ASTM A320 L7 Double End Stud

QS Fastener: ASTM A320 L7 Double End Stud

Name: ASTM A320 L7 Double End Stud
Standard: ASTM
Material: A320 L7
Size: M20
Lenght: 100 mm
Surface: Black/ PTFE/ Zinc

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ASTM A320 L7 Double End Stud is manufactured from Cr-Mo alloy steel in accordance with ASTM’s low-temperature and high-pressure standard. Size M20 × 100 mm; finish may be plain black, PTFE-coated or hot-dip galvanized. Tensile strength remains ≥860 MPa at –101 °C, making it ideal for cyclic cold-and-hot services such as LNG lines, valves and pressure vessels. Fully threaded design gives stable installation torque and permits repeated dis- and re-assembly. Stock items available; length and finish can be customized to drawing.

What material is the A320 L7 stud?
ASTM A320 L7 Double End Stud is not “aerospace aluminium”. It is a low-temperature alloy steel covered by ASTM A320, nominally Cr-Mo and in essence an upgraded and closely controlled version of AISI 4140/4142. The mill must vacuum-degas and calcium-treat the heat, holding sulphur ≤0.040 % and phosphorus ≤0.035 %. After quenching and tempering (minimum tempering temperature 595 °C) the hardness is held at HB 235-302 (HRC 22-32), giving high strength with retained toughness. Room-temperature properties: tensile ≥860 MPa, yield ≥725 MPa, elongation ≥16 %. Most critically, Charpy V-notch impact tests at –101 °C (normal LNG storage temperature) average ≥27 J for three specimens, no single value <20 J, guaranteeing that ASTM A320 L7 Double End Stud will not suffer brittle fracture in a bath of liquid methane.

Features and advantages
1. Low-temperature toughness: plain carbon steels become “blue-brittle” below 0 °C, whereas the fine-grained tempered sorbite plus finely dispersed Mo₂C in ASTM A320 L7 Double End Stud drives the ductile-to-brittle transition down to –120 °C, making it suited for liquid oxygen, nitrogen, ethylene and LNG piping.

2. High strength: the 860 MPa grade lets an M20 ASTM A320 L7 Double End Stud carry ~190 kN in tension—higher than A193 B7, the equivalent room-temperature material—so flanges can be downsized and valve weight saved.

3. Resistance to hydrogen embrittlement: hardness ≤HRC 32 is well below the HRC 38 threshold above which high-strength bolts become prone to sulphide stress cracking (SSC) in wet, H₂S-containing natural gas.

4. Weldability: carbon equivalent CE ≈ 0.55 %; not “easy to weld” but far cheaper than nickel alloys. Field repair by welding ASTM A320 L7 Double End Stud saves roughly 80 % of the cost of replacing the entire bolt.

5. Flexible surface treatment: plain, phosphated, PTFE, hot-dip galvanized or Xylan coatings are all possible, covering bare use at –101 °C as well as coastal high-salt-spray environments.

Application examples
① Guangdong Dapeng LNG terminal: –162 °C unloading-arm flanges use M36 × 220 mm ASTM A320 L7 Double End Stud with PTFE coating; 15 years of service without a single brittle failure.

② Hainan refinery ethylene-cracking plant: –101 °C demethanizer top flange originally fitted with stainless tie rods leaked frequently; after changing to ASTM A320 L7 Double End Stud preload rose 30 % and the maintenance interval stretched from 1 to 4 years.

③ Launch-site liquid-oxygen tank: at –183 °C silver-plated ASTM A320 L7 Double End Stud prevents galling and low-temperature seizure, successfully used on the Long-March-5 filling system.

④ Polar FPSO: Norwegian North-Sea project, seawater –40 °C plus wave cyclic loading; ASTM A320 L7 Double End Stud with Xylan 1424 coating has run 15 years maintenance-free, saving USD 600 000 in bolt-replacement costs per vessel.

Summary: with its three-fold merits of “not brittle at low temperature, not soft at high strength, not high in cost”, ASTM A320 L7 Double End Stud has become the default fastener for pressure-containing flanges below –101 °C, safely and economically replacing expensive nickel-base bolting in the energy, chemical, aerospace and polar engineering sectors.

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