Hot dipped galvanised bolts? really?.... 9

[Thedraffy]

One of the design engineers (the lead) in the office has made a change to a set of drawing notes to the tune of: BOLTS AND WASHERS TO BE ZINC NICKEL ELECTROPLATED and replaced this with HOT DIPPED GALVANISED...

Am I correct in saying that bolts are not actually hot dipped galvanised... as they would be covered in a thick layer of zinc and the nut would not fasten?

that’s why bolts that require a "galvanised" finish are electroplated.... i.e. a thin layer of zinc is bonded to the bolt surface.

Cheers,

The Draffy

TheDraffy

 

[SJones]

No. You are not correct. Consult BS 7371-6 and ASTM F2329 amongst others.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

 

[Thedraffy]

Thanks Steve,

Appreciated

C


TheDraffy

 

[TVP]

To add to Steve's comments, structural applications frequently use thick hot dip galvanized coatings. The nuts are overtapped to accommodate for the increased coating thickness. Standards such as ISO 965-5 have been created to address this (tolerance class 6AZ).

http://www.modernsteel.com/Uploads/Issues/June_2011/062011_June11_Bolting_web.pdf

http://www.galvanizeit.org/images/u...nces_for_Galvanized_Fasteners.pdf?tracked=yes

 

[TomDOT]

Some of the structural guys have started pushing for mechanically galvanized bolts instead of hot-dip for more reliable tensioning. I prefer hot-dipped for the improved corrosion protection versus mechanically galvanized. Mechanical galvanizing is a porous coating, while hot-dip is effectively solid.

Zinc plating is typically very thin and provides minimal corrosion protection.

 

[dvd]

There are several issues associated with hot-dip galvanized structural bolts.

This Specification addresses many:

http://www.boltcouncil.org/files/2009RCSCSpecification.pdf

Avoiding hot-dip galvanized A-490 bolts is important.