NUBOTECK manufactures ASTM A194 Grade 7 Hex Nuts which are applied to critical bolted joints used in refineries, petrochemical plants, offshore platforms, LNG facilities, pressure vessels, valves, heat exchangers and piping systems.
Grade 7 is the most widely specified alloy steel bolting material extensively used for pressure vessels, valves, flanges, and fittings especially for low-temperature service. Grade 7 hex nuts provide excellent strength, toughness and reliability, making them the preferred choice throughout the oil & gas industry.
ASTM A194 standard governs the requirements specifically for Grade 7. However, the requirements given in ASTM A194 are said to be fully achieved, only when the generic/ common bolting requirements of ASTM A962 have been fully met.
Specification API 20E introduces enhanced requirements for manufacturing process control, qualification testing, traceability, metallurgical examination and documentation. These checks and controls are in addition to the regular requirements given for this grade by the ASTM standards (ASTM A194, ASTM A962)
ASTM A194 Grade 7 hex nuts are manufactured from chromium-molybdenum alloy steel which is quenched and tempered to achieve the required mechanical properties. Proper heat treatment ensures optimum strength, toughness and reliability for high-pressure service conditions.
Typical manufacturing sequence:
- Raw Material Verification
- Heat Treatment - Austenitizing, Quenching, Tempering
- Mechanical Property - Verification
- Hot Forming
- Machining
- Threading - Rolling/ Cutting
- Inspection & Testing
- Documentation and Certification
API-20E requirements for Hardness Testing of Bars:
In case of heat treatment using induction process, all readings for hardness must be within 3 HRC. Conversion between hardness scales shall be in conformance with ASTM E140. Test frequency shall conform to ASTM F1470-19, Table 3, sample size A
Manufacturing Parameter ASTM/ API-20E BSL-1 API-20E BSL-2 API-20E BSL-3 Melting Practice Basic-oxygen, Electric-furnace, Vacuum Induction Melting (VIM) Electric-furnace, Vacuum Induction Melting (VIM) Molten steel may be vacuum treated prior to or during pouring of the ingot or strand casting. The primary melting may incorporate separate degassing or refining and may be followed by secondary melting such as electroslag remelting or vacuum remelting The steel shall be fully killed. When steel of different grades is continuously cast identification of the resultant transition material is required. The steel producer shall remove the transition material by an established procedure that positively separates the grades Secondary refining or ladle refining, shall be performed. When multiple heats of the same chemical composition range are sequentially strand cast, the heats shall be separated by an established procedure such that intermix material shall not be supplied (ASTM A962/A962M) Casting Continuous, Ingot Continuous, Ingot Ingot Top pouring during Ingot casting not permitted unless the VIM is used Reduction Ratio 4.0:1 Min 4.0:1 Min 10.0:1 Min
Element ASTM/ API-20E BSL-1 API-20E BSL-2 API-20E BSL-3 Carbon 0.38 – 0.48 Sulfur 0.040 Max 0.025 Max 0.015 Max Phosphorus 0.035 Max 0.025 Max 0.015 Max Manganese 0.75 – 1.00 Silicon 0.15 – 0.35 Chromium 0.80 – 1.10 Molybdenum 0.15 – 0.25 Vanadium 0.05 Max Niobium 0.05 Max Boron (residual) 0.0005 Max 0.0005 Max
Property ASTM Requirement API-20E Requirement Hardness 24 - 35 HRC 24 - 34 HRC for Low Temperature (Charpy Impact) Min 20J Avg 27J @ -101⁰C
1/2" to 2-1/2"
M12 to M64
API-20E BSL-1 API-20E BSL-2 API-20E BSL-3 ASTM A193 B7, ASTM A320 L7 ASTM A193 B7, ASTM A320 L7 ASTM A193 B7, ASTM A320 L7
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