A516 NACE HIC is the industry shorthand for ASTM A516 or ASME SA516 pressure vessel quality carbon steel plate ordered for sour service with demonstrated resistance to hydrogen-induced cracking (HIC). The term does not identify a standalone ASTM material grade. Instead, it describes A516 plate supplied with additional metallurgical controls, inspection requirements, and HIC test acceptance criteria for wet H2S-containing environments.
In refineries, gas processing plants, petrochemical units, LNG facilities, and upstream oil and gas projects, standard A516 compliance alone may be insufficient where hydrogen damage is a credible failure mechanism. Purchase orders for sour-service plate usually add requirements for low sulfur chemistry, clean steelmaking practice, inclusion shape control, heat treatment condition, ultrasonic testing, hardness limits, 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 often specified for sour applications are Grade 60, Grade 65, and Grade 70. Of these, Grade 70 is commonly selected because it offers 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 in requisitions and data sheets include:
- NACE TM0284 for evaluation of hydrogen-induced cracking resistance
- 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
- ASTM A20 / ASME SA20 for general plate supply requirements
- End-user or EPC sour-service specifications defining chemistry, hardness, UT, and HIC acceptance limits
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 actual 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, and residual stress, sulfide stress cracking (SSC) may also be a concern.
For this reason, sour-service A516 plate is generally produced with tighter control than standard commercial pressure vessel plate. The objective is to reduce crack initiation sites, improve through-thickness cleanliness, and ensure the finished plate meets project acceptance criteria after testing.
Typical Requirements for A516 NACE HIC Plate
The exact requirements vary by end user, but the following controls are common for A516 HIC-resistant plate:
- Low sulfur chemistry, often with restrictive maximum sulfur content
- Clean steelmaking practice, such as vacuum degassing or equivalent secondary metallurgy
- Calcium treatment or inclusion shape control to reduce elongated sulfide inclusions
- Controlled rolling and/or normalizing depending on thickness and project specification
- Hardness limitations where SSC susceptibility must be controlled
- Ultrasonic examination to ASTM A578 or project-defined acceptance levels
- HIC testing to NACE TM0284 with specified crack ratio limits
- Documented traceability by heat number, MTC, and test report package
These requirements are not automatically included by citing ASTM A516 alone. If the purchase order only states “A516 Grade 70,” the mill may supply standard pressure vessel plate without the sour-service controls expected for wet H2S duty.
Common Base Grades and Specification References
| Item | Typical Requirement | Purpose in Sour Service |
|---|---|---|
| Base material | ASTM A516 / ASME SA516 Gr 60, 65, or 70 | Pressure vessel plate specification |
| Most common grade | Grade 70 | Balance of strength and weldability |
| General supply standard | ASTM A20 / ASME SA20 | Dimensional, testing, and delivery requirements |
| HIC test method | NACE TM0284 | Evaluates resistance to hydrogen-induced cracking |
| SSC test method | NACE TM0177 | Assesses sulfide stress cracking where required |
| Material selection guidance | NACE MR0175 / ISO 15156 | Defines suitability in H2S service environments |
| UT examination | ASTM A578 or project-specific | Detects laminations and internal discontinuities |
| Heat treatment | As-rolled, normalized, or as specified | Affects toughness, cleanliness response, and hardness |
How A516 NACE HIC Plate Is Usually Ordered
A complete order description should define the base grade, thickness range, heat treatment condition, supplementary testing, and acceptance criteria. In practice, many project problems arise because the term “NACE” is used without enough detail to make the requirement enforceable at the mill.
A technically complete purchase order for A516 NACE HIC commonly includes:
- ASTM A516 or ASME SA516 grade, for example SA516 Grade 70
- Plate dimensions and quantity
- Normalized or controlled-rolled condition, if required
- Maximum sulfur and other chemistry restrictions
- Hardness limit, if specified by project or service condition
- UT standard and acceptance level
- HIC testing method, solution, sample orientation, and acceptance criteria
- Any SSC testing requirement
- Charpy impact testing, if required by code or project specification
- Documentation package including MTC, HIC report, UT report, and traceability records
Without these details, suppliers may interpret the requirement differently, leading to noncompliance, retesting, or rejection during fabrication review.
Difference Between Standard A516 and A516 HIC Plate
Standard A516 plate is designed for pressure vessel service, but it is not inherently qualified for wet H2S sour environments. A516 HIC plate is standard A516 with additional process control and verification aimed at hydrogen damage resistance. The difference is not only in testing; it also involves steel cleanliness, segregation control, inclusion morphology, and inspection rigor.
This distinction matters because HIC performance cannot be assumed from mechanical properties alone. Tensile strength, yield strength, and elongation may satisfy ASTM A516 while the plate still fails project HIC acceptance limits if the internal cleanliness and metallurgical structure are unsuitable.
Applications of A516 NACE HIC Plate
A516 HIC-resistant plate is commonly used in pressure-containing equipment exposed to wet H2S or other sour conditions. Typical applications include separators, knock-out drums, amine units, sour water strippers, inlet vessels, storage bullets, heat exchanger shells, and process columns in oil, gas, and refining service.
Selection should always be based on the actual service environment, design code, corrosion study, and end-user specification. In some cases, HIC resistance alone is not sufficient, and additional controls for SSC, PWHT response, low-temperature toughness, or corrosion allowance may be required.
FAQ
Is A516 NACE HIC a separate ASTM material grade?
No. A516 NACE HIC is not a standalone ASTM grade. It refers to ASTM A516 or ASME SA516 plate supplied with additional sour-service requirements such as low sulfur chemistry, HIC testing, and project-defined acceptance criteria.
Which A516 grade is most commonly used for HIC service?
Grade 70 is the most commonly specified base grade because it offers a useful combination of strength, weldability, and fabrication performance. However, Grades 60 and 65 are also used where design conditions or project standards make them more suitable.
Does NACE MR0175 automatically mean the plate is HIC tested?
No. NACE MR0175 / ISO 15156 provides material selection guidance for H2S service, but it does not by itself guarantee HIC testing or define a purchasable plate grade. The purchase order must explicitly require HIC testing, the test method, and the acceptance limits.