Xylan Coated

1. Introduction to Xylan Coated Fasteners

Xylan coated fasteners are high-performance engineered fastening systems utilizing fluoropolymer-based dry film coatings designed to improve corrosion resistance, reduce friction coefficients, enhance chemical resistance, and provide controlled torque–tension characteristics under critical operating conditions.

These coatings are widely specified in:

• Offshore platforms
• Refinery piping systems
• LNG terminals
• Structural steel assemblies
• Petrochemical plants
• Marine equipment
• High-temperature process systems
• OEM mechanical assemblies

Xylan coatings are typically applied over carbon steel, alloy steel, stainless steel, duplex stainless steel, and nickel alloy fasteners to improve operational reliability under aggressive environments.

For EPC contractors, OEM manufacturers, and industrial procurement teams, Xylan-coated fasteners are selected where conventional zinc plating or phosphate coatings fail to provide sufficient durability, anti-galling protection, or chemical resistance.

2. Technical Definition of Xylan Coating

Xylan is a family of fluoropolymer-based industrial coatings incorporating:

• PTFE (Polytetrafluoroethylene)
• FEP (Fluorinated Ethylene Propylene)
• PFA (Perfluoroalkoxy Alkane)
• MoS₂ lubricants
• Reinforced organic binders

The coating forms a thin-film engineered barrier providing:

• Corrosion resistance
• Dry lubrication
• Low friction coefficient
• Chemical resistance
• Anti-seize properties
• Reduced galling
• Controlled tightening performance

Typical coating thickness ranges:

Coating System	Typical Thickness
Single coat	20–30 microns
Two-coat system	25–50 microns
Heavy-duty offshore system	50–80 microns

3. Industrial Importance of Xylan Coated Fasteners

3.1 Offshore & Marine Systems

Salt-laden environments accelerate galvanic and crevice corrosion. Xylan coatings provide:

• Chloride resistance
• Salt spray durability
• Reduced seizure during maintenance
• Extended inspection intervals

Typical applications:

• Flange bolting
• Subsea connectors
• Valve assemblies
• Structural brackets

3.2 Oil & Gas Processing Facilities

Hydrocarbon facilities require controlled preload performance under elevated temperatures and corrosive media.

Xylan coatings help minimize:

• Thread galling
• Hydrogen-assisted corrosion
• Fastener seizure
• Maintenance downtime

Used in:

• Pressure vessels
• Heat exchangers
• Pipeline systems
• Compressor skids

3.3 Structural & Infrastructure Projects

Structural steel joints require reliable torque transfer and long-term atmospheric corrosion protection.

Xylan-coated assemblies are widely used in:

• Bridges
• Metro infrastructure
• Wind towers
• Transmission structures
• Coastal construction

4. Functional Role of Xylan Coated Fasteners

The fundamental role of a fastener is to create and maintain clamp load between assembled components.

Xylan coating improves fastening performance by influencing:

• Friction coefficient
• Torque consistency
• Clamp load repeatability
• Corrosion durability
• Installation efficiency

5. Load Mechanics in Bolted Joints

5.1 Clamping Force Principle

A bolted joint functions by converting tightening torque into preload.

The preload creates compressive force between joined components.

The relationship between torque and preload is approximated by:

$T = KFD$

Where:

• $T$ = tightening torque
• $K$ = nut factor
• $F$ = preload force
• $D$ = nominal bolt diameter

Xylan coatings significantly reduce the nut factor due to lower friction.

Typical nut factor values:

Surface Condition	Nut Factor (K)
Plain steel	0.20–0.25
Zinc plated	0.18–0.22
Xylan coated	0.10–0.16
PTFE coated	0.08–0.14

5.2 Torque–Tension Relationship

Lower friction increases preload consistency.

Advantages include:

• Reduced scatter in clamp load
• Improved assembly reliability
• Reduced overtightening risk
• Better gasket sealing integrity

This is especially critical in:

• Pressure-containing flanges
• Dynamic vibration systems
• Thermal cycling assemblies

6. Preload Calculation Example

Example

Given:

• Bolt size: M20
• Property class: 10.9
• Tensile stress area = 245 mm²
• Yield strength = 940 MPa
• Target preload = 70% of yield

Preload:

$F = 0.7 \times A_s \times S_y$$$F = 0.7 \times 245 \times 940$$

$$F = 0.7 \times 245 \times 940$$

Torque with Xylan coating:

Assume:

• K = 0.14
• D = 20 mm = 0.02 m

$$T = 0.14 \times 161210 \times 0.02$$

$$T \approx 451 \text{ Nm}$$

7. Joint Design Principles

7.1 Importance of Proper Joint Design

Fastener failures are often caused by poor joint design rather than inadequate bolt strength.

Critical design considerations include:

• Preload retention
• Joint stiffness
• Thermal expansion compatibility
• Vibration resistance
• Corrosion compatibility

7.2 Joint Stiffness Ratio

The stiffness ratio between the bolt and clamped material influences fatigue resistance.

Higher joint stiffness improves:

• Load sharing
• Vibration resistance
• Fatigue life

Xylan coatings assist by maintaining stable preload under cyclic conditions.

7.3 Thread Engagement Requirements

Recommended minimum engagement:

Material Combination	Minimum Engagement
Steel to steel	1 × diameter
Stainless steel	1.5 × diameter
Aluminum	2 × diameter
Cast iron	1.5 × diameter

8. Friction & Tribological Performance

8.1 Coefficient of Friction

Xylan coatings reduce friction significantly.

Typical dynamic friction coefficients:

Coating Type	Coefficient of Friction
Plain steel	0.50–0.80
Zinc plated	0.18–0.25
Xylan PTFE	0.08–0.15
MoS₂ dry film	0.05–0.12

8.2 Galling Prevention

Stainless steel fasteners are highly susceptible to galling.

Xylan coatings provide:

• Surface separation
• Lubrication
• Reduced adhesive wear
• Improved assembly repeatability

Commonly specified for:

• Austenitic stainless steel bolts
• Duplex fasteners
• Nickel alloy studs

9. Mechanical Behavior Under Service Loads

9.1 Tensile Loading

Tensile loads act parallel to the bolt axis.

The fastener must resist:

• Yielding
• Fracture
• Relaxation

9.2 Shear Loading

Shear forces act perpendicular to the bolt axis.

Joint performance depends on:

• Bolt diameter
• Shear plane location
• Material hardness
• Clamp load retention

9.3 Fatigue Loading

Fatigue is a primary cause of industrial fastener failure.

Caused by:

• Cyclic loading
• Vibration
• Thermal expansion cycles

Xylan coatings assist indirectly by improving preload consistency.

10. Failure Mechanisms in Xylan Coated Fasteners

10.1 Hydrogen Embrittlement

High-strength fasteners above 39 HRC are susceptible.

Risk increases during:

• Acid cleaning
• Electroplating
• Corrosive exposure

Xylan coatings themselves do not eliminate embrittlement risk.

Mitigation measures:

• Controlled baking
• Mechanical cleaning
• Non-electrolytic coating systems
• Hardness control

10.2 Stress Corrosion Cracking

Occurs in:

• Chloride environments
• H₂S service
• High tensile stress conditions

Critical for:

• Offshore structures
• Sour gas systems

Applicable standards:

11. Thermal Performance of Xylan Coatings

Typical operating limits:

Xylan Series	Temperature Range
Standard PTFE systems	-40°C to +150°C
High-temperature fluoropolymer	Up to +260°C
Specialty systems	Up to +315°C

12. Corrosion Resistance Mechanism

Xylan coatings protect through:

• Barrier protection
• Moisture isolation
• Chemical inertness
• Reduced galvanic interaction

Performance depends on:

• Surface preparation
• Coating thickness
• Cure quality
• Substrate material

13. Corrosion Resistance vs Environment

Environment	Carbon Steel	Zinc Plated	Xylan Coated	Duplex + Xylan
Coastal atmosphere	Moderate	Good	Excellent	Excellent
Offshore splash zone	Poor	Moderate	Very good	Excellent
H₂S environment	Poor	Poor	Good	Excellent
Acidic chemical exposure	Poor	Poor	Good	Excellent
High humidity	Moderate	Good	Excellent	Excellent
LNG cryogenic systems	Moderate	Moderate	Excellent	Excellent

14. Fastener Joint Reliability in EPC Projects

Critical EPC requirements include:

• Traceability
• Repeatable preload
• Corrosion durability
• International standards compliance
• Third-party inspection compatibility

Xylan-coated fasteners are widely accepted where:

• Controlled assembly torque is mandatory
• Anti-galling is required
• Extended maintenance intervals are critical

15. SM Fasteners Engineering Capability

SM Fasteners manufactures precision-engineered coated fastening systems for industrial and EPC applications using:

• Carbon steel
• Alloy steel
• Stainless steel
• Duplex & super duplex stainless steel
• Nickel alloys
• PEEK engineering polymers

Supported by:

• ISO 9001 quality systems
• MSME certification
• UKAF-aligned quality framework

Capabilities include:

• Custom coating systems
• Precision thread manufacturing
• Dimensional inspection
• Traceability control
• Export-oriented packaging systems

16. Summary — Engineering Significance

Xylan-coated fasteners provide a critical combination of:

• Corrosion resistance
• Controlled friction behavior
• Galling resistance
• Chemical durability
• Torque consistency

These characteristics make them essential in:

• Offshore engineering
• Oil & gas systems
• Structural steel
• Chemical processing
• High-reliability industrial assemblies

The engineering performance of the coating must always be evaluated alongside:

Base material properties

Joint design

Service environment

Torque control methodology

Applicable international standards

17. Product Types of Xylan Coated Fasteners

Xylan coating systems are applied across a wide range of industrial fastening products depending on load requirements, environmental exposure, assembly accessibility, and maintenance conditions.

Typical coated fastening products manufactured by SM Fasteners include:

• Hex Bolt
• Heavy Hex Nut
• Socket head cap screws
• Stud bolts
• Threaded rods
• Hex nuts
• Heavy hex nuts
• Lock nuts
• Washers
• Anchor fasteners
• Structural bolting assemblies
• U-bolts
• Custom-machined fasteners
• PEEK-coated and hybrid fastening systems

18. Hex Head Xylan Coated Bolts

Hex bolts are the most widely used industrial fasteners for structural and pressure-containing applications.

Functional Characteristics

• High torque transfer capability
• Easy field installation
• Compatible with hydraulic tensioning systems
• Suitable for heavy preload applications

Common Applications

• Pipe flanges
• Structural steel joints
• Pump assemblies
• Valve systems
• Heavy machinery

19. Heavy Hex Bolts

Heavy hex bolts provide increased bearing surface area and higher wrenching strength.

Advantages

• Better load distribution
• Improved resistance to head deformation
• Enhanced suitability for high-pressure joints

Common Standards

Standard	Description
ASTM A193	Alloy steel bolting for pressure service
ASTM A320	Low-temperature bolting
ASTM F3125	Structural bolting
DIN 6914	High-strength structural bolts

20. Socket Head Cap Screws

Used where compact assembly geometry or recessed installation is required.

Features

• High tensile capability
• Precision-machined heads
• Reduced external clearance requirement
• Suitable for automation systems

Typical Industries

• Aerospace support systems
• Precision machinery
• Automotive systems
• Robotics
• OEM equipment

21. Stud Bolts

Stud bolts are extensively used in flange connections and pressure-retaining assemblies.

Configuration

Fully threaded rods with nuts on both ends.

Benefits

• Uniform clamping force
• Easier flange alignment
• Better load distribution
• Simplified maintenance replacement

Common Standards

Standard	Description
ASTM A193 B7	High-temperature alloy steel stud bolts
ASTM A320 L7	Low-temperature bolting
ASTM A453	Stainless bolting
DIN 976	Threaded studs

22. Threaded Rods

Threaded rods are used for:

• Structural suspension
• Pipe support systems
• Embedded anchoring
• Equipment mounting

Xylan-coated threaded rods are preferred in corrosive outdoor environments and chemical processing plants.

23. Xylan Coated Nuts

Nuts are coated either independently or as matched assemblies with bolts.

Key Engineering Requirement

The coating friction coefficient between nut and bolt must remain controlled and repeatable.

Improper coating thickness can affect:

• Thread fit
• Torque values
• Clamp load accuracy

24. Washer Configurations

Washers are essential for:

• Load distribution
• Surface protection
• Joint relaxation control
• Electrical isolation

Common Types

Washer Type	Function
Flat washer	Load distribution
Spring washer	Vibration resistance
Hardened washer	Structural preload support
Belleville washer	Controlled spring preload
Insulating washer	Electrical isolation

25. Structural Fastener Assemblies

Structural assemblies generally include:

• Bolt
• Nut
• Hardened washers

Used in:

• Bridges
• Wind towers
• Transmission structures
• Industrial steel frames

Typical standards:

Standard	Description
ASTM F3125	Structural bolting
EN 14399	High-strength preloaded assemblies
DIN 6914/6915	Structural bolting systems

26. PEEK Hybrid Fastening Systems

PEEK (Polyether Ether Ketone) fasteners are increasingly used in specialized industrial systems where:

• Electrical insulation is required
• Weight reduction is critical
• Chemical resistance is necessary
• Non-metallic fastening is preferred

Applications include:

• Semiconductor systems
• Electrical assemblies
• Chemical processing equipment
• Cryogenic systems

SM Fasteners supports advanced material fastening solutions including PEEK fasteners and coated hybrid assemblies.

27. Fastener Geometry Fundamentals

Fastener geometry directly affects:

• Clamp load
• Stress concentration
• Fatigue resistance
• Installation torque
• Joint stiffness

Critical geometric elements include:

• Head dimensions
• Shank diameter
• Thread profile
• Pitch
• Bearing surface
• Fillet radius

28. Thread Geometry Principles

28.1 Thread Pitch

Thread pitch determines axial movement per revolution.

Metric Threads

Pitch measured in millimeters.

Example:

• M20 × 2.5
• M16 × 2.0

Unified Threads

Threads per inch (TPI).

Example:

• 3/4″-10 UNC
• 3/4″-16 UNF

28.2 Coarse vs Fine Threads

Parameter	Coarse Thread	Fine Thread
Assembly speed	Faster	Slower
Stripping resistance	Higher	Moderate
Vibration resistance	Moderate	Better
Tensile stress area	Lower	Higher
Galling tendency	Lower	Higher
Preferred application	Structural	Precision/mechanical

29. Metric Thread Standards

Metric threads comply primarily with ISO standards.

Applicable Standards

Standard	Scope
ISO 261	Metric thread series
ISO 262	Preferred metric combinations
ISO 965	Thread tolerances
ISO 68-1	Basic thread profile
ISO 724	Basic dimensions

30. Unified Thread Standards

Unified threads are widely used in North American industrial systems.

Thread Series

Thread Type	Description
UNC	Unified National Coarse
UNF	Unified National Fine
UNEF	Extra fine
8UN	Large-diameter pressure service

Applicable Standards

Standard	Description
ASME B1.1	Unified inch threads
ASME B18 series	Fastener dimensions

31. British Thread Standards

British thread systems remain common in maintenance and legacy infrastructure.

Thread Standard	Description
BSW	British Standard Whitworth
BSF	British Standard Fine
BSP	British Standard Pipe

32. Thread Tolerance Classes

Thread tolerance controls:

• Assembly fit
• Coating allowance
• Load distribution
• Interchangeability

Metric Thread Classes

Internal Thread	External Thread	Fit Type
6H	6g	Standard industrial fit
5H	4h	Precision fit
7H	8g	Loose fit

33. Thread Standards & Tolerances Table

System	Standard	External Class	Internal Class	Typical Application
Metric ISO	ISO 965	6g	6H	General industrial
Unified UNC	ASME B1.1	2A	2B	Structural
Unified UNF	ASME B1.1	3A	3B	Precision
BSW	BS 84	Medium fit	Medium fit	Legacy systems
BSF	BS 84	Fine fit	Fine fit	Mechanical systems

34. Fastener Head Configurations

Common Head Types

Head Type	Engineering Use
Hex head	Heavy industrial
Heavy hex	Structural/high preload
Socket head	Compact assemblies
Countersunk	Flush surfaces
Button head	Low-profile installations
Stud	Flanged joints

35. Dimensional Logic in Fastener Selection

Key dimensional parameters:

• Nominal diameter
• Grip length
• Thread length
• Head height
• Across flats dimension
• Bearing area

These dimensions influence:

• Load transfer
• Joint stiffness
• Installation access
• Tool compatibility

36. Metric Hex Bolt Dimensions

ISO 4014 / ISO 4017 Reference Dimensions

Size	Pitch	Head Width (s)	Head Height (k)	Standard Length Range
M6	1.0	10 mm	4 mm	10–80 mm
M8	1.25	13 mm	5.3 mm	16–120 mm
M10	1.5	16 mm	6.4 mm	20–150 mm
M12	1.75	18 mm	7.5 mm	25–200 mm
M16	2.0	24 mm	10 mm	30–300 mm
M20	2.5	30 mm	12.5 mm	40–400 mm
M24	3.0	36 mm	15 mm	50–500 mm
M30	3.5	46 mm	18.7 mm	70–600 mm

37. UNC Thread Dimensions

Nominal Size	Threads Per Inch	Across Flats	Typical Applications
1/4″-20	20	7/16″	General machinery
3/8″-16	16	9/16″	Structural/mechanical
1/2″-13	13	3/4″	Heavy equipment
5/8″-11	11	15/16″	Pressure systems
3/4″-10	10	1-1/8″	Pipeline flanges
1″-8	8	1-1/2″	Heavy industrial

38. Dimensional Considerations for Xylan Coating

Coating thickness affects:

• Pitch diameter
• Thread engagement
• Assembly fit

Engineering compensation may include:

• Oversized tapped holes
• Controlled coating thickness
• Post-coating gauging

39. Coating Build-Up Control

Typical maximum coating buildup:

Thread Size	Recommended Coating Thickness
M6–M12	20–25 microns
M16–M24	25–40 microns
M30+	40–60 microns

40. Mechanical Property Classes

ISO Property Classes

Property Class	Tensile Strength	Yield Ratio
8.8	800 MPa	0.8
10.9	1000 MPa	0.9
12.9	1200 MPa	0.9

41. ASTM Fastener Grades

ASTM Grade	Material Type	Application
A193 B7	Alloy steel	High temperature
A320 L7	Low temperature
A193 B8	Stainless steel
A453 Gr 660	High-temperature stainless
F3125 A325	Structural steel
F3125 A490	High-strength structural

42. Proof Load & Tensile Strength Table

Size	Grade/Class	Proof Load (kN)	Ultimate Tensile Load (kN)
M12	8.8	61	84
M12	10.9	86	104
M16	8.8	113	157
M16	10.9	159	196
M20	8.8	176	245
M20	10.9	248	306
M24	8.8	253	353
M24	10.9	357	441

43. Structural Bolting Standards

EN Structural Standards

Standard	Description
EN 14399	High-strength preloaded assemblies
EN 15048	Non-preloaded structural assemblies

ASTM Structural Standards

Standard	Description
ASTM F3125	Structural bolts
ASTM F436	Hardened washers
ASTM A563	Structural nuts

44. Pressure Vessel & Piping Standards

Xylan-coated fasteners are frequently specified in pressure-containing systems.

Applicable standards:

Standard	Scope
ASME B16.5	Pipe flanges
ASME PCC-1	Bolted flange assembly
API 6A	Wellhead systems
API 17D	Subsea equipment
MSS SP-44	Pipeline flanges

45. Offshore & Sour Service Requirements

Applicable Standards

Standard	Relevance
NACE MR0175	Sour service material control
ISO 15156	H₂S environments
ASTM G48	Pitting corrosion testing
ISO 9227	Salt spray testing

46. Dimensional Inspection Requirements

Critical dimensional checks include:

• Major diameter
• Minor diameter
• Pitch diameter
• Thread angle
• Head dimensions
• Straightness
• Concentricity

Inspection tools:

• GO/NO-GO gauges
• Optical comparators
• Coordinate measuring machines (CMM)
• Micrometers
• Thread ring gauges

47. Interchangeability Considerations

Industrial projects frequently involve mixed-standard systems.

Engineering review is required for:

• Metric vs inch conversion
• Head geometry differences
• Thread pitch compatibility
• Torque value adjustments
• Coating thickness allowances

Incorrect interchangeability can cause:

• Galling
• Thread failure
• Clamp load reduction
• Leakage

48. Torque Tightening Considerations

Torque values vary depending on:

• Coating friction coefficient
• Lubrication
• Surface finish
• Thread condition
• Fastener grade

Xylan-coated fasteners typically require lower torque compared with zinc-plated or plain steel fasteners.

49. Tightening Torque Chart

Approximate Torque Values for Xylan-Coated Metric Bolts

Size	Class 8.8	Class 10.9	Lubrication Condition
M8	18 Nm	26 Nm	Xylan coated
M10	36 Nm	52 Nm	Xylan coated
M12	62 Nm	88 Nm	Xylan coated
M16	152 Nm	214 Nm	Xylan coated
M20	300 Nm	430 Nm	Xylan coated
M24	520 Nm	740 Nm	Xylan coated
M30	1030 Nm	1450 Nm	Xylan coated

Actual field torque values should always be validated using project-specific preload requirements and calibrated tightening procedures.

50. Weight Chart for Industrial Fasteners

Approximate Weight Table — Hex Bolts

Size × Length	Weight per Piece	Weight per 100 pcs
M10 × 50	0.039 kg	3.9 kg
M12 × 60	0.067 kg	6.7 kg
M16 × 80	0.158 kg	15.8 kg
M20 × 100	0.312 kg	31.2 kg
M24 × 120	0.540 kg	54.0 kg
M30 × 150	1.020 kg	102.0 kg

Weight alignment is important for:

• Export logistics
• EPC quantity estimation
• Container optimization
• Offshore lifting calculations

SM Fasteners supports customized dimensional and weight requirements for project-specific procurement packages.

51. Engineering Summary

Product geometry, thread standards, dimensional tolerances, and mechanical classifications collectively determine the reliability of Xylan-coated fastening systems.

Proper engineering selection requires evaluation of:

• Service environment
• Mechanical loading
• Torque requirements
• Corrosion exposure
• International standards compatibility
• Coating thickness interaction with thread tolerances

In industrial EPC and OEM applications, coated fastener assemblies must be treated as precision-engineered systems rather than