alloy steel bolting and that hot dipped spun galvanised bolting has provided better corrosion protection at reduced cost. Bolts can be supplied with a variety of surface treatments. The common options are:
Type
Standard
Minimum Thickness
Zinc and Cadmium Electroplate
BS 1706
8 mm
PTFE Coating + Phosphate
-
30 mm PTFE
PTFE Coating + Electroplate (Zn or Cd)
-
30 mm PTFE / 8 mm Zn/Cd
Sheradising (Barrelled in Hot Zinc Dust)
BS 4921 Class 1/2
30 mm / 15 mm
Spun Galvanised (Dipped in Molten Zinc)
BS 729
43 mm
Note that bolts with different coatings require different torque values to achieve the same bolt tension. It is therefore important not to mix studbolts with different coatings on a given flange, as it will be difficult to achieve a uniform bolt tension on all the studbolts. Full procedures are available on bolt tightening and should be consulted. A Note of Warning: Cadmium plated components give off toxic fumes when heated to sufficiently high temperatures. Therefore, heat should not be applied to release tight bolts. Furthermore, gloves should be worn when handling cadmium plated components to prevent skin abrasions.
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03000785, May 2000