Related Specifications
Surface Treatments
Certifications
- ISO 9001 - 2015 Certified
- PED 2014/68/EC
- API 6A ; API 20E; API 20F
- NACE MR0175/ISO 15156-2
- NORSOK M-650
- DFAR
- MERKBLATT AD 2000 W2/W7/W10
NACE MR0175 / ISO 15156-3 Compliance for ASTM A193 Grade B8M Bolting
Sour-service piping engineers ask the same question every project: can a 316 stainless stud bolt go into an H2S-bearing flange? The short answer for ASTM A193 Grade B8M is yes, but only in the right metallurgical condition. NACE MR0175 / ISO 15156-3 governs which austenitic stainless steel bolting is acceptable for upstream oil and gas service, and the standard draws a hard line between solution-annealed B8M (Classes 1, 1A, 1D) and strain-hardened B8M (Class 2, 2B, 2C). This page walks through the qualification logic, the hardness ceilings that decide acceptance, and the documentation a buyer should expect on the MTC.
What MR0175 / ISO 15156-3 Actually Covers
ANSI/NACE MR0175 / ISO 15156 is the petroleum and natural-gas industries materials standard for use in H2S-containing environments. Part 3 of the standard addresses cracking-resistant CRAs (corrosion-resistant alloys) and other alloys including austenitic stainless steels such as 316 / UNS S31600, the parent alloy of A193 B8M. Per Part 3 scope, it addresses resistance to sulfide stress cracking (SSC), stress-corrosion cracking (SCC), and galvanically induced hydrogen stress cracking (GHSC).
The standard accepts materials by two pathways:
- Annex A acceptance. Materials that have been pre-qualified appear in the materials selection tables of Annex A with their composition, metallurgical condition, and any environmental limits. A buyer who specifies a B8M Class 1 stud bolt for service inside the Annex A envelope does not need to retest.
- Annex B laboratory qualification. When a buyer wants to use a material or condition not covered by Annex A, the user must define qualification requirements per Part 1 and run a minimum of three SSC test specimens per test batch in accordance with Annex B. The test batch is qualified only if all specimens pass.
For B8M bolting, the practical implication is straightforward. Solution-annealed 316 SS in the Class 1, 1A, or 1D condition falls within the austenitic stainless steel grouping in Annex A. Strain-hardened Class 2 does not, and any attempt to use it in sour service requires Annex B testing the buyer almost never authorises.
The Hardness Boundary That Decides Compliance
Cold work raises hardness. Hardness above the austenitic-SS limit cited in ISO 15156-3 Annex A pushes a 316 bolt out of the pre-qualified envelope. ASTM A193 / A193M defines the maximum hardness of every B8M class in Table 3 (inch-pound units), and the gap between the solution-annealed classes and the strain-hardened Class 2 is wide.
| A193 Class | Condition | Hardness max (HBW) | Hardness max (Rockwell) | Tensile min (ksi) | Yield min (ksi) |
|---|---|---|---|---|---|
| Class 1 | Carbide solution treated | 223 HBW | 96 HRBC | 75 | 30 |
| Class 1A (B8MA) | Carbide solution treated in the finished condition | 192 HBW | 90 HRB | 75 | 30 |
| Class 1D | Carbide solution treated (high-temperature applications) | 223 HBW | 96 HRBC | 75 | 30 |
| Class 2 (D ≤ 3/4 in) | Solution treated and strain hardened | 321 HBW | 35 HRC | 110 | 95 |
| Class 2 (D over 1-1/4 to 1-1/2 in) | Solution treated and strain hardened | 321 HBW | 35 HRC | 90 | 50 |
The Rockwell HRB scale used for Class 1 and 1A converts to an HRC value well below the threshold the standard sets for austenitic stainless steel in Annex A. The strain-hardened Class 2 ceiling of 35 HRC sits far above that threshold, which is why Class 2 sees blanket rejection on sour-service material requisitions.
Source values are taken directly from ASTM A193/A193M Table 3, the inch-pound tensile and hardness table for austenitic grades. SI equivalents in Table 3M match these limits in MPa.
B8M Class-by-Class Compliance Matrix
| A193 Grade / Class | UNS | Condition | NACE MR0175 / ISO 15156-3 status | Typical sour-service use |
|---|---|---|---|---|
| B8M Class 1 | S31600 | Solution annealed | Acceptable under Annex A austenitic SS category | Standard stud bolting for flanged joints in sweet and sour service |
| B8MA Class 1A | S31600 | Solution annealed in finished condition | Acceptable under Annex A; tighter hardness ceiling than Class 1 | Bolting where post-machining corrosion resistance is critical (e.g., subsea, wet H2S) |
| B8M Class 1D | S31600 | Solution annealed, high-temperature service | Acceptable under Annex A, same hardness as Class 1 | High-temperature bolting that still must satisfy sour-service rules |
| B8M Class 2 | S31600 | Solution treated and strain hardened | Not acceptable under Annex A; requires Annex B qualification per batch, almost never approved | High-strength bolting for non-sour service only |
| B8M2 Class 2B | S31600 | Strain hardened, larger diameters | Not acceptable under Annex A | Large-diameter high-strength bolting, non-sour |
| B8M3 Class 2C | S31600 | Strain hardened, largest diameters | Not acceptable under Annex A | Heaviest sections, non-sour service only |
For a deeper read on the Class 2 strain-hardening route and why it sits outside the sour-service envelope, see B8M Class 2 strain-hardened stud bolts. For the two compliant routes, B8M Class 1 solution-annealed bolts and B8M Class 1A bolts annealed in the finished condition document the metallurgical conditions in detail.
Latest MR0175 Version and Revision Cycle
The current document is published jointly as ANSI/NACE MR0175 / ISO 15156 in three parts. Part 1 sets general principles and qualification requirements. Part 2 covers carbon and low-alloy steels, including the cast-iron exclusions. Part 3 covers CRAs and other alloys, which is the part relevant to B8M. Each part is on its own revision cycle and is amended through Technical Circulars (TCs) and through full revisions, so a project specification should cite the year of issue or the current edition at the time of purchase order placement. A B8M MTC referencing only "NACE MR0175" without an edition year is technically incomplete; the certificate should name the part and the edition.
MR0175 vs MR0103: Why the Difference Matters
Many refinery and downstream specifications cite NACE MR0103 (now also issued as ANSI/NACE MR0103 / ISO 17945) rather than MR0175. The two standards address related cracking mechanisms in H2S environments but apply to different industries. MR0175 / ISO 15156 governs upstream oil and gas production and processing. MR0103 / ISO 17945 governs petroleum refining, petrochemical, and similar downstream wet-H2S service.
The two standards are not interchangeable. They have different qualification routes, different test environments, and different acceptable-material lists. A B8M stud bolt destined for an offshore wellhead is qualified to MR0175. The same bolt for a refinery hydrotreater amine service is qualified to MR0103. The buyer must specify which standard applies, and the MTC must reference that standard by full title including the edition. Confusing the two on a tender is a common source of project rework.
B8M Qualification Process on a TorqBolt Order
When a buyer places an order for ASTM A193 B8M Class 1 stud bolts to sour service, qualification flows through five checkpoints:
- Heat selection. The 316 / UNS S31600 heat must satisfy ASTM A193 composition: 0.08 C max, 16.0-18.0 Cr, 10.0-14.0 Ni, 2.00-3.00 Mo, 2.00 Mn max, 1.00 Si max, 0.045 P max, 0.030 S max. The heat-analysis report is preserved in the file.
- Heat treatment. Carbide solution treatment is performed and recorded with time-temperature-quench data. For Class 1A (B8MA), solution treatment is carried out in the finished machined condition.
- Hardness verification. Brinell or Rockwell hardness is measured on the production lot. Class 1 must read 223 HBW or 96 HRBC and below. Class 1A must read 192 HBW or 90 HRB and below.
- Tensile and elongation. Tensile, yield, elongation, and reduction of area are tested per A193 to confirm the solution-annealed condition.
- MTC issuance. EN 10204 3.1 or 3.2 certification is issued referencing ASTM A193/A193M, the class, the heat number, the lot hardness, and a clear NACE MR0175 / ISO 15156-3 compliance statement keyed to the edition cited on the purchase order.
Strain hardening is excluded from the route for sour-service Class 1 and 1A orders. There is no cold-drawing step. There is no straightening below the solution-annealing temperature. The mill certificate must reflect this.
Qualification Testing: When Annex B Comes Into Play
If a project specification calls for a material or condition outside Annex A, NACE MR0175 / ISO 15156-3 Annex B governs the test programme. The buyer or end user defines the qualification environment based on intended service. A minimum of three specimens per test batch must satisfy the acceptance criteria for each cracking mechanism qualified (SSC, SCC, or GHSC, as applicable). The standard requires that test solution chemistry, pH control, H2S partial pressure, and temperature be defined and recorded.
For B8M bolting the buyer should treat Annex B testing as a special-case activity. Three reasons:
- Test programmes take 30 days at minimum and add cost that production bolting cannot absorb.
- Strain-hardened 316 routinely fails SSC testing at chloride concentrations typical of produced water.
- The qualification is batch-specific. A successful test on one heat does not transfer to the next heat.
Specifying Class 1 or Class 1A from the start is the cheaper, faster, and more reliable path. Annex B is for the projects that genuinely cannot use a solution-annealed bolt.
Documents the Buyer Should See
A B8M bolt that is fit for NACE MR0175 service arrives with a documentation package, not just a stamping. TorqBolt QA-QC supplies the following with every sour-service-qualified shipment:
- EN 10204 3.1 or 3.2 mill test certificate referencing ASTM A193/A193M and the applicable edition of ANSI/NACE MR0175 / ISO 15156-3.
- Heat number, lot number, and traceability back to GRN.
- Chemical analysis showing 316 / UNS S31600 composition inside A193 limits.
- Tensile, yield, elongation, reduction of area, and Brinell or Rockwell hardness results per A193 Table 3.
- Heat-treatment record (solution annealing, temperature, soak time, quench medium).
- Where ordered, NDT report (PT, UT, or magnetic-particle on heavier sections).
- Stamp impression record matching the head marking to the lot.
If any of these are missing, the bolting is not properly qualified. A receiving inspector should reject the shipment back to the supplier rather than accept it into a sour-service flange.
Common B8M Sour-Service Mistakes
From field experience, the recurring errors on B8M sour-service orders are predictable:
- Specifying Class 2 by mistake. A buyer who wants higher strength sometimes asks for Class 2 without realising that Class 2 voids NACE compliance. The right answer is to upsize the bolt diameter and stay with Class 1.
- Mixing MR0175 and MR0103 on the same line. A flange tag that says "NACE MR0103 / MR0175" leaves the supplier guessing which one applies. One standard per line item.
- Accepting a 3.1 cert without an edition year. A certificate that just says "NACE compliant" is not enough. The edition year and the part number (Part 3) belong on the cert.
- Skipping the hardness-test entry on the MTC. Audit-trail traceability for sour-service bolting requires actual hardness numbers in the MTC, not just "within limits."
- Cold straightening after solution annealing. Any cold work after solution treatment risks pushing the bolt out of the Class 1 envelope. If a bolt is straightened, it must be re-annealed and re-tested.
For the underlying alloy data referenced throughout this page, see B8M UNS S31600 material data and international equivalents. For the ASME pressure-vessel designation of the same material, see ASME SA-193 B8M bolting specification. For the parent specification overview and the full class hierarchy, return to the ASTM A193 B8M bolting hub.
Order ASTM A193 B8M for Sour Service
TorqBolt supplies ASTM A193 / SA-193 Grade B8M Class 1, 1A, and 1D stud bolts, hex bolts, and threaded rods qualified to NACE MR0175 / ISO 15156-3 from stock heats in Mumbai and Rajkot. EN 10204 3.1 and 3.2 certification, full PMI, and Brinell hardness records on every lot. For RFQs and tender bids, contact info@torqbolt.com.
Related references
Spec hub: ASTM A193 / SA-193 B8M overview (covers NORSOK M-650 qualification, EN 10204 inspection, A194 8M companion nuts, F436 washers, B16.5 flange pairing, and the full applications register). Compliant classes: B8M Class 1 (solution annealed, NACE-qualified), B8M Class 1A (annealed in finished condition), B8M Class 1D (rapid-cool from rolling temperature). Non-compliant class: B8M Class 2 (strain-hardened, excluded from sour service). Material data: UNS S31600 datasheet. ASME variant: ASME SA-193 B8M specification.
Satisfaction Survey
