Zinc Nickel PTFE Xylan Coated Fasteners, Stud Bolts & Screws

Stud Bolts, Nuts, Screws, Threaded Rod & Washers

This Specification outlines the requirement for Bolt and nut coating for onshore and offshore oil and gas facilities including subsea applications.
We at Torqbolt provide the following detailed coating system of Stud Bolts and Nuts operating at temperature below 200°C:
Basecoat( First Coat) which provides resistance of Zinc Nickel Plating as per ASTM B841/F1941 or ISO 4042/10576 with an average thickness of 10-18µm.
TopCoat ( Second Coat) PTFE POLY TETRA FLUORO ETHYLENE based Whitford Xylan coating namely Xylan 1014, Xylan 1070, Xylan 1424 or Dupont Teflon 174 SBC
We hereby suggest to used the above specified combination of base coat and top coats for the following grades

Recommended Base Coats & Top Coats

Surface Preparation

Mechanical cleaning and /or chem ical treatments shall be used to produce a satisfactory surface for subsequent plating/ deposition and finish coating, i.e. free from soils, environmental matter, drawing compounds, oil grease, discolouration oxides, scale and other foreign matter. Materials used for cleaning shall have no damaging effects on the base metal. Surface Preparation Of Zinc Nickel Plating shall comply to ASTM B322 and B183 and must include the following

  • Over Tapped Nuts
  • Degreasing and/or water rinsing
  • Acid Pickling and/or water rinsing
  • Abrasive Blasting and water rinsing

Coating System

Basecoat Zinc Nickel Plating

Zinc Nickel alloyed coating deposited from an alkaline; cyanide free; electrolyte shall have a composition of the coating to be in the range of 12-18% Nickel balance being Zinc. The bolting materials coated with Zinc Nickel alloyed coating shall be phosphate treated in accordance with ASTM D 2092, Method A (12-18 µm) or equal. The phosphate treatment is to ensure basecoat is adherent to topcoat . The general plating process shall be as per below:

  • Zinc Nickel Plating
  • Visual Inspection
  • Rinsing
  • Phosphate conversion treatment
  • Rinsing and drying
  • Inspection and testing
Note: Chromate (instead of phosphate) conversion treatment is required for stud bolts and nuts with only Zinc Nickel plating.

PTFE Based Top Coat

A PTFE based coating shall be applied as secondary coating corrosion barrier and to reduce torque-up friction during installation. The general coating process shall be as per below:

  • Conventional spray
  • Baking (oven cured)
  • Inspection and testing
Ideal choice of colour depends on the user however we suggest
Blue for High temperature & Green for Low temperature for Carbon steel fasteners & Red / Black for Stainless steel fasteners
This specification covers requirements for zinc-nickel coating, colourless passivated without hexavalent chromium (chromium VI), deposited from an alkaline cyanide-free electrolyte and applied to fasteners like stud bolts, nuts, washers, screws & hex bolts to protect them from corrosion.
Electroplating, as specified here after, shall be used where heavy corrosion protection is required. Moreover, zinc-nickel alloy coating shall be used for components directly exposed to temperature stress in addition to heavy corrosion. It describes an alkaline zinc-nickel coated fasteners highly used in automotive industry to provide corrosion protection. This technical deposit allows excellent corrosion resistance with good adhesion of the coating on the base metal and excellent stability up to 250 °C. Hardness and wear resistance of this deposit are roughly four times higher than a pure zinc coating.