A516 Grade 70 NACE HIC is a common procurement term for ASTM A516 Grade 70 or ASME SA516 Grade 70 pressure vessel steel plate ordered with additional requirements for wet H2S sour service. It does not identify a separate ASTM material grade. Instead, it describes a base carbon steel plate combined with supplementary controls intended to reduce susceptibility to hydrogen induced cracking (HIC), stepwise cracking (SWC), blistering, and related damage mechanisms in aqueous hydrogen sulfide environments.
This distinction matters in engineering, purchasing, and inspection. Standard SA516 Grade 70 may satisfy the base tensile and yield requirements of the specification yet still be unsuitable for severe sour service if internal cleanliness, segregation control, hardness, ultrasonic quality, HIC test performance, and documentation are not explicitly defined in the purchase order.
What A516 Grade 70 NACE HIC Means
A516/SA516 Grade 70 is a carbon-manganese steel plate widely used for welded pressure vessels in moderate and lower temperature service. Typical applications include separators, absorbers, scrubbers, amine units, knockout drums, towers, columns, reactors, and storage vessels. The material is selected because it offers a practical combination of strength, weldability, formability, and broad mill availability.
When service contains aqueous H2S, buyers often add the terms NACE and HIC to indicate that the plate must be suitable for sour environments and must be laboratory verified by recognized test methods. In practice, the shorthand phrase alone is incomplete. A technically correct order should define the exact standards edition, test method, acceptance criteria, plate thickness range, sampling frequency, and certification package required by the project, owner, or licensor.
Applicable Standards and Industry References
A complete specification for A516 Grade 70 NACE HIC plate usually references several standards, each covering a different part of compliance:
- ASTM A516 / ASME SA516 — base specification for pressure vessel plate, including chemistry and mechanical properties.
- NACE MR0175 / ISO 15156 — materials selection guidance for H2S-containing environments in oil and gas production and associated systems.
- NACE MR0103 — materials requirements for sulfide stress cracking resistant materials in refinery and process plant equipment.
- NACE TM0284 — standard test method for evaluating resistance to hydrogen induced cracking.
- NACE TM0177 — test methods for sulfide stress cracking, when separately specified.
- ASTM A578 / A578M — ultrasonic examination of rolled steel plates for internal soundness.
Because project requirements vary, the purchase order should state the edition year of each standard and any owner-specific deviations. This is especially important where acceptance limits for crack length ratio, crack thickness ratio, crack sensitivity ratio, hardness, or ultrasonic acceptance class differ from default market practice.
Why Standard SA516 Grade 70 May Be Inadequate in Wet H2S Service
In wet H2S environments, corrosion reactions at the steel surface can generate atomic hydrogen. Some of this hydrogen diffuses into the steel matrix and accumulates at inclusions, laminations, segregation bands, and other microstructural discontinuities. The result can be internal blistering, planar cracking, or linked crack networks known as stepwise cracking.
Resistance to these damage mechanisms depends not only on nominal chemistry and tensile properties, but also on steelmaking quality and plate processing. Lower sulfur, improved inclusion shape control, reduced segregation, controlled rolling, normalized condition where required, and better through-thickness soundness can all influence performance. For this reason, sour-service plate is commonly ordered with tighter controls than the base ASTM specification alone requires.
Typical Technical Requirements for A516 Grade 70 NACE HIC Plate
Project specifications differ, but the following items are frequently included when ordering A516 Grade 70 NACE HIC plate:
- Base grade: ASTM A516 Grade 70 or ASME SA516 Grade 70.
- Heat treatment: normalized, or normalized rolling if accepted by the project specification.
- HIC testing: NACE TM0284 on representative samples, with stated acceptance criteria.
- SSC testing: NACE TM0177 only when specifically required.
- Hardness limit: maximum hardness defined by project or end-user requirement.
- Ultrasonic testing: ASTM A578/A578M to a stated acceptance level.
- Chemical restrictions: tighter sulfur and phosphorus limits than standard commercial plate.
- Cleanliness and segregation control: often addressed through mill practice and qualification history.
- Impact testing: where design code, MDMT, or project specification requires notch toughness.
- Documentation: mill test certificates, heat treatment records, HIC reports, UT reports, and traceability.
The exact values should not be assumed from the phrase “NACE HIC” alone. The purchaser should state the required acceptance criteria directly in the material requisition.
Typical Specification Elements and Their Purpose
| Requirement | Typical Reference | Purpose in Sour Service |
|---|---|---|
| Base mechanical properties | ASTM A516 / ASME SA516 Gr 70 | Establishes minimum tensile strength, yield strength, and general plate requirements. |
| HIC resistance test | NACE TM0284 | Verifies resistance to hydrogen induced cracking under laboratory sour exposure. |
| SSC evaluation | NACE TM0177 | Used when sulfide stress cracking resistance must be separately demonstrated. |
| Material selection compliance | NACE MR0175 / ISO 15156 or MR0103 | Aligns plate selection with the intended H2S service environment. |
| Ultrasonic examination | ASTM A578 / A578M | Controls laminations and internal discontinuities that can act as crack initiation sites. |
| Hardness restriction | Project specification | Reduces risk of cracking related to hard microstructures in sour conditions. |
| Low sulfur / improved cleanliness | Mill agreement or project requirement | Helps reduce inclusion-related hydrogen trapping and crack propagation. |
How HIC Testing Is Usually Interpreted
HIC testing is commonly performed in accordance with NACE TM0284 using plate samples exposed to a sour test solution for a defined period. The resulting internal cracking is then evaluated metallographically. Purchasers often specify acceptance limits for parameters such as CLR (crack length ratio), CTR (crack thickness ratio), and CSR (crack sensitivity ratio), although the exact limits vary by project.
It is important to understand that test methodology, specimen orientation, sampling location, number of specimens, and acceptance thresholds all affect whether a plate is considered acceptable. A mill statement that material is “HIC tested” is not enough unless the report identifies the test standard, solution, duration, sample traceability, and measured results.
Ordering Guidance for Engineers and Buyers
For procurement clarity, the purchase order should avoid relying only on the phrase a516 grade 70 nace hic. A more complete line item would identify the base standard, plate dimensions, heat treatment condition, HIC test method, acceptance criteria, UT standard and level, impact test requirement if applicable, and the required certification package.
Typical commercial and technical checkpoints include:
- Confirm whether the project calls for ASTM A516 or ASME SA516 stamping.
- State normalized condition if required by code, licensor, or end user.
- Define HIC acceptance criteria rather than using generic wording.
- Specify ASTM A578 UT level and any edge exclusion rules.
- Request actual HIC test reports linked to heat numbers.
- Confirm whether third-party inspection and witness points are required.
- Verify supplementary requirements for forming, PWHT, or low-temperature service.
These details reduce ambiguity, improve bid comparability, and help prevent nonconforming material from entering vessel fabrication.
Common Applications
A516 Grade 70 NACE HIC plate is commonly specified for pressure-containing equipment exposed to wet H2S in upstream, midstream, refining, gas processing, and petrochemical facilities. Typical examples include separators, amine contactors, sour water drums, flash vessels, absorbers, and storage or process vessels where carbon steel remains acceptable but enhanced resistance to hydrogen-related damage is required.
Final material selection should always be based on the actual process environment, including H2S partial pressure, pH, chloride content, cyanides if present, operating temperature, and expected corrosion mechanism. The plate specification is only one part of the overall sour-service integrity strategy.
FAQ
Is A516 Grade 70 NACE HIC a separate ASTM grade?
No. It is not a separate ASTM designation. It refers to ASTM A516 Grade 70 or ASME SA516 Grade 70 plate ordered with additional sour-service and HIC-resistance requirements.
Does NACE HIC automatically mean the plate complies with MR0175 or MR0103?
Not automatically. The purchase order should explicitly reference the applicable standard and edition, because NACE HIC in market usage may only indicate HIC testing unless broader compliance is stated.
What should be included in a purchase order for A516 Grade 70 NACE HIC plate?
At minimum, specify the base grade, dimensions, heat treatment condition, HIC test method and acceptance criteria, ultrasonic testing standard and level, hardness limits if required, any impact test requirement, and the full certification and traceability package.