Pipeline Transition Piece 2

[cadiehl]

I'm doing a pipeline project. Only my second one. Been a piping designer in shipbuilding and various plants for over 30 years. I have a situation where I have 10" STD wall (.365") pipe going to an 8" SCH80 wall (.500") pipe. I am told I need a transition piece. I just figured this would be a reducer, but I am not sure. Usually when going from a large pipe to a smaller pipe the wall gets thinner. In this case the wall thickness is greater. What exactly is a transition piece in the pipeline world, and how to I transition in my situation? This is a 1200 psi system. The wall thicknesses I state above are required at this location in the system by the client. So I have no options. I have to make the transition.

Thanks,
CAD

 

[LittleInch]

You should be able to get a reducer that does this if you specify it on the data sheet as it is not unusaul for wall thicknesses to change as you change sizes, normally thicker, but in your case thinner. This could be however because of the grade of steel or material, e.g. 8" Grade B to say 10" X60. You need to supply this information.

A transition piece in pipeline terminology is normally the same size, but "transitions" from a higher grade material to a lower grade material, made out of the higher grade material. E.g. a 10" X60 pipe of 10mm wall thickness (wt) transitioning to a 10" Grade B pipe of 18mm wt would be a short pup piece (say 500mm long), made of X60 18mm wt, with one end machined down at an internal angle of at least 1:4 or better to a wt of 10mm.

In the pipeline world, material strength of pipe is the thing to look for as this is directly inversely proportional to the wall thickness allowed.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[zdas04]

An additional consideration is that someone will always regret you burying a pipe-size transition. I've never seen a buried reducer that did not create some (often many) problems for operations. Most common problem is running pigs, but water collection and associated corrosion is right up there. If I have to change pipe sizes, I do it on the surface with a launcher/receiver pair. Usually when I run the economics of a single pipe size vs. launcher/receiver pair the apparent savings vanish and I run the big size from the beginning to the end.

I've inherited problems on several system that the Engineer got "clever" and ran 5 miles of one size then transitioned to the next bigger size because of the velocity increase due to the friction drop. I've frequently said really ugly things about the clever Engineers.

If you must do it, then like LittleInch said it is often possible to transition the pipe wall thickness in the reducer.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"

 

[cadiehl]

This is located at a meter station, outside of the pigging limits. I am going to do it with a reducer. The client has agreed to this method. No custom transition piece required. Thank both of you for your invaluable input.

CAD