Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Re: A490 bolts

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Javier,
 
As Mr. Hunt and Mr. Getaz have so rightly expressed, the prohibition on plating/coating of A490s is attributable to concern over hydrogen-embrittlement or hydrogen-assisted stress-corrosion cracking.
 
That said, there is a program which is under development which may enable one to qualify coatings/platings for use on A490 bolts.  This effort I believe was initiated by the Industrial Fasteners Institute (IFI) and has benefited from input from ASTM and Research Council members.
 
The effort got under way as an attempt to accommodate the willingness of the suppliers of "Dacromet" (a common product used in automotive applications) who wished to undergo whatever test regimen would be necessary to qualify their coatings for use on structural bolts of all strength levels.
 
The documents we have historically relied upon at ASTM in support of the ban are not completely clear with respect to whether the problems associated with coated and plated A490s were largely due to acid pickling practices, the service environments, or a combination.  Material susceptibility is another factor.  And, of course, stress is a big factor as well. 
 
Were it not for the fact that we tighten structural fasteners into yield, we might get away with plating this strength level of fasteners just as the automotive industry does with their Grade 8 fasteners.  (Theirs are typically only tightened to between 75% and 85% of yield, depending upon the OEM.)
 
David Sharp
TurnaSure LLC 
----- Original Message -----
Sent: Tuesday, October 15, 2002 9:19 PM
Subject: A490 bolts

Does anybody know why galvanizing A490 bolts is not allowed? Also, what measures are usually taken to protect these bolts against corrosion?
 
Javier Encinas
Encinas & Associates