ASTM A516 Gr. 60 NACE Plates: HIC, SSCC & SOHIC Testing

ASTM A516 Gr. 60 NACE Plates and Sour-Service Testing

Wet H₂S environments break down ordinary carbon steel from the inside out. ASTM A516 Gr. 60 NACE MR 0103 Plates answer this problem in pressure vessels, separators and process equipment where sour service is part of daily operation. Hydrogen atoms generated by H₂S corrosion enter the steel and collect at internal defects, and three distinct cracking mechanisms follow from that entry: HIC, SSC/SSCC and SOHIC. Each one behaves differently, and each demands its own test method. ASTM A516 Gr. 60 NACE MR 0103 / MR0175 Plates are manufactured and tested against these exact requirements.

Why Sour-Service Testing Matters for A516 Gr. 60 Plates

H₂S reacts with the steel surface and releases atomic hydrogen as a corrosion byproduct. Hydrogen does not stay on the surface. It diffuses into the steel matrix and accumulates at inclusions, laminations and other internal discontinuities, building pressure inside the microstructure. Left unchecked, this process cracks the plate from within, often without any visible surface warning. ASTM A516 Grade 60 HIC Plates are produced with controlled sulphur content and clean steelmaking practices specifically to limit the internal defects where hydrogen can concentrate. Testing confirms whether that control actually worked.

HIC Testing: What Does NACE TM0284 Evaluate?

Hydrogen-Induced Cracking, or HIC, forms when trapped hydrogen builds enough internal pressure to crack the steel between inclusions, parallel to the plate surface, without any external stress applied. NACE TM0284 is the laboratory test method written specifically to evaluate this mechanism. A steel specimen sits in a controlled solution containing H₂S under defined exposure conditions, then gets sectioned and examined for cracking. Three ratios come out of that examination: Crack Length Ratio (CLR), Crack Thickness Ratio (CTR) and Crack Sensitivity Ratio (CSR). These figures describe how much cracking occurred and how severe it was, and the applicable project specification sets the acceptance limits against them. A516 Gr. 60 HIC Tested Plates carry documented CLR, CTR and CSR values on their test reports, giving buyers a traceable basis for acceptance rather than a bare pass/fail claim. NACE MR0103 Plates reference this test as part of their qualification for sour-service equipment used in oil and gas production and refining.

SSC or SSCC Testing: How Is It Different From HIC?

Sulfide Stress Cracking, commonly abbreviated as SSC or SSCC, is a fundamentally different issue. Where HIC needs no applied load, SSC requires both H₂S exposure and tensile stress acting together on the material. NACE TM0177 is the standard laboratory method for this evaluation, typically run using constant-load, tensile or bent-beam specimens held under stress in an H₂S environment for a fixed duration. A specimen that survives the test period without failure passes; one that cracks under load does not. This is the key distinction buyers need to hold onto: HIC testing checks for cracking without stress, while SSC testing checks for cracking specifically because of stress. NACE MR0175 Plates are qualified with SSC resistance as a core requirement, since this standard governs materials for oil and gas equipment operating directly in sour environments under load.

SOHIC: Understanding Stress-Oriented Hydrogen-Induced Cracking

Stress-Oriented Hydrogen-Induced Cracking, or SOHIC, sits in the space between the other two mechanisms. It involves hydrogen-assisted cracking that develops in a stacked, stress-oriented pattern rather than the scattered pattern typical of standard HIC damage, and it is influenced by the local stress field around welds and other high-stress zones. A plate marked HIC tested has not automatically demonstrated resistance to SOHIC, SSC, or any other sour-service degradation mode. Each mechanism has its own driving conditions and its own test method, so buyers should confirm exactly which mechanism a test report addresses rather than assuming broad coverage from a single certificate. Where SOHIC resistance is a project requirement, the applicable test method and acceptance criteria should be confirmed against the governing specification before order placement.

HIC vs SSCC vs SOHIC: Key Testing Differences

NACE TM0284 itself states plainly that it evaluates HIC and does not address SSC, pitting or other sour-environment effects. One test result should never be read as automatic proof of compliance with a different cracking mechanism.

What Should Buyers Check When Ordering A516 Gr. 60 NACE Plates?

Start with the exact NACE specification called for on the project, whether that is MR0103, MR0175, or both. Confirm the HIC test requirement and which method applies, request the full material test certificate (MTC) with CLR, CTR and CSR values included, and check hardness requirements where the specification calls for them. Ask whether ultrasonic testing is specified for internal soundness, and verify heat and plate traceability back to the original cast. Match every acceptance criterion to the actual project document rather than a generic standard, since sour-service requirements vary by end-use application.

Selecting the Right A516 Gr. 60 NACE Plate

The right plate comes down to matching the actual sour-service environment against the correct test requirement, not defaulting to whichever certificate happens to be on hand. HIC, SSC/SSCC and SOHIC each address a different failure mode, and project specifications typically call out exactly which ones apply. RPF Pipes & Fittings supplies ASTM A516 Gr. 60 NACE MR 0103 Plates and ASTM A516 Gr. 60 NACE MR 0175 Plates with documented test reports covering these requirements. Get in touch to confirm stock and test documentation for your project specification.