ASTM A194 Grade 2H Heavy Hex Nut

ASTM A194 Grade 2H heavy hex nuts are quenched-and-tempered carbon steel nuts specified for bolted connections involving pressure-containing equipment, piping, valves, and industrial flanges. Their heavy hexagonal geometry provides a wider bearing surface and greater nut thickness than standard hex nuts of comparable nominal thread size.

Grade 2H nuts are commonly paired with ASTM A193 Grade B7 stud bolts in refinery piping, petrochemical equipment, power generation systems, and pressure vessel assemblies. Material requirements are defined by ASTM A194/A194M, while applicable dimensions are covered by ASME B18.2.2 for inch-series nuts.

Quenched-and-Tempered Carbon Steel: Heat treatment develops the mechanical properties specified for Grade 2H. Hardness requirements vary by nominal size, so inspection criteria must correspond to the applicable dimensional range.

Heavy Hex Geometry: The six-sided profile provides wrench clearance and a larger external envelope than a standard hex nut of the same nominal thread diameter. Dimensions should match the applicable ASME standard and mating fastener.

Thread Compatibility: UNC and 8-UN threads are common in industrial bolting assemblies. The correct thread series and fit depend on nominal diameter, mating stud bolt, and purchase specifications.

Identification and Traceability: Grade markings and manufacturer identification support product identification. Heat-number traceability and accompanying material records should be confirmed against the supplier's marking and inspection procedures.

Surface Finish Options: Plain or lightly oiled finishes are suitable for specified general-service requirements. Hot-dip galvanizing, zinc plating, zinc-nickel, and fluoropolymer coatings may be available for selected applications. Coating compatibility, thread allowance, lubrication, and tightening procedures must be evaluated before ordering.

Operating Conditions: Confirm design pressure, operating temperature, minimum design temperature, process media, and applicable engineering code. Grade 2H should not be assigned a universal service-temperature limit without supporting design data.

Sour Service: Wet hydrogen sulfide environments require an assessment against NACE MR0175/ISO 15156 and the applicable project requirements. Grade 2HM may be specified where its hardness and other material requirements are appropriate; grade selection should be confirmed by the responsible materials engineer.

Thread and Coating Compatibility: Match nut threads to the stud bolt's nominal diameter and thread series. Hot-dip galvanizing changes thread dimensions, so the coating specification and applicable thread allowances must be coordinated before production. Coated assemblies may also require a specified lubricant or tightening procedure.

Inspection and Documentation: Define required chemical analysis, hardness testing, proof-load testing, dimensional inspection, marking, and material certification in the purchase order. Do not assume that every shipment includes every supplementary test unless it is part of the agreed inspection plan.

For an accurate quotation, provide the nut grade, nominal size, thread series, applicable standard and edition, quantity, surface finish, mating stud-bolt specification, and required inspection documents. Include operating conditions or project drawings when special service requirements apply.

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