ASTM A516 Grade 70, also supplied as ASME SA516 Grade 70, is a pressure vessel quality carbon steel plate used in boilers, separators, columns, scrubbers, heat exchangers, knockout drums, and storage vessels. The grade is selected where reliable notch toughness, weldability, and strength are required for moderate and lower temperature service. In oil and gas, refinery, and petrochemical projects, the material is frequently purchased with supplementary sour service requirements and referred to in the market as A516 Grade 70 HIC or A516 Grade 70 NACE HIC.
It is important to separate the base material specification from the additional sour service qualification. ASTM A516 / ASME SA516 defines the plate grade and core mechanical requirements. Resistance to hydrogen induced cracking (HIC) and sulfide stress cracking (SSC) is not inherent in the grade name alone; it is typically demonstrated through steelmaking controls, heat treatment, restricted chemistry, hardness control, ultrasonic examination, and project-specific testing to NACE methods.
What is A516 Grade 70?
A516 Grade 70 is a carbon steel plate for pressure vessel service with higher tensile strength than A516 Grade 60. It is one of the most commonly specified plate grades for fabricated equipment operating under internal pressure. The grade is valued because it combines practical forming and welding characteristics with mechanical properties suitable for a broad range of vessel designs.
For sour environments containing wet H2S, buyers often require normalized plates with low sulfur, cleaner steel practice, inclusion shape control, and HIC testing. In such cases, purchase orders may call up additional requirements such as NACE TM0284, NACE TM0177 where applicable, ASTM A578 ultrasonic testing, maximum hardness limits, and EN 10204 inspection documents.
A516 Grade 70 Standards and Designations
The following standards are commonly associated with A516 Grade 70 plate procurement and inspection:
- ASTM A516 / ASME SA516 - pressure vessel plates, carbon steel, for moderate and lower temperature service
- ASTM A20 / ASME SA20 - general requirements for pressure vessel plates
- NACE TM0284 - evaluation of steels for resistance to hydrogen induced cracking
- NACE TM0177 - laboratory testing for sulfide stress cracking resistance where specified
- ASTM A578 - ultrasonic examination of steel plates
- EN 10204 3.1 / 3.2 - inspection documentation and certification
In project specifications, the grade may be ordered as ASTM A516 Gr 70, ASME SA516 Gr 70, A516 Grade 70 normalized, or A516 Grade 70 HIC tested plate. The exact wording matters because supplementary requirements can materially affect plate route, lead time, testing scope, and acceptance criteria.
Chemical and Mechanical Properties of A516 Grade 70
Exact chemistry limits can vary with thickness, edition of the standard, and purchaser requirements. For sour service, end users often impose tighter sulfur and phosphorus limits than the base standard and may also require vacuum degassing, calcium treatment, and controlled rolling or normalizing. Mechanical properties likewise vary with thickness, but the minimum strength level remains the key reason Grade 70 is chosen over lower grades.
| Property | Typical Requirement / Industry Reference | Procurement Note |
|---|---|---|
| Specification | ASTM A516 Grade 70 / ASME SA516 Grade 70 | Confirm edition and any supplementary requirements |
| Plate type | Carbon steel pressure vessel plate | Used for boilers and welded pressure vessels |
| Minimum tensile strength | 70-90 ksi (approximately 485-620 MPa) | One reason for selection over Grade 60 |
| Minimum yield strength | 38 ksi (approximately 260 MPa) | Check thickness-based requirements |
| Heat treatment | As rolled or normalized; normalized often preferred for HIC service | Project specs may mandate normalizing |
| Sulfur control | Often lower than base standard for sour service | Low S supports improved HIC performance |
| Ultrasonic testing | Often ASTM A578 | Acceptance level should be stated on PO |
| HIC testing | Often NACE TM0284 | CLR, CTR, CSR limits are usually project-specific |
| SSC testing | When specified to NACE TM0177 | Not always required for every vessel plate order |
| Certification | EN 10204 3.1 or 3.2 | Review traceability and test report content |
Because owner specifications differ, purchasers should avoid relying only on generic online property summaries. Vessel design code, corrosion study, process fluid composition, thickness, PWHT condition, and fabrication route all influence the final material requirement.
A516 Grade 70 HIC and NACE Requirements
When A516 Grade 70 is intended for wet H2S service, the market often uses the term “NACE HIC plate.” In practice, this usually means the plate has been manufactured and tested to demonstrate improved resistance to hydrogen damage mechanisms relevant to sour service. The most common reference is NACE TM0284 for HIC evaluation. Some end users also require SSC assessment to NACE TM0177, especially when hardness, stress state, and service severity justify additional qualification.
Typical sour service purchase requirements may include:
- Normalized plate or normalized rolling route
- Low sulfur and phosphorus with cleaner steel practice
- Vacuum degassing and inclusion shape control
- Calcium treatment where specified
- Maximum hardness limit for base metal and sometimes HAZ/weld procedure qualification
- HIC test acceptance criteria for CLR, CTR, and CSR as defined by project documents
- Ultrasonic examination to a stated ASTM A578 level
- Full traceability and mill test certification
These controls matter because HIC resistance depends not only on nominal grade but also on segregation control, inclusion morphology, steel cleanliness, and heat treatment condition. For this reason, two plates both described as A516 Grade 70 may not offer equivalent sour service performance unless the supplementary requirements are clearly aligned.
Applications of A516 Grade 70 Plate
A516 Grade 70 is used across process industries where pressure-retaining equipment is fabricated from carbon steel plate. Common applications include:
- Pressure vessels and storage vessels
- Oil and gas separators
- Scrubbers and knockout drums
- Fractionation and process columns
- Heat exchanger shells
- Boiler components
- Refinery and petrochemical equipment
- Sour service vessels handling wet H2S when HIC-qualified
The grade is especially common where fabricators require a balance of weldability, availability, and code familiarity. For low-temperature or high-severity corrosion service, however, the final selection should always be checked against design code and corrosion engineering requirements.
How to Specify A516 Grade 70 Correctly
Procurement problems often arise when the purchase order states only “A516 Grade 70” without the supplementary requirements needed for the actual service. A more complete specification should define the governing standard, heat treatment condition, sour service testing scope, UT level, certification, and any owner-specific chemistry or hardness restrictions.
A practical purchase description may include the following points:
- ASTM A516 Grade 70 or ASME SA516 Grade 70
- Required thickness, dimensions, and quantity
- Normalized condition if mandatory
- NACE TM0284 HIC tested with stated acceptance criteria
- NACE TM0177 if SSC qualification is required
- ASTM A578 ultrasonic testing and acceptance level
- Maximum sulfur, phosphorus, and hardness limits
- EN 10204 3.1 or 3.2 certification
- Any project, EPC, refinery, or end-user specification references
This level of detail reduces ambiguity between mills, stockists, fabricators, and inspectors. It also helps ensure that the delivered plate is suitable not just for code compliance, but for the actual process environment and inspection regime of the project.
A516 Grade 70 vs Base Grade-Only Ordering
Ordering by base grade alone may be acceptable for general pressure vessel service, but it is often insufficient for sour service applications. The base ASTM or ASME standard does not automatically guarantee HIC resistance, SSC resistance, restricted chemistry, or UT acceptance to an owner-defined level. Where wet H2S is present, the purchaser should treat HIC qualification as an additional technical requirement rather than an assumed property of the grade name.
In engineering review, the key distinction is straightforward: A516 Grade 70 defines the pressure vessel plate grade, while A516 Grade 70 HIC / NACE HIC indicates the same grade supplied with additional manufacturing and testing controls for sour service suitability.
FAQ
Is A516 Grade 70 the same as SA516 Grade 70?
They are closely related designations. ASTM A516 is the ASTM material specification, while SA516 is the ASME-adopted specification used in boiler and pressure vessel code applications. In procurement, the required code of construction usually determines which designation is stated on documents.
Does A516 Grade 70 automatically meet NACE HIC requirements?
No. The base grade does not automatically guarantee HIC or SSC performance. If sour service is involved, the order should specify the required HIC testing standard, acceptance criteria, heat treatment condition, chemistry restrictions, hardness limits, and any owner-specific supplementary requirements.
Why is normalized A516 Grade 70 often preferred for sour service?
Normalized plate can provide a more uniform microstructure and is commonly specified by end users seeking improved consistency in mechanical properties and sour service performance. Whether it is mandatory depends on the project specification, plate thickness, service severity, and mill qualification route.