Bolting Set: Nut Grade ASTM A194 2H/7/8

Component Specifications

Definition

A bolting set for pressure vessel manway assemblies is a precision-engineered fastening system comprising bolts, nuts, washers, and sometimes studs, designed to create a high-integrity seal between the manway cover and vessel flange. These components work together to withstand internal pressures, thermal cycling, and mechanical stresses while maintaining a leak-tight closure that meets stringent safety standards for industrial pressure vessels.

Working Principle

The bolting set operates on the principle of creating controlled clamping force through torque application. When tightened, the bolts elongate slightly, generating tensile stress that compresses the gasket between the manway cover and vessel flange. This compression creates a seal that prevents fluid or gas leakage. The set distributes load evenly across the flange face to maintain uniform gasket compression and prevent localized stress concentrations that could lead to failure.

Materials

High-strength alloy steels (ASTM A193 Grade B7, A320 L7), stainless steels (ASTM A193 B8/B8M for corrosion resistance), with nuts typically matching or exceeding bolt strength (ASTM A194). Washers are often hardened steel (ASTM F436) or non-metallic for electrical isolation when required.

Technical Parameters

Parameter	Typical range	Notes & selection driver
Nut Grade	ASTM A194 2H/7/8
Bolt Grade	ASTM A193 B7/B8/B8M
Thread Type	Unified National Coarse (UNC) or Fine (UNF)
Pressure Rating	Up to 10,000 psi (690 bar)
Preload Accuracy	±10% of target torque
Temperature Range	-50°C to 540°C (material dependent)
Torque Requirements	As per ASME PCC-1 guidelines
Corrosion Protection	Zinc plating, hot-dip galvanizing, or Xylan coating

Ranges are indicative industry figures for RFQ preparation, not a supplier commitment. Confirm every value and standard with the legal manufacturer before ordering.

Standards

ISO 898-1, DIN 931, ASME B1.1, ASME B18.2.1

Parent Products

This component is used in the following industrial products

Pressure Vessel Manway Assembly

A standardized manway assembly providing safe, pressure-tight access to the interior of metal tanks, reservoirs, and pressure vessels.

View Product Details

Manhole

A manhole is a critical safety and maintenance component of a steam drum, providing a sealed entry point for personnel to access the interior of the drum.

View Product Details

Engineering Analysis

Risks & Mitigation

Over-torquing causing bolt fracture
Under-torquing leading to leakage
Corrosion-induced stress cracking
Thermal cycling fatigue
Improper alignment causing uneven load distribution

FMEA Triads

Trigger: Incorrect torque application during installation
Failure: Bolt over-elongation or insufficient preload
Mitigation: Use calibrated torque wrenches with angle monitoring, follow ASME PCC-1 procedures, implement torque verification protocols

Trigger: Corrosion in aggressive chemical environments
Failure: Reduced cross-sectional area leading to tensile failure
Mitigation: Select appropriate corrosion-resistant materials (stainless, coated), implement regular inspection schedules, apply protective coatings

Trigger: Thermal cycling without proper retorquing
Failure: Loss of clamping force due to differential expansion
Mitigation: Schedule retorquing after thermal cycles, use high-temperature alloys, consider tension-controlled bolting systems

Industrial Ecosystem

Compatible With

Typical Suppliers & Equivalents

Compliance & Inspection

Tolerance

Thread tolerance: 6g for bolts, 6H for nuts per ISO 965-1; Length tolerance: ±1.5mm for bolts under 150mm

Test Method

Ultrasonic testing for internal defects, hardness testing per ASTM E18, tensile testing per ASTM A370, salt spray testing per ASTM B117 for corrosion resistance

Procurement Evaluation Criteria

A practical evidence checklist for RFQ preparation and supplier evaluation.

Technical documentation

Request current drawings, revision history, and a signed specification sheet.

Manufacturing capability

Verify equipment lists, process limits, capacity, and representative production evidence.

Inspection readiness

Confirm test methods, calibrated equipment, sampling plans, and traceable reports.

Supplier transparency

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Manufacturers of Bolting Set

Manufacturer profiles associated with Bolting Set.

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Frequently Asked Questions

What is the purpose of a bolting set in pressure vessel applications?

The bolting set creates and maintains a secure, leak-tight seal between the manway cover and vessel flange, ensuring pressure containment, structural integrity, and operational safety under varying pressure and temperature conditions.

How often should pressure vessel bolting sets be inspected?

Regular inspection should occur during each vessel opening, with torque verification recommended annually or per manufacturer guidelines. Complete replacement is typically required after 3-5 thermal cycles or if corrosion exceeds 10% of original diameter.

Can different grade bolts be mixed in a manway assembly?

No, mixing bolt grades is prohibited as it creates uneven load distribution and potential failure points. All bolts in a set must be identical in material, grade, and dimensions to ensure uniform clamping force.

Data Basis

Editorial classification, named public sources where available, and source-reviewed manufacturer records. See the editorial policy.

Preliminary Technical Classification

This page supports structured research, RFQ preparation, and supplier evaluation. It does not replace buyer-led supplier qualification, standards review, or technical approval.

Bolting Set