can any one tell me why in some plant designs, the piping is designed using schdule and in the same plant, other piing is designed using wall thickness?
Up to a certain size, 10 inch I think, schedule 40 is the same as standard wall. In larger sizes, std wall is 3/8" and schedule 40 is thicker than that so unless you need the heavier wall, call out std wall.
The company I work for has been doing power plant stuff for decades. The call outs for the piping used to transport pulverized coal are all over the place. The "correct" method seems to vary about as frequently as popular baby names.
It could be that by specifying "thickness", people are trying to imply "minimum thickness", thereby avoiding the 12.5% mill tolerance otherwise imposed by ASME B36.10.
They could just as easily specify "SCH XXX minimum"...
Oilfield applications are typically nominal OD and wall weight. Valves use piping schedule as do plants and mainline transportation systems. Pretty much all the same, some variance due to commercial availability and desired material needed to custom suit the application.
Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada
The younger engineers and especially the 'offshore' CADD people in our group constantly have to be reminded that Sch 40 is not always standard wall in all sizes. They seem to think that if they have called out Sch 40, they have called out std wall and we get into sizes where that is certainly not true.
