What Is HIC in Pressure Vessel Steel? When Is HIC Testing Required?
You may receive an inquiry for SA516 Grade 70 or Q345R with an additional requirement: HIC testing.
Does every pressure vessel steel plate need HIC testing?
No. HIC is mainly related to the service environment — especially wet H₂S / sour service conditions. Not every pressure vessel application requires HIC-resistant steel.
1. What Does HIC Mean in Steel?
1.1 HIC = Hydrogen Induced Cracking
Hydrogen Induced Cracking (HIC) is a type of internal cracking that occurs in steel when hydrogen atoms diffuse into the material and accumulate at internal defects such as inclusions or laminations. The accumulation of hydrogen creates internal pressure, which can lead to cracks.
1.2 Why Is HIC a Concern for Pressure Vessel Steel?
HIC is particularly relevant in industries where equipment is exposed to wet hydrogen sulfide (H₂S) environments:
- ✔ Oil and gas equipment
- ✔ Refineries and petrochemical plants
- ✔ Sour gas processing facilities
- ✔ Storage tanks
- ✔ Pressure vessels in sour service
💡 Key point: HIC is not simply a problem caused by the steel grade itself. Steel cleanliness, inclusions, chemical composition, and manufacturing process can all affect HIC resistance.
2. How Does Hydrogen Induced Cracking Occur?
The process can be simplified into three steps:
Step 1: Hydrogen Enters the Steel
In wet H₂S environments, hydrogen atoms are generated through corrosion reactions and can diffuse into the steel surface.
Step 2: Hydrogen Accumulates Inside the Steel
Hydrogen atoms diffuse through the steel and accumulate at internal defects — such as non-metallic inclusions, laminations, or other discontinuities.
Step 3: Internal Pressure Leads to Cracking
As hydrogen accumulates, internal pressure builds, eventually leading to the formation of cracks. These cracks can reduce the integrity of the steel and compromise the safety of pressure equipment.
3. When Is HIC Testing Required?
HIC testing may be required when:
- ✔ Equipment is designed for sour service
- ✔ The operating environment contains wet H₂S
- ✔ The project specification specifically requires HIC testing
- ✔ The end user or EPC contractor specifies HIC-resistant steel
- ✔ NACE / AMPP requirements are included in the project documents
⚠️ Important: Not every pressure vessel steel plate requires HIC testing. SA516 Gr.70 or Q345R do not automatically require HIC. The decision depends on the service environment and project specification.
4. HIC Testing Standard: NACE TM0284
NACE TM0284 is the most widely used standard for evaluating the HIC resistance of steel plates. It specifies the test method for assessing hydrogen-induced cracking in carbon and low-alloy steels.
The test involves exposing a steel specimen to a specified test solution for a defined period, followed by inspection to measure cracks.
Common test results reported:
- CLR — Crack Length Ratio
- CTR — Crack Thickness Ratio
- CSR — Crack Sensitivity Ratio
📌 Note: Acceptance criteria should be confirmed from the project specification or purchaser's requirements. Different projects may have different acceptance levels.
5. HIC Does Not Mean a Different Steel Grade
A common misconception among buyers: "SA516 Grade 70" equals "HIC-resistant." That is not the case.
- ✖ SA516 Gr.70 ≠ automatically HIC resistant
- ✖ Q345R ≠ automatically HIC resistant
What it actually means:
- ✔ HIC is generally an additional performance requirement rather than simply another steel grade.
- ✔ The same base grade can be supplied with or without HIC testing, depending on the project.
🛑 Red flag: If a supplier claims every SA516 Gr.70 is HIC-tested, ask for the test report and confirm the standard and acceptance criteria. The base grade does not guarantee HIC performance.
6. What Makes Steel More Resistant to HIC?
HIC resistance is influenced by several factors in the steelmaking and production process.
Steel Cleanliness
- ✔ Control of sulfur and phosphorus content
- ✔ Reduction of non-metallic inclusions
- ✔ Inclusion shape control
Manufacturing Process
- ✔ Steelmaking and secondary refining
- ✔ Vacuum treatment
- ✔ Slab quality control
- ✔ Rolling process and final heat treatment
💡 What this means for buyers: HIC-resistant steel requires stricter production controls. This is one reason why HIC-tested plates are more expensive than standard plates of the same grade.
7. HIC vs Hydrogen Embrittlement vs SSC
⚠️ Important: HIC, SSC, and hydrogen embrittlement are not the same thing. For oil and gas applications, these terms often appear together — but they refer to different failure mechanisms. Don't confuse them during procurement.
8. What Should You Tell Your Steel Supplier?
When requesting HIC-tested pressure vessel steel, provide the following information:
- ✓ Steel grade — e.g., SA516 Grade 70, Q345R
- ✓ Thickness — e.g., 30mm, 50mm
- ✓ Plate dimensions — width × length
- ✓ Quantity — total weight or number of plates
- ✓ Applicable standard — ASME, GB/T, EN, etc.
- ✓ HIC testing requirement — required or not
- ✓ Testing standard — NACE TM0284 or other
- ✓ Test solution — Solution A or B
- ✓ Acceptance criteria — CLR, CTR, CSR limits
- ✓ Additional requirements — PWHT, impact test, UT
📌 Example: SA516 Grade 70, 30mm × 2500mm × 12000mm, HIC tested according to NACE TM0284, acceptance criteria as per project specification.
9. Does HIC Testing Affect the Price of Pressure Vessel Steel?
HIC testing generally increases the cost of steel plates because it requires:
- ✔ Stricter steelmaking controls
- ✔ Additional refining requirements
- ✔ Production control for HIC resistance
- ✔ Additional testing and inspection
- ✔ Extended production time
💡 Note: HIC-tested steel plate is normally more expensive than standard plate of the same grade. The exact price difference depends on the grade, thickness, quantity, mill, and testing requirements.
10. Frequently Asked Questions
❓ What does HIC mean in pressure vessel steel?
HIC stands for Hydrogen Induced Cracking — a type of internal cracking that occurs when hydrogen diffuses into steel and accumulates at internal defects. It is a major concern for pressure vessels used in wet H₂S (sour) environments.
❓ Does SA516 Grade 70 require HIC testing?
Not automatically. SA516 Grade 70 can be supplied with or without HIC testing. HIC testing is only required when the project specification or service conditions demand it — especially for sour service applications.
❓ Is HIC testing mandatory for all pressure vessel steel?
No — HIC testing is not mandatory for all pressure vessel steel. It depends on the service environment, project specification, and applicable design code. Only sour service or wet H₂S applications typically require HIC testing.
❓ What is NACE TM0284?
NACE TM0284 is the standard test method for evaluating hydrogen-induced cracking resistance of steel plates. It specifies the test procedure, solution, and evaluation criteria used to assess HIC performance.
❓ What is the difference between HIC and SSC?
HIC (Hydrogen Induced Cracking) is internal cracking caused by hydrogen accumulation. SSC (Sulfide Stress Cracking) is a form of hydrogen embrittlement that occurs under tensile stress in sour environments. They are different failure mechanisms.
❓ Can Q345R be used for sour service?
Yes — Q345R can be supplied with HIC testing and used in sour service, provided it meets the project's HIC acceptance criteria. However, not every Q345R plate is HIC-resistant by default. The HIC requirement must be specified.
❓ What information should I provide when ordering HIC-tested steel?
Provide the steel grade, thickness, dimensions, quantity, applicable standard, HIC testing standard (e.g., NACE TM0284), test solution, acceptance criteria (CLR/CTR/CSR limits), and any additional requirements such as PWHT or impact testing.
11. Final Thoughts
Before ordering pressure vessel steel for sour service, confirm the service environment first. If wet H₂S is involved, ask whether HIC testing is required by the project specification.
The right approach is not to assume that every pressure vessel steel plate is HIC-tested. Instead, provide the grade, thickness, size, quantity, HIC requirement, and testing standard when requesting a quotation.
💡 Our view: We've seen orders delayed because the buyer assumed the steel was HIC-tested — but never specified it. Confirming the HIC requirement upfront, in writing, is one of the simplest ways to avoid material rejection and project delays.
📚 Further Reading & Related Content
- 🔗 Q345R vs SA516 Grade 70 – Comparison Guide
- 🔗 How to Read a Steel Plate Mill Test Certificate (MTC)
- 🔗 Ultrasonic Testing (UT) for Steel Plates – Buyer Guide
- 🔗 Pressure Vessel Steel Plate Standards Explained: ASME vs EN vs GB
- 🔗 Z-Quality Steel Plate Explained: Z15, Z25 and Z35
- 📄 NACE TM0284, NACE MR0175, ISO 15156, GB/T 8650
Need HIC-Tested Pressure Vessel Steel Plates?
CEHE STEEL supplies pressure vessel steel plates with HIC testing according to NACE TM0284 or customer-specified requirements. Send us your grade, thickness, and HIC acceptance criteria — we'll confirm availability and provide full documentation.