A516 NACE HIC is an industry shorthand for ASTM A516 pressure vessel quality carbon steel plate supplied with additional requirements for wet H2S sour service and tested for hydrogen induced cracking (HIC) resistance. In most projects, the grades involved are ASTM A516 Grade 60, Grade 65, and especially Grade 70. The key engineering point is that ASTM A516 alone does not automatically mean NACE compliant or HIC tested. Sour service suitability must be established by the purchase order, project specification, and final inspection documents.
For pressure vessels, separators, columns, drums, and related fabricated equipment used in refineries, gas plants, and petrochemical units, buyers often specify A516 plate with tighter chemistry, steel cleanliness, hardness limits, heat treatment controls, and laboratory testing than the base ASTM standard requires. As a result, the phrase a516 nace hic should always be read as a combined material and testing requirement rather than as a standalone ASTM grade designation.
What A516 NACE HIC Means
In procurement and engineering practice, the term combines three separate requirement groups:
- ASTM A516 – carbon steel plate for pressure vessel service, particularly at moderate and lower temperatures.
- NACE sour service requirements – typically linked to material selection for wet H2S environments under NACE MR0175 / ISO 15156, NACE MR0103, or owner-specific refinery and gas plant standards.
- HIC resistance – demonstrated by laboratory testing, commonly to NACE TM0284, with acceptance criteria based on CLR (crack length ratio), CTR (crack thickness ratio), and CSR (crack sensitivity ratio).
Because market usage is inconsistent, a plate described only as “A516 HIC” or “A516 NACE” is not fully defined. Technical review should confirm the exact test solution, specimen orientation, number of samples, exposure duration, acceptance limits, heat treatment condition, hardness requirement, ultrasonic examination level, and documentation package.
Common ASTM A516 Grades for Sour Service
The most frequently specified grades are A516 Gr 60, A516 Gr 65, and A516 Gr 70. Among them, A516 Gr 70 NACE HIC is the most common commercial requirement because it provides a practical balance of strength, weldability, fabrication familiarity, and mill availability for pressure vessel construction.
For HIC-resistant plate, mills generally apply cleaner steelmaking practices than the base ASTM specification requires. These may include low sulfur melting, calcium treatment or inclusion shape control, vacuum degassing, segregation control, and tighter internal quality requirements. Depending on thickness and project specification, the plate may be supplied as-rolled or normalized, with normalized condition often preferred where improved toughness consistency and more uniform microstructure are required.
Typical Technical Requirements Added to ASTM A516
Project specifications vary, but the following supplementary controls are commonly applied when ordering A516 NACE HIC plate:
- Low sulfur chemistry, often significantly below standard ASTM limits.
- Controlled phosphorus and segregation to reduce susceptibility to internal cracking.
- Normalized or controlled-rolled condition where required by the end user.
- Hardness limitation based on project sour service rules.
- HIC testing to NACE TM0284 with stated acceptance criteria.
- Optional SSC evaluation where sulfide stress cracking resistance is also specified.
- Ultrasonic testing, often to ASTM A578 or equivalent acceptance level.
- Impact testing when low-temperature toughness is part of the vessel design basis.
- Full traceability and MTC documentation including heat number, chemistry, mechanicals, and test reports.
These controls matter because HIC performance is influenced not only by nominal grade strength but also by steel cleanliness, inclusion morphology, centerline segregation, microstructure, and fabrication route.
Relevant Standards and Test References
When evaluating A516 NACE HIC plate, the following standards are commonly referenced in technical discussions and purchase specifications:
| Standard / Reference | Primary Purpose | Why It Matters for A516 NACE HIC |
|---|---|---|
| ASTM A516 / A516M | Pressure vessel carbon steel plate specification | Defines base grade chemistry, tensile properties, and general delivery requirements |
| NACE TM0284 | Evaluation of HIC resistance in steels | Provides the laboratory test method used to verify HIC performance |
| NACE MR0175 / ISO 15156 | Material selection for H2S-containing oil and gas environments | Used to assess suitability for upstream and related sour service conditions |
| NACE MR0103 | Materials resistant to sulfide stress cracking in corrosive petroleum refining environments | Frequently cited for refinery process equipment and downstream sour service |
| ASTM A578 / A578M | Ultrasonic examination of steel plates | Controls internal soundness and lamination acceptance |
| Project or end-user specification | Owner-specific supplementary requirements | Usually governs actual chemistry limits, hardness, HIC criteria, and documentation |
In practice, the end-user specification controls the final acceptance basis. Two plates may both be sold as A516 NACE HIC but differ materially in sulfur limit, hardness cap, test solution, or HIC acceptance thresholds.
How HIC Testing Is Usually Reported
HIC resistance is commonly verified by testing in accordance with NACE TM0284. The test report typically includes specimen identification, heat number, sampling location, orientation, solution used, exposure period, and measured crack ratios. Buyers should review whether the acceptance criteria are stated as maximum allowable CLR, CTR, and CSR, since these values are often defined by the project rather than by ASTM A516 itself.
It is also important to confirm whether the plate is ordered only for HIC resistance or for both HIC and SSC-related sour service controls. HIC resistance does not automatically confirm compliance with every sour service material selection rule, especially where hardness restrictions, weld procedure controls, or heat affected zone performance are part of the specification.
Procurement Checklist for A516 NACE HIC Plate
For purchasing and technical clarification, the following data should be stated clearly on the inquiry and purchase order:
- ASTM A516 grade: Gr 60, Gr 65, or Gr 70
- Plate thickness, width, length, and quantity
- Delivery condition: as-rolled, normalized, or normalized rolled
- Applicable sour service reference: MR0175 / ISO 15156, MR0103, or owner standard
- HIC test method and exact acceptance criteria
- Required hardness limit and test frequency
- Ultrasonic testing standard and acceptance level
- Impact test temperature and absorbed energy requirement, if applicable
- Weldability or carbon equivalent restrictions, if specified
- Documentation: MTC EN 10204 3.1 / 3.2, HIC report, UT report, and heat treatment record
This level of detail reduces the risk of receiving plate that meets ASTM A516 mechanically but does not satisfy the intended sour service requirement.
Why the Exact Specification Matters
The phrase a516 nace hic is widely used in search and trade language, but it is not a complete engineering specification by itself. A compliant plate for one refinery project may be rejected on another project if the sulfur maximum, hardness cap, HIC acceptance criteria, or ultrasonic testing level differs. For that reason, material review should focus on the full technical package rather than on the shorthand product name alone.
For fabricators, another practical point is that base plate compliance does not eliminate the need to control welding consumables, heat input, post-weld heat treatment requirements, and hardness in the weld and heat affected zone where these are specified by the design code or owner standard.
FAQ
Is ASTM A516 automatically NACE compliant?
No. ASTM A516 is a base pressure vessel plate specification. NACE compliance and HIC resistance require supplementary controls such as chemistry limits, hardness restrictions, heat treatment requirements, and testing to standards such as NACE TM0284.
Which grade is most commonly ordered as A516 NACE HIC?
ASTM A516 Grade 70 is the most commonly requested grade because it offers a useful balance of strength, weldability, and availability for pressure vessel fabrication in sour service applications.
What should be checked on an A516 NACE HIC mill test package?
Review the heat number, full chemical analysis, mechanical properties, delivery condition, hardness results, ultrasonic test results, HIC test report with CLR/CTR/CSR values, and the exact standard or project specification referenced for acceptance.