Hydrogen Induced Cracking HIC/SOHIC
- 09 Aug 2024
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Hydrogen Induced Cracking HIC/SOHIC
- Updated on 09 Aug 2024
- 6 Minutes to read
- Contributors
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Take Note
There are some specific cases where the S-RBI assessment approach in IMS PEI changes, depending on the Degradation Mechanism.
This section gives guidance for Hydrogen Induced Cracking HIC/SOHIC.
This section gives guidance for Hydrogen Induced Cracking HIC/SOHIC.
Hydrogen Blistering, Hydrogen-Induced Cracking (HIC), and Stress-Oriented Hydrogen-Induced Cracking (SOHIC) are all DMs associated with the formation of hydrogen in the metal that occur when it is charged with atomic hydrogen produced by aqueous corrosion of the metal surface in the presence of water and (usually) hydrogen sulphide (H2S).
Parameters Affecting IOW – Step 2
See Step 2:
See below the relevant parameters affecting HIC/SOHIC severity and an indication of those that should be included in the IOW.
HIC/SOHIC Parameters affecting severity & IOW:
Parameter | Influence | IOW |
|---|---|---|
Material | Mainly ferritic carbon and low alloy steels | |
Presence of water (Yes or No) | Determine whether free water is present in the Equipment/piping. Consider not only normal operating conditions, but also start-up, shutdown, process upsets, etc. If there is no water present, then the Equipment / piping is considered not susceptible. | Yes |
H2S content of water | Determine the H2S content of the water phase. If analytical results are not readily available, it can be estimated. | Yes |
pH of water | Determine the pH of the water phase. If analytical results are not readily available, a knowledgeable process engineer should estimate it. Note: This determines severity. | Yes |
Presence of cyanides (Yes or No) | If possible, determine the presence of cyanides through sampling and/or field analysis. Consider primarily normal and upset conditions but also start-up and shutdown conditions. | Yes |
Sulphur content, heat treatment and testing ("Z" quality or "HIC" tested) of Plate Steel | Determine the sulphur content, heat treatment and testing of the steel plate used to fabricate the Equipment/piping. This information should be available in Equipment files. If not available, it can be estimated from the material specification of the steel listed in the fabrication records in consultation with a materials engineer. Steel plate that has not been given a grain refining heat treatment (normalising) should be considered as equivalent to high sulphur steel, irrespective of the actual sulphur content. Similarly, plate should be considered as equivalent to high sulphur steel if it has not been tested as "Z quality" or "HIC" tested. | No |
Steel product form (Plate or Pipe) | Determine what product form of steel was used to fabricate the Equipment/piping. Most Equipment is fabricated from rolled and welded steel plates (e.g., A285, A515, A516, etc.), but some small-diameter Equipment is fabricated from steel pipe and piping Components. Most small-diameter piping is fabricated from steel pipe (e.g., A106, A53, API 5L, etc.) and piping Components (e.g., A105, A234, etc.), but most large diameter piping (above approximately 16 NPS diameter) is fabricated from rolled and welded plate steel. | No |
PWHT of weldments (Yes or No) | Determine whether all the weldments of the Equipment/piping have been properly post-weld heat treated after welding. | No |
StF – Step 7
See Step 7.
Take Note
If there is no water present, then the Equipment/piping is considered not susceptible to hydrogen blistering and HIC/SOHIC.
Also, small-diameter Equipment and piping fabricated from steel pipe and piping Components welded from one side should be considered to have a low susceptibility to hydrogen blistering and HIC/SOHIC unless it has not been post-weld heat treated and is exposed to a high severity environment, in which case it should be considered to have a medium susceptibility.
Otherwise, for Equipment and large-diameter piping fabricated from rolled and welded plate steel, the Environmental Severity (see the Environmental Severity table below) and the data, listed in Parameters table in Step 2 above, should be used to determine the Susceptibility to hydrogen blistering and HIC/SOHIC (see StF table below). Note: If still unsure of the Susceptibility, use the HIC/SOHIC SCC RBI calculator to refine the calculation with input of process and material properties.
Environmental Severity
If there is water present, then the basic data from the table below should be used to determine the Environmental Severity class (potential level of hydrogen flux).
Guidance to determine Environmental Severity for HIC/SOHIC:
pH of Water | Cyanide content [mg/kg (ppmw)] | Sulphide content of water [mg/kg (ppmw)] | |||
<2 | 2 to 49 | 50 - 1000 | >1000 | ||
Environmental Severity | |||||
<4 | NA | L | M | M | M |
4.0 - 7.5 | NA | N | L | L | M |
7.6 - 7.9 | <50 | N | L | M | M |
7.6 - 7.9 | ≥50 | L | M | M | H |
≥8.0 | <20 | N | L | M | M |
≥8.0 | ≥20 | L | M | H | H |
The Severity obtained from above table can then be inputted into the StF table below to determine the StF.
Susceptibility to Cracking (HIC/SOHIC-H2S cracking):
StF | Sulphur Content in Steel | ||||||
High Sulphur Steel > 0.01 wt.%S | Low Sulphur Steel 0.002-0.01 wt.%S | Ultra Low Sulphur Steel < 0.002 wt.%S | |||||
As-Welded | PWHT | As-Welded | PWHT | As-Welded | PWHT | ||
Environmental Severity | H | H | H | H | M | M | L |
M | H | M | M | L | L | N | |
L | M | L | L | L | N | Not | |
N | L | N | N | N | Not | Not | |
Confidence – Step 10
See Step 10.
Follow the guidance below to determine answers for an HIC/SOHIC Confidence Assessment.
HIC/SOHIC Confidence Assessment Guidance:
Key Questions | Guidance |
|---|---|
Degradation mechanism can be properly controlled. |
|
Relevant process parameters are reliably monitored. |
|
Reliable inspections were carried out. |
|
MII – Step 11
See Step 11.
IMS implements the slow acting SCC lookup table to determine the MII.
Take Note:
- “No inspection” requires review during RBI revalidation / updates.
- Inspection intervals less than 4 years or low and very low confidence ratings must be followed by an engineering evaluation of the materials of construction, establishment of IOWs to control exposure to cracking conditions, and specific Inspection Effectiveness to improve the confidence rating.
IS – Step 11
See Step 11.
IMS implements the Slow (and Moderate) acting SCC lookup table to determine the IS.
Required Inspection Effectiveness – Step 11 & Step 12
Use the Required Inspection Effectiveness rating, determined in Step 11, to determine the required combination of Inspection technique and coverage. The table below provides examples of appropriate inspection activities for hydrogen blistering and HIC/SOHIC.
HIC/SOHIC Required Inspection Effectiveness examples:
Required Inspection Effectiveness | Intrusive Inspection | Non-Intrusive Inspection |
|---|---|---|
A (Highly) Effective | WFMPT3 of 50–100% of weldments in susceptible areas1, or ACFM3 of 50 -100% of the susceptible1 welds as initial screening tool for those pieces of Equipment with a history of cracking inspection, or those with a low cracking susceptibility. | Automated shear wave ultrasonic testing of 50 –100% of weldments in susceptible areas.1 |
B (Usually) Effective | WFMPT3 of 20–49% of weldments in susceptible areas1, or ACFM3 of 20-49% of the susceptible1 suspect welds as initial screening tool for those pieces of Equipment with a history of cracking inspection, or those with a low cracking susceptibility. | Automated shear wave ultrasonic testing of 30–49% of weldments in susceptible areas1 or Acoustic Emission (AE) testing with follow-up shear wave UT at acoustic hits.2 |
C (Fairly) Effective | WFMPT3 of less than 20% of weldments in susceptible areas1, or ACFM3 of less than 20% of the suspect welds as initial screening tool for those pieces of Equipment with a history of cracking inspection, or those with a low cracking susceptibility. | Automated shear wave ultrasonic testing of 15 to less than 29% of weldments in susceptible areas1; or manual shear wave ultrasonic testing of 20–100% of weldments. |
D (Poorly) Effective | Visual inspection for hydrogen blisters. | Manual shear wave ultrasonic testing of 5 to less than 14% of weldments in susceptible areas.1 |
E Ineffective | No inspection | Radiographic testing. |
Notes:
- Susceptible areas are those parts of the Equipment where the damage is expected to occur as defined by the corrosion / materials engineer or another knowledgeable specialist.
- AE should be used only after a review of the application with NDE specialist and Shell Global Solutions NDE support.
- HIC resistant steels subject to HIC / SOHIC cracking should be inspected using the methods outlined in the non-intrusive table. The surface inspection techniques ACFM and WFMPT used for intrusive HIC / SOHIC cracking inspections are not effective for the HIC resistant steels; non-intrusive volumetric inspection techniques, such as automated shear wave, should be used.
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