Expanded/nonexpanded ERW piping

[reichertc]

Hi folks. I was looking through the ASTM A53 specification and noticed that ERW piping can be supplied either nonexpanded or cold expanded, at the option of the manufacturer. What does this mean? I believe that it has something to do with getting the piping to the final tolerances, but am not sure of that. Any advice on when I would want to specify one over the other? I'd typically be looking at refinery applications, and am not interested in either hot or cold bending the piping.

Any insights appreciated. I am also posting this in the Piping & Fuid Mechanics Forum.

 

[bmoorthy]

Expanded pipes are very common in API Line pipe applications for cross country lines. If yourefer to API 5l you may get further insight.

There are couple of reasons for expansion of pipes.
Expansion not only corrects the dimension of pipes but also distribute the stresses caused due to bending/forming and edge crimping. Generally expansion is around 0.8% to 1.5% of the OD of pipe. By expanding Yield and Tensile properties are enhanced. But Y/Ts ratio should be restricted to max of 0.9. Generally it is common to expand the pipe to get higher Yield as in the case of X60 and X 70 grades of API 5L.

One manufacturer informed me that expansion of pipes induces stress in opposite direction(some thing like compressive stress. That is the pipe after expansion would tend to come inwards there by providing pre stress in the opposite direction.

I have witnessed residual stress in expanded pipe and unexpanded pipe. It was found that in expanded pipe the residual stress was marginally less as compared to unexpanded pipe. But the heats of the pies were different hence the results are not essentially comparable.