Hot Dip Galvanizing reduces strength by 20%?

[durablack2]

Any basis in this claim? I am aware HD Galvanizing can cause hydrogen embrittlement but does it reduce overall strength of 'smaller' steel parts by 20%? By 'smaller' I mean 1/2" to 1" diameter rod or bolts.

 

[swall]

How would HD galvanizing cause hydrogen embrittlement?

 

[TugboatEng]

The metal is exposed to acid during the pickling step.

 

[blacksmith37]

Hot dip galvanizing is done about 800 F ;
depending on the condition of the steel it could temper to a lower strength. The high temperature and following slow cool will bake out ( or reduce to low level ) any hydrogen in the steel

 

[mk3223]

but does it reduce overall strength of 'smaller' steel parts by 20%? By 'smaller' I mean 1/2" to 1" diameter rod or bolts.

not sure about the percentage of the lower strength will be. But, as for the HDG bolting and nut, some extra material need to be trimmed to accommodate the thick HDG layer. IMO, it may be resulted in the lower strength of the HDG bolting parts.

 

[kingnero]

HDG should not be done on high-strength steels (10.9 bolts and above) unless the process is very well under control.
Hydrogen embrittlement is a possibility, cracking due to picking up Zn in the base material is another one.

This reduces the strength of the base material to zero if cracking occurs. Haven't ever heard of the 20% reduction.

 

[durablack2]

Thanks everyone. Perhaps the 'tempering' effect due to high temp at which galvanizing is done at (as blacksmith mentioned) is what has caused a strength reduction in the past on this particular part (150ksi tensile and about 5/8" diameter. My boss has a lot of experience and is usually right about these kind of things but his scientific explanation is not always spot on.

 

[ATSE]

For mild steel and HSLA and fasteners up to about 120 ksi tensile, AISC (structural steel) recognizes no appreciable strength reduction. HD galv fastener structural capacity and black steel capacity for A325 grade bolts (similar to grade 5) are identical.