Galvanic corrosion in lifting lug joint

[vessexst]

Hello,

My vendor is welding a A 36 lifting on a vessel made of SA 240 316L. The pad material used for the same lug is SA 240 316L. However, the weld joint between lifting lug and pad is a CS to SS joint. The vessel is not painted and is insulated. I want to ask if there is chance of galvanic corrosion in this joint since it is for lifting lug so there will be no electrolyte (vessel working fluid) in continuous contact with lifting lug. The service is wet sour. The air moisture may not come in contact with it since the vessel is insulated.
However, I am confused if I should ask the vendor to change the material to SS for lifting lug or not? Suggestions required

 

[r6155]

Horizontal or vertical vessel?

Regards

 

[SJones]

Don't be so sure that the insulation will keep things dry. Try looking at API RP 571, subsection 4.3.3. and thinking about the required life of the lug.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[Dhurjati Sen]

Dear vessexst,

Go for SS lugs. Incorporate that in the drawing Bill of Materials.

How much would those cost and how difficult would it be to procure those?

You may have a problem after 10 years of service, expecting a service life of 25 years for the vessel.

It might be a general corrosion of the CS lugs which might call for their replacement and you would require a shutdown for that.

Why get into such situations which are entirely avoidable at the time of construction?

Regards.

DHURJATI SEN
Kolkata, India

 

[mk3223]

Suggest to file verify what's the condition of the lifting lug on other vessels in your plant before changing CS to SS material if needed.
IMO, it's acceptable to have a CS lifting lug welded on the SS pad. Once installed the vessel in place, there is no use for the lifting lug. If need to be used in the future, the lugs should be inspected before lifting. Or, if the CUI is a concern, may consider to paint the CS/SS material under the insulation.

 

[r6155]

Horizontal PV?: avoid lifting lugs on shell, you can install lifting lugs on sadlles. Best design is with slings.
Always with spreader bar.

Regards

 

[CuMo]

One should consider the cost of stainless steel lugs vs the cost of a PQR for dissimilar materials.
It might be cheaper to use stainless steel lugs and save yourself the hassle.