welding 8mm SS316L pipe

Hi, We want to close one end of a 8mm dia pipe, 1mm thick, SS316L to be inserted in car battery acid.

We plugged one end of pipe with a SS316L insert keeping it 2mm above the pipe and Tig welded it by fusion (no filler used).

It covered the pipe end fully. However, every time we receive complaint that the 'cap' falls off after 1-2 months whereas there is not corrosion observed on pipe.

They say SS316L ia their trusted material for sulpuric acid used in a car battery. I used Carpenter alloy 20, one of the best material for sulphuric acid service. But complaint persisted.

I now fear something wrong in our welding process. Can you please guide me if I am doing anything wrong? Thanks.

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It seems that the corrosion attacks only the cast microstructure of the weld metal.

you may have to add filler metal in order for the weld metal to last long enough in service.

many times when fusion welds like this are done, there is a very small cross sectional thickness of the weld.

any stress corrosion cracking will cause the weld to fail because the weld is insufficient in the first place.

hope this helps,

jody