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, especially resistance to hydrogen induced cracking (HIC). It is important to define the term accurately: it is not a separate ASTM material grade. Instead, the purchase order combines the base pressure vessel plate specification with supplementary controls for steelmaking practice, plate soundness, heat treatment, hardness, laboratory testing, ultrasonic examination, and mill documentation.
This distinction matters in refineries, gas processing plants, amine systems, separators, absorbers, and other pressure-retaining equipment built to ASME Section VIII. A standard SA516 Grade 70 plate may satisfy base tensile and yield requirements but still be unsuitable for severe sour environments. In aqueous hydrogen sulfide service, corrosion reactions generate atomic hydrogen that can diffuse into steel and accumulate at inclusions, segregation bands, laminations, and similar internal discontinuities. The result may be hydrogen blistering, planar HIC, or stepwise cracking, all of which are critical degradation mechanisms for carbon steel pressure vessel plate.
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 because it offers a practical balance of strength, weldability, formability, and availability across common thickness ranges. The base ASTM A516 / ASME SA516 specification defines chemistry, mechanical properties, heat treatment provisions, and standard testing requirements, but by itself it does not confirm suitability for wet H2S exposure.
Typical fabricated equipment includes separators, scrubbers, towers, knock-out drums, storage bullets, reactors, columns, and process vessels. Where the process stream contains aqueous H2S, purchasers normally add explicit sour-service requirements to the plate order rather than relying only on the base grade description.
What “NACE HIC” Adds to the Base Plate
The terms NACE and HIC are often grouped together, 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 materials selection guidance for H2S-containing environments in oil and gas production and related sour service.
- NACE MR0103 may be referenced for materials in H2S-containing refinery environments.
- NACE TM0284 is the commonly referenced laboratory test method for evaluating HIC resistance of plate samples.
- NACE TM0177 may also be specified where sulfide stress cracking or related evaluation is required by the project.
Accordingly, a technically complete purchase order should not simply state A516 Grade 70 NACE HIC without supporting acceptance criteria. End users typically define the HIC test solution, exposure duration, sample orientation, acceptance thresholds, maximum hardness, ultrasonic testing level, heat treatment condition, and certification package to be supplied with the plate.
Why HIC Resistance Is Critical in Sour Service
Hydrogen induced cracking occurs when atomic hydrogen generated by corrosion enters the steel and recombines at internal trap sites. If the steel contains unfavorable inclusion morphology, centerline segregation, or planar discontinuities, pressure can build locally and initiate cracking parallel to the plate surface. In severe cases, separate cracks link through the thickness to form stepwise cracking (SWC).
For pressure vessel service, the risk is not only metallurgical but also structural. Cracking can reduce through-thickness integrity, impair weld region performance, and shorten equipment life. This is why sour-service plate procurement usually emphasizes clean steel production, controlled sulfur levels, calcium treatment where applicable, normalized condition, and ultrasonic examination in addition to HIC laboratory testing.
Typical Technical Requirements for A516 Grade 70 NACE HIC Plate
Project specifications vary, but the following controls are commonly requested for HIC-resistant SA516 Grade 70 plate:
- Base specification: ASTM A516 Grade 70 or ASME SA516 Grade 70.
- Heat treatment: normalized, if required by project or thickness.
- HIC testing: tested in accordance with NACE TM0284 with stated acceptance criteria.
- Hardness limit: purchaser-defined maximum hardness for sour service.
- Ultrasonic testing: UT to the specified standard and acceptance level.
- Steel cleanliness: low sulfur and inclusion control to improve HIC resistance.
- Documentation: mill test certificate showing chemistry, mechanical properties, heat treatment, UT, and HIC results.
Because project requirements differ, the plate should be evaluated against the end user specification, EPC datasheet, and applicable code requirements rather than by trade description alone.
Reference Standards and Their Role
| Standard / Document | Primary Role | Why It Matters for A516 Grade 70 NACE HIC |
|---|---|---|
| ASTM A516 / ASME SA516 | Base pressure vessel plate specification | Defines grade, chemistry limits, tensile properties, and general supply condition |
| NACE MR0175 / ISO 15156 | Materials selection in H2S environments | Provides framework for selecting materials suitable for sour service |
| NACE MR0103 | Refinery sour-service materials guidance | Often referenced for process industry and refinery equipment |
| NACE TM0284 | HIC test method | Measures resistance to hydrogen induced cracking under laboratory exposure |
| NACE TM0177 | SSC / environmental cracking test method | May be added where sulfide stress cracking evaluation is required |
| ASME Section VIII | Pressure vessel construction code | Governs design and fabrication context for many SA516 Gr 70 applications |
How to Specify the Plate on a Purchase Order
Many procurement issues arise because the order description is too short. A more complete order line should identify the plate grade and each supplementary requirement separately. A practical specification checklist includes:
- ASTM A516 Gr 70 or ASME SA516 Gr 70
- Plate dimensions and quantity
- Normalized condition, if required
- HIC testing to NACE TM0284
- Acceptance criteria for CLR, CTR, and CSR, if project-defined
- Sample orientation and number of test specimens
- Maximum hardness requirement
- Ultrasonic testing standard and acceptance level
- Impact testing, if required by design temperature or code case
- Third-party inspection and documentation requirements
This level of detail helps avoid ambiguity between standard pressure vessel plate and plate specifically qualified for sour service.
Common Applications
A516 Grade 70 NACE HIC plate is commonly used for vessels and fabricated components exposed to wet H2S or process streams where hydrogen damage is a recognized risk. Typical applications include:
- Oil and gas separators
- Amine contactors and regenerators
- Sour water strippers
- Absorbers and scrubbers
- Knock-out drums and flash vessels
- Refinery process vessels and storage bullets
Final material selection should always be based on actual service conditions, including H2S partial pressure, pH, cyanides, chlorides, temperature, stress level, and expected corrosion mechanism.
Inspection, Certification, and Traceability
For industrial buyers, documentation is as important as nominal grade. Mill test certificates should show heat number traceability, chemical analysis, mechanical properties, heat treatment condition, and supplementary test results. Where HIC-tested plate is supplied, the report should identify the test method, laboratory, specimen orientation, exposure solution, duration, and acceptance results. UT reports and third-party inspection release notes may also be required depending on project criticality.
Traceability from plate marking to MTC is important for code fabrication and quality assurance. If the vessel is intended for regulated refinery or upstream service, purchasers should verify that the supplied plate matches the exact project specification rather than a generic commercial description.
FAQ
Is A516 Grade 70 NACE HIC a separate ASTM grade?
No. It is ASTM A516 Grade 70 or ASME SA516 Grade 70 plate ordered with additional sour-service requirements, commonly including HIC testing, hardness limits, and ultrasonic examination.
Does SA516 Grade 70 automatically comply with NACE requirements?
No. The base SA516 Grade 70 specification covers pressure vessel plate properties, but sour-service suitability depends on supplementary requirements and project-specific qualification for wet H2S exposure.
What test is usually referenced for HIC-resistant plate?
NACE TM0284 is the most commonly referenced laboratory test method for evaluating hydrogen induced cracking resistance in plate for sour-service applications. The purchase order should also state the required acceptance criteria and reporting format.