Name: China ASTM A193 B7M Double-ended Stud Manufacturers Factory - Shuangzhong Intelligent Technology
Brand: Shuangzhong
SKU: 296263697

Description

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ASTM A193 B7M Double-ended Stud & A194 2HM Nut Overview

Our ASTM A193 B7M double-ended studs are manufactured from Cr-Mo alloy steel and heat treated to meet the stringent requirements of NACE MR0175 / MR0103 for sour (H₂S) service. Each stud is paired with an A194 grade 2HM heavy hex nut, engineered specifically for sulfide stress corrosion cracking (SSC) resistance in acidic environments.

This combination is the standard specification for bolting in oil and gas refineries, chemical processing plants, and high-temperature pressure vessel applications where standard B7 / 2H fasteners are not permitted due to hardness limits.

Specifications

Standard: ASTM A193/A193M, ASTM A194/A194M, ASME B18.2.2
Material: A193 Gr. B7M (stud) + A194 Gr. 2HM (nut)
Type: Double-ended stud, fully threaded stud, heavy hex nut
Thread: UNC, 8UN, Grade 2A (stud) / 2B (nut)
Size Range: Imperial 1/4" – 4" | Metric M6 – M100
Temperature Range: -29°C to 538°C (-20°F to 1000°F)
SSC Resistance: Yes - compliant with NACE MR0175 / MR0103

Chemical Composition - B7M Stud (A193 Gr. B7M)

C: 0.38–0.48 | Mn: 0.75–1.00 | P: ≤0.035 | S: ≤0.040
Si: 0.15–0.35 | Cr: 0.80–1.15 | Mo: 0.15–0.25

Chemical Composition - 2HM Nut (A194 Gr. 2HM)

C: ≥0.15 | Mn: ≤1.00 | P: ≤0.04 | S: ≤0.05 | Si: ≤0.40

Mechanical Properties:

B7M Stud:
Min Tensile Strength: 100 KSI (689 MPa)
Min Yield Strength: 80 KSI (551 MPa)
Elongation: ≥18%
Hardness: HB 197–235 (max 235)
Heat Treatment: Quenched & tempered

2HM Nut:
Proof Load: 150 KSI (1034 MPa)
Hardness: HB 159–237
Heat Treatment: Quenched & tempered

Why Choose B7M + 2HM Over Standard B7 + 2H?

The B7M grade is a low-hardness variant of B7, designed specifically for environments where sulfide stress cracking (SSC) is a risk:

Hardness control: B7M limits maximum hardness to HB 235 vs. standard B7 which can exceed this threshold after heat treatment.
SSC resistance: B7M + 2HM is NACE compliant for H₂S-containing environments; B7 + 2H is not.
Toughness: Stricter impact toughness verification per batch vs. standard-grade fasteners.
Mandatory pairing: A193 B7M studs must be used with A194 2HM nuts. Grade 2H nuts are not a substitute.
Testing: 100% individual hardness test on every stud and nut. Batch impact toughness verification.

Surface Treatment Options:

Blackening (black oxide) - mild corrosion protection, standard for indoor service
Phosphating - improves lubricity and provides base for oil coating
PTFE (Xylan) coating - anti-galling, chemical resistant for sour service
Hot-dip galvanizing - heavy-duty corrosion protection for external environments
Cadmium plating - excellent corrosion resistance and lubricity (military/aerospace)

Installation Guidelines:

Use ASTM F436 hardened washers under both nut faces.
Apply anti-seize compound to threads before installation.
Tighten to rated torque only - avoid over-tightening to prevent stress concentration.
Do not mix with 2H nuts or standard carbon steel washers.

Typical Applications:

Oil & Gas Extraction: Wellhead equipment, Christmas trees, pipeline flanges in sour wells
Refining & Petrochemical: Hydrocracking units, amine systems, sour water strippers, high-pressure reactors
Power Generation: Boiler feedwater systems, turbine casings, heat exchanger connections
Pressure Vessels: Vessels, valves, and pumps handling sulfur-containing media

Quality Assurance:

Each order includes material traceability certified to ASTM specifications. We provide mill test reports (MTRs) with chemical composition, mechanical properties, and heat treatment records. Our facility is equipped with Brinell hardness testers, tensile testing machines, and impact testers for in-house quality verification.