A516 Grade 70 NACE HIC is a common project term used for ASTM A516 Grade 70 or ASME SA516 Grade 70 pressure vessel steel plate ordered with additional requirements for wet H2S (sour) service, especially resistance to hydrogen induced cracking (HIC). In refinery, gas processing, separator, amine, and pressure vessel procurement, the phrase is widely understood, but it is important to state the technical meaning clearly: it is not a standalone ASTM material designation. It is a base pressure vessel plate specification combined with supplementary controls for steel cleanliness, hardness, ultrasonic integrity, heat treatment condition, HIC testing, and certification.
This distinction matters because a standard SA516 Gr 70 plate can satisfy the tensile and yield requirements of ASTM A516 / ASME SA516 while still being unsuitable for severe sour duty. Wet H2S environments can generate atomic hydrogen during corrosion, and that hydrogen may diffuse into the steel and accumulate at inclusions, segregation bands, laminations, or other internal discontinuities. The result can be blistering, planar cracking, or stepwise cracking. For that reason, end users and EPC contractors usually specify additional metallurgical and testing requirements when ordering a516 grade 70 nace hic plate.
What A516 Grade 70 Means
A516 Grade 70 is a carbon steel plate intended for welded pressure vessels for moderate and lower temperature service. It is widely used because it offers a practical combination of strength, weldability, forming capability, and commercial availability. The base standard establishes chemistry and mechanical property requirements, but by itself it does not guarantee suitability for sour service or resistance to hydrogen damage.
In pressure vessel fabrication, SA516 Gr 70 is commonly selected for drums, separators, columns, knock-out vessels, and process equipment where code compliance and fabrication performance are important. When the service contains aqueous H2S, however, the material selection process must go beyond the base plate grade and address cracking resistance explicitly.
What “NACE HIC” Adds to the Base Plate Specification
The terms NACE and HIC are often grouped together in purchase orders, but they refer to different aspects of sour-service control:
- ASTM A516 / ASME SA516 defines the base pressure vessel plate grade.
- NACE MR0175 / ISO 15156 provides material selection guidance for H2S-containing environments in oil and gas production.
- NACE TM0284 is the commonly referenced laboratory test method for evaluating HIC resistance of plate samples in sour test solutions.
- NACE TM0177 may be referenced where sulfide stress cracking or related sour-service testing is required for specific applications.
Accordingly, a technically complete order does not simply say “NACE plate.” It should define the base standard, the plate condition, the test method, the acceptance criteria, and any project-specific restrictions on chemistry, hardness, and internal soundness.
Typical Technical Requirements for A516 Grade 70 NACE HIC Plate
Although exact requirements vary by end user, project specification, and severity of service, the following controls are commonly requested for HIC-resistant SA516 Gr 70 plate:
- Fully killed steel with controlled steelmaking practice and improved cleanliness.
- Normalized or normalized and stress-relieved supply condition where specified.
- Restricted sulfur and phosphorus levels to reduce inclusion-related cracking risk.
- Calcium treatment or inclusion shape control where required by project practice.
- Hardness limits, often stated as a maximum Brinell or equivalent value.
- Ultrasonic testing to a defined standard and acceptance level for internal soundness.
- HIC testing to NACE TM0284 with stated acceptance criteria for CLR, CTR, and CSR.
- Mill test certificates showing heat number traceability and supplementary test results.
These requirements are intended to reduce susceptibility to hydrogen blistering and cracking by controlling both the steel microstructure and the internal defect population. In practice, the steelmaking route, segregation control, and plate quality can be as important as the nominal chemistry.
Reference Standards and Their Relevance
| Reference | Primary Scope | Relevance to A516 Grade 70 NACE HIC |
|---|---|---|
| ASTM A516 / ASME SA516 | Carbon steel plate for pressure vessels | Defines base grade, chemistry, tensile strength, yield strength, and general supply condition |
| NACE MR0175 / ISO 15156 | Material selection for H2S-containing environments | Used as service guidance for sour environments; does not replace the base plate standard |
| NACE TM0284 | Evaluation of HIC resistance | Common laboratory test method for qualifying plate performance in wet H2S exposure |
| ASTM / EN UT standards | Ultrasonic examination of plate | Used to verify internal soundness and screen for laminations or discontinuities |
| Project specification / end-user standard | Supplementary procurement controls | Defines hardness, chemistry restrictions, acceptance criteria, heat treatment, and documentation |
Mechanical Properties of the Base Grade
For orientation, ASTM A516 / ASME SA516 Grade 70 is generally associated with a minimum tensile strength of approximately 70–90 ksi (485–620 MPa) and a minimum yield strength of approximately 38 ksi (260 MPa), subject to the applicable edition and thickness range. These values define the base pressure vessel grade, but they do not by themselves establish sour-service suitability.
That is why procurement documents should not rely only on the phrase “A516 Gr 70 NACE HIC.” The order should state the exact code edition, thickness, plate condition, supplementary tests, and acceptance criteria. Otherwise, two plates with the same base grade may differ substantially in sour-service performance.
Why HIC Resistance Matters in Sour Service
In wet H2S service, corrosion reactions can produce hydrogen atoms that enter the steel. If the steel contains elongated inclusions, centerline segregation, or planar discontinuities, hydrogen may collect at those sites and create internal pressure. This can lead to:
- Hydrogen blistering
- Hydrogen induced cracking (HIC)
- Stepwise cracking (SWC)
- Reduced reliability in pressure boundary service
For vessels operating in sour environments, these damage mechanisms are a materials engineering issue, not only a code compliance issue. A plate that meets the base mechanical properties but lacks adequate cleanliness and HIC qualification may create avoidable fabrication and service risk.
How to Specify A516 Grade 70 NACE HIC Correctly on a Purchase Order
A robust purchase description should identify the material in a way that a mill, stockholder, inspector, and fabricator can all interpret consistently. A practical specification format typically includes:
- Base standard: ASTM A516 Gr 70 or ASME SA516 Gr 70
- Plate dimensions and quantity
- Supply condition: normalized, or normalized and stress relieved if required
- Maximum hardness requirement
- HIC test method and acceptance criteria
- Ultrasonic testing standard and acceptance level
- Chemistry restrictions such as sulfur and phosphorus limits
- Documentation: MTC, heat treatment record, HIC report, and traceability
Where project specifications are severe, buyers may also request vacuum degassing, low residual elements, through-thickness quality controls, or additional impact testing. The exact package depends on the process environment, partial pressure of H2S, pH, chloride content, operating temperature, and end-user standard.
Common Procurement and Inspection Points
From a practical procurement standpoint, the most frequent issues with A516 Grade 70 NACE HIC plate are not the base tensile properties but the supplementary requirements. Buyers should verify that the offered material is backed by actual HIC test reports, not only by a generic statement of “NACE compliance.” They should also confirm whether the test was performed on production plate from the same heat and thickness range, and whether the acceptance criteria match the project specification.
Inspection teams commonly review the mill certificate, heat treatment condition, ultrasonic examination results, hardness values, and HIC test report together. This combined review is more meaningful than checking the base ASTM grade alone.
FAQ
Is A516 Grade 70 NACE HIC a separate ASTM grade?
No. It is not a separate ASTM designation. It is ASTM A516 Grade 70 or ASME SA516 Grade 70 plate supplied with additional sour-service and HIC-resistance requirements defined by the purchaser or project specification.
Does NACE MR0175 itself certify a plate as HIC resistant?
No. NACE MR0175 / ISO 15156 provides material selection guidance for H2S environments, but HIC resistance is usually demonstrated through supplementary testing, commonly to NACE TM0284, together with chemistry, hardness, and quality controls.
What should be checked before buying SA516 Gr 70 for sour service?
At minimum, check the base standard, plate condition, hardness limit, HIC test method and acceptance criteria, ultrasonic testing requirement, chemistry restrictions, and mill documentation. A standard SA516 Gr 70 plate without these details may not be suitable for wet H2S duty.