NACE HIC steel plates are carbon steel and low-alloy steel plates manufactured for sour service where wet hydrogen sulfide can introduce atomic hydrogen into the steel and cause internal cracking. In procurement language, the term usually refers to plate supplied with hydrogen induced cracking (HIC) resistance, low sulfur chemistry, inclusion shape control, and documented qualification testing for refinery, gas processing, petrochemical, offshore, and pressure vessel applications.
These plates are commonly ordered to a base material specification such as pressure vessel quality steel, with additional sour service requirements added by the purchaser, EPC contractor, fabricator, or end user. The objective is not only to meet strength and toughness requirements, but also to reduce susceptibility to HIC, stepwise cracking (SWC), and related damage mechanisms that can occur in aqueous H2S environments.
What Are NACE HIC Steel Plates?
NACE HIC steel plates are steels intended for service where exposure to wet H2S creates a risk of hydrogen absorption. Once hydrogen diffuses into the steel, it can accumulate at non-metallic inclusions, segregation bands, laminations, or other internal discontinuities. If the steel cleanliness and microstructure are not adequately controlled, this can result in crack initiation parallel to the rolling plane and, in severe cases, linked crack arrays known as stepwise cracking.
For this reason, sour service plates are produced with tighter metallurgical control than general-purpose plate. Typical requirements include low sulfur content, restricted phosphorus, vacuum degassing or other clean steelmaking practices, calcium treatment for inclusion modification, and heat treatment or controlled rolling to achieve a uniform microstructure. Plates may be supplied in normalized, normalized and tempered, or thermomechanically controlled processed condition depending on grade and project specification.
How Sour Service Requirements Are Specified
The phrase nace hic steel plates is widely used in industry, but procurement documents usually combine several standards and supplementary requirements rather than relying on a single plate standard alone. Purchasers often specify a base plate grade together with HIC test acceptance criteria, ultrasonic examination, impact testing, hardness limits where relevant, and third-party inspection documentation.
In practice, project specifications may reference material selection requirements associated with NACE sour service guidance, while the plate itself is ordered to ASTM, ASME, or EN pressure vessel standards. The most common approach is to define the mechanical property grade first and then add sour service qualification requirements as supplementary conditions.
- Base plate standard: ASTM A516, ASTM A537, ASTM A387, or equivalent pressure vessel grades
- Sour service qualification: HIC testing in wet H2S solution to project or client acceptance criteria
- Steel cleanliness: low sulfur, low phosphorus, controlled residuals, inclusion modification
- Inspection: ultrasonic testing for internal soundness, dimensional checks, surface examination
- Documentation: mill test certificates, heat treatment records, HIC test reports, third-party release notes
Common Grades Used for NACE HIC Steel Plates
NACE HIC qualification is not a single steel grade by itself. It is more accurately a sour service performance requirement applied to suitable carbon steel or low-alloy steel plate grades. The final selection depends on design temperature, pressure, thickness, toughness requirements, welding procedure, and corrosion allowance.
| Base Grade | Typical Use | Why Used for Sour Service | Common Additional Requirements |
|---|---|---|---|
| ASTM A516 Gr. 60/65/70 | Pressure vessels, separators, drums | Widely accepted PVQ plate with good weldability | HIC test, UT, normalized condition, impact test |
| ASTM A537 Class 1/2 | Higher strength pressure vessel service | Improved strength with vessel quality properties | HIC qualification, toughness verification, UT |
| ASTM A387 alloy grades | Elevated temperature vessels | Used where alloy content and temperature capability are needed | Sour service review, HIC testing where specified |
| EN 10028 P265GH / P355GH equivalents | European code pressure equipment | Common for fabricated vessels under EN design routes | Project-specific HIC criteria, Z-quality, UT |
Among these, ASTM A516 Grade 70 HIC-tested plate is one of the most frequently requested materials for separators, absorbers, knock-out drums, and other equipment in wet H2S service. However, the correct material should always be selected against the service environment and the governing project specification.
Key Metallurgical Features of HIC-Resistant Plate
Resistance to hydrogen induced cracking depends heavily on steelmaking quality and through-thickness integrity. Plates intended for HIC service are usually produced with measures that reduce internal crack initiation sites and improve hydrogen tolerance.
- Low sulfur chemistry: lower sulfur reduces elongated manganese sulfide inclusions that can act as hydrogen traps.
- Inclusion shape control: calcium treatment modifies inclusion morphology and improves resistance to crack linkage.
- Clean steelmaking: vacuum degassing and strict secondary metallurgy reduce harmful inclusions and segregation.
- Controlled microstructure: normalized or TMCP conditions help achieve uniformity and toughness.
- Through-thickness soundness: ultrasonic testing helps detect laminations and internal discontinuities before fabrication.
For thick plate and critical vessel shells, buyers may also request improved through-thickness properties, tighter centerline segregation control, and more restrictive acceptance criteria than those applied to standard commercial plate.
HIC Testing, Acceptance Criteria, and Inspection
HIC testing is central to qualification. Test specimens are exposed to a standardized wet H2S environment for a defined duration, after which they are sectioned and evaluated for crack length ratio (CLR), crack thickness ratio (CTR), and crack sensitivity ratio (CSR), or equivalent project-defined metrics. Acceptance limits vary by client and end use, so the purchase order should state the required test method and maximum allowable values.
In addition to HIC testing, procurement packages often include:
- 100% ultrasonic testing for internal defects
- Charpy impact testing at specified temperature
- Tensile and bend test verification to the base grade
- Heat treatment records and traceability by heat number
- Third-party inspection by agencies such as BV, DNV, LR, TUV, or client-approved inspectors
Where welded components will operate under stress in sour environments, the purchaser may also review hardness control, welding consumables, post-weld heat treatment, and sulfide stress cracking considerations for the complete fabricated item. Plate qualification alone does not guarantee performance if fabrication controls are inadequate.
Typical Applications of NACE HIC Steel Plates
These plates are used where process fluids contain water and hydrogen sulfide and where internal corrosion or hydrogen damage mechanisms are credible. Typical applications include pressure vessels, separators, scrubbers, amine units, sour water strippers, storage tanks, heat exchanger shells, and offshore process modules.
End users in oil and gas, refining, LNG, petrochemical, and fertilizer sectors commonly specify HIC-tested plate for equipment handling sour hydrocarbons, acid gas, condensate, and associated produced water. The exact requirement depends on H2S partial pressure, pH, chloride content, cyanides, temperature, stress state, and the corrosion management philosophy of the project.
What Buyers Should Check Before Ordering
When sourcing nace hic steel plates, the purchase specification should be precise. A generic request for “NACE plate” is often insufficient because mills and stockholders need the full technical basis for supply and certification.
- Base material grade and thickness range
- Delivery condition: as rolled, normalized, N+T, or TMCP
- Required HIC test method and acceptance criteria
- Ultrasonic testing standard and acceptance level
- Impact test temperature and absorbed energy requirements
- Maximum sulfur and phosphorus limits
- Need for third-party inspection and end-user approval
- ASME, ASTM, EN, or project documentation format
Clear ordering data helps avoid mismatches between standard pressure vessel plate and genuinely HIC-qualified sour service plate. It also improves traceability during fabrication, code inspection, and final dossier submission.
FAQ
Is NACE HIC steel plate a separate material grade?
No. In most cases it is a standard carbon steel or low-alloy pressure vessel plate grade supplied with additional sour service requirements such as HIC testing, controlled chemistry, and enhanced inspection.
What is the difference between HIC resistance and general pressure vessel quality?
General pressure vessel quality addresses strength, toughness, and code compliance, while HIC-resistant plate adds metallurgical cleanliness and sour service testing to reduce susceptibility to hydrogen induced cracking in wet H2S environments.
Which documents are usually required with NACE HIC steel plates?
Typical documentation includes mill test certificates, chemical and mechanical test results, heat treatment records, ultrasonic test reports, HIC test reports, traceability details, and third-party inspection certificates where specified.