Choosing Bolts & Studs

Quick pick (TL;DR)

Standard service → A193 B7 studs + A194 2H nuts.
Sour (NACE) → B7M / 2HM (hardness ≤ 22 HRC).
Low temperature → A320 L7 / L7M.
High temperature → A193 B16.
Coat for corrosion (Xylan/PTFE) and always lubricate.
Tighten to seat the gasket (target bolt stress), tensioning for large/critical joints.

Step 1 — Grade by temperature & service

Service	Stud / nut
Standard	A193 B7 / A194 2H
Sour	A193 B7M / 2HM
Low temperature	A320 L7 / L7M + A194 7 / 7M
High temperature	A193 B16 / A194 4 or 7
Stainless	A193 B8/B8M (lubricate to prevent galling)

Step 2 — Bolt load to seat the gasket

Bolts must reach the gasket seating stress y and resist the pressure end force.

Worked example

Given Gasket seating y = 10,000 psi (spiral-wound) Gasket effective area Ag ≈ 18 in² 8 × 3/4" B7 studs (tensile area ≈ 0.334 in² each) Step 1 — Seating force F = y × Ag = 10,000 × 18 = 180,000 lbf Step 2 — Stress per stud σ = F / (n × At) = 180,000 / (8 × 0.334) σ = 180,000 / 2.67 = 67,400 psi Step 3 — Check B7 yield ≈ 105,000 psi → target ~50–70% = OK → 8 × 3/4" B7 adequate (use ~50% yield target)

Step 3 — Coating, lubricant & tightening

Coating: Xylan/PTFE; galv outdoor.
Always lubricate (torque–tension via k).
Torque general; tensioning for large/critical.
Follow ASME PCC-1 (cross-pattern, staged).

Failure modes

Symptom	Cause & fix
Joint leaks	Under-load → lubricate + PCC-1.
Stud cracking	Sour → B7M/2HM hardness limit.
SS galling	SS → anti-seize.

Flange bolt stress calculator

Gasket seating bolt stress

F = y·Ag; σ = F/(n·At). Keep at 50–70% of yield.

Seating y (psi)

Gasket area (in²)

Bolts n

Bolt At (in²)

Bolt yield (psi)

Gasket-seating screening — also check the operating load case.

Requisition & datasheet

Grade, size, thread, length, coating, lube.
Tightening method, target, PCC-1, qty.

Frequently asked questions

What should I know about Choosing Bolts & Studs?

Standard service → A193 B7 studs + A194 2H nuts. Sour (NACE) → B7M / 2HM (hardness ≤ 22 HRC). Low temperature → A320 L7 / L7M. High temperature → A193 B16. Coat for corrosion (Xylan/PTFE) and always lubricate. Tighten to seat the gasket (target bolt stress), tensioning for large/critical joints.

Which standards or codes apply?

ASTM A193 (B7/B7M/B16/B8), A194 (nuts), A320 (low-temp); ASME B16.5 bolt tables; ASME PCC-1 (assembly); NACE MR0175 (sour hardness).

Standards — ASTM A193/A194/A320; ASME B16.5; PCC-1; NACE MR0175.