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Flange Bolt Kits & Assemblies
A comprehensive engineering reference for EPC contractors, procurement engineers and piping teams — covering ASME B16.5 bolt count and size tables for all pressure classes, stud bolt length calculation, stud bolt and nut material pairings, gasket inclusion, Xylan and specialty coating specifications, large-bore B16.47 bolt kits, heat exchanger bolt kits, and full project documentation for pre-kitted flange bolt assemblies.
Flange Bolt Kit Contents, Bolt Count
& Kit Assembly Engineering
Class 150–2500 · Gasket Inclusion · Pre-Kitted · Tagged
What is a Flange Bolt Kit
A flange bolt kit (also called a flange bolt pack or flange bolt set) is a pre-counted, pre-measured and pre-packaged set of all fastener and gasket components required to make up one complete flanged joint — stud bolts, heavy hex nuts, washers (where specified) and gasket. Pre-kitting eliminates the most common source of site delay and error in flange assembly: incorrect bolt length, wrong bolt count, mismatched nut grade, or missing gasket. Each kit is labelled with the flange NPS, pressure class, bolt material, nut material, coating, gasket type and PO reference — ensuring that the correct assembly components reach the correct flange on site without manual sorting or re-verification.
The standard ASME B16.5 flange bolt kit for one flanged joint contains: (a) the correct number of stud bolts per the B16.5 bolt count for the NPS and pressure class; (b) twice the bolt count in heavy hex nuts (two nuts per stud bolt); (c) washers if specified (one per nut face, so 2 × bolt count washers per joint); and (d) one gasket of the specified type and material for the flange face type. The stud bolt length is calculated to provide the correct thread engagement and protrusion per ASME B18.31.2.
Pre-kitted bolt sets reduce site assembly cost and risk in three ways: (1) Elimination of sorting errors — on large EPC projects with thousands of flanges, bulk fastener supply leads to mixing of bolt lengths, grades and coatings; each incorrectly assembled bolt must be identified, torqued off, sorted and replaced — at high site labour rates; (2) Material traceability — each kit contains fasteners from the same verified heat/lot, with a single MTC covering the kit, rather than requiring traceability reconstruction from bulk bins; (3) Torque table alignment — because the kit contains a known bolt material, coating and nut combination, the site engineer can assign a single K factor and torque table to the entire kit, eliminating the uncertainty that arises when bolts and nuts from different stocks are assembled.
Kit Types — Engineering Descriptions
ASME B16.5 Bolt Count & Stud Length
Reference Tables for All Pressure Classes
Bolt Count · Bolt Size · Stud Length · Thread Engagement
Stud Bolt Length Calculation
The stud bolt length L for a flanged joint is calculated as: L = T₁ + T₂ + 2×G + 2×E, where T₁ and T₂ are the thicknesses of the two flanges being joined (from face to back face), G is the gasket thickness (for raised face / flat face joints, or zero for RTJ), and E is the thread engagement length per ASTM A193 (minimum 1× nominal bolt diameter). For RTJ gaskets, the ring sits in the grooves and the flange faces do not close to zero gap — the ring protrusion must be accounted for. ASME B18.31.2 provides the stud bolt length increments (typically 5 mm or 1/4" increments) — always round up to the next standard length above the calculated minimum.
For pre-kitted bolt sets, the stud bolt length is calculated by RR Hydraulics' technical team based on the exact flange specification (NPS, pressure class, facing, gasket type and thickness) supplied in the purchase order — eliminating the site error of incorrect bolt length selection.
| NPS | Cl.150 — No. / Size | Cl.300 — No. / Size | Cl.600 — No. / Size | Cl.900 — No. / Size | Cl.1500 — No. / Size | Cl.2500 — No. / Size |
|---|---|---|---|---|---|---|
| ½" | 4 / M12 | 4 / M16 | 4 / M16 | 4 / M22 | 4 / M22 | 4 / M22 |
| 1" | 4 / M16 | 4 / M16 | 4 / M20 | 4 / M22 | 4 / M27 | 4 / M27 |
| 1½" | 4 / M16 | 4 / M20 | 4 / M22 | 4 / M27 | 4 / M33 | 4 / M33 |
| 2" | 4 / M16 | 8 / M16 | 8 / M20 | 8 / M22 | 8 / M27 | 8 / M33 |
| 3" | 4 / M16 | 8 / M20 | 8 / M22 | 8 / M27 | 8 / M33 | 8 / M36 |
| 4" | 8 / M16 | 8 / M20 | 8 / M22 | 8 / M27 | 8 / M36 | 8 / M42 |
| 6" | 8 / M20 | 12 / M20 | 12 / M27 | 12 / M33 | 12 / M42 | 12 / M48 |
| 8" | 8 / M20 | 12 / M24 | 12 / M33 | 12 / M36 | 12 / M48 | 12 / M56 |
| 10" | 12 / M24 | 16 / M24 | 16 / M33 | 16 / M42 | 16 / M56 | 12 / M64 |
| 12" | 12 / M24 | 16 / M27 | 20 / M33 | 20 / M42 | 20 / M56 | 12 / M72 |
| 16" | 16 / M27 | 16 / M33 | 20 / M42 | 20 / M48 | 20 / M64 | — |
| 20" | 20 / M27 | 20 / M33 | 24 / M42 | 20 / M56 | 20 / M72 | — |
| 24" | 20 / M30 | 20 / M36 | 24 / M48 | 20 / M64 | 20 / M72 | — |
ASME B16.5-2017. Bolt sizes given as nearest metric equivalent to ASME B18.31.2 UNC stud bolt designations. For precise ASME bolt sizing in inch UNC (5/8", 3/4", 7/8", 1", 1-1/8", 1-1/4", 1-3/8", 1-1/2", 1-5/8" etc.), refer directly to ASME B16.5 bolt tables. Bolt count is the total number of stud bolts per joint. Nut count = 2 × bolt count. Class 2500 NPS 16"+ requires B16.47 Series B for larger bore — contact RR Hydraulics for large-bore kits.
| NPS | Bolt Size (ASME) | Cl.150 Length (mm) | Cl.300 Length (mm) | Notes |
|---|---|---|---|---|
| 2" | 5/8" ≈ M16 | 140 | 165 | SWG 3.2mm thick; RF raised face 1.6mm (Cl.150) / 6.4mm (Cl.300) |
| 3" | 5/8" ≈ M16 | 152 | 178 | Cl.150: 4 bolts; Cl.300: 8 bolts |
| 4" | 5/8" ≈ M16 | 165 | 191 | Add 25mm for RTJ ring instead of SWG |
| 6" | 3/4" ≈ M20 | 178 | 216 | Verify actual stud length against specific flange thickness |
| 8" | 3/4" ≈ M20 | 191 | 229 | Class 600 bolts significantly longer than Cl.300 |
| 10" | 7/8" ≈ M22 | 216 | 254 | Thread engagement min = 1×bolt diameter each end |
| 12" | 7/8" ≈ M22 | 229 | 267 | Always confirm actual flange dimensions for kit length |
Indicative stud bolt lengths for ASME B16.5 raised face flanges with 3.2mm spiral-wound gasket. Actual stud bolt length must be calculated from the specific flange thicknesses and gasket thickness — these vary by material, manufacturer and schedule. Always request actual flange dimensional data when ordering bolt kits for critical service. RTJ flanges require longer studs (by approximately the ring groove depth × 2). For heat exchanger bolt kits, the channel and shell flange thicknesses must be obtained from the TEMA data sheet.
Bolt Kit Material Specifications,
Coatings & Gasket Integration
Xylan 1070 · SWG · RTJ · Full-Face · Kammprofile
| Service / Flange Material | Stud Bolt (ASTM) | Heavy Hex Nut (ASTM) | Coating | Typical Application |
|---|---|---|---|---|
| CS / General process | A193 B7 | A194 2H | Bare or Xylan 1070 | Standard process piping, utilities, onshore O&G |
| CS / Outdoor or marine | A193 B7 | A194 2H | Xylan 1070 (mandatory) | Offshore topsides, coastal plants, marine |
| CS / Low-temperature (−46°C) | A320 L7 (LTCS) | A194 4 or 7 | Xylan or bare | LNG, cryogenic, low-temp process |
| CS / High-temperature (>538°C) | A193 B16 (Cr-Mo-V) | A194 4 or 7 | Bare | High-temp steam, power plant |
| SS 304/316 flanges | A193 B8M Cond. S1 | A194 8MA | Xylan or anti-seize | Chemical, pharma, food, cryogenic |
| Duplex 2205 flanges | A182 F51 / A453 660 | Duplex 2205 heavy hex | Xylan or anti-seize | Offshore sour, seawater |
| Super Duplex 2507 flanges | A182 F53 | Super Duplex 2507 heavy hex | Xylan or anti-seize | Subsea, HPHT, severe sour |
| Inconel 625 flanges | B446 N06625 (Inconel 625) | N06625 or N08825 heavy hex | Xylan 1070 or EN-PTFE | Offshore Class 600+, highly corrosive |
| Titanium flanges | B348 Gr.2 (Ti) | Titanium Gr.2 heavy hex | Xylan (Ti on Ti only) | Seawater, chlorine, desalination |
| Cast iron / FRP flanges | A307 Gr.B (low-strength CS) | A563 Gr.A | Zinc electroplate | Flat-face Class 150 water/utility service |
Gasket Integration in Bolt Kits
The most common gasket types included in complete flange bolt kits are:
- Spiral-Wound Gasket (SWG) — The standard gasket for raised face flanges in process piping. A spiral of pre-formed metallic strip wound with a soft filler material (PTFE, graphite, mica, or ceramic fibre). The inner and outer guide rings are critical — the inner ring prevents blow-out under high pressure and the outer ring (also called the centering ring) aligns the gasket on the bolt circle. Specified by the spiral material, filler material, inner ring material and gasket class per ASME B16.20. Most common: SS 304 or 316 spiral with graphite filler for carbon steel piping, SS 316 spiral with PTFE filler for chemical or food-grade service.
- Ring Type Joint (RTJ) Gasket — Solid metal oval or octagonal ring gasket per ASME B16.20. Used with RTJ-faced flanges in Class 600–2500 high-pressure service. The ring number must match the RTJ groove designation of the flange — R, RX or BX series. Softer than the flange groove material (typically soft iron, mild steel or SS 304/316) to ensure the ring deforms and seals. Kit must specify the ring number and material.
- Full-Face Rubber/PTFE Gasket — Used for flat-face flanges (cast iron, FRP). The full-face gasket has bolt holes and covers the entire flange face. Prevents the raised section of a raised-face flange from cracking a flat-face cast iron or FRP flange under bolt load.
- Kammprofile Gasket — A solid metal core (usually SS 316L) with serrated concentric grooves on both seating faces, overlaid with a soft sealing layer (graphite or PTFE). Higher blow-out resistance than SWG; used in heat exchangers, high-pressure and high-temperature service where SWG may blow out under cycling loads.
The stud bolt and nut in a flange joint must be compatible in strength and material. The most dangerous assembly error is using a high-strength stud bolt (e.g. A193 B7, yield 724 MPa) with an under-strength nut (e.g. A194 Grade A, yield 207 MPa). When the joint is torqued to the stud bolt specification, the under-strength nut strips — it may appear to torque correctly initially (as the nut turns against the stripped thread) and fail under pressure or thermal cycling. The pre-kitted bolt approach prevents this error by supply the correct nut grade in the same package as the stud bolt. A193 B7 studs must always be paired with A194 2H nuts; A193 B8M studs with A194 8M or 8MA nuts; A320 L7 studs with A194 Grade 7 or 4 nuts.
Large-Bore & Heat Exchanger Kits, Applications
& Quality Control and Documentation
Petrochemical · Power · Tagged per FLN · EN 10204 3.1/3.2
Large-Bore Bolt Kits — ASME B16.47
For large-bore flanges above NPS 24" (up to NPS 60"), ASME B16.47 governs the bolt count and bolt size, replacing ASME B16.5. ASME B16.47 has two series: Series A (formerly MSS SP-44, heavier flanges with more bolt holes) and Series B (formerly API 605, lighter flanges with fewer bolt holes). Series A and Series B flanges of the same NPS and pressure class have different bolt circles, bolt counts and bolt sizes — they are NOT interchangeable with each other or with B16.5 flanges. Large-bore bolt kits must explicitly reference whether the flange is B16.47 Series A or Series B.
Large-bore bolt kits for NPS 26"–60" typically involve stud bolts in M36–M72 diameter and lengths from 350 mm to 900 mm, with very high individual bolt weight. Large-bore kits must include provisions for bolt handling — bolt tensioners (hydraulic or mechanical) rather than torque wrenches are used for large bore flanges where wrench torque approach would be impractical, and the bolt kit should be accompanied by the recommended bolt tensioning procedure specifying load, sequence and target elongation.
Heat Exchanger Bolt Kits — TEMA Standard
Heat exchangers have multiple distinct flanged connections requiring separate bolt kits: (1) Shell-side inlet and outlet nozzle flanges; (2) Tube-side (channel) inlet and outlet nozzle flanges; (3) Shell-to-channel flange (the large-bore flange joining the shell body to the channel); and (4) Floating head cover flange (internal to the shell for floating head designs; the most difficult to access and therefore the most important to kit correctly). Each of these flange connections may require different bolt materials, gaskets and coatings — a heat exchanger bolt kit must be structured to address all four joint types with clear individual labelling. TEMA R, C or B designation determines the flange thickness and therefore the stud bolt length for each connection type.
Applications by Industry
Large EPC projects (refineries, gas plants, offshore topsides) have thousands of flanged joints with complex material specifications, sizes and pressure classes. The most efficient supply method is to issue bolt kits tagged to the Flange Line Number (FLN) from the piping isometric drawing — each kit bag or box is labelled with the FLN, pipe line tag, NPS, class, material grade, coating and gasket type. The site piping crew simply picks up the kit for the flange they are working on and assembles it without any further specification checking. RR Hydraulics provides this service: from the piping isometric Material Take-Off (MTO), we compile, kit, tag and deliver pre-packaged bolt kits sorted by isometric drawing and FLN reference.
Offshore topsides piping per NORSOK M-630 requires Xylan 1070-coated A193 B7/A194 2H bolt kits for all Class 300 and above carbon steel process piping flanges. The kit must include: Xylan 1070-coated stud bolts and nuts (both coated — never coat only the bolts), SWG or RTJ gasket per the piping specification, coating QC documentation (DFT, salt spray, K-factor reports), and EN 10204 3.1 MTC for the bolt and nut material. For sour (H≶S) service, A193 B7 is the standard but NACE hardness verification is mandatory (≤22 HRC); for critical corrosive service, Inconel 625 kit with EN 10204 3.2 TPI documentation is required.
During plant turnarounds, pre-kitted bolt sets for every flange scheduled to be broken out and reassembled allow the turnaround team to work without fastener shortage delays. Turnaround bolt kits are typically supplied with new gaskets (used gaskets must always be replaced at each break-out per ASME PCC-1) and new Xylan-coated fasteners (used coated fasteners should be inspected and recoated or replaced if the PTFE layer is worn). The kit is pre-assigned to each flange by equipment tag number and flange number from the turnaround work pack.
Quality Control and Traceability
QC for pre-kitted flange bolt sets covers: (1) Stud bolt dimensional inspection — length (within ±1.5 mm of specified), thread gauge (Go/No-Go per ASME B1.1 2A or ISO 965 6g), shank diameter; (2) Nut dimensional inspection — thread gauge (Go/No-Go, 2B or 6H), across-flats dimension; (3) Material verification — hardness per heat (A193 B7: 22–35 HRC; A194 2H: 159–235 HB; exotic alloys: per alloy NACE limits); (4) PMI — 100% on SS, duplex and exotic alloy kit components; (5) Coating QC — DFT (ISO 2808), salt spray (ISO 9227), K-factor test (IFI-125) for coated kits; (6) Kit count verification — every kit sealed and counted before dispatch, with count confirmed on the kit label; (7) Gasket dimensional and material verification — gasket class, inner/outer diameter, ring number (RTJ), and material confirmed against the kit specification.
Export Packaging
- Individual flange bolt kits packed in sealed poly bags or rigid boxes labelled with: FLN or flange reference, NPS, pressure class, bolt material/grade, nut material/grade, coating, gasket type, bolt count, nut count and PO reference
- Gaskets packed separately within the kit (inside a separate inner bag) to prevent thread damage from gasket edges; RTJ rings wrapped individually in bubble wrap within the kit
- Kits for the same isometric drawing packed in the same outer carton or crate, sorted and stacked by FLN order for easy field identification
- Packing list inside every carton cross-referencing each kit bag to its FLN; duplicate packing list on the outside of the carton
- Consolidated MTC package (EN 10204 3.1 or 3.2) covering all fasteners in the consignment, plus individual coating QC reports (DFT, salt spray, K-factor) and PMI reports for alloy kits, in a waterproof sealed envelope attached to the consignment
| # | Document | Standard / Reference | Minimum Requirement |
|---|---|---|---|
| 01 | Stud Bolt MTC | EN 10204 3.1 / 3.2 | 3.1 standard; 3.2 (TPI) for offshore / NACE / exotic alloy kits |
| 02 | Nut MTC | EN 10204 3.1 / 3.2 | 3.1 standard; 3.2 (TPI) for offshore / NACE / exotic alloy kits |
| 03 | Dimensional Inspection Report | ASME B18.31.2 / B1.1 | Stud length, thread gauge, shank diameter, nut hex AF — per AQL |
| 04 | Hardness Test Report (per heat) | ASTM E18 / E10 | B7: 22–35 HRC; 2H: 159–235 HB; NACE limits for sour service |
| 05 | PMI Report (XRF / OES) | Project specification | 100% SS, duplex, Inconel and all exotic alloy kit components |
| 06 | Coating Application Certificate | IFI-125 / ISO 10683 | Coating grade, DFT, cure conditions confirmed per coating spec. |
| 07 | Coating QC Report (DFT + Salt Spray + K) | ISO 2808 / ISO 9227 / IFI-125 | DFT per batch, salt spray hours confirmed, K-factor measured — all mandatory for coated kits |
| 08 | Gasket MTC / Certificate | ASME B16.20 / EN 10204 | Gasket material, class, inner/outer OD, ring number (RTJ) confirmed |
| 09 | ISPM-15 Phytosanitary Certificate | IPPC / FAO | All wood packing for international export |
RR Hydraulics supplies flange bolt kits and assemblies for all ASME B16.5 and B16.47 flange applications — Class 150–2500, NPS ½"–60". Standard kits in A193 B7 / A194 2H (bare and Xylan 1070 coated), A193 B8M / A194 8MA (SS 316), A320 L7 / A194 4 (LTCS), Duplex 2205 / Super Duplex 2507 and Inconel 625. Pre-kitted per FLN from piping isometrics for EPC projects. Complete assembly kits including SWG, RTJ, full-face gaskets and Kammprofile. Coating test reports (DFT, salt spray, K-factor) per IFI-125. EN 10204 3.1/3.2 MTC, PMI, hardness, thread gauge certificates. Large-bore B16.47 kits and TEMA heat exchanger kits available. 48-hour express dispatch on standard in-stock kits.