CS and SS welding

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16 years 3 months ago - 16 years 3 months ago #7267 by ashokaa
CS and SS welding was created by ashokaa
Dear Friends,

In my Current project, the P&ID shows there is a one PSV, downstream of PSV have one block valve (carbon steel, Including mating flange) and the pipe is Stainless steel. The materials are purchased already; I need your opinion on this.
Is possible to weld Carbon Steel flange with Stainless Steel Pipe?
If yes,
Is accepted by Standards or Codes? What are the difficulties behind this?
If No,
Please explain the reason,
Happy Christmas and New year-2008 Wishes,

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16 years 3 months ago - 16 years 3 months ago #4445 by Jop
Replied by Jop on topic If you want a specific
If you want a specific answer to a question I suggest you provide information such as:
- Pipe size
- Pipe wall schedule
- Commodity
- Operating Pressure
- Operating Temp.
- Country of installation
- Piping Code
- Other

Do it once and Do it Right

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16 years 3 months ago - 16 years 3 months ago #4446 by gpsvn
Replied by gpsvn on topic I suggest that you use
I suggest that you use the arrangement described below

- Use an SS flange welded to SS pipe.
- The flange joint between SS flange and CS valve should be acceptable. (*)

Note:
(*) Depending on specific type of SS, there is galvanic potential different between the SS flange/pipe and CS valve. However, I think this is negligible for two reasons:

1. Many CS valves have SS trim (ball, seats, etc...)
2. Spiral wound gaskets are widely used with SS spiral. So the block valve will have to be in contact with SS anyway, which is acceptable.

Should the SS pipe and flange are of exotic materials (duplex, super duplex) and the fluid is highly corrosive, then you could coat the pipe internal with non-conductive coating.

With the above, you can avoid the weld between SS and CS. I do not mean you can not weld SS to CS but I do not think it's necessary in this case.

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16 years 3 months ago - 16 years 3 months ago #4447 by gpsvn
Replied by gpsvn on topic CS and SS welding

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16 years 3 months ago - 16 years 3 months ago #4448 by ashokaa
Replied by ashokaa on topic Jop, This is for your information, The
Jop,

This is for your information,

The Line Size is 3",
Pipe Schedule is 10S,
Operating pressure is 200 Barg,
Operating Temperature is 37.5 Deg. C,
Installation country is Brazil,
Code B31.3,
This is a Flare Header of one module.
The valve Ratting is 300# and pipe is 150#.


gpsvn,

Thanks for your suggestion, I am also thinking like what you suggest,
I asked the qustion because to know the Difficulties of CS&SS welding.

One more.. i have one qustion, If i go through your suggestion..
The SS Flange (300#) Schedule is 40S (73mm I/D) and Pipe is Schedule 10S (83mm I/D), I faced this type of problem (missmatching Schedule) some times, I don't know how to weld in fabrication shop, Just i followed the Piping Spec. Please Advise me....

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16 years 3 months ago - 16 years 3 months ago #4449 by gpsvn
Replied by gpsvn on topic ashokaa, are you sure that
ashokaa, are you sure that the OP is 200 barg, not 20 barg. The 300# flange, can't take 200 barg.

Now, back to the questions you have for me.
1. First of all, I see no reason why you need to have a CS/SS weld in this case.
2. If you really want to know, then you must provide the exact material destination of the SS and CS materials, is it 316L to A352 LCB or whatever your materials are. And the question should be raised to your welding engineer, he should be able to tell you if he has a WPS covers that kind of weld. For the sake of one weld, I think it's not wise to qualify a new WPS.
3. Mismatching schedule in this case is not a problem as the flange neck is much thicker than the pipe. On the drawing, you just provide a note that says "bore to match", most of the fabricator will know what to do. Usually the tapper is no more than 1 to 4.

Don't work to hard. Merry Christmas.

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