Specifications
Surface Treatments
Certifications
- ISO 9001 - 2015 Certified
- PED 2014/68/EC
- NACE MR0175/ISO 15156-2
- NORSOK M-650
- DFAR
- MERKBLATT AD 2000 W2/W7/W10
Flange Bolt Chart per ASME B16.5
Stud bolt length calculation methodology and material selection guide for ASME B16.5 raised-face, ring-joint, lap-joint and male-female pipe flanges across Class 150 through Class 2500.
TorqBolt manufactures ASTM A193 + A194 stud bolt + nut sets for ASME B16.5 flange service across the full Class 150 to Class 2500 rating range, NPS 1/2 through NPS 24 (NPS 1/2 to NPS 12 for Class 2500). This page covers the stud bolt length calculation methodology per ASME PCC-1 Appendix M and ASME B16.5 Annex F, together with the material selection rules engineers need to specify a complete flange joint correctly the first time.
Need a quote on a complete flange stud + nut set? Email info@torqbolt.com or call +91-22-66157017 with your line list. Standard lead time on B7/2H carbon-alloy sets is two weeks ex-Mumbai; B8M and NACE MR0175 B7M sets typically four weeks with full 3.2 EN 10204 certification.
What ASME B16.5 covers for flange bolting
ASME B16.5 is the dimensional and pressure-temperature standard for pipe flanges and flanged fittings in sizes NPS 1/2 through NPS 24, with rating classes 150, 300, 400, 600, 900 and 1500 across the full size range and Class 2500 from NPS 1/2 through NPS 12. The standard fixes flange outside diameter, bolt-circle diameter, bolt-hole count, bolt-hole diameter and the resulting bolt size. It also lists acceptable bolting in Table 1.1-2, sorted into high-strength (A193 B7, B16; A320 L7 series; A354; A540), intermediate-strength (A193 B5, B6, B6X, B7M, austenitic Cl.2 grades; A449; A453) and low-strength (A193 austenitic Cl.1; A307 Gr.B) groups.
Stud bolts must be dimensioned to ASME B18.31.2 with nuts to ASME B18.2.2 heavy hex, external threads UNC Class 2A up through 1 inch and 8-thread series above (Table 1.1-3). The standard itself does not tabulate stud lengths directly. Engineers read bolt-circle and flange-thickness data from B16.5 Tables 8 through 19, then compute the required stud length from gasket, washer and nut stack-up using the calculation method described in ASME PCC-1.
How stud bolt length is calculated
Per ASME PCC-1 (Guidelines for Pressure Boundary Bolted Flange Joint Assembly) and ASME B16.5 Annex F, the total stud bolt length L for a flange pair is determined by adding every component in the bolted-joint stack:
| Stack Component | Source Standard | Value Used |
|---|---|---|
| Flange thickness (each face, x 2) | ASME B16.5 raised-face WN flange dimensional tables, by class and size | 0.44 to 8.25 in (Class 150 NPS 1/2 through Class 2500 NPS 12) |
| Hardened washer thickness (each end, x 2) | ASME B18.22.1 / ASTM F436 | 0.20 in per washer |
| Heavy hex nut height (each end, x 2) | ASME B18.2.2 heavy hex, H values from 1/2 in (0.484) to 3 in (2.953) | see B18.2.2 table excerpt below |
| Gasket compressed thickness | Spiral wound spec: 1.5 mm compressed | 0.06 in (RF); replaced by ring-groove geometry for RTJ |
| Thread stickout reserve (each end, x 2) | ASME PCC-1: minimum 2 full threads past nut face | 2 x UNC pitch per side |
The governing formula used to compute every chart value on this page:
L_total = 2(flange_thk) + 2(washer_thk) + 2(nut_ht) + gasket_compressed + 2(thread_stickout)
Working in inches, with hardened washer = 0.20 in each side, spiral-wound gasket = 0.06 in compressed, and 2-thread stickout per side based on UNC pitch (1/2"-13, 5/8"-11, 3/4"-10, 7/8"-9, 1"-8 and 8UN above 1"). Nut height comes from ASME B18.2.2 heavy hex (H = 31/64 at 1/2 in stud through 2-61/64 at 3 in stud). Flange thickness comes from the ASME B16.5 raised-face weld-neck dimensional tables. Every L_total below is rounded upward to the next 1/4 in procurement length.
Worked check, NPS 6 Class 300 RF, 3/4 in stud, 12 bolts: L = 2(1.872) + 2(0.20) + 2(0.734) + 0.06 + 2(0.20) = 3.744 + 0.40 + 1.468 + 0.06 + 0.40 = 6.072 in, round up to 6-1/4 in. The same flange in RTJ adds approximately 0.31 in for the octagonal-ring groove geometry per ASME B16.20, giving 6-1/2 in.
For RTJ flanges the spiral-wound gasket term is replaced by the metal-ring groove geometry per ASME B16.20: the octagonal ring sits in machined grooves on both flange faces, and the effective seating engagement adds roughly 0.31 in to the bolted stack versus the matching RF joint. RTJ stud lengths therefore run typically 0.25 to 0.50 in longer than the same-class same-size RF length.
Material selection by service: recommended A193 + A194 sets
ASME B16.5 Table 1.1-2 lists the bolting material families authorised for each flange-material group. The table below distils that into the most common stud + nut pairings for ASME B16.5 service. Validate temperature limits, sour-service status and project-specific overrides (NORSOK L-002, Shell DEP, Saudi Aramco SAES-L) before ordering.
| Flange Service / Class | Stud Bolt | Nut (ASTM A194) | Service Notes |
|---|---|---|---|
| Class 150 to 1500 carbon-steel, non-sour, −29 to 400 degC | A193 B7 (Cr-Mo Q&T) | A194 Gr.2H | Industry baseline; Table 1.1-2 high-strength group |
| Class 150 to 1500 sour-service per NACE MR0175 / ISO 15156 | A193 B7M (B7 with 22 HRC max) | A194 Gr.2HM | Mandatory for wellhead, x-mas tree, sour gas separator |
| Cryogenic flange to −46 degC (LNG, ethylene) | A320 L7 (or L7M for sour cryogenic) | A194 Gr.4 or Gr.7 | Charpy impact at −101 degC; Note (10) in B16.5 |
| Stainless flange, marine/chloride service | A193 B8M Cl.1 (316 SS) | A194 Gr.8M | Lower yield than B7; oversize one Class up if duty permits |
| Stainless flange, higher strength | A193 B8 Cl.1 (304 SS) | A194 Gr.8 or Gr.8 strain-hardened | Cl.2 doubles yield; not for sour service |
| Creep-range power flange, 480 to 540 degC | A193 B16 (1Cr-1Mo-1/4V) | A194 Gr.7 or Gr.4 | Engineered for sustained creep service above B7 limit |
RF vs RTJ vs LJ vs MF: when each facing is used
Raised Face (RF) is the default ASME B16.5 facing for Class 150 through Class 900, used with spiral-wound or soft-sheet gaskets in general process service. Ring-Joint (RTJ) uses a hardened metal ring (oval or octagonal) seated in machined grooves on both flange faces; standard for Class 900, 1500, 2500 and most Class 600 oilfield service. Lap-Joint (LJ) mates a stub-end with a backing flange that rotates freely, simplifying field assembly on long piping runs. Male-Female (MF) uses a raised tongue seated into a recessed groove on the mating flange, retaining the gasket in the female recess; used in proprietary heat exchanger and exchanger-channel bolting.
How to determine stud bolt length
Step 1: confirm flange rating class and facing from the line list or P&ID. Step 2: pull flange thickness, bolt-circle diameter, bolt count and bolt diameter from ASME B16.5 Tables 8 through 19 for that class and size. Step 3: select the stud grade and matching nut grade from the material selection table based on service temperature, sour-service status and flange material group. Step 4: pick gasket type and look up compressed thickness from the gasket data sheet (spiral wound, soft-sheet) or RTJ ring geometry. Step 5: pick washer thickness from ASTM F436 / ASME B18.22.1. Step 6: apply the length formula in the calculation methodology section: L_total = 2(flange) + 2(washer) + 2(nut) + gasket + 2(stickout). Step 7: round up to the nearest 1/4 in stud length and add coating allowance (Xylan, PTFE, zinc-nickel) per coating data sheet. Step 8: issue the bolting BOM with stud grade, nut grade, surface treatment, applicable ASTM and supplementary requirement codes (S3, S4, S6) plus EN 10204 certificate level (3.1 standard, 3.2 critical service).
Related stud bolt and dimensional pages
Continue with: B7 (UNS G41400) stud bolts for Class 150 to 1500 carbon-steel flange service; B7M (NACE MR0175 sour-service) for Class 600 to 1500 oilfield assemblies; B8 Class 1 (304 SS) and B8M Class 1 (316 SS) for stainless-flange service; ASME B16.5 full-thread stud bolts for the companion dimensional reference; ASME B18.2.1 heavy hex bolts for cap-screw flange variants; ASTM A194 companion nuts (2H, 2HM, 8, 8M) for nut selection; and NACE MR0175 A193 stud bolts for the full sour-service compliance overview.
References
- ASME B16.5-2020: Pipe Flanges and Flanged Fittings, NPS 1/2 through NPS 24 Metric/Inch Standard. Tables 8 through 19 for drilling and recommended stud length per class and facing; Table 1.1-2 for bolting material specifications; Table 1.1-3 for flange bolting dimensional recommendations.
- ASTM A193/A193M: Standard Specification for Alloy-Steel and Stainless Steel Bolting for High Temperature or High Pressure Service.
- ASTM A194/A194M: Standard Specification for Carbon Steel, Alloy Steel and Stainless Steel Nuts for Bolts for High Pressure or High Temperature Service.
- ASME PCC-1: Guidelines for Pressure Boundary Bolted Flange Joint Assembly. Appendix C documents the stud length calculation procedure.
- NACE MR0175 / ISO 15156-3: Materials for use in H2S-containing environments in oil and gas production.
Frequently Asked Questions
- How do I calculate stud bolt length for ASME B16.5 flanges?
- Stud bolt length = (2 × flange thickness) + (2 × washer thickness) + (2 × nut height) + gasket-compressed thickness + thread-stickout allowance. Flange thickness comes from ASME B16.5 Tables 8 through 19 per class and size. Nut height is per ASME B18.2.2 (heavy hex H ≈ nominal bolt diameter). Washer thickness is per ASME B18.22.1 (3 to 5 mm hardened). Spiral-wound gasket compressed thickness is typically 1.5 mm. Thread stickout reserve is minimum 2 full threads past the nut face per ASME PCC-1 §10.5. Round up to the next 1/4 inch procurement length.
- What is the difference between RF and RTJ flange stud lengths?
- RF (Raised Face) and RTJ (Ring-Type Joint) flanges of the same class and size use the SAME stud bolt diameter and bolt count, but the stud LENGTH differs because of the gasket type. RF uses a flat or spiral-wound gasket (1.5 to 3 mm compressed) while RTJ uses an oval or octagonal metal ring gasket seated in machined grooves (typically 5 to 9 mm engagement depth). For the same flange, RTJ studs are commonly 5 to 12 mm longer than RF studs.
- Which stud bolt material pairs with Class 600 carbon-steel flanges?
- The default specification for Class 600 carbon-steel flange bolting is ASTM A193 Grade B7 studs with ASTM A194 Grade 2H heavy hex nuts. For sour service per NACE MR0175 / ISO 15156-3, substitute A193 B7M studs with A194 2HM nuts. For stainless flanges or chloride service, use A193 B8M Class 1 studs with A194 Grade 8M nuts. For elevated-temperature service above 427 °C, step up to A193 B16 studs with A194 Grade 4 or 7 nuts.
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