A516 NACE HIC is the common industry term for ASTM A516 or ASME SA516 pressure vessel quality carbon steel plate ordered for sour service with demonstrated resistance to hydrogen-induced cracking (HIC). The term does not identify a standalone ASTM material grade. Instead, it describes A516 plate supplied with additional metallurgical controls, testing, and acceptance criteria for fabrication into vessels, separators, columns, drums, and other equipment exposed to wet H2S-containing process environments.
In refinery, gas processing, amine treating, LNG, petrochemical, and upstream oil and gas applications, standard A516 compliance alone may be insufficient where hydrogen damage is a credible failure mechanism. Purchase orders for A516 Grade 70 NACE HIC, A516 Grade 65 NACE HIC, or A516 Grade 60 NACE HIC typically add low-sulfur chemistry limits, clean steelmaking practice, inclusion shape control, hardness restrictions, ultrasonic examination, and HIC test requirements to recognized NACE methods.
What A516 NACE HIC Means
ASTM A516 / ASME SA516 covers carbon steel plates for pressure vessel service at moderate and lower temperatures. The grades most often specified for sour applications are Grade 60, Grade 65, and Grade 70. Among these, A516 Grade 70 NACE HIC is widely selected because it offers a practical balance of strength, weldability, and fabrication performance for pressure-containing equipment.
When a project specifies A516 NACE HIC plate, the intent is normally that the plate has been manufactured and qualified to resist hydrogen damage associated with wet H2S exposure. Common references include NACE TM0284 for HIC evaluation, NACE TM0177 where sulfide stress cracking testing is additionally required, NACE MR0175 / ISO 15156 for material selection guidance in H2S-containing oil and gas production environments, and ASTM A20 / ASME SA20 for general plate supply requirements.
It is important to distinguish material selection guidance from the product specification. NACE MR0175 / ISO 15156 does not create a plate grade called “NACE plate.” The order must still identify the underlying ASTM or ASME specification together with all supplementary sour-service requirements, testing methods, and acceptance criteria.
Why HIC Resistance Is Required in Sour Service
In wet H2S environments, atomic hydrogen can enter the steel and accumulate at inclusions, segregation bands, laminations, or other internal discontinuities. Under unfavorable metallurgical conditions, this can produce hydrogen-induced cracking, typically appearing as internal cracking roughly parallel to the plate surface. In more severe cases, crack linkage can form stepwise cracking (SWC). Depending on hardness, stress level, residual stress, and service severity, sulfide stress cracking (SSC) may also be a concern.
For this reason, sour-service A516 plate is generally produced with tighter control of steel cleanliness and centerline segregation than standard pressure vessel plate. End users often require low sulfur content, calcium treatment or other inclusion shape-control practices, vacuum degassing, controlled rolling, and through-thickness quality suitable for critical pressure equipment fabrication.
Typical Requirements for A516 NACE HIC Plate
Project specifications vary by owner, licensor, EPC, and service severity, but the following requirements are commonly added to standard A516 / SA516 supply conditions:
- ASTM A516 or ASME SA516 base specification, usually Grade 60, 65, or 70
- Low sulfur chemistry, often with a maximum sulfur limit significantly below standard plate levels
- Clean steelmaking practice and control of non-metallic inclusions
- Calcium treatment or equivalent inclusion shape control where specified
- Hardness limits for base metal and, where applicable, heat affected zones after fabrication qualification
- 100% ultrasonic examination to ASTM A578 or project-specific acceptance levels
- HIC testing to NACE TM0284 with stated solution, duration, sample orientation, and acceptance criteria
- Optional SSC testing to NACE TM0177 if required by the end user
- Normalized or controlled-rolled delivery condition, depending on thickness and project requirements
- Full traceability, heat-by-heat mill test certification, and supplementary inspection documentation
Relevant Standards and How They Apply
| Standard | Primary Purpose | How It Relates to A516 NACE HIC |
|---|---|---|
| ASTM A516 / ASME SA516 | Pressure vessel carbon steel plate specification | Defines the underlying plate grade such as Grade 60, 65, or 70 |
| ASTM A20 / ASME SA20 | General requirements for steel plate supply | Applies supplementary requirements, testing, marking, and certification framework |
| NACE TM0284 | Test method for HIC resistance | Used to verify resistance to hydrogen-induced cracking in sour environments |
| NACE TM0177 | Test method for SSC resistance | Specified when sulfide stress cracking evaluation is additionally required |
| NACE MR0175 / ISO 15156 | Material selection guidance for H2S service | Guides suitability in sour production environments but does not define a standalone plate grade |
| ASTM A578 | Ultrasonic examination of steel plates | Commonly used for lamination screening and internal soundness requirements |
Common Grades and Selection Considerations
A516 Grade 70 NACE HIC is the most frequently requested option because it combines higher tensile strength with good forming and welding characteristics. Grade 65 may be selected where a moderate strength level is adequate and tighter control of hardness or weld procedure qualification is preferred. Grade 60 is less common but remains relevant for certain lower-strength vessel designs.
Grade selection should not be based on strength alone. The designer and purchaser should also consider:
- Partial pressure of H2S and the presence of free water
- Operating stress levels and cyclic service conditions
- Plate thickness and through-thickness quality requirements
- Post weld heat treatment requirements
- Fabrication route, including forming severity and weld heat input
- Owner-specific HIC acceptance criteria and inspection hold points
How to Specify A516 NACE HIC Correctly
Many procurement issues arise because “A516 NACE HIC” is written on an inquiry without enough technical detail. To avoid ambiguity, the purchase order should define the complete material package rather than relying on shorthand terminology alone.
A clear specification normally includes the base grade, plate thickness range, delivery condition, HIC test method, number of test coupons, solution and duration for testing, acceptance criteria, ultrasonic examination level, hardness limits, and any supplementary requirements for chemistry, heat treatment, impact testing, or third-party inspection.
A practical ordering description may resemble the following: ASME SA516 Grade 70 plate, normalized, sour service quality, HIC tested to NACE TM0284, low sulfur, 100% UT to ASTM A578, with project-specific acceptance criteria and full MTC traceability. The exact wording should always follow the governing project specification.
Inspection, Certification, and Documentation
For pressure equipment used in sour service, documentation is as important as the nominal grade. End users commonly require mill test certificates showing chemical composition, mechanical properties, heat treatment condition, HIC test results, ultrasonic examination results, and traceability to heat number and plate number. Depending on project criticality, third-party witnessing, EN 10204 inspection documents, or additional owner data book requirements may also apply.
Because HIC performance depends on steel cleanliness and process control rather than on chemistry alone, certification should be reviewed in conjunction with the actual testing scope and acceptance criteria. A plate described only as “NACE compliant” without supporting test data is not a complete technical basis for sour-service acceptance.
FAQ
Is A516 NACE HIC a separate ASTM grade?
No. A516 NACE HIC is not a standalone ASTM designation. It is industry shorthand for ASTM A516 or ASME SA516 plate supplied with additional sour-service requirements such as low sulfur chemistry, ultrasonic testing, and HIC qualification testing.
What is the difference between A516 Grade 70 and A516 Grade 70 NACE HIC?
A516 Grade 70 identifies the base pressure vessel plate grade. A516 Grade 70 NACE HIC means that the same base grade is supplied with extra controls and test requirements intended for wet H2S service, including demonstrated resistance to hydrogen-induced cracking.
Does NACE MR0175 guarantee that a plate is HIC resistant?
No. NACE MR0175 / ISO 15156 provides material selection guidance for H2S-containing environments, but it does not by itself certify a plate as HIC resistant. HIC resistance is normally demonstrated through project-defined testing, most commonly to NACE TM0284, together with specified acceptance criteria.