Guide
What is Xylan coating, and when should a fastener or valve part get it?
Xylan coating is a family of resin-bonded dry-film coatings, sold by PPG, that combine a binder resin with a fluoropolymer lubricant and are sprayed on and oven-cured to give a part controlled low friction plus a barrier against corrosion and chemicals. Choose it for studs, bolts and valve or actuator parts that must assemble, torque and come apart again; do not choose it for a hidden bracket that only needs to resist rust, where zinc plating is the simpler answer.
By Saola Manufacturing engineering team · Published · Updated
“Xylan” is a trade name, and buyers often use it the way people use “Teflon”: as a shorthand for any blue or black PTFE-type coating on a stud. That shorthand causes trouble on drawings, because the family spans many grades with different binders, cure schedules and film builds. This guide explains what the coating is, how it changes thread fit, how it compares with zinc plating, and what the drawing and RFQ need to say. If you are weighing zinc flake against zinc plating instead, see zinc flake coating vs zinc plating.
On this page
What is a Xylan coating made of, and how is it applied?
It is an organic coating, not a plating: a resin binder carrying fluoropolymer and other lubricating fillers, applied as a liquid over a prepared surface and baked to cure.
PPG describes its Xylan 142X series as waterborne “resin bonded high temperature resistant dry films,” and lists fasteners, valves and actuators, tools and metal sealing rings among the typical uses (PPG, Xylan 142X series). The same family includes a zinc-flake grade that can be used alone or as a primer under a Xylan topcoat (PPG, Xylan Zinc-Flake).
In practice the coater cleans the steel, applies a pretreatment such as a grit blast or a phosphate conversion coating so the film has something to key into, sprays one or more coats, and cures the part in an oven. Because nothing is electroplated, the coating step itself does not charge the steel with hydrogen the way zinc electroplating does, but an acid pickling or phosphating step before it still can. Ask what pretreatment the coater uses before assuming that hardened fasteners are safe.
Grade matters. Different Xylan grades are formulated for different jobs, from a thin low-friction film on a fastener to a heavier chemical-resistant film on a valve body. The drawing should name the grade or the performance it must meet, not just the brand.
How does a Xylan coating compare with zinc plating?
Zinc plating protects steel sacrificially and is cheap and conductive; a Xylan-type fluoropolymer film protects as a barrier, adds controlled low friction and chemical resistance, and costs more.
The two are often combined rather than competing: a zinc or zinc-flake base gives sacrificial protection at scratches and cut edges, and a fluoropolymer topcoat adds lubricity and a barrier. The table below sets out the differences that decide the choice for a machined or threaded part. For electroplated fasteners, ASTM F1941/F1941M covers the application, performance and dimensional requirements, including precautions for hydrogen embrittlement and embrittlement relief on high-strength and surface-hardened fasteners.
| Question | Zinc electroplating | Fluoropolymer dry film (Xylan type) |
|---|---|---|
| How it protects | Sacrificial: zinc corrodes first | Barrier film; sacrificial only if a zinc base is underneath |
| Friction and torque | Depends on the passivate and any sealer | Low and controlled, the main reason to choose it |
| Chemical resistance | Limited; attacked by acids and alkalis | Good against many industrial fluids, grade dependent |
| Electrical conductivity | Conductive | Insulating; poor for grounding studs |
| Hydrogen risk from the process | Yes on hardened steel; bake required | Not from the coating; check the pretreatment |
| Heat during processing | Bath temperature, plus any bake | Oven cure; check against the part’s temper |
| Thickness measurement | Per the plating specification | Dry film gauge per ASTM D7091 on flat areas |
| Color coding | Clear, yellow, black passivates | Wide color range used to identify grades or sizes |
How does a Xylan coating affect thread fit?
The film builds on both flanks of the thread, so it eats into the thread allowance; a coated external thread must be made to leave room for the film, or it will not accept the mating nut or the go gauge after coating.
Industry guidance for 60° threads is that a uniform coating on the flanks raises the pitch diameter of an external thread by about four times the coating thickness, so even a thin film consumes a real share of the allowance. Inch threads to class 2A carry an allowance below basic size that is meant to absorb coatings; class 3A threads have no allowance, and a 3A thread coated after machining will usually gauge tight. PPG itself markets its zinc-flake grade as reducing the need for increased thread coating clearance allowances (PPG), which tells you the issue is real for the other grades.
There are three workable ways to handle it on a machined part:
- Machine the thread undersize for the coating. Write “thread dimensions apply after coating” and let the shop size the pitch diameter so the coated thread gauges. This is the usual answer for studs.
- Mask the thread. Practical for an internal thread in a valve body, where coating the thread adds little and makes gauging hard.
- Accept a looser fit. If the joint can tolerate it, gauge the thread before coating and accept that coated parts may run tight with standard nuts. Say so on the drawing; do not leave it implicit.
Whichever you choose, state whether thread acceptance is by gauge before or after coating. A go/no-go check after coating is the test the assembler cares about.
When is a Xylan coating worth the extra cost?
When the part has to be tightened to a repeatable preload, taken apart after service, or exposed to chemicals that would strip zinc; otherwise zinc plating is usually enough.
The strongest cases are bolting where preload matters and disassembly is expected: flange studs and nuts in process plants, actuator and valve fasteners, and parts that seize when the coating corrodes. PPG lists “low friction for torque tension and release” as a benefit on its fastener page (PPG, fastener coatings). The low friction is also the main risk: a torque value written for a dry or zinc-plated fastener will give a much higher preload on a lubricated film. Ask for torque-tension data for the specific grade before you change the coating on an existing joint.
Weaker cases are cosmetic covers, internal brackets, grounding points and parts that will be painted later. For those, the insulating, lubricious film is either wasted or a problem. On a sliding valve component, a fluoropolymer film can help break-away torque, but it is a thin wearing film, not a replacement for a hard wear surface.
How do you specify and accept a Xylan coating on the drawing?
Name the grade (or an equivalent performance requirement), the pretreatment, the color, the dry film thickness range taken from the coating data sheet, the masked features and the acceptance tests.
A complete note covers these points:
- Coating and grade: the trade name and grade number, followed by “or approved equal” if you will accept another maker’s fluoropolymer film.
- Pretreatment: blast, phosphate, or a zinc or zinc-flake base, as the system requires.
- Dry film thickness: the range from the grade’s data sheet, measured on a flat area with a magnetic or eddy-current gauge per ASTM D7091, which covers nonmagnetic coatings on ferrous metals. Thread flanks cannot be measured this way, so the thread is accepted by gauge.
- Thread condition: “thread dimensions apply after coating” or “mask thread,” plus the gauge used for acceptance.
- Corrosion test, if needed: neutral salt spray per ASTM B117 for the hours your specification sets, with the failure criterion stated.
- Base material: grade and hardness, so the coater can check the cure temperature against the temper and choose a pretreatment that does not embrittle hardened parts.
On receipt, check color and coverage visually, run the go/no-go thread gauge on a sample, and check film thickness on a flat face. Ask the coater for the cure record with the lot.
Can Saola supply machined parts with a Xylan coating?
The machining, yes; the fluoropolymer coating is not on our current finish menu, so it has to be raised at drawing review before quoting.
Turned studs, pins and bushings are machined at our lead CNC plant in Vietnam on CNC turning, where threads are checked with go/no-go gauges. Our managed surface finishing menu covers eight finishes applied at partner plants, including zinc plating and RoHS blue trivalent chromate, but not fluoropolymer dry films. If your drawing calls for Xylan, send it anyway and flag the coating: at drawing review we will tell you whether it can be arranged, and if not, the thread can be machined to suit coating by your own coater. Material grade and bar stock are also confirmed at drawing review. Send the drawing for a quote.
Frequently asked
Is Xylan the same as Teflon?
No. Both are trade names, and Xylan grades contain fluoropolymer, but a Xylan coating is a resin-bonded film with fillers chosen for friction, wear or chemical resistance. Name the grade on the drawing rather than a generic “PTFE coating.”
Why are Xylan-coated studs often blue?
Color is a choice, not a property of the chemistry. PPG lists color coding of components as a benefit, and many specifications use a color to identify the coating system. Put the color on the drawing if receiving inspection will use it.
Can a Xylan-coated part be welded or heated after coating?
Avoid it. Welding burns off the film and fluoropolymer decomposition products are hazardous. Weld and heat treat first, coat last.
Does a Xylan coating need a bake for hydrogen embrittlement?
The coating step does not introduce hydrogen, but an acid pickle or phosphate pretreatment can. For hardened fasteners, specify a non-acid pretreatment or a relief bake per your fastener standard.
Should torque values change when switching from zinc plating to Xylan?
Almost always. Lower friction means more of the applied torque becomes preload. Re-establish the torque from torque-tension testing on the coated parts rather than reusing the plated value.
Sources
- Xylan 142X Series High Temperature Low Friction Coatings, PPG Industries product page, accessed November 2026
- Xylan Zinc-Flake, PPG Industries product page, accessed November 2026
- Fastener Coatings, PPG Industries, accessed November 2026
- ASTM D7091-22, Nondestructive Measurement of Dry Film Thickness of Nonmagnetic Coatings Applied to Ferrous Metals and Nonmagnetic, Nonconductive Coatings Applied to Non-Ferrous Metals, ASTM International, 2022
- ASTM F1941/F1941M, Electrodeposited Coatings on Mechanical Fasteners, ASTM International, 2016 edition, reapproved 2025
- ASTM B117, Standard Practice for Operating Salt Spray (Fog) Apparatus, ASTM International, 2026