA damage progression has likely occurred.
• Detection using advanced ultrasonic techniques is possible.
• Component load carrying capacity has likely reduced and maximum
potential depth of embrittled wall fraction has increased.
0.25 < D < 0.4
• Significant HTHA damage progression may have occurred.
• Detection using advanced ultrasonic techniques is possible.
• Component load carrying capacity may be reduced and inner
surface likely embrittled.
0.1 < D < 0.25
• HTHA damage progression has occurred.
• Detection using advanced ultrasonic techniques may be possible.
• Component load carrying capacity may have been reduced and
inner surface likely embrittled.
D < 0.1
• Aligns well with full hydrogen emersion incubation testing data.
• Single-sided HTHA damage initiation near the ID surface and may
have caused inner surface to become embrittled.
• Component load carrying capacity is essentially unaffected.
Figure 3: Feed-Effluent Exchanger daily average temperature and hydrogen partial pressures
for all retrievable dates in the distributed control system (DCS).
Figure 4: Feed-Effluent Exchanger instantaneous DI rate is shown for the provided data.
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10
Figure 5: Feed-Effluent Exchanger cumulative DI is shown from start of in-service.
(a)
(b)
Figure 6: Effective conditions (red circle), based on provided temperature and hydrogen partial
pressures for the hydrocracker feed-effluent exchanger plotted (a) relative to the timedependent PWHT C-0.5Mo data set. HTHA crack growth (b) from the minimum detection limit to
the critical flaw size.
Table 2
2017 Hydrocracker Feed-Effluent Exchanger Inspection Summary
Applied NDT Technique
AUBT/ABSA
WFMT
Conventional PAUT
HSWFMT
FMC
Scoop Sampling
Inspection Results
No findings.
No findings.
No findings.
Indications detected on long seams, multiple circumferential welds, inlet
nozzle, and outlet nozzle.
Indications detected on long seams, multiple circumferential welds, inlet
nozzle, and outlet nozzle.
Metallurgical examination confirmed that the detected HSWFMT and FMC
indications were HTHA damage.
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11
Figure 7: FMC screen capture showing the deepest damage on a long seam weld.
Base metal near ID surface; Original magnification:
500X.
Base metal 0.25 inch from ID surface; Original
magnification: 1000X.
Base metal near ID surface; Original magnification:
200X.
Figure 8: Micrographs adjacent to the shell long seam showing volumetric HTHA damage with
fissuring and decarburization in the base metal. Etchant: 2% nital.
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12
Original magnification: 50X.
Cracking in weld metal/HAZ. Original magnification:
200X.
Cracking in weld metal/HAZ. Original magnification:
200X.
Decarburization and fissures in HAZ. Original
magnification: 1000X.
Figure 9: Micrographs from the outlet nozzle-to-shell weld showing crack-like HTHA damage in
the C-0.5Mo weld metal and HAZ. Etchant: 2% nital.
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13
REFERENCES
1. G. Nelson, "Hydrogenation Plant Steels," in API 1949 Proceedings, Washington DC, 1949.
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©2019 by NACE International.
Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to
NACE International, Publications Division, 15835 Park Ten Place, Houston, Texas 77084.
The material presented and the views expressed in this paper are solely those of the author(s) and are not necessarily endorsed by the Association.
14
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©2019 by NACE International.
Requests for permission to publish this manuscript in any form, in part or in whole, must be in writing to
NACE International, Publications Division, 15835 Park Ten Place, Houston, Texas 77084.
The material presented and the views expressed in this paper are solely those of the author(s) and are not necessarily endorsed by the Association.
15