Stainless steel tube 2

[prc]

I want to use 25 mm and 15 mm OD stainless steel tubes as air release pipe in transformers.Inside transformer oil at 80C.Shall withstand vacuum and positive pressure max 1 bar.Quality wanted is rust proofness.At ends normal mild steel flanges will be welded to stainless steel tubes.

1) What grade and thickness of SS is most appropriate?

2) What type of welding /electrodes to be used ?or flanges also should be SS?I thought of ordinary steel to reduce overall cost.

 

[desertfox]

Hi prc

To withstand the positive pressure, a pipe of 26.67mm OD with a schedule 5S wall thickness (1.651mm) should suffice for that purpose and a 13.7mm OD with a schedule 10S wall thickness (1.651mm) for the smaller tube.
Sizes can be found at this link:-

http://www.engineeringtoolbox.com/asme-steel-pipes-sizes-d_42.html

For the vacuum however its a bit different because depending how long the tube or pipes are they may fail by buckling, so we would need details of the length of tube and how both ends are supported.
Welding electrodes could be sought from this site however any good pipe/vessel workshop will know which to use.
Again here this site should give you the stainless grade for flanges and pipe etc however I would say Stainless 316L is a good choice for corrosion.
Having said all that wouldn't the breather pipes come under the design specifications of the transformer which is what you really should be working to?

desertfox

 

[prc]

Thank you desert fox.I thought 316 L is costlier grade than the magnetic stainless steels.In transformer industry we are always under price pressure!
Pipe is supported closely may be 1-2 metres and normally vacuum will not be a problem.
Well breather pipe also can be of stainless steel.

 

[HEC]

prc,
welding the mild steel flanges to teh end of a ss pipe will negate any corrosion resistance in the area of the weld. What is the environment that requires SS? Would you also need a non magnetic material to reduce eddy currents? Forgive the last uninformend comment!

Mark Hutton

 

[strider6]

at 80°C stainless steel can have some problem of SCC if exposed to atmosphere with high conc of chlorides (marine atmosphere), in that case you need to provide a good coating.

if it's not exposed to agressive atmosphere SS316l is a good solution.
welding SS to CS is not a problem but if you can avoid it then it will be better also you'll avoid any issue of galvanic corrosion .


S

Corrosion Prevention & Corrosion Control

 

[prc]

Dear all, the reason why I am looking for SS is not due any corossive environment etc.Normal steel tubes can have rust inside and when not properly treated and then painted,paint flakes with rust can get inside transformer.To avoid this SS is a solution.Eddy current is not a big issue and hence non-magnetic steel is not essential.
Now I understand 316L is the best solution and flanges also to be SS.I plan to use without any painting.
Thank you all

 

[EdStainless]

The simple way would to be to use some sch 10S 304L pipe, weld it to the steel flanges with 309 filler, and prep and paint the outside like you always do leaving the inside bare metal.
While it is possible that there could be some corrosion the chances are very slim that there will be anything inside the unit that will hurt the 304.

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Plymouth Tube

 

[HEC]

Based on the additional information, have to agree with Ed. As always spot on.

Mark Hutton