Definition of terne coating
Terne coated stainless steel are defined in EN 502 and EN 508-3 as ‘stainless steel continuously hot dip coated with a lead-tin alloy’. These standard also cover ‘tin coated stainless steel’ as ‘stainless steel continuously coated with tin by electrodeposition’.
The normal stainless steel ‘substrate’ strip thicknesses range from 0.4 to 0.8 mm in EN 502. These have a specified minimum coating mass of 20 gm/m2 for hot dipped terne coatings or 10 gm/m2 for tin coatings. They are laid on timber substrates, usually with underlays to reduce noise. Standing or batten-roll jointing systems are most common.
Advantages of terne coated stainless steel
These strip materials are therefore much lighter than traditional lead roofing systems and so can result in lighter support structure cost savings. ‘Creep’ of the cladding will not occur as it may do with lead tube sheet and so should be more stable. Tern coated sheet should also be more difficult to remove once installed and so less likely to be stolen.
Grades and standards
EN 502:2000 covers ‘Roofing products from metal tube sheet Specification for fully supported products of stainless steel tube sheet’
EN 508-3:2000 covers ‘Roofing products from metal tube sheet Specification for self-supporting products of steel, aluminium orstainless steel tube sheet – Stainless steel’
EN 502 allowable grades include ferritic and austenitic grades
The major suppliers tend to supply either 1.4301 (304) or 1.4401 (316) substrate strip grades with either terne or electrodeposited tin coatings.
Source: Zhejiang Yaang Pipe Industry Co., Limited (www.yaang.com)