Just as a point of interest, I had a PE 250 pipe as well as a 400 one split apart at one stage, the two expnsion chamber diametres are identical in diametre apart from the baffling that is fitted to the inside of them, on the 400 the baffle is spot welded as mentioned - and is fairly difficult to remove, each spot weld has to be ground away carefully so as not to cut into the pipe body. The 250 however is very easy to remove because internally it is a made to be a smaller diametre, so the baffle is held away from the chamber walls on little mounting brackets which do not require the same degree of finess to cut free - hope this helps.