Xylan

Common applications: Subsea bolting, refinery flanges, chemical service, valve trim

What Xylan and fluoropolymer coatings actually do

A plain steel stud bolted to a flange for five years in seawater or sulfur-bearing crude will gall, seize, and corrode. When it's time to rework the flange, breaking those studs free is a day-long job with cutting torches and cursing. A fluoropolymer coating solves both problems:

• Corrosion barrier — the coating isolates the steel from the environment
• Anti-galling / low friction — the PTFE content lets nuts thread on and off cleanly even after years in service
• Predictable torque-tension — a coated fastener develops the same bolt tension for a given torque every time, which is critical for flange joint integrity

The coating is a liquid paint-like system applied by spray, then cured in an oven at 350–400°F. Finished thickness for fastener applications is typically 0.5 to 2 mil (12–50 microns) per coat, depending on grade and specification.

Xylan vs "fluoropolymer coating"

"Xylan" is the brand name for a family of coatings produced by Whitford (now part of PPG). The name has become common industry shorthand the way "Kleenex" stands in for tissues. Competing fluoropolymer coatings from other manufacturers (Takecoat, Molykote, Dicronite, various Everlube products) perform similarly and are often cross-specified.

When a drawing says "Xylan 1424 or equivalent," it's calling for the performance characteristics — corrosion resistance, friction coefficient, temperature rating — that Xylan 1424 is known for, and approved substitutes are allowed.

How Xylan and fluoropolymer coatings are specified

There's no single ASTM or SAE standard that governs Xylan the way F2329 governs hot-dip galvanizing. Because Xylan is a brand-name coating family, specifying it on a drawing invokes a stack of documents rather than one standard:

• Whitford / PPG product data sheets per grade (1424, 1070, and so on) are the governing specifications. They define chemistry, cure schedule, thickness range, friction coefficient, and performance claims. When a drawing calls out a specific Xylan grade, it's invoking the corresponding data sheet.
• ASTM and ISO test methods verify the finished coating. These are how a coating certificate demonstrates the part meets spec — they don't specify the coating, they verify it.
• Customer purchase specifications are where real-world procurement lives. Shell DEP, ExxonMobil GP, Chevron, Petronas, and other major operators each publish their own coating specs that approve Xylan grades directly or list them as "or equivalent." These supersede generic references on most offshore and refinery work.
• Application standards — NORSOK M-501 System 7 references fluoropolymer systems for offshore bolting; ASME PCC-1 publishes torque guidance for coated bolted joints.

The practical takeaway: when specifying a coated fastener, name the coating grade (or acceptable equivalents) and reference whichever customer spec or application standard applies to the job. There's no cleaner single-standard callout available because the standards body doesn't publish one.

Common Xylan grades for fasteners

Color choice is sometimes about performance and sometimes about visual traceability — a project will specify, say, "B7 studs blue-coated, B8M studs green-coated" so installers can distinguish material grades by eye on a crowded flange.

Service environments

• Subsea / offshore — The dominant use case. Saltwater immersion, high pressure, 20+ year service life, high-consequence disassembly. Xylan 1424 and 1070 are the workhorses.
• Refinery and chemical plant — Hydrocarbon and chemical service, H₂S exposure, frequent maintenance cycles. Xylan 1070 common.
• Flue gas desulfurization (FGD) — Power generation wet scrubbers; highly corrosive.
• Valve trim and internals — For anti-galling of threaded components.

Temperature ratings

Continuous service for most fluoropolymer coatings tops out at 500°F (260°C). Above that, the PTFE begins to degrade and the coating loses both its corrosion barrier and its low-friction properties. For service above 500°F, specify a high-temperature grade (Xylan 5230 or equivalent) or move to a different coating system entirely.

At the cold end, fluoropolymer coatings remain functional well below -100°F. They're routinely specified on A320 L7 studs for cryogenic and LNG service.

Torque, friction, and why coating changes the calculation

A plain steel fastener has a friction coefficient (K-factor) around 0.18 to 0.22. A fluoropolymer-coated fastener runs 0.08 to 0.13 — roughly half. If you apply the same torque you'd use on a plain stud, you'll over-tension a Xylan-coated stud by 40–50% and potentially yield or snap it.

Flange joint assembly procedures (ASME PCC-1 is the reference) account for this with published torque tables specific to coating type. When ordering coated studs, always:

1. Confirm the coating grade being applied
2. Get the K-factor from the coating manufacturer's data sheet
3. Recalculate torque targets for the joint

California Fastener provides K-factor data with every coated order for this reason.

Application and quality control

Coating is applied after manufacturing — the studs are blasted to a surface profile, coated by spray in a controlled booth, then oven-cured. Finished parts are verified against a standard suite of test methods:

Finished parts ship with a coating certificate showing grade applied, batch number, thickness readings, cure verification, and adhesion test results.

Note on coefficient of friction vs K-factor: The coefficient of friction reported on a coating data sheet (per ASTM D1894) is a material property of the cured coating film. The K-factor used in joint torque calculations is a whole-joint value that also includes underhead friction and thread geometry. They are related but not interchangeable — always use the K-factor from your coating supplier's fastener-specific data, not the raw coating COF, when calculating torque.

What the coating is NOT

• Not a replacement for material selection. A Xylan-coated A193 B7 stud is still a B7 stud chemically. In sour (H₂S) service, the underlying stud material still needs to be B7M per NACE requirements; the coating doesn't make B7 sour-service acceptable.
• Not a high-temperature solution by itself. Above 500°F, the coating degrades. Material selection still governs service temperature.
• Not a permanent barrier against every chemical. Most common hydrocarbons, acids, alkalis, and solvents are fine; strong oxidizers and certain solvents at elevated temperature can attack the film. Reference the coating manufacturer's chemical compatibility chart for specific service fluids.

Cadmium-plated alternatives

Cadmium plating (QQ-P-416 / AMS-QQ-P-416) was historically the go-to anti-galling, corrosion-resistant fastener coating for aerospace and defense. It has been largely phased out due to environmental and health restrictions on cadmium processing. Fluoropolymer coatings are one of the accepted modern replacements for many (not all) cadmium-plated applications. Drawings that call for cadmium plating on new-build parts are increasingly being revised to specify fluoropolymer or other zinc-flake alternatives.

Related references

Coating specifications (the primary spec source):

• Whitford / PPG product data sheets per Xylan grade

Application and installation standards (where fluoropolymer systems are referenced):

• NORSOK M-501 — Surface preparation and protective coatings for offshore; System 7 references fluoropolymer bolting systems
• ASME PCC-1 — Guidelines for pressure boundary bolted joint assembly (coated-fastener torque guidance)

Test methods (used to verify coating performance):

• ASTM B117 — Neutral salt spray
• ASTM D3359 — Cross-hatch adhesion
• ASTM D4541 — Pull-off adhesion
• ASTM D1894 — Coefficient of friction
• ASTM D543 — Chemical resistance
• DIN 50018 / ISO 3231 — Kesternich cyclic SO₂ corrosion

Base fastener specifications (what the coating goes on):

• A193 — High-temperature / high-pressure bolting
• A320 — Low-temperature bolting
• A194 — Heavy hex nuts
• F436 — Hardened washers

Documentation

Xylan and fluoropolymer coatings are applied to California Fastener orders as a coordinated special-process step rather than stocked coated inventory. Every coated order ships with mill certs for the base material plus a coating certificate showing grade, batch, thickness readings, cure verification, and K-factor data for torque calculation. Color-coded grade systems can be coordinated on request.