SW & BW Piping 1

[DGrayPPD]

Good morning,

Question regarding the use of both BW and SW components in the same line. Our material engineer is suggesting to use BW fittings (elbows and tees) throughout the piping with SW valves at the control valve station and at the various isolation points. The client spec pretty much allows the use of both SW and BW fittings.

My question is, is it okay to use both butt weld and socket weld components in the same line run? I cannot recall seeing situations where this has been done. What reasons, if any, are there that this should be avoided?

Commodity = Hot Oil
NPS = 2"
Material = A106 Gr. B
Oper. Press. = 100 PSIG
Oper. Temp. = 400 Degrees F

Thanks,
DGrayPPD

 

[pennpiper]

Does the Material Engineer state any basis for this mix of construction joint methods?
The options would be all Socket Weld construction or all Butt Weld construction.
What connections will the Control Valves have?
There must be a cost issue involved.

Sometimes its possible to do all the right things and still get bad results

 

[moltenmetal]

Yes, it's permitted.

And yes, doing the whole line socket weld WILL be cheaper. A lot cheaper.

One reason, or excuse, to opt with butt welding for part of the line, might be a concern with the stress intensification factors associated with socket welded fittings, resulting in problems when you carry out thermal/flexibility analysis. But since the lines are 2", you probably won't have to do too much stress analysis anyway, unless the runs are short and cramped for some reason.

 

[DGrayPPD]

Pennpiper,

You asked:
Does the Material Engineer state any basis for this mix of construction joint methods? The basis was that the socket weld valves would save space compared to the flanged valves, which would also require the RFWN flange. I am assuming space is limited.

What connections will the Control Valves have? The control valve would still be flanged and require a set of RFWN flanges.

This is not my project. I am asking this question for a colleague who is unsure whether or not to proceed with this suggestion.

 

[DGrayPPD]

I am mistaken about the control valve station. There will be 2 hot oil lines (one in, one out). There will not be a control valve station. One line will contain 3 ball valves (all 2" NPS) and the other line will have 5 valves (4 ball valves, 1 check valve, all 2" NPS).

Each line is roughly 20 feet of pipe total with a limited amount of working space. I believe the decision has been made to route all piping and components SW.

However, I am also glad to know that it is permissible to use both welding methods for possible future projects.

 

[pennpiper]

DGray.
I agree with moltenmetal, it is okay to use both connections in this service and these conditions.

Sometimes its possible to do all the right things and still get bad results

 

[MickMc]

It would be unusual to see both SW & BW fittings on the same size of pipe but if SW allowed at that size then BW IMO would also be acceptable as the more stringent method.