A516 NACE HIC is the common industry shorthand for ASTM A516 or ASME SA516 pressure vessel quality carbon steel plate supplied for sour service with demonstrated resistance to hydrogen-induced cracking (HIC). The phrase does not identify a standalone ASTM material grade. Instead, it describes A516 plate ordered with additional metallurgical controls, testing, and acceptance criteria for equipment exposed to wet H2S-containing environments.
In refinery, gas processing, petrochemical, LNG, amine treating, separators, and upstream oil and gas service, standard A516 compliance alone may be insufficient where hydrogen damage is a credible failure mechanism. Purchase orders for A516 Grade 70 NACE HIC, A516 Grade 65 NACE HIC, or A516 Grade 60 NACE HIC typically add requirements for low sulfur chemistry, clean steelmaking practice, inclusion shape control, hardness limits, ultrasonic examination, and HIC testing to recognized NACE methods.
What A516 NACE HIC Means
ASTM A516 / ASME SA516 covers carbon steel plates for pressure vessel service at moderate and lower temperatures. The grades most frequently specified for sour applications are Grade 60, Grade 65, and Grade 70. Among these, A516 Grade 70 NACE HIC is commonly selected because it provides a practical balance of strength, weldability, and fabrication performance for pressure-containing equipment.
When a project specifies A516 NACE HIC plate, the intent is normally that the plate has been manufactured and qualified to resist hydrogen damage mechanisms associated with wet H2S exposure. Typical references include NACE TM0284 for HIC evaluation, NACE TM0177 where sulfide stress cracking testing is additionally required, NACE MR0175 / ISO 15156 for material selection guidance in H2S-containing oil and gas production environments, and ASTM A20 / ASME SA20 for general plate supply requirements.
It is important to distinguish material selection guidance from the product specification. NACE MR0175 / ISO 15156 does not create a plate grade called “NACE plate.” The order must still identify the underlying ASTM or ASME specification and all supplementary sour-service requirements.
Why HIC Resistance Is Required in Sour Service
In wet H2S environments, atomic hydrogen can enter the steel and accumulate at inclusions, segregation bands, laminations, or other internal discontinuities. Under unfavorable metallurgical conditions, this can produce hydrogen-induced cracking, typically appearing as internal cracking roughly parallel to the plate surface. In more severe cases, crack linkage can form stepwise cracking (SWC). Depending on hardness, stress level, residual stress, and service severity, sulfide stress cracking (SSC) may also be a concern.
For this reason, sour-service A516 plate is generally produced with tighter control of steel cleanliness and centerline segregation than standard pressure vessel plate. End users often require low sulfur content, calcium treatment or other inclusion shape control, vacuum degassing, controlled rolling or normalizing, and restrictions on hardness and repair practices. These measures reduce susceptibility to internal hydrogen damage and improve consistency through thickness.
Typical Grades and Project Requirements
The base specification remains ASTM A516 or ASME SA516, but project documents often add supplementary requirements tailored to the sour environment and the equipment design code. The exact values vary by end user, EPC, and operating company standard.
| Item | Typical Requirement for A516 NACE HIC | Purpose |
|---|---|---|
| Base material | ASTM A516 / ASME SA516 Gr 60, 65, or 70 | Pressure vessel plate at moderate/lower temperature |
| Sulfur | Low S, often project-limited | Improves cleanliness and reduces crack initiation sites |
| Steelmaking | Fully killed, clean steel, often vacuum degassed | Reduces inclusions and segregation |
| Inclusion control | Calcium treatment or equivalent shape control | Improves HIC resistance |
| Heat treatment | Normalized or controlled rolled, per project need | Refines microstructure and consistency |
| Hardness | Maximum hardness limit may be specified | Helps control SSC susceptibility |
| UT inspection | 100% ultrasonic examination, often to SA578/SA578M | Detects laminations and internal discontinuities |
| HIC test | NACE TM0284 with agreed acceptance criteria | Verifies resistance to hydrogen-induced cracking |
Common Testing Standards and Acceptance Criteria
The most frequently cited laboratory method for HIC qualification is NACE TM0284. Test coupons are exposed to a sour solution under controlled conditions, then sectioned and evaluated for cracking. Results are commonly reported using ratios such as CLR (crack length ratio), CTR (crack thickness ratio), and CSR (crack sensitivity ratio), although the exact reporting format and limits depend on the project specification.
Where the service is more severe or where fabrication and residual stress are significant concerns, purchasers may also request NACE TM0177 testing related to sulfide stress cracking behavior. In addition, ultrasonic testing, through-thickness quality checks, and hardness verification are often included in the inspection and test plan.
Because there is no single universal acceptance level for all sour service, procurement documents should state the required test solution, sample orientation, frequency, retest rules, and acceptance criteria. A plate described only as “NACE” without these details can create ambiguity during purchasing and inspection.
How A516 Grade 70 NACE HIC Is Usually Ordered
For many pressure vessel applications, A516 Grade 70 NACE HIC is the most common order description. However, the correct purchase description should be more complete than the shorthand used in conversation. A technically sound order normally identifies the base standard, grade, dimensions, heat treatment condition, supplementary testing, and sour-service qualification requirements.
- Base standard: ASTM A516 or ASME SA516
- Grade: 60, 65, or 70
- Plate dimensions and quantity
- Required heat treatment condition, if applicable
- Maximum sulfur and any additional chemistry restrictions
- Hardness limit and test frequency
- Ultrasonic examination standard and acceptance level
- HIC testing to NACE TM0284 with stated acceptance criteria
- Any SSC testing to NACE TM0177, if required
- Documentation such as MTC, test reports, and traceability requirements
This level of detail helps align the mill, fabricator, inspector, and end user on what “A516 NACE HIC” must mean for the specific service environment.
Applications for A516 NACE HIC Plate
A516 NACE HIC plate is commonly used in fabricated equipment where wet H2S exposure is expected and pressure vessel quality carbon steel remains an acceptable material choice. Typical applications include separators, scrubbers, amine contactors, knockout drums, desalters, storage vessels, reactor effluent systems, and other refinery or gas processing equipment.
The suitability of carbon steel in these services depends on the process chemistry, partial pressure of H2S, pH, cyanides, chlorides, temperature, stress state, and the governing design and corrosion management philosophy. For that reason, plate qualification should be considered only one part of overall material selection. Welding procedure qualification, post-weld heat treatment where applicable, hardness control in the heat-affected zone, and fabrication quality are also critical to performance in sour service.
Key Distinctions Buyers Should Know
Several misunderstandings are common in the market. First, A516 NACE HIC is not a separate ASTM grade. Second, compliance with NACE MR0175 / ISO 15156 alone does not prove HIC resistance of a specific plate. Third, the term “sour service plate” can refer to different combinations of chemistry control, HIC testing, SSC testing, and inspection depending on the project.
Accordingly, buyers should review mill capability, historical sour-service supply, and the exact wording of the project specification before placing an order. The most reliable approach is to define the underlying plate standard and every supplementary requirement explicitly rather than relying on shorthand terminology.
FAQ
Is A516 NACE HIC a separate ASTM specification?
No. It is industry shorthand for ASTM A516 or ASME SA516 plate ordered with additional sour-service requirements, typically including low-sulfur chemistry, cleanliness controls, inspection, and HIC testing.
What is the difference between A516 Grade 70 and A516 Grade 70 NACE HIC?
A standard A516 Grade 70 plate meets the base pressure vessel specification. A516 Grade 70 NACE HIC adds project-specific requirements intended to improve resistance to hydrogen damage in wet H2S service, such as HIC testing to NACE TM0284, tighter chemistry limits, and enhanced inspection.
Does NACE MR0175 guarantee HIC-resistant plate?
No. NACE MR0175 / ISO 15156 provides material selection guidance for H2S-containing environments, but it does not by itself create a product grade or certify that a specific plate has passed HIC testing. The purchase order must state the actual plate specification and required sour-service qualification criteria.