Corrosion of B7 Studs
Corrosion of B7 Studs
(OP)
Good Afternoon,
I have attached a picture for reference. We supply ASTM A193-B7 studs that are Zinc Yellow plated to a customer who uses them to build a compressor. The studs are corroding quicker than expected. The flanges that these studs bolt up, are made of stainless steel so I suspect that galvanic corrosion is taking place. Would this be correct? The unit is located in-doors so it is away from outside elements. I asked my customer how long the studs have been in service and he guessed a couple of years, but if the unit is in-doors, corrosion on a plated stud should not happen this fast. We have B7, Zinc Plated studs that sit on our shelves for years that don't show any corrosion. Should I try to convince my customer to move to stainless steel studs? Any insight would be greatly appreciated!
I have attached a picture for reference. We supply ASTM A193-B7 studs that are Zinc Yellow plated to a customer who uses them to build a compressor. The studs are corroding quicker than expected. The flanges that these studs bolt up, are made of stainless steel so I suspect that galvanic corrosion is taking place. Would this be correct? The unit is located in-doors so it is away from outside elements. I asked my customer how long the studs have been in service and he guessed a couple of years, but if the unit is in-doors, corrosion on a plated stud should not happen this fast. We have B7, Zinc Plated studs that sit on our shelves for years that don't show any corrosion. Should I try to convince my customer to move to stainless steel studs? Any insight would be greatly appreciated!
Greg
System 22, Inc.





RE: Corrosion of B7 Studs
RE: Corrosion of B7 Studs
However, the picture is not quite clear, how could any moisture get to close-up a galvanic circuit, to initiate the galvanic corrosion. In some cases, the poor electrolytic galvanizing could start a separate corrosion process on the thread, weather the galvanic corrosion is normally localized to the contact area with the large mass of stainless steel (inside the bolt hole). Nevertheless, I would also look for the source of moisture and signs of condensation on metallic surfaces.
Cheers,
gr2vessels
RE: Corrosion of B7 Studs
RE: Corrosion of B7 Studs
Petrotrim Services
www.petrotrim.com
RE: Corrosion of B7 Studs
Look for (galvanic) corrosion on the link:-
http://www.bssa.org.uk/topics.php?article=95
RE: Corrosion of B7 Studs
Could the bolts be corroding even before they are installed ?
Also, I disagree with gr2vessels who claims the general rule stated above that "B7 studs should never have been used"
According to both NORSOK guidelines and PIP piping standards, B7 studs are acceptable for use on stainless steel flanges.
RE: Corrosion of B7 Studs
RE: Corrosion of B7 Studs
RE: Corrosion of B7 Studs
Consider somebody washing the floor every nightshift with chlorox or a bleach solution. A spill three months ago of sulfuric acid that was wiped off, but got in and around the bolts.