A516 Grade 70 NACE HIC is a common project and procurement term used for ASTM A516 Grade 70 or ASME SA516 Grade 70 pressure vessel plate supplied with additional requirements for wet H2S (sour) service, especially hydrogen induced cracking (HIC) resistance. The phrase is widely used in refinery, gas processing, amine, separator, and pressure vessel packages, but it does not identify a standalone ASTM material designation. In practice, the buyer specifies the base plate standard and then adds supplementary requirements covering chemistry limits, steel cleanliness, heat treatment condition, ultrasonic testing, hardness, HIC qualification, and certification.
This distinction matters in technical procurement. A standard SA516 Gr 70 plate may meet the tensile and yield requirements of ASTM A516 / ASME SA516, yet still be unsuitable for severe sour duty if the steelmaking route, inclusion control, internal soundness, and HIC acceptance criteria are not defined. For that reason, EPC contractors and end users often use the shorthand expression a516 grade 70 nace hic to describe a combined requirement: pressure vessel plate plus additional metallurgical and testing controls for sour environments.
What A516 Grade 70 Means
A516 Grade 70 is a carbon steel plate for welded pressure vessels intended for moderate and lower temperature service. It is widely selected because it offers a practical balance of strength, weldability, fabrication performance, and availability. The base specification establishes mechanical properties and general supply conditions, but it does not by itself guarantee suitability for wet H2S exposure.
When the same plate is intended for sour service, resistance to internal hydrogen damage becomes a key material selection criterion. Hydrogen generated by corrosion in H2S-containing aqueous environments can diffuse into steel and accumulate at inclusions, segregation bands, laminations, or other discontinuities. The result may be blistering, planar cracking, or stepwise cracking. Therefore, HIC-resistant SA516 Gr 70 is usually produced with tighter process and quality controls than standard commercial plate.
Base Standard vs NACE and HIC Requirements
For technical accuracy, the base material standard should be separated from the sour-service references. ASTM A516 / ASME SA516 defines the pressure vessel plate grade and its mechanical properties. NACE / sour-service references are used for material selection guidance, environmental severity, and test methods relevant to H2S service. A purchase order should identify both the base plate standard and the additional project requirements.
| Reference | Primary Scope | Relevance to A516 Grade 70 NACE HIC |
|---|---|---|
| ASTM A516 / ASME SA516 | Carbon steel plate for pressure vessels | Defines base grade, chemistry limits, tensile strength, yield strength, and general supply condition |
| NACE MR0175 / ISO 15156 | Material selection for H2S-containing environments in oil and gas production | Used as service guidance for sour environments; often referenced in project specifications |
| NACE TM0284 | Test method for evaluating HIC resistance | Commonly specified to qualify plate for hydrogen induced cracking resistance |
| NACE TM0177 | Test methods for sulfide stress cracking and stress corrosion cracking | May be referenced where SSC-related evaluation is required in addition to HIC |
| Project / end-user specification | Supplementary procurement requirements | Sets actual acceptance criteria for chemistry, hardness, UT level, impact testing, and documentation |
Typical Additional Requirements for Sour Service Plate
Because HIC performance depends heavily on steel cleanliness and internal quality, buyers normally add supplementary clauses beyond the base SA516 Gr 70 standard. Exact values vary by end user, but the following controls are commonly requested for A516 Grade 70 NACE HIC plate:
- Low sulfur chemistry to reduce inclusion-related crack initiation sites
- Restricted phosphorus to improve through-thickness integrity
- Calcium treatment or other inclusion shape control, where specified
- Fully killed, fine-grain steelmaking practice
- Normalized or controlled-rolled supply condition, depending on project requirements
- Ultrasonic testing for internal soundness and lamination control
- Hardness limits for sour-service acceptance
- HIC testing to NACE TM0284 with defined solution, duration, and acceptance criteria
- Charpy impact testing where design code or project specification requires it
- Traceable mill test certificates, heat-wise reports, and third-party inspection records
These added controls are the reason why not all SA516 Gr 70 plates are interchangeable for sour service. Two plates may satisfy the same base ASTM grade while showing different HIC behavior due to differences in segregation control, inclusion morphology, centerline soundness, and steelmaking route.
Chemistry, Cleanliness, and Hardness Considerations
In wet H2S service, metallurgical quality is often more important than nominal strength level alone. Lower sulfur content generally reduces manganese sulfide inclusions that can act as hydrogen traps and crack initiation sites. Lower phosphorus helps limit segregation and improves resistance to through-thickness damage. Cleaner steel with better inclusion control typically performs better in HIC testing than plate produced only to standard commercial practice.
Hardness is also reviewed because excessive hardness can increase susceptibility to sour-service cracking mechanisms. Project specifications may impose maximum hardness values on the plate, weld metal, heat-affected zone, or all three. Where fabrication is involved, the plate purchase requirement should be coordinated with the welding procedure specification, post-weld heat treatment requirements, and any code or owner limits applicable to the completed vessel.
How HIC Testing Is Usually Specified
When a buyer requests A516 Grade 70 NACE HIC, the most common qualification route is HIC testing in accordance with NACE TM0284. The purchase order should not stop at the words “NACE HIC”; it should define the actual test basis and acceptance criteria. Otherwise, different mills may apply different internal practices.
- State the base material standard and grade: ASTM A516 Gr 70 or ASME SA516 Gr 70.
- State the supply condition: normalized, as-rolled, or controlled rolled, as applicable.
- Define chemistry restrictions, especially sulfur and phosphorus maximums.
- Specify UT requirement and acceptance level for internal soundness.
- Specify HIC testing standard, sample orientation, frequency, and acceptance criteria.
- State hardness limits and whether they apply to base metal only or also fabricated condition.
- List impact test requirements, if required by design temperature or project spec.
- Require heat-wise MTCs and third-party witnessing if applicable.
Acceptance is often expressed through crack length ratio (CLR), crack thickness ratio (CTR), and crack sensitivity ratio (CSR), although the exact limits are owner-specific. Because these values can vary across projects, the procurement document should always state the required thresholds rather than relying on generic wording.
Common Applications
SA516 Grade 70 HIC-tested plate is commonly used for pressure vessels and process equipment exposed to sour water or wet H2S service. Typical applications include separators, amine absorbers, knockout drums, slug catchers, refinery vessels, gas processing equipment, and storage or process vessels where internal hydrogen damage is a known risk. The material is selected not because “NACE HIC” is a separate steel grade, but because the project requires a pressure-vessel carbon steel with documented resistance to hydrogen-related damage mechanisms.
Procurement Wording and Documentation
A technically complete purchase description should avoid ambiguity. Instead of ordering only “A516 Grade 70 NACE HIC,” it is better to specify the full requirement, for example: ASME SA516 Grade 70 plate, normalized, HIC tested to NACE TM0284, with specified sulfur and phosphorus limits, UT tested, hardness-controlled, and supplied with heat-wise MTCs. This format separates the base code material from the sour-service qualification requirements and reduces the risk of receiving plate that meets strength requirements but not service expectations.
Documentation is equally important. Buyers typically require mill test certificates showing heat chemistry, mechanical properties, heat treatment condition, plate dimensions, UT results, and HIC test reports. For critical projects, third-party inspection, traceability by heat and plate number, and review of manufacturing route may also be required.
FAQ
Is A516 Grade 70 NACE HIC a separate ASTM material grade?
No. It is a procurement description for ASTM A516 Grade 70 or ASME SA516 Grade 70 plate ordered with additional sour-service and HIC-resistance requirements. The base grade remains A516/SA516 Gr 70.
Does standard SA516 Grade 70 automatically meet NACE HIC requirements?
No. Standard SA516 Grade 70 may satisfy the base mechanical requirements but may not meet project-specific HIC, hardness, cleanliness, or UT requirements for wet H2S service. Those requirements must be explicitly specified and verified by testing and documentation.
What should be included in a purchase order for A516 Grade 70 NACE HIC plate?
The order should include the base standard and grade, plate thickness and dimensions, supply condition, chemistry restrictions, HIC test standard and acceptance criteria, UT requirement, hardness limits, impact testing if required, and documentation such as heat-wise MTCs and third-party inspection reports.