A516 Grade 70 NACE HIC is a common procurement term for ASTM A516 Grade 70 or ASME SA516 Grade 70 pressure vessel steel plate supplied with additional requirements for wet H2S sour service. In practice, the phrase does not identify a separate ASTM material grade. It describes a base carbon steel plate combined with supplementary controls for steelmaking practice, plate quality, laboratory testing, hardness, ultrasonic examination, and documentation.
This distinction matters because standard SA516 Grade 70 plate may satisfy base tensile and yield requirements while still being unsuitable for severe aqueous hydrogen sulfide environments. In sour service, corrosion reactions can generate atomic hydrogen that diffuses into steel and accumulates at inclusions, segregation bands, laminations, and other internal discontinuities. The resulting damage mechanisms can include hydrogen blistering, hydrogen induced cracking (HIC), and stepwise cracking (SWC).
What A516 Grade 70 Means
A516 Grade 70 is a carbon steel plate intended for welded pressure vessels in moderate and lower temperature service. It is widely specified for separators, scrubbers, absorbers, amine units, knockout drums, towers, columns, reactors, and storage vessels because it offers a practical balance of strength, weldability, formability, and availability.
The base ASTM A516 / ASME SA516 specification defines chemistry, mechanical properties, heat treatment provisions, and standard testing requirements. However, the base specification alone does not confirm suitability for wet H2S exposure. Where the process stream contains aqueous H2S, purchasers usually add explicit sour-service requirements rather than relying only on the grade designation.
What “NACE HIC” Adds to the Base Plate
The terms NACE and HIC are related but not identical. In project specifications, they generally refer to a package of materials selection rules and laboratory verification methods rather than one single standard.
- ASTM A516 / ASME SA516: defines the base pressure vessel plate grade.
- NACE MR0175 / ISO 15156: provides materials selection guidance for H2S-containing environments in oil and gas production and related sour service.
- NACE MR0103: may be referenced for materials used in H2S-containing refinery environments.
- NACE TM0284: commonly specified test method for evaluating HIC resistance of steel plate samples.
- NACE TM0177: may be added when sulfide stress cracking or related testing is required by project documents.
Accordingly, a technically complete order should not simply state “A516 Grade 70 NACE HIC.” It should define the applicable edition of the standards, the test method, the acceptance criteria, the sample orientation and frequency, hardness limits, UT level, and required certification.
Typical Supplementary Requirements for Sour Service Plate
Project specifications vary by licensor, end user, and service severity, but the following controls are commonly requested for A516 Grade 70 NACE HIC plate:
- Fully killed steel with controlled steelmaking practice and low residual elements.
- Normalized plate condition where required by the project specification.
- Clean steel with restrictions on segregation, inclusions, and centerline soundness.
- Hydrogen induced cracking testing to NACE TM0284 with stated acceptance criteria.
- Stepwise cracking evaluation where specified by the purchaser.
- Hardness control for base metal and, where relevant, heat affected zones after fabrication procedure qualification.
- Ultrasonic testing to an agreed acceptance level, often tighter than minimum commodity plate practice.
- Mill test certification showing chemistry, mechanical properties, heat treatment, HIC results, UT results, and traceability.
These additions are intended to reduce susceptibility to internal hydrogen damage by improving plate cleanliness and by verifying performance through laboratory exposure testing.
Relevant Standards and How They Are Used
| Standard | Primary purpose | Relevance to A516 Grade 70 NACE HIC |
|---|---|---|
| ASTM A516 / ASME SA516 | Base specification for pressure vessel carbon steel plate | Defines grade, chemistry, tensile properties, and basic supply condition |
| NACE MR0175 / ISO 15156 | Materials selection for H2S-containing environments | Used as environmental and materials-selection guidance in sour service |
| NACE MR0103 | Materials requirements for refinery sour environments | Often referenced in refining, upgrading, and process plant applications |
| NACE TM0284 | Laboratory method for HIC testing of steels | Used to verify resistance to hydrogen induced cracking |
| NACE TM0177 | SSC and environmental cracking test methods | May be specified for additional sour-service qualification |
| ASTM A578 / A578M | Ultrasonic examination of steel plates | Common basis for UT acceptance level on pressure vessel plate |
HIC Test Reporting and Acceptance Criteria
When buyers request A516 Grade 70 NACE HIC plate, the most important technical point is that test acceptance criteria must be written into the purchase order. NACE TM0284 is a test method; by itself it does not define one universal pass/fail threshold for every project. End users or EPC specifications usually state maximum values for crack length ratio, crack thickness ratio, and crack sensitivity ratio, together with sample location, number of specimens, and reporting format.
Because acceptance limits vary, a supplier should confirm the exact project requirement before quoting. The order may also define whether the plate is intended only for HIC resistance or for both HIC and SWC evaluation. For critical pressure vessel service, purchasers frequently require full traceability between plate heat number, test coupons, UT records, and mill certificates.
Hardness, Heat Treatment, and Fabrication Considerations
Hardness control is often included because elevated hardness can increase susceptibility to sour-service cracking mechanisms. For plate supply, this usually means confirming the base metal hardness limit stated by the project or end user specification. In fabricated equipment, hardness control may also extend to weld metal and heat affected zones through qualified welding procedures, heat input control, and post weld heat treatment where applicable.
Normalized plate is commonly preferred for sour service because it can improve microstructural uniformity and toughness compared with as-rolled supply, depending on thickness and mill route. Purchasers may also request restrictions on sulfur, phosphorus, and residual elements, along with calcium treatment or other steel cleanliness measures intended to reduce elongated sulfide inclusions and improve resistance to hydrogen damage.
How to Specify A516 Grade 70 NACE HIC Correctly
A clear purchase description helps avoid disputes and reduces the risk of receiving standard commodity plate instead of tested sour-service plate. A practical order description should include the following items:
- Material: ASTM A516 Grade 70 or ASME SA516 Grade 70
- Plate condition: as required, often normalized
- Service: wet H2S / sour service
- HIC testing: NACE TM0284, edition to be stated
- Acceptance criteria: purchaser or project-specific limits for HIC and, if required, SWC
- UT requirement: ASTM A578 / A578M level or project-specific acceptance
- Hardness limit: maximum permitted value and test method
- Supplementary requirements: steelmaking cleanliness, sample frequency, traceability, and certification
Without these details, the phrase “A516 Grade 70 NACE HIC” remains incomplete and open to interpretation. For pressure vessel procurement, the technical specification should always govern over shorthand commercial descriptions.
Common Applications
A516 Grade 70 NACE HIC plate is commonly used in equipment exposed to aqueous H2S-containing process streams, including separators, absorbers, amine contactors, knockout drums, scrubbers, flare knock-out vessels, process columns, and storage or surge vessels in refinery and gas processing service. Final material selection should always be checked against the actual fluid composition, pH, chloride level, cyanides if present, operating temperature, pressure, and the governing end-user standard.
FAQ
Is A516 Grade 70 NACE HIC a separate ASTM grade?
No. It is not a standalone ASTM designation. It normally means ASTM A516 Grade 70 or ASME SA516 Grade 70 plate ordered with additional sour-service requirements such as HIC testing, hardness limits, UT, and enhanced certification.
Does NACE TM0284 alone guarantee suitability for all sour service?
No. NACE TM0284 is a laboratory test method for assessing HIC resistance. Suitability for service also depends on the actual environment, project acceptance criteria, fabrication variables, hardness control, and the governing materials selection standard such as MR0175/ISO 15156 or MR0103.
What should appear on the mill certificate for A516 Grade 70 NACE HIC plate?
The certificate should normally show the plate grade, heat number, chemistry, mechanical properties, heat treatment condition, HIC test results, UT results, dimensions, quantity, and traceability to the applicable specification and purchase order requirements.