NACE HIC steel plates are carbon steel and low-alloy steel plates intended for sour service environments where exposure to wet hydrogen sulfide (H2S) can drive atomic hydrogen into the steel and cause internal cracking. In engineering and procurement practice, the term does not identify one standalone grade. It generally refers to plate supplied to a recognized base specification such as ASTM, ASME, or EN pressure vessel standards, combined with supplementary requirements for hydrogen induced cracking (HIC) resistance, low sulfur chemistry, inclusion shape control, ultrasonic integrity, and qualification testing.
These plates are commonly specified for separators, absorbers, amine units, pressure vessels, drums, heat exchangers, pipelines, and related process equipment handling sour fluids in refineries, gas processing plants, petrochemical plants, and offshore facilities. The design objective is to meet strength, toughness, weldability, and fabrication requirements while reducing susceptibility to HIC, stepwise cracking (SWC), and related hydrogen-assisted damage mechanisms associated with aqueous H2S service.
What Are NACE HIC Steel Plates?
NACE HIC steel plates are steels manufactured with tighter metallurgical control than general-purpose plate because wet H2S service creates a risk of hydrogen entry into the steel matrix. Hydrogen can accumulate at elongated non-metallic inclusions, segregation bands, laminations, and other internal discontinuities. If steel cleanliness and microstructure are not adequately controlled, cracks may initiate parallel to the rolling plane and in severe cases link together as stepwise cracking.
For that reason, sour service plate production commonly includes low sulfur and phosphorus limits, vacuum degassing or equivalent clean steelmaking practice, calcium treatment for inclusion modification, controlled rolling, and heat treatment where required by grade and project specification. Depending on the application, plates may be supplied in normalized, normalized and tempered, or thermomechanically controlled processed condition.
How NACE and HIC Requirements Are Normally Specified
The search term nace hic steel plates is widely used in industry, but project documents usually define a base plate grade first and then add sour service requirements. The base standard establishes minimum tensile properties, yield strength, elongation, dimensional tolerances, and product form requirements. The sour service clauses then define acceptance criteria for hydrogen damage resistance and internal quality.
In practice, end users, EPC contractors, and fabricators often order pressure vessel quality steels to ASTM, ASME, or EN standards with additional clauses for HIC testing, ultrasonic examination, impact testing, hardness limits where relevant, steel cleanliness restrictions, and third-party inspection documentation. Requirements may be aligned with refinery standards, upstream operator specifications, pressure equipment codes, and purchaser-specific material requisitions.
Relevant Standards and Industry References
Because terminology is often used loosely in the market, it is important to distinguish between the corrosion environment standard and the product qualification requirements. NACE documents define the service environment and material selection framework, while plate standards and purchaser specifications define the actual product requirements.
| Reference | Typical Role in Procurement | Why It Matters |
|---|---|---|
| NACE MR0175 / ISO 15156 | Material selection for H2S-containing oil and gas production environments | Sets the framework for sour service suitability and hardness-related restrictions |
| NACE TM0284 | HIC test method for plate and line pipe steels | Used to evaluate resistance to hydrogen induced cracking |
| NACE TM0177 | Sulfide stress cracking test methods | Applied where SSC resistance must also be demonstrated |
| ASTM / ASME plate standards | Base mechanical and chemical requirements | Defines grade, strength class, heat treatment, and product form |
| EN 10028 series | European pressure vessel plate basis | Common for boiler and pressure vessel applications with added sour service clauses |
| ASTM A578 / equivalent UT standard | Ultrasonic examination of plate | Controls internal discontinuities and laminar defects |
Typical Base Grades Used for Sour Service Plate
NACE HIC requirements are often applied to pressure vessel plate grades rather than sold as a separate nominal grade. Common examples in project specifications include ASTM A516 Gr. 60/65/70, ASTM A537 classes where applicable, and EN pressure vessel grades such as P265GH, P355GH, or normalized fine-grain grades when supported by purchaser requirements. For low-temperature or higher-toughness service, normalized or normalized-and-tempered grades may be selected.
The final choice depends on design temperature, thickness, code basis, impact test requirements, weldability, and process fluid severity. In many cases, the purchase order will state the base grade, plate condition, HIC test standard, acceptance criteria, ultrasonic testing level, and documentation package rather than simply stating "NACE plate."
Key Metallurgical Features of HIC Resistant Plates
- Low sulfur chemistry: reduces elongated manganese sulfide inclusions that can act as hydrogen traps.
- Low phosphorus and controlled segregation: helps limit banding and crack propagation paths.
- Clean steelmaking practice: often includes vacuum degassing and controlled secondary metallurgy.
- Calcium treatment or inclusion modification: changes inclusion morphology to improve resistance.
- Controlled rolling and heat treatment: refines microstructure and improves through-thickness quality.
- Ultrasonic soundness: reduces the risk of laminations and internal defects relevant to hydrogen damage.
- Documented HIC qualification testing: demonstrates conformance to project acceptance criteria.
These controls do not make steel immune to all sour service damage mechanisms, but they materially reduce the probability of HIC initiation under defined service conditions when correctly specified and fabricated.
HIC Testing, Acceptance Criteria, and Inspection
HIC resistance is commonly verified by testing in accordance with NACE TM0284. Test coupons are exposed to a sour solution under controlled conditions, and the resulting cracking is evaluated using parameters such as crack length ratio (CLR), crack thickness ratio (CTR), and crack sensitivity ratio (CSR). The exact acceptance limits are not universal; they are typically set by the purchaser, end user, or project specification.
Additional requirements may include ultrasonic examination to ASTM A578 or equivalent, Charpy impact testing, hardness verification where sour service restrictions apply, through-thickness properties for highly restrained welded joints, and macro-etch or cleanliness review depending on criticality. Mill test certificates, heat treatment records, HIC test reports, and third-party inspection release documents are often required for traceability.
Applications of NACE HIC Steel Plates
These plates are used where aqueous H2S exposure can create a realistic hydrogen damage risk. Typical applications include:
- Pressure vessels and separators in upstream and midstream sour service
- Amine absorbers, regenerator systems, and associated drums
- Refinery process equipment handling sour water or H2S-bearing streams
- Heat exchanger shells, channel components, and vessel internals where specified
- Storage and process equipment in gas processing and petrochemical facilities
Service severity depends on water presence, H2S partial pressure, pH, cyanides, operating temperature, stress state, and fabrication details. Material selection should therefore be reviewed against the actual process conditions rather than based on keyword terminology alone.
Procurement Checklist for NACE HIC Steel Plates
To avoid ambiguity during purchasing, a technical requisition for NACE HIC steel plates should normally identify the following:
- Base material standard and grade
- Plate thickness, width, length, and quantity
- Supply condition: as rolled, normalized, normalized and tempered, or TMCP as applicable
- HIC test method and acceptance criteria
- Ultrasonic testing standard and acceptance level
- Impact test temperature and absorbed energy requirements
- Hardness limits if required by sour service specification
- Documentation: MTC, HIC report, NDT reports, heat treatment records, and inspection release
This approach is more technically accurate than ordering only by the phrase "NACE HIC steel plate," because it links the product to measurable and auditable requirements.
FAQ
Is NACE HIC a separate steel grade?
No. In most cases it is not a standalone grade designation. It usually means a standard plate grade, such as an ASTM, ASME, or EN pressure vessel plate, supplied with additional sour service and HIC resistance requirements.
What is the difference between HIC and SSC?
HIC refers to hydrogen induced cracking that develops internally, often parallel to the rolling plane, due to hydrogen accumulation at inclusions or segregation zones. SSC, or sulfide stress cracking, is a stress-oriented cracking mechanism associated with tensile stress, hardness, and sour exposure. Some projects require evaluation of both.
Which test standard is commonly used for HIC resistant plates?
NACE TM0284 is the most commonly referenced laboratory test method for assessing HIC resistance in plate and pipe steels. Purchaser specifications usually define the acceptance limits for CLR, CTR, and CSR, along with any supplementary inspection requirements.