Chemical & Petrochemical Fasteners | ASTM A193 B7/2H Studs and NACE Sour Service
Bolting for reactors, exchangers, towers and pipe flanges: complete A193 B7 + A194 2H inch stud sets, sour-service B7M + 2HM (max 235 HB, 100% hardness inspected), B16 for the 540°C class and A320 L7 for -101°C service - every batch traceable to heat number with heat-treatment records for acceptance and turnaround lookup.
Key Technical Challenges
Above 235 HB in sour (H₂S) service means sulfide stress cracking - B7M/2HM with 100% hardness inspection is mandatory
Thermal cycling relaxes flange bolt stress until it leaks; sizing must check diameter-class strength
POs that just say "stud bolts" and allow DIN commodities break the ASTM hardness, capacity and traceability chain - acceptance fails
ASME B16.5 bolt holes and bolting are a closed inch system; metric studs neither fit nor should be fitted
Xin Rui Da Fastener Solutions
Closed ASTM-system supply: B7+2H / B7M+2HM / B16+A194 4 / L7+A194 7, hardness and strength to the latest edition classes
Heat-number traceability: mill records with every batch for turnaround lookup, third-party reports alongside
Free bolting lists: give flange model, pressure class and gasket type and we compute stud lengths (flange thickness + 2 nut heights + 2 exposed threads) and counts
Finishes per spec: Teflon, zinc or project coatings, avoiding field re-plating and hydrogen pickup
Technical Parameters
| B7 / 2H | 4140 Q&T · Rm ≥ 860 MPa (≤2.5") |
| B7M / 2HM | 690-760 MPa · ≤235 HB · 100% check · NACE MR0175 |
| B16 / A194 4 | CrMoV · 540°C class |
| A320 L7 / 7 | 4140 LT · -101°C class |
| Metric Option | 35CrMo studs (DIN/GB) for metric flanges |
Frequently Asked Questions
Yes. The ASTM system pairs within families: B7 with A194 2H; sour or low-temperature B7M with 2HM. Mixing in DIN nuts breaks the hardness, capacity and traceability chain, and petrochemical acceptance fails.
B7M is the lower-strength version: tensile pulled into the 690-760 MPa window, hardness capped at 235 HB with 100% inspection, for sour service where sulfide stress cracking must be controlled; B7 starts at about 860 MPa (up to the 2.5" class) for general high-temperature flanges.
Stay in the DIN/GB system: 35CrMo double-ended studs (DIN975/976 form) with grade and testing per contract. Do not have B7 made in metric - its diameter-strength relationship is fixed in the inch series by ASTM A193.
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