Low-Temperature Bolting, Corrosion and Breakout — An Application Case for PTFE-Coated A320 L7M Assemblies
The Scenario
A coastal LNG receiving terminal faces a combination of demands on its flanged, bolted connections that few fastener options can satisfy simultaneously:
-
Cryogenic service — process piping designed for minimum temperatures in the –50 °C range during upset and cool-down conditions
-
Marine corrosion — salt spray and splash-zone exposure attacking bare bolt surfaces year-round
-
Maintainability — scheduled turnarounds where studs must break free without galling, and be reusable
One bolt must survive all three: low-temperature toughness, corrosion resistance, and easy breakout.
Why Common Options Fall Short
| Option | Limitation |
|---|---|
| Zinc-plated carbon steel (e.g. A193 B7, plated) | Zinc offers limited salt-spray life; B7 carries no low-temperature impact verification |
| Bare A320 L7 alloy steel | Correct cryogenic toughness, but corrodes rapidly in marine exposure |
| Stainless steel fasteners | Good corrosion resistance, but higher cost and well-known galling tendency |
| PTFE-coated A320 L7M |
Addresses all three requirements in one assembly |
The Solution — Requirement by Requirement
1. Low-temperature toughness. The assembly is manufactured to ASTM A320 Grade L7M: chromium-molybdenum alloy steel, quenched and tempered, with Charpy V-Notch impact testing at –73 °C (–100 °F). Hardness is capped at 99 HRB, and modified chemistry improves notch toughness in cryogenic service.
2. Corrosion defense. A Teflon (PTFE) coating provides a chemically inert barrier with low-friction, non-stick properties. Resistance to acids, alkalis, salt spray and moisture far exceeds conventional zinc plating, and the coating performs across a service range of –200 °C to +260 °C — comfortably bracketing both the coldest upset condition and ambient summer heat.
3. Anti-galling and easy breakout. The PTFE low-friction surface reduces thread galling during installation and significantly lowers breakout torque after years of corrosive service — the difference between a routine turnaround and cut-off torches on the flange.
Assembly consistency. Bolts, studs and nuts ship as a matched set — ASTM A320 L7M fasteners with ASTM A194 Grade 7M hex nuts, one grade, one coating, one uniform blue finish. Every piece carries the "L7M" end-face stamp, and the blue coating provides instant visual identification against mixed-grade hardware on site.
What We Supply
-
Size range: 1/4" – 1-1/2" UNC/UNF (M6–M42 equivalent); larger sizes on request
-
Nuts: ASTM A194 Grade 7M hex nuts, same PTFE blue coating
-
Washers (optional): blue PTFE coated plain washers per ISO/ASME/DIN/JIS/GB standards, grades 4.8–12.9, standard and customized sizes
-
Quality: ISO 9001 certified quality system; EN 10204 3.1 material certificates available per order
-
Response: quotation within 48 hours
RFQ Checklist
When requesting a quotation for low-temperature bolting, include:
-
Design minimum temperature and medium
-
Corrosion environment (marine, splash zone, chemical, insulation)
-
Size, length and thread specification
-
Complete assembly or bolts only (nuts / washers)
-
Certificate requirements (e.g. EN 10204 3.1)
-
Coating color requirements
Related Products
Contact
Shaanxi Flourish Industrial Co., Ltd. · Xi'an, China Email: flrs@mechanical-fasteners.com · Tel: +86-29-86613868 Send us your inquiry for a quotation and full specification list within 48 hours.
