Joining perpendicular piping as "pipe in pipe"
Joining perpendicular piping as "pipe in pipe"
(OP)
Hello all,
Currently the company I work for services as technical advisor for the construction of CHP plant. The contractor, instead of joining perpendicular pipes by tees (T-elements), is going to join pipes as "pipe in pipe". This is regarding for example steam bleeds / extraction pipings from the turbine (DN150 - DN 350). They are probably going to weld this joints on site. We are afraid of quality of the welds, because this is kinda tricky to obtain and finish suitable shapes on site, and then weld it. Besides, this kind of joints have lower strength, and there is graeter turbulence in this places, which implies greater pressure drop and heat exchange. From the contractor point of view it is obviously advantageous, because there is only one weld instead of three, and they do not spend money for the tees. But I am of the opinion that it is not "state of the art". I would like to ask you, what is your opinion about this - is this kind of joining pipes / pipings acceptable? Do you know if there is any standard (European prefered) that treats this issue?
Many thanks for your help.
Pederator
Currently the company I work for services as technical advisor for the construction of CHP plant. The contractor, instead of joining perpendicular pipes by tees (T-elements), is going to join pipes as "pipe in pipe". This is regarding for example steam bleeds / extraction pipings from the turbine (DN150 - DN 350). They are probably going to weld this joints on site. We are afraid of quality of the welds, because this is kinda tricky to obtain and finish suitable shapes on site, and then weld it. Besides, this kind of joints have lower strength, and there is graeter turbulence in this places, which implies greater pressure drop and heat exchange. From the contractor point of view it is obviously advantageous, because there is only one weld instead of three, and they do not spend money for the tees. But I am of the opinion that it is not "state of the art". I would like to ask you, what is your opinion about this - is this kind of joining pipes / pipings acceptable? Do you know if there is any standard (European prefered) that treats this issue?
Many thanks for your help.
Pederator





RE: Joining perpendicular piping as "pipe in pipe"
RE: Joining perpendicular piping as "pipe in pipe"
RE: Joining perpendicular piping as "pipe in pipe"
I would like to pass on some information that normally covers this type of issue.
The Piping Material Engineer for the original Engineer/Designer of record will create/write a set of Piping Material Line Class Specifications (PMLCS). This document includes the specific material, fittings, flanges, valves and connection methods for each of the commodities by pressure/temperature ratings.
Branch connection methods are included in each of the individual line classes. A Stub-in branch connection may be allowed in some low to medium pressure line classes. You, as the technical adviser for the construction of CHP plant should have access to an 'Approved for Construction" copy. The Constructor should also have a copy and should be following it without deviation.
Why is this important? Consider this, say five years from now one of these joints fail. Someone is killed. The original PMLCS called for a TEE fitting. Based on your approval of the "cheaper" justification, the Stub-In was used. The family of the victim sues the construction company.
The construction company says "the technical adviser for the construction of CHP plant" said it is alright to use the cheaper method.
Now, you have a real problem.
Sometimes its possible to do all the right things and still get bad results
RE: Joining perpendicular piping as "pipe in pipe"
Pederator
RE: Joining perpendicular piping as "pipe in pipe"
Where are you located (USA or other)?
Is the Construction Company working under a 'Sub-Contract' agreement?
if so,
Do you have a 'Contracts Administrator'(CA)?
if so,
What does the CA have to say about 'Deviations'?
Does the CA have a complete set of the Contract documents?
Do the Contract Documents include a set of Piping Material Line Class Specifications (or the equivalent)?
What Piping Code is this plant designed to(ASME B31.1 or ASME B31.3)?
Sorry, the questions could go on and on, don't approve deviations without a sound basis.
Sometimes its possible to do all the right things and still get bad results
RE: Joining perpendicular piping as "pipe in pipe"
Thanks for your effort, Pennpiper.
Pederator
RE: Joining perpendicular piping as "pipe in pipe"
RE: Joining perpendicular piping as "pipe in pipe"
Thanks for your involvement.
Pederator
RE: Joining perpendicular piping as "pipe in pipe"
RE: Joining perpendicular piping as "pipe in pipe"
the risks of failure are increased because the joint is more severely eroded (steam flows and flow erosion on both inside and outside of the pipe joints) and because the joints are invisible for years at a time between outages - if they are opened and inspected at all.
RE: Joining perpendicular piping as "pipe in pipe"
RE: Joining perpendicular piping as "pipe in pipe"