Stud Bolts — Engineering Reference | RR Hydraulic

Engineering Reference Document

Stud Bolts

A world-class technical reference for EPC contractors, piping and pressure vessel engineers, procurement heads, TPI inspection agencies, and global project buyers specifying stud bolts in high-pressure, high-temperature, and corrosive industrial systems.

ASTM A193 / A320 ASTM A194 ASME B16.5 / B16.47 DIN 976 / DIN 939 ISO 898-1 NACE MR0175 EN 10204 3.1 / 3.2 ISO 9001:2015

Part 01 / Technical Definition

Industry Context,
Sealing Principles
& Load Characteristics

Stud bolts are fully threaded fasteners without a head, engaging nuts at both ends to clamp flanged joints in high-pressure piping, pressure vessels, heat exchangers, and valve bonnets. They are the primary bolting hardware in ASME B16.5 / B16.47 flanged systems and form the structural backbone of pressure-retaining joints in Oil & Gas, LNG, Power, and Petrochemical installations.

1.1 — Technical Definition and Functional Role in EPC Systems

A stud bolt is a headless, continuously threaded rod — typically with full-length thread or defined thread engagement zones at each end — used to clamp two flanged faces together with a heavy hex nut at each end. Unlike bolts (which have an integral head), stud bolts distribute clamping load symmetrically and allow precise torquing from both ends, making them the preferred bolting solution in pressure-retaining flange assemblies per ASME PCC-1, ASME B31.3, and related piping codes.

In EPC projects, stud bolts appear in virtually every flanged connection: wellheads, pipelines, pressure vessel nozzles, heat exchanger channel flanges, valve bodies, compressor cylinders, turbine casings, and instrumentation flanges. The correct specification — covering material grade, dimensional standard, heat treatment, coating, and certification level — is a critical engineering deliverable on every project BOM.

Full-Thread Stud Bolt

Thread continuous along the entire shank length. Standard configuration per ASME B16.5 for Class 150–2500 flanges. Allows nut position to be adjusted along the full length; preferred for standard piping flanges.

Double-End Stud Bolt

Threaded at both ends with a plain (unthreaded) shank in the centre. Thread length at each end equals 1× nominal diameter (or per project specification). Used in high-pressure Class 900–2500 and special flange applications.

Single-End / Tap-End Stud

One end threaded for engagement into a tapped hole in the equipment body (e.g., valve bonnet, pressure vessel flange). The other end accepts a nut. Thread engagement depth into tapped body typically 1.25×d to 1.5×d minimum.

Continuous Thread Rod (CTR)

Full-length threaded rod cut to length; used in low-pressure general construction. Not acceptable as a substitute for precision-machined stud bolts in pressure-retaining service without explicit engineering approval.

Flange Stud Bolt

Precisely manufactured stud bolt with chamfered ends, accurate length per ASME B16.5 bolt dimension tables, and thread per ASME B1.1 (2A class). Supplied with two heavy hex nuts per ASME B18.2.2 / ASTM A194.

High-Pressure / Special Stud

Custom-engineered stud bolts for Class 4500, API 6A, subsea tree, and wellhead applications. May require Inconel, Super Duplex, or exotic alloy materials, with custom thread forms and extended documentation.

1.2 — Role of Stud Bolts in Flanged Joint Sealing

The primary function of stud bolts in a flanged joint is to generate and maintain the gasket seating stress required to prevent leakage under operating pressure. The joint sealing mechanism follows a defined mechanical chain:

Bolt preload (F_b): Applied torque generates axial bolt load, compressing the gasket between the flange faces.
Gasket seating: Gasket must be compressed to minimum seating stress (y) to close surface irregularities and achieve initial seal.
Operating condition: Internal pressure exerts hydrostatic end force that partially unloads the bolts; residual gasket stress must remain above the minimum operating gasket stress factor (m × P) defined in ASME BPVC Section VIII, Div. 1, Appendix 2.
Preload retention: Embedment relaxation, thermal cycling, and vibration reduce effective preload post-installation; initial preload must include these deductions.

Critical Design Requirement: Stud bolt selection must account for the combined requirements of gasket seating stress AND operating load. Under-specification of stud bolt grade or cross-sectional area results in insufficient gasket seating stress — the primary cause of flange joint leaks in high-pressure piping systems.

1.3 — Flanged Joint Selection: Stud Bolts vs Alternative Bolting

Table 1.A — Bolting Type Comparison for Flanged Joints

Bolting Type	Engagement Method	Load Symmetry	Pressure Class Suitability	Code Preference	Remarks
Full-Thread Stud + 2 Nuts	Both ends through flange bolt holes	Symmetric	Class 150–2500	ASME B16.5 preferred	Standard for pressure piping
Hex Bolt + 1 Nut	Head bears on one flange face	Asymmetric	Class 150–600	Acceptable; less common	Not preferred in high-temp cycling
Tap-End Stud + 1 Nut	One end into tapped body	Semi-symmetric	Any	Valve bonnets, compressor heads	Engagement depth critical
Tension-Controlled Stud	Hydraulic tensioning both ends	Fully symmetric	Class 900–2500	ASME PCC-1 preferred	Offshore, critical joints
Threaded Rod (field cut)	Both ends, nuts	Symmetric	Low pressure only	Not code-compliant for pressure	Never use in rated pressure service

1.4 — Bolt Preload Behaviour: Embedment, Thermal Cycling & Vibration

Bolt preload loss is inevitable after initial tightening. Engineers must understand the three principal relaxation mechanisms to specify appropriate initial preload targets:

Embedment Relaxation

Surface asperities on thread flanks and under nut bearing faces plastically deform under initial load, reducing effective preload by 5–15% within the first 24–72 hours. Counteracted by re-torquing or initial preload targeting 1.15× design preload.

Thermal Cycling

Differential thermal expansion between stud bolt and flange material causes cyclic preload variation. High-temperature service (above 300°C) requires ASTM A193 B7 or B16 grade with creep-resistant properties. Retorquing at operating temperature is mandatory in some codes.

Vibration Loosening

Transverse vibration (Junker effect) causes progressive nut rotation and preload loss. Mitigated by: achieving target preload (≥75% yield), using prevailing torque nuts, or applying thread locking compounds. Compressor and pump piping connections are high-risk zones.

Gasket Creep Relaxation

Compressed gaskets creep under sustained load, reducing the reaction force on the bolt. Spiral wound and ring-type joint (RTJ) gaskets exhibit less creep than soft gaskets; stud bolt preload targets must account for gasket type relaxation factor.

1.5 — Pressure Cycling Performance and Fatigue

In process plants with frequent startup/shutdown cycles, pressure fluctuations, or thermal transients, stud bolts are subject to cyclic loading. Fatigue life is assessed using Miner’s cumulative damage rule, with stress amplitude at the thread root being the critical location. Thread root stress concentration factor (Kt) for standard UNC threads ranges from 3.0 to 4.5.

Gasket Seating Load — ASME BPVC Appendix 2

W_m2 = b × π × G × y

W_m2 = minimum bolt load for gasket seating (N)
b = effective gasket seating width (mm)
G = mean gasket diameter (mm)
y = minimum design seating stress for gasket type (MPa)

Operating condition bolt load:
W_m1 = H + H_p = (π/4 × G² × P) + (2b × π × G × m × P)

Worked Example — 6″ Class 600 RF Flange, Spiral Wound Gasket:
G = 168.3 mm, b = 6.3 mm, P = 10 MPa (operating), m = 3.0, y = 69 MPa
W_m2 = 6.3 × π × 168.3 × 69 = 229,800 N = 229.8 kN
W_m1 = (π/4 × 168.3² × 10) + (2 × 6.3 × π × 168.3 × 3.0 × 10) = 222,480 + 199,800 = 422,280 N
Design bolt load governs at W_m1 = 422.3 kN → distribute across 8 stud bolts → 52.8 kN per bolt.

Specifying stud bolts for a pressure piping project?
Submit your flange class, material specification, and quantity for a documented RFQ within 24 hours.

Part 02 / Standards & Dimensional Design

Dimensional Design,
Pressure Classes
& Standards Compliance

Stud bolt dimensions are governed by ASME B16.5, ASME B16.47, ASME B1.1, DIN 976, and ISO 898-1. Each pressure class and flange size combination defines a specific stud bolt diameter, thread pitch, and nominal length. Non-compliance with dimensional tables results in joint under-loading and code non-compliance.

Stud Bolt Dimensional Reference — RR Hydraulic

Formal R.F.Q. — Stud Bolts for EPC / O&G Projects
Submit grade, flange class, size, and quantity to sales@rrhydraulics.com for a certified commercial offer.

2.1 — ASME B16.5 Stud Bolt Dimensional Table (Class 150–2500)

The following table provides representative stud bolt nominal dimensions per ASME B16.5 for raised-face (RF) and ring-type joint (RTJ) flanges. All lengths are nominal; actual length is determined by flange thickness + gasket thickness + nut height × 2 + 2 thread pitches protruding beyond each nut.

Table 2.A — ASME B16.5 Stud Bolt: Diameter × Class × Nominal Bolt Data

Flange Size (NPS)	Class 150 Bolt Ø × Length (in)	Class 300 Bolt Ø × Length (in)	Class 600 Bolt Ø × Length (in)	Class 900 Bolt Ø × Length (in)	Class 1500 Bolt Ø × Length (in)	Class 2500 Bolt Ø × Length (in)	No. of Bolts
½”	½ × 3½	½ × 3½	½ × 3½	¾ × 4	¾ × 4½	¾ × 5	4
1″	½ × 3½	⅝ × 4	⅝ × 4½	⅞ × 5	⅞ × 5½	1 × 6½	4
2″	⅝ × 3¾	¾ × 4½	¾ × 5½	1 × 6½	1⅛ × 7	1¼ × 9	8
3″	⅝ × 4	¾ × 5	⅞ × 6	1⅛ × 7½	1¼ × 8½	1½ × 11	8
4″	⅝ × 4	¾ × 5	1 × 6½	1¼ × 8½	1½ × 10	1¾ × 13	8
6″	¾ × 4½	¾ × 5½	1⅛ × 7½	1⅜ × 9½	1¾ × 12	2 × 15½	12
8″	¾ × 4½	⅞ × 5½	1¼ × 8	1½ × 11	2 × 14	2¼ × 18	12
10″	⅞ × 5	1 × 6	1⅜ × 9	1¾ × 12½	2¼ × 16	2½ × 21	16
12″	⅞ × 5	1⅛ × 6½	1½ × 10	2 × 14	2½ × 18	2¾ × 23	20
16″	1 × 5½	1¼ × 7½	1¾ × 12	2¼ × 16½	3 × 22	—	20–28
20″	1⅛ × 6	1¼ × 8	2 × 14	2½ × 19	—	—	24–32
24″	1¼ × 6½	1½ × 9	2¼ × 16	3 × 22	—	—	24–36

2.2 — Pressure Rating Table: ASME B16.5 Classes vs Temperature

Pressure–temperature ratings per ASME B16.5 are a function of flange material group. The following table shows maximum allowable non-shock working pressure (MAWP) for Group 1.1 (ASTM A105 / A216 WCB equivalent) flanges — the most common piping material group. Stud bolt selection must support the rated MAWP at the specified operating temperature.

Table 2.B — ASME B16.5 Pressure Rating (Group 1.1) — Max Working Pressure (Bar g)

Temperature (°C)	Class 150	Class 300	Class 600	Class 900	Class 1500	Class 2500
−29 to 38	19.6	51.1	102.1	153.2	255.3	425.5
50	19.2	50.1	100.2	150.4	250.6	417.7
100	17.7	46.6	93.2	139.8	233.0	388.3
150	15.8	45.1	90.2	135.3	225.5	375.8
200	13.8	43.8	87.6	131.4	219.0	365.0
250	12.1	41.9	83.8	125.7	209.5	349.2
300	10.2	39.8	79.6	119.4	199.0	331.6
350	8.4	38.6	77.2	115.8	193.0	321.7
400	6.5	36.5	73.0	109.5	182.5	304.2
450	5.1	31.6	63.2	94.8	158.0	263.3
500	—	26.5	53.0	79.5	132.5	220.8

2.3 — Applicable Standards and Compliance Framework

ASTM A193

Primary standard for alloy steel and stainless steel bolting materials for high-temperature service. Grade B7 (4140/4142 alloy steel, Q&T) is the most widely specified grade for Carbon Steel pressure piping. Grade B8/B8M covers SS 304/316 bolting.

ASTM A320

Alloy steel and stainless steel bolting for low-temperature service. Grade L7 (4140 alloy, impact tested) and L43 for cryogenic piping. Charpy impact testing at −101°C for LNG service grades. Mandatory for flanges below −29°C.

ASTM A194

Standard for carbon and alloy steel nuts for bolting at high-pressure or high-temperature service. Grade 2H heavy hex nut is the standard companion to A193 B7 stud bolts. Grade 8 / 8M for stainless pairings.

ASME B16.5

Pipe Flanges and Flanged Fittings, NPS ½ through NPS 24. Defines stud bolt dimensions, number, and grade requirements for each flange class and size combination. The primary dimensional reference for piping stud bolt procurement.

ASME B16.47

Large Diameter Steel Flanges, NPS 26 through NPS 60. Series A (MSS SP-44) and Series B (API 605) — different bolt circle and bolt diameter conventions. Stud bolt dimensions differ from B16.5; always verify series before ordering.

DIN 976 / DIN 939

German standards for metric threaded studs. DIN 976 covers continuous thread studs; DIN 939 covers studs with different thread engagements at each end. Used in European EPC projects and equipment manufactured to DIN/EN piping codes.

ISO 898-1

Mechanical properties of fasteners — bolts, screws, and studs. Defines property classes 4.6 through 12.9 for metric fasteners. Cross-referenced with DIN standards for metric stud bolt supply in European and Asian EPC projects.

ASME PCC-1

Guidelines for Pressure Boundary Bolted Flange Joint Assembly. Specifies bolt tightening sequences, target preload levels, torque or tension methodology, and retorquing requirements for pressure-retaining flange joints in ASME-coded systems.

NACE MR0175 / ISO 15156

Materials for use in H₂S-containing environments in oil and gas production. Defines hardness limits for carbon and low-alloy steel stud bolts in sour service: maximum 22 HRC (237 HB) for A193 B7. Mandatory for all sour service bolting specifications.

2.4 — Thread Form and Compatibility Reference

Table 2.C — Thread Compatibility Reference for Stud Bolts

Thread System	Standard	Size Range	Pitch / TPI	Tolerance Class	Regional Application	Remarks
UNC (Unified Coarse)	ASME B1.1	¼”–4″	4–20 TPI	2A/2B (std); 3A/3B (precision)	USA, Canada, global ASME	Standard for ASME B16.5 stud bolts
UNF (Unified Fine)	ASME B1.1	¼”–1½”	12–28 TPI	2A/2B	Precision, small bore	Rare for standard flanges
Metric Coarse (ISO)	ISO 261 / DIN 13	M6–M100	1.0–6.0 mm	6g/6H	Europe, Asia, DIN-coded plants	DIN 976 / DIN 939 studs
Metric Fine	ISO 261	M8–M52	0.75–3.0 mm	6g/6H	High-pressure German equipment	Must specify; not interchangeable
BSW (Whitworth)	BS 84	⅛”–4″	2.5–28 TPI	Class 1–3	UK legacy, BS-coded systems	Not interchangeable with UNC
ACME / Trapezoidal	ASME B1.5 / DIN 103	Custom	Project-specific	Class 2G	Valve stems, actuators	Not used for flange stud bolts

2.5 — Torque Chart: Stud Bolt Installation

Table 2.D — Installation Torque Reference — A193 B7 Stud Bolts with A194 2H Nuts

Bolt Ø (in)	TPI (UNC)	Stress Area (in²)	Target Preload (kN) @ 50% Yield	Dry Torque (Nm)	Lubricated Torque (Nm) K=0.15	MoS₂ Torque (Nm) K=0.12	ASME B16.5 Class Range
½”	13	0.1419	59.3	95	71	57	150–600
⅝”	11	0.2260	94.4	190	143	114	150–900
¾”	10	0.3340	139.5	338	254	203	150–1500
⅞”	9	0.4620	193.0	543	407	326	300–1500
1″	8	0.6060	253.2	814	610	488	300–2500
1⅛”	8	0.7630	318.8	1153	864	692	600–2500
1¼”	8	0.9690	404.8	1625	1218	975	600–2500
1½”	8	1.4050	586.9	2837	2127	1702	900–2500
1¾”	8	1.9000	793.8	4450	3338	2670	1500–2500
2″	8	2.5000	1044.8	6720	5040	4032	2500
2¼”	8	3.2500	1358.3	9808	7356	5885	2500 / special
2½”	8	3.9500	1650.5	13260	9945	7956	Special / API

Torque Coefficient (K Factor) Note: K = 0.20 for dry uncoated threads, K = 0.15 for lightly oiled / machine oil lubrication, K = 0.12 for MoS₂ or PTFE-based lubricants. Always specify and record the lubricant used during assembly; mixed K factors on the same joint create unequal bolt loading — a leading cause of localised gasket crushing and joint leakage. ASME PCC-1 Appendix A provides detailed K factor guidance.

2.6 — Preload Calculation Guide

Bolt Preload from Applied Torque

F_b = T / (K × d)

F_b = Bolt preload force (N)
T = Applied tightening torque (Nm)
K = Nut factor / torque coefficient (dimensionless) — see table above
d = Nominal bolt diameter (m)

Target preload range: 50–70% of bolt yield load = A_s × S_y × 0.50 to 0.70
A_s = stress area (m²); S_y = yield strength (Pa)

Worked Example — 1″ UNC A193 B7 Stud, MoS₂ Lubricant:
d = 0.0254 m, K = 0.12, T = 488 Nm
F_b = 488 / (0.12 × 0.0254) = 488 / 0.003048 = 160,105 N ≈ 160.1 kN

B7 Yield = 723 MPa; A_s = 390.9 mm²; Yield Load = 282.6 kN
Preload % of Yield = 160.1 / 282.6 = 56.6% ✓ (within 50–70% target)

Part 03 / Materials & Manufacturing

Material Grades,
Heat Treatment
& Manufacturing

Stud bolt material selection is the most consequential procurement decision in bolted flange engineering. RR Hydraulic manufactures stud bolts in all standard and exotic grades, including ASTM A193 B7/B8/B8M, A320 L7/L43, duplex, super duplex, Inconel, and Hastelloy — with full heat treatment documentation and NACE compliance.

3.1 — Material Grade Overview and Selection Logic

Table 3.A — Material Comparison: UTS, Yield, Temperature Range, Use Case

Grade	ASTM Spec	UTS (MPa)	Yield (MPa)	Elong. (%)	Temp Range (°C)	Hardness Max (HRC)	Primary Service
B7	A193 Gr.B7	860–1000	723 min	16	−45 to +454	35 (26 NACE)	Standard CS piping, most common grade
B7M	A193 Gr.B7M	690–862	552 min	18	−45 to +454	22 (NACE compliant)	Sour service, H₂S environments
L7	A320 Gr.L7	860 min	723 min	16	−101 to +343	35	Low-temperature, LNG, cryogenic
L7M	A320 Gr.L7M	690–862	552 min	18	−101 to +343	22 (NACE)	Sour + low-temp combined service
B8 Cl.1	A193 Gr.B8 Cl.1	515 min	205 min	30	−254 to +816	—	SS 304 — corrosive, high-temp
B8M Cl.2	A193 Gr.B8M Cl.2	690 min	414 min	12	−254 to +816	—	SS 316 strain-hardened, high strength
B8T	A193 Gr.B8T	515 min	205 min	30	−200 to +900	—	SS 321 — high-temp stabilised
Duplex S31803	A182 F51	620 min	450 min	25	−50 to +315	28 max	Offshore, subsea, sour+chloride
Super Duplex S32750	A182 F53	750 min	550 min	20	−50 to +260	32 max	Seawater, high Cl⁻, HISC-sensitive
B80A (Alloy 718)	A193 Gr.B80A	1241 min	1034 min	12	−254 to +650	—	High-temp, critical bolting, sour

3.2 — Yield Strength and Mechanical Properties Reference

Table 3.B — Mechanical Properties by Heat Treatment Condition

Grade / Spec	Heat Treatment	UTS (MPa)	0.2% Yield (MPa)	Elongation (%)	Reduction of Area (%)	Hardness (HB)	Charpy CVN @ −45°C (J)
A193 B7 (<2½”)	Q&T 860°C/620°C	860–1000	723	16	50	248–302	54 (not req.)
A193 B7 (2½”–4″)	Q&T 860°C/600°C	793–965	655	15	50	233–285	—
A193 B7M	Q&T (max hardness)	690–862	552	18	50	200–235	—
A320 L7	Q&T, impact tested	860 min	723	16	50	248–302	20 min @ −101°C
A320 L43	Q&T, impact tested	860 min	655	16	50	248–302	20 min @ −101°C
A193 B8 Cl.1	Solution Annealed	515	205	30	50	Max 192	— (austenitic)
A193 B8M Cl.2	Solution Ann. + Strain Hard.	690	414	12	35	260–321	—
Duplex 2205	Solution Annealed	620	450	25	45	Max 293	—
Super Duplex S32750	Solution Annealed	750	550	20	40	Max 310	—

3.3 — Corrosion Resistance by Material vs Service Media

Table 3.C — Corrosion Resistance Matrix for Stud Bolt Materials

Material	H₂S Sour*	CO₂ / Wet	Cl⁻ / Seawater	HCl (dilute)	Alkaline	High Temp (>400°C)	Atmosphere (Offshore)
A193 B7 (HDG/PTFE)	Conditional*	Fair	Poor	Poor	Good	Good to 454°C	Fair
A193 B7M (NACE)	Good*	Fair	Poor	Poor	Good	Good to 454°C	Fair
A193 B8 (SS 304)	Fair	Good	Poor (SCC risk)	Fair	Very Good	Good to 816°C	Good
A193 B8M (SS 316)	Good	Very Good	Fair	Good	Very Good	Good to 816°C	Very Good
Duplex 2205	Very Good	Excellent	Very Good	Very Good	Very Good	Limited >315°C	Excellent
Super Duplex S32750	Excellent	Excellent	Excellent	Excellent	Excellent	Limited >260°C	Excellent
Inconel 625	Excellent	Excellent	Excellent	Excellent	Excellent	Excellent to 980°C	Excellent
Hastelloy C-276	Excellent	Excellent	Excellent	Excellent	Excellent	Excellent to 1090°C	Excellent

* Sour service compliance requires hardness ≤22 HRC per NACE MR0175 / ISO 15156. B7 standard hardness (up to 35 HRC) is NOT acceptable for sour service without B7M designation.

3.4 — Manufacturing Process

3.4.1 — Bar Stock vs Forging

Stud bolts are manufactured from hot-rolled or cold-drawn bar stock conforming to ASTM A193 raw material requirements. Unlike structural bolts, stud bolts for pressure service are not forged — they are precision CNC-machined from bar stock, with threads cut or rolled to dimensional specification.

Thread Rolling vs Thread Cutting: Thread rolling (cold-forming) produces superior fatigue life compared to thread cutting because it creates compressive residual stress at the thread root and maintains the continuous grain flow of the bar stock. For stud bolts in cyclic pressure service, fatigue-critical applications, or hydrogen service, rolled threads are preferred and should be specified explicitly on the purchase order.

3.4.2 — CNC Machining Tolerances

Thread form: ASME B1.1, Class 2A (standard); Class 3A on request for precision joints
Thread pitch diameter tolerance: per ASME B1.1 Table 3 for Class 2A
Nominal length tolerance: +0 / −½ pitch (per ASME B16.5 bolt length tables)
Straightness: max 0.5 mm per 300 mm of length (measured on surface plate)
Chamfer at thread ends: 15°–30° from shank axis; minimum 1 full thread depth
Surface finish of shank: Ra ≤ 3.2 µm; thread form Ra ≤ 1.6 µm
Concentricity of thread axis to shank: max 0.1 mm TIR for studs >25 mm diameter

3.5 — Surface Finish Options

Table 3.D — Surface Finish Comparison for Stud Bolts

Finish	Specification	Thickness (µm)	Salt Spray Resistance (h)	Max Temp (°C)	Effect on K Factor	Typical Application
Plain / Bare	ASTM A193 standard	—	<24	454	K=0.20 (dry)	Torqued immediately; assembly lube applied
Black Phosphate	MIL-DTL-16232	5–15	24–72	150	K=0.15–0.17	Short-term storage; standard CS studs
Zinc Electroplate	ASTM B633 Type II	5–25	96–200	120	K=0.18–0.20	General EPC, indoor service
Hot Dip Galvanize (HDG)	ASTM A153 / ISO 1461	45–85	2000+	200	K=0.20–0.22 (over-size nut required)	Outdoor, marine atmosphere; HDG nut pair required
PTFE / Teflon Coat	Proprietary / ASTM	20–50	1000+	260	K=0.10–0.12	Precise torque control; flange assembly
Molykote / MoS₂	Applied at assembly	—	—	450	K=0.11–0.13	High-temperature flange assembly standard
Geomet / Dacromet	ISO 10683	8–12	1000–1500	300	K=0.13–0.16	Offshore deck hardware; EPC outdoor service
Passivation (SS/Duplex)	ASTM A380 / A967	Passive layer	500–2000+	Per alloy grade	K=0.20	All stainless and duplex grade studs

Part 04 / QC, Applications & Export

Inspection & QC,
Industry Applications
& Documentation

RR Hydraulic maintains end-to-end traceability from raw material heat to final packed shipment. All stud bolt orders include dimensional inspection reports, EN 10204 MTRs, and full EPC documentation packages. Third-party inspection by SGS, Bureau Veritas, and Lloyds is coordinated on request.

Stud Bolt QC and Inspection — RR Hydraulic

4.1 — Inspection & NDT Protocol

100%

Dimensional Inspection

Thread gauging with Go/No-Go gauges per ASME B1.1 on every lot. Length, diameter, chamfer, and straightness checked to drawing tolerances.

MPI

Magnetic Particle Inspection

Applied on all carbon and alloy steel studs in NACE service and sizes >1½”. Thread root is primary inspection zone. Per ASTM E709 / EN ISO 9934.

LPI

Liquid Penetrant Inspection

Full surface inspection for SS, duplex, and non-magnetic grades. Per ASTM E165 / EN ISO 3452. Mandatory for B8/B8M and duplex stud bolt lots.

PMI

Positive Material Identification

XRF gun verification on 100% of SS, duplex, and exotic grade stud bolts. Prevents material mix-up between visually similar grades (B8 vs B8M; 2205 vs S32750).

HRC

Hardness Testing

100% hardness testing on all NACE service stud bolts. Max 22 HRC for B7M / L7M. Brinell per ASTM E10; Rockwell per ASTM E18. Both conversion reported on MTC.

CVN

Charpy Impact Testing

Mandatory for all A320 grade stud bolts (low-temp service). Test temperature per application: −45°C (L7), −73°C or −101°C (L43 / L7M special). 20J minimum per ASTM A320.

4.2 — EN 10204 Material Test Certificate Requirements

Table 4.A — EN 10204 Certificate Types and EPC Application

Certificate	Content	Signatory	Standard EPC Requirement	When Mandatory
2.1	Conformity declaration only	Manufacturer	Non-critical utility lines	General procurement only
2.2	Non-specific test results	Manufacturer	Low-pressure, non-coded service	Rarely accepted in EPC O&G
3.1	Heat-specific mechanical + chemical results; traceable to production lot	Manufacturer’s authorised QC Inspector	Standard minimum for all pressure service	All Class 150+ stud bolt supply
3.2	Same as 3.1 + countersigned by independent TPI (SGS / BV / Lloyds / DNV)	Manufacturer + TPI Inspector	Critical joints, NACE service, offshore	Class 900+, sour service, cryogenic

4.3 — Pressure Test Protocol for Assembled Joints

Stud bolts themselves are not hydrotested individually; hydrostatic / pneumatic testing is performed on the assembled flange system. Post-assembly leak test requirements for pressure piping joints per ASME B31.3:

Hydrostatic test pressure: 1.5 × MAWP at test temperature (per ASME B31.3 Cl. 345)
Pneumatic test pressure: 1.1 × MAWP (where hydrostatic not practical)
Sensitive leak test: 0.1 × MAWP, min 105 kPa (Category D fluid service)
Hold time: Minimum 10 minutes at test pressure before inspection
Acceptance: No visible leaks at any joint, including stud bolt threads and nut faces
NACE sour service: Post-hydrostatic drying mandatory to prevent wet H₂S exposure; stud bolts must be retorqued after drying per ASME PCC-1

4.4 — First Article Inspection (FAI)

A First Article Inspection is conducted on the first production unit of each unique stud bolt configuration (grade + size + thread + finish + standard combination) on new project orders. The FAI report documents: dimensional compliance to all drawing callouts, thread gauge results, hardness readings, visual inspection results, surface finish measurement, and cross-reference to raw material MTC. FAI release is required before batch production proceeds.

4.5 — Applications by Industry

Oil & Gas — Upstream Oil & Gas — Midstream Oil & Gas — Downstream / Refinery LNG Terminals Petrochemical Power — Steam & Gas Turbine Offshore & Subsea Pressure Vessels / Heat Exchangers Hydrogen Plants Desalination Mining Nuclear (Class 2 / 3)

Oil & Gas — Upstream / Wellhead

API 6A wellhead and Xmas tree bolting. High-pressure Class 2000–20000 psi service. Sour service NACE compliance mandatory. Typically Inconel 718 (B80A) or Super Duplex for subsea tree bolting. Full EN 10204 3.2 documentation with TPI witness required.

Refinery / Petrochemical

ASME B31.3 process piping stud bolts. Grade A193 B7 / B7M for most services; B8M for acid and chloride-containing streams. High-temperature catalytic reformer and hydrocracker service requires B16 (2¼Cr-1Mo) or B7 with creep assessment above 370°C.

LNG Terminals

Cryogenic piping in ASTM A320 L7 or L7M for service temperatures down to −165°C. Charpy impact testing at −196°C on special project specifications. All stud bolts supplied with Austenitic SS or aluminium-coated surfaces to prevent galling at cryogenic temperatures.

Power Generation

Steam turbine casing, boiler pressure vessel, and feedwater heater stud bolts. High-temperature grades: A193 B16 (Cr-Mo-V, to +593°C) and B7 (to +454°C). Retorquing at operating temperature required on high-temperature joints per OEM specification.

Offshore / Subsea

Topside piping in SS 316 or Duplex 2205 for marine atmosphere resistance. Subsea tree and manifold bolting in Super Duplex S32760 or Inconel 625. HISC (Hydrogen Induced Stress Cracking) assessment mandatory for super duplex in cathodic protection zones.

Hydrogen Service

Emerging critical application. Stud bolt material must comply with API 941 (Nelson Curves) for high-temperature hydrogen service to prevent HTHA (High-Temperature Hydrogen Attack). Austenitic SS grades (B8 / B8M) and nickel alloys preferred. Carbon and alloy steel require careful temperature-hydrogen partial pressure assessment.

4.6 — Export Packaging and Documentation

4.6.1 — Export Packaging Specification

Individual stud bolts wrapped in VCI (Volatile Corrosion Inhibitor) poly film — prevents rust formation during ocean freight and warehouse storage periods up to 24 months
Thread end protection: plastic thread protector caps on both ends of all stud bolts; prevents thread damage during transit and handling
Bundle tagging: each bundle labelled with heat number, material grade, ASTM standard, size, length, quantity, and PO reference — full traceability maintained through shipping chain
Inner box / polybag: per size and lot — segregated by heat to prevent mixing during goods receipt inspection at site
Outer crating: ISPM-15 heat-treated pine wooden crates for all export shipments; crate dimensions optimised to standard container loading
Crate stencilling: Project PO, Item tag, NDE status, gross weight, net weight, dimensions (L×W×H), country of origin, “THIS SIDE UP” and fragile handling symbols per ASTM D5276
Packing list enclosed inside lid and externally attached in waterproof envelope; cross-referenced to MTC certificate numbers

4.6.2 — Full EPC Project Documentation Package

Table 4.B — Complete Documentation Package for EPC Stud Bolt Supply

#	Document	Standard / Format	Mandatory / Conditional
01	Material Test Certificate (MTC)	EN 10204 3.1 / 3.2	Mandatory — all pressure service
02	Chemical Composition Report	Heat/lot certified lab analysis	Mandatory (within MTC)
03	Mechanical Properties Report	Tensile, yield, elongation, RA, hardness	Mandatory (within MTC)
04	Hardness Test Report	Per ASTM E10 / E18; Brinell + Rockwell	Mandatory — NACE / sour service
05	Charpy Impact Test Report	ASTM A370 / EN 10045	Mandatory — A320 / cryogenic service
06	Dimensional Inspection Report	Per ASME B1.1 / drawing dimensions	Mandatory
07	Thread Gauge Inspection Report	Go / No-Go per ASME B1.1 Class 2A	Mandatory
08	First Article Inspection (FAI) Report	Project-specific format	Mandatory — new item / first batch
09	MPI / LPI Report	ASTM E709 / E165 / EN ISO 9934	Conditional — NACE, Class 900+
10	PMI Report (XRF)	Per lot; all SS / duplex / exotic grades	Mandatory — non-CS grades
11	TPI Witness Certificate	SGS / BV / Lloyds / DNV countersigned	Mandatory — EN 10204 3.2 orders
12	NACE MR0175 Compliance Statement	Hardness + heat treatment confirmation	Mandatory — sour service supply
13	ISO 9001:2015 Certificate	Third-party QMS certification	Mandatory — EPC projects
14	Country of Origin Certificate	Chamber of Commerce issued	Mandatory — all export
15	Packing List	Per shipment; item-level detail	Mandatory
16	Commercial Invoice	Per INCOTERMS 2020	Mandatory
17	Bill of Lading / Air Waybill	Per freight mode	Mandatory
18	MSDS / Safety Data Sheet	For coated / treated surfaces	Conditional — HDG, PTFE, Geomet

4.7 — ISO and Quality System Compliance

ISO 9001:2015

Quality Management System covering design review, supplier qualification, in-process control, inspection, and traceability. Mandatory qualification criterion for all EPC and O&G project procurement. RR Hydraulic holds current ISO 9001:2015 certification.