Shims between CS baseplate and SS Pump 1

[adula29]

I have a question. It is necessary to use shims between carbon steel baseplate and stainless steel pump?
API610 (p.7.3.6.) there is that shims shall not be use under the pump, but what if there is a difference of potential between this two materials.

 

[EdStainless]

If this is dry there is no risk of corrosion, if it is wet fix the leaks.
There is almost nothing that you can use that is non-conductive and rigid enough to make a good shim.

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P.E. Metallurgy

 

[TugboatEng]

Provided the new baseplate and pump feet are reasonably flat and smooth, the clamp force of the bolts will exclude water and prevent corrosion between the baseplate and pump. The rest of the baseplate will waste away but under the pump will be just fine.

I have seen an intriguing idea lately. A stainless steel tape is applied prior to painting the metal. This protects the corrodable metals and eliminates a lot of mess during disassembly and assembly. I have only seen it to protect gasketed surfaces but could possibly work under a foundation.

 

[adula29]

But what if the pump is installed in a coastal zone where the risk of corrosion arises from vapors sea salt in the atmosphere

 

[EdStainless]

Then you should be using a composite or SS base plate.
In coastal areas though 304 and 316 SS will eventually rust and pit unless they are regularly washed with fresh water (like rain).
Just make sure that you don't paint SS unless you plan on doing a fantastic job, bad paint will accelerate corrosion in any material.

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P.E. Metallurgy

 

[Tmoose]

A creepy rust preventative like LPS 3 is pretty good at protecting assembled faying surfaces.

 

[kingnero]

I have no practical experience with this, so take this idea with a grain of salt (pun not intended):
Assuming the pumps get revised/checked regularly, would using aluminum shims (which are anodic to both carbon and stainless steel) be an option? These would corrode the most, leaving both the base plate and the pump feet in a relatively well condition, and those cost nearly nothing to replace yearly (or during each maintenance operation - preventative or as necessary) ?

 

[TugboatEng]

You would not want to use a "sacrificial" shim. They swell as they corrode and could affect the alignment of the system.

If the surfaces are reasonably flat and the bolts tight there usually isn't any corrosion of the mating surfaces. The trouble is that the paint chips on the edges of the shim and you get corrosion around the shimmed areas. This adds much time to maintenance as any time the joint is disturbed you have to descale and repaint.

 

[MJCronin]

As always, EdStainless gives good advice !!!

MJCronin
Sr. Process Engineer

 

[0707]

I agree with EdStainless.

luis marques

 

[DAVIDSTECKER]

Look at a product called "Chockfast".
It is an epoxy grouting system for machinery.

 

[GetAtMeWolf]

You won't see issues so long as the area isn't wetted. I've worked in an offshore environment with stainless steel pressure vessels bolted to carbon steel support legs which did see corrosion but even in that very long process, galvanic corrosion cells were readily apparent and were easily arrested by re-coating the area. Worst-case scenario, install a shroud around the connection point and you should be ok.