Corrosion of bolts on pump casing
Corrosion of bolts on pump casing
(OP)
Hello all,
We have 4140 bolts on a SDSS pump casing on an offshore installation. A concern was raised regarding the possibility of galvanic corrosion occurring between the bolts and casing due to the high humidity and marine environment.
My understanding is that galvanic corrosion initiates in the presence of an electrolyte (i.e. very high humidity will not initiate galvanic coupling). Perhaps atmospheric corrosion of the bolts is the actual concern.
Moreover, a proposition was made to galvanize the bolts. My understanding is that hot dip galvanizing 300 grade stainless steels is not a good idea as it will peel off. How about galvanizing 4140?
Appreciate your thoughts,
midris
We have 4140 bolts on a SDSS pump casing on an offshore installation. A concern was raised regarding the possibility of galvanic corrosion occurring between the bolts and casing due to the high humidity and marine environment.
My understanding is that galvanic corrosion initiates in the presence of an electrolyte (i.e. very high humidity will not initiate galvanic coupling). Perhaps atmospheric corrosion of the bolts is the actual concern.
Moreover, a proposition was made to galvanize the bolts. My understanding is that hot dip galvanizing 300 grade stainless steels is not a good idea as it will peel off. How about galvanizing 4140?
Appreciate your thoughts,
midris





RE: Corrosion of bolts on pump casing
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RE: Corrosion of bolts on pump casing
According to API 610, the use of 4140 is allowed 'unless otherwise specified' in spite of showing SDSS as the first choice. Looks like there was no otherwise. 4140 is used for B7 bolts and that is routinely galvanised.
Steve Jones
Corrosion Management Consultant
http://www.linkedin.com/pub/8/83b/b04
All answers are personal opinions only and are in no way connected with any employer.
RE: Corrosion of bolts on pump casing
Galvanizing carbon steel bolts can be a good choice, but not if it is in contact with stainless steel. Either use a stainless steel alloy for the bolts or use a non-metallic coating like those provided by Xylan or Magni.
RE: Corrosion of bolts on pump casing
Steve: thanks for shedding light on the issue of galvanic corrosion in this application. Would you therefore suggest coating the galvanized 4140 bolts as a preventive measure against galvanic corrosion?
cloa and CoryPad: I have forgot to mention that coating the bolts with Xylan or Takecoat as with the carbon steel bolts has been considered. Thanks for your suggestions.
RE: Corrosion of bolts on pump casing
Steve Jones
Corrosion Management Consultant
http://www.linkedin.com/pub/8/83b/b04
All answers are personal opinions only and are in no way connected with any employer.
RE: Corrosion of bolts on pump casing
RE: Corrosion of bolts on pump casing