Safety CriticalJune 2026 · 9 min read

NACE HIC Steel Plates — Essential for Sour Service Environments

Q: What does NACE HIC mean?

NACE refers to NACE MR-01-75 (now ANSI/NACE MR0175/ISO 15156) — a standard specifying material requirements for sour (H₂S-containing) environments. HIC means Hydrogen Induced Cracking — internal cracking caused by atomic hydrogen diffusing into steel and recombining at inclusion sites. NACE HIC plates are specifically manufactured with ultra-low sulphur, calcium treatment, and controlled rolling to resist this failure mechanism.

Q: When do I need NACE HIC plates?

NACE HIC plates are required when equipment will contain fluids with H₂S partial pressure exceeding 0.05 psi (0.3 kPa) — the threshold defined in NACE MR-01-75. This includes: sour gas separators, amine absorbers/regenerators, sour water strippers, crude oil storage with H₂S, desulphurisation units, and any vessel/pipeline handling wet H₂S in oil & gas refineries.

Q: What are the HIC test acceptance criteria?

Per NACE TM-0284 (standard test method): CLR (Crack Length Ratio) ≤ 15%, CTR (Crack Thickness Ratio) ≤ 5%, CSR (Crack Sensitivity Ratio) ≤ 2%. Test conditions: specimens immersed in Solution A (5% NaCl + 0.5% CH₃COOH, saturated with H₂S) for 96 hours at 25°C, then ultrasonically examined for internal cracks.

In oil and gas processing, equipment failure in sour (H₂S-containing) service doesn't just mean downtime — it means potential explosion, toxic gas release, and loss of life. NACE HIC steel plates are specifically engineered to resist hydrogen-induced cracking in these lethal environments. As India's trusted NACE HIC steel plate supplier and carbon steel SA 516 plate stockist, Creative Metal Industries supplies HIC-tested plates with complete documentation for the country's most critical refinery and offshore projects.

What is NACE HIC and Why It Matters for Oil & Gas

NACE refers to NACE International (now AMPP) standard MR-01-75 (current version: ANSI/NACE MR0175/ISO 15156), which defines material requirements for metallic equipment used in H₂S-containing (sour) oil and gas production environments. It mandates hardness limits, heat treatment conditions, and specific testing to prevent catastrophic in-service failures.

HIC stands for Hydrogen Induced Cracking — a specific failure mechanism where atomic hydrogen (generated by corrosion in H₂S environments) diffuses into steel and accumulates at manganese sulphide (MnS) inclusions, creating internal blisters and cracks that propagate parallel to the plate surface. Unlike mechanical fatigue, HIC requires zero applied stress — even unstressed plates in storage can crack if manufactured from susceptible material.

Hydrogen Induced Cracking — The Mechanism Explained

Corrosion reaction: H₂S in the process fluid attacks the steel surface: Fe + H₂S → FeS + 2H⁰ (atomic hydrogen)
Hydrogen absorption: Atomic hydrogen (H⁰) is tiny — it diffuses directly into the steel lattice
Hydrogen trapping: H atoms accumulate at planar inclusion sites (elongated MnS stringers from rolling)
Molecular recombination: H⁰ + H⁰ → H₂ (molecular hydrogen gas) at the inclusion interface
Pressure build-up: H₂ molecules cannot diffuse back out — internal pressure builds to thousands of atmospheres
Crack initiation: Internal pressure exceeds local yield — a blister/crack forms parallel to the rolling direction
Crack linking: Adjacent cracks connect through the thickness via stepwise cracking (SOHIC) → through-wall failure

Chemical Requirements for HIC Resistance

HIC-resistant plates require fundamentally different steelmaking than standard SA 516:

Parameter	Standard SA 516 Gr.70	HIC-Resistant SA 516 Gr.70	Why
Sulphur (S)	0.035% max	≤ 0.002% (target 0.001%)	MnS inclusions are the primary HIC initiation sites
Calcium Treatment	Not required	Mandatory	Spheroidises sulphide inclusions — no elongated stringers
Phosphorus (P)	0.035% max	≤ 0.015% preferred	Reduces grain boundary segregation
Carbon Equivalent	Not controlled for HIC	CE ≤ 0.43 (IIW formula)	Lower hardness = less hydrogen trapping
Hardness	Not specified for HIC	≤ 200 HBW (≤ 22 HRC)	Mandatory per NACE MR-01-75
Delivery Condition	As-rolled acceptable	Normalised required	Uniform fine grain = fewer hydrogen trap sites
Inclusion Control	Standard	Shape-controlled (spherical)	Eliminates planar inclusions that initiate cracks

Key Applications — Where NACE HIC Plates are Mandatory

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Sour Gas Separators

Primary/test separators handling wellhead fluids with H₂S. The most common application for HIC plates in India's ONGC and RIL operations.

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Amine Systems

Amine absorber columns and regenerators in gas sweetening units. Wet H₂S + amine corrosion products create ideal HIC conditions.

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Sour Water Strippers

Process sour water from various refinery units. High H₂S + ammonia + cyanide creates extremely aggressive hydrogen charging.

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Desulphurisation Units

Hydrotreater and hydrocracker reactor shells, feed/effluent exchangers. High-pressure H₂ + H₂S environment.

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Offshore Platforms

Wellhead equipment, subsea manifolds, production separators on platforms like Mumbai High, KG Basin, and Bombay High.

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Crude Storage

Floating roof tanks storing sour crude oil. Vapour space contains H₂S that attacks roof plates and upper shell courses.

Testing and Certification Standards

Test	Standard	Acceptance Criteria
HIC (Hydrogen Induced Cracking)	NACE TM-0284	CLR ≤ 15%, CTR ≤ 5%, CSR ≤ 2%
SSC (Sulphide Stress Cracking)	NACE TM-0177 Method A	No failure at 720 hours, 90% AYS
Hardness	NACE MR-01-75	≤ 200 HBW (≤ 22 HRC) base metal + HAZ
Ultrasonic Testing	SA 435 Level B / SA 578 Level B	No lamination or inclusion clusters
Charpy Impact	Per ASME code	As specified by design temperature
Chemistry	Ladle + Product analysis	S ≤ 0.002%, Ca-treated, CE per IIW

Why Source NACE HIC Plates from Creative Metal Industries?

Specialist stockist: We maintain dedicated HIC-tested stock separate from standard plates — SA 516 Gr.60/70, SA 537 Cl.1/2, SA 387 Gr.11/22 in NACE/HIC condition
Complete test documentation: Every plate comes with HIC test report (TM-0284) showing CLR, CTR, CSR values per specimen, plus SSC report (TM-0177) on request
Tighter acceptance available: Some clients (Shell, ONGC) require CLR ≤ 10%, CTR ≤ 3% — we source plates meeting these stricter criteria from AMNS and TATA
Approved mills: AMNS (ArcelorMittal Nippon Steel), TATA Steel, SAIL (Bokaro HIC line), and imported plates from POSCO, Dillinger
Third-party inspection: DNV GL, TUV SUD, Bureau Veritas, Lloyd's inspection at our Vadodara facility before dispatch
Also stocking: Standard SA 516 plates, TMT bars, and structural steel as a complete steel trading company in Gujarat

Frequently Asked Questions — NACE HIC Plates

What does NACE HIC mean?

NACE = material standard for sour (H₂S) service per MR-01-75/ISO 15156. HIC = Hydrogen Induced Cracking — internal cracking caused by hydrogen diffusing into steel at MnS inclusion sites. NACE HIC plates are manufactured with ultra-low sulphur (≤ 0.002%), calcium treatment, and normalised delivery to resist this mechanism.

When do I need NACE HIC plates?

When equipment contains fluids with H₂S partial pressure > 0.05 psi (0.3 kPa). Applications: sour gas separators, amine absorbers, sour water strippers, desulphurisation reactors, crude storage with H₂S, and any wet H₂S service in oil & gas refineries and offshore platforms.

What are the HIC test acceptance criteria?

Per NACE TM-0284: CLR ≤ 15%, CTR ≤ 5%, CSR ≤ 2%. Test: specimens in Solution A (5% NaCl + 0.5% acetic acid + H₂S saturated) for 96 hours at 25°C, then UT examined for cracks. Some clients specify tighter limits (CLR ≤ 10%, CTR ≤ 3%) — we can source accordingly.