Protect the pressure boundary. Critical bolting for sour service, high pressure, elevated temperature, LNG and corrosive process environments.
NACE / ISO 15156 context
ASTM A193 / A194
PMI & MTC support
Turnaround-ready kits
Oil, gas and petrochemical bolting is selected around containment risk: pressure class, design temperature, gasket behavior, medium chemistry and inspection access decide the stud, nut, washer, coating and lubricant combination.
Sour service, chlorides, seawater splash, caustic media and high-temperature oxidation require different material routes. A193 B7, B7M, B8M, B16 and nickel alloys should not be treated as interchangeable upgrades.
Turnaround work succeeds when every flange set arrives with the correct stud length, nut grade, washer rule, coating condition, lubricant note, tightening method and heat-traceable documents already tied to the line list.
Salt spray, splash-zone wet/dry cycling, H2S exposure and limited maintenance access make corrosion control and hardness discipline more important than a simple strength upgrade.
Sour-service stud bolts with ASTM A194 compatible heavy hex nuts, corrosion-resistant washers where specified, and PTFE, Xylan-style or zinc-flake coating selected by operator approval list.
Where controlled-hardness bolting is specified, B7M belongs to the ASTM A193 service route and L7M to the ASTM A320 low-temperature route. Neither grade name alone proves sour-service compliance; confirm the actual H2S environment, temperature and project standard.
A corrosion-resistant alloy can still fail if nut material, galling control and coating friction are not specified together.
Process piping flange joints are sensitive to gasket relaxation, thermal cycling, vibration and friction variation between coated studs and nuts.
Use the project-approved grade pairing: ASTM A193 B7 with A194 2H, B7M with 2HM, or B16 with a compatible high-temperature nut such as A194 7 where specified. Add hardened washers only where the flange procedure requires them, with an approved lubricant or fluoropolymer coating.
B7 remains the common refinery and petrochemical workhorse; B16 is used when sustained high temperature requires better creep and relaxation resistance.
Replacing a single missing stud with an unmatched coating or nut grade can disturb load distribution across the flange.
Manways, exchanger channels and reactor closures combine pressure, temperature, gasket seating stress and aggressive media; relaxation or corrosion under deposits can undermine preload.
B8M Class 2, B16, Inconel 718, Inconel 625 or Hastelloy C276 stud-bolt assemblies with compatible heavy hex nuts and anti-galling lubrication.
Select B8M stainless only after checking the specific medium, chlorides, temperature, strength class and code allowables. Use B16 or 718 where sustained-temperature strength and relaxation control govern; use 625 or C276 where the defined corrosion environment justifies the alloy route.
Choosing only by “corrosion resistant” language can miss high-temperature strength loss or nickel-alloy galling at installation.
Turnaround bolting risk is driven by compressed schedules, mixed legacy standards, seized hardware and urgent flange reinstatement after inspection findings.
Pre-kitted B7 / B16 / B8M stud bolt sets with matching ASTM A194 nuts, lubricant instructions, spare percentage and tag-level packing for each flange package.
Use the original line-class material as the baseline; upgrade only when engineering approves a change for temperature, sour service, chloride or operator standard updates.
A fast shipment without line-class control can create hidden mismatches that are discovered only during flange closure.
Only current public products are linked below. Grade, temperature range, corrosion limits, companion nuts and inspection requirements must still follow the project specification.
| Product type | Typical application |
|---|---|
| ASTM A193 B7 & B7M Stud Bolts | Refinery piping, flange joints and turnaround replacement sets |
| ASTM A193 B16 Stud Bolts | Sustained high-temperature process flanges, valves and pressure equipment |
| ASTM A194 2H, 2HM & 7 Heavy Hex Nuts | Matched heavy-hex nut systems for ASTM pressure bolting |
| ASTM A320 L7 & L7M Stud Bolts | Low-temperature process piping, LNG flanges and controlled-hardness L7M assemblies |
| ASTM A194 Grade 7L & 7M Heavy Hex Nuts | Grade 7L impact-tested nuts for A320 L7 and Grade 7M controlled-hardness nuts for A320 L7M |
| ASTM A193 B8M Stainless Stud Bolts | Corrosion-sensitive process equipment and pressure closures |
| Duplex Hex Head Bolts | Chloride, offshore and mixed-corrosion equipment joints |
| Inconel 625 & 718 Stud Bolts | Alloy 625 for chloride and seawater corrosion, or Alloy 718 for high-load and elevated-temperature equipment |
| Nickel Alloy Stud Bolts | Severe corrosion or temperature service defined by project grade |
| Nickel Alloy Hex Nuts | Compatible nut systems for specified nickel-alloy bolting |
| Nickel Alloy Flat Washers | Bearing and material-compatible washer requirements |
| Insulating Shoulder Washers | Electrical isolation and dissimilar-metal interface control |
No. B7 is common, but sour service, elevated temperature, cryogenic duty and chloride corrosion can require B7M, B16, A320 L7, B8M, duplex or nickel alloy routes. A grade name alone does not prove sour-service compliance; apply MR0175 / ISO 15156 or MR0103 / ISO 17945 only where the project invokes the relevant scope.
Yes. Coating changes friction, corrosion life and installation behavior. The coating, lubricant, nut grade and tightening method should be approved as one flange bolting system.
It is organized by line class and flange tag, not just by diameter. The kit should include correct lengths, nut pairings, documents and spare allowance for the outage sequence.
Use the site or engineering procedure as the authority. High-pressure, large-diameter or critical flange joints often need a defined tensioning sequence because torque alone can be sensitive to coating, lubricant and thread condition.
The practical minimum is heat-traceable MTC, grade and nut pairing, coating or lubricant condition, hardness where relevant, and tag-level packing. PMI and special tests are added where alloy or pressure-equipment files require them.
Planning a project or turnaround?
