Oil & Gas Fasteners | Wellhead and Manifold B7/B7M Studs, Sour Service and Desert Coatings
Bolting for wellheads, Christmas trees, separators and high-pressure manifolds: complete ASTM A193 B7 + A194 2H inch stud sets; sour service takes B7M/2HM with hardness held at max 235 HB under 100% inspection to block sulfide stress cracking; desert heat and salt call Dacromet or hot-dip carbon parts - heat-number certificates and test reports with every batch.
Key Technical Challenges
In sour gas, any hardness above the limit triggers sulfide stress cracking - a safety red line
Cycling pressure and temperature relax manifold bolt stress until joints leak
Desert day-night swings and sandblast degrade outdoor coatings fast
Field-mixed off-system parts (DIN nuts on B7 studs) break capacity and traceability and fail acceptance
Xin Rui Da Fastener Solutions
Complete inch-system sets: B7+2H general, B7M+2HM sour, L7 for low-temperature toughness - hardness and heat-treatment records shipped with goods
NACE MR0175-style 100% hardness inspection on sour-service lots keeps hydrogen cracking behind the gate
Outdoor protection: Dacromet 500-1000 h+ (≤300°C, hydrogen-free) or HDG 1000 h+, contract-stated hours
Free stud length/quantity lists from flange class; document sets built for customs and project acceptance
Technical Parameters
| System | ASTM A193/194 · ASME B16.5 inch loop |
| Sour Service | B7M/2HM ≤235 HB · 100% hardness check |
| Low Temp | A320 L7 / A194 7 (impact tested) |
| Outdoor Finish | Dacromet 500-1000 h+ · HDG 1000 h+ |
| Docs | Heat-number MTR · third-party reports |
Frequently Asked Questions
Above 235 HB, steel in a hydrogen-sulfide environment is highly prone to sulfide stress cracking. Sour service therefore mandates B7M with strength and hardness held down plus 100% hardness inspection, mated with 2HM nuts - the core of NACE MR0175, not an option.
Dacromet leads: 500-1000 h+ NSS, service to 300°C, no electrolytic hydrogen, and at 4-10 um it fits standard nuts. Large heavy-duty members take hot-dip (1000 h+) with oversize nuts.
State five things: standard/size (e.g. ASTM A193 B7, 1-1/8" x 5-1/2") + mating nut (A194 2H) + finish per design + mill certificate by heat number. Length = flange thickness + 2 nut heights + 2 exposed threads; send the flange model and we compute it for you.
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Send the joint duty — load, media, temperature and size — and our engineers reply with class selection and quotation within 24 hours.