higher schedule pipe

[farhad2474]

My question is .Why we use higher schedule number thickness for pipe1/2 - 1 ½ in refinery but pipe thickness calculation shows, we can use schedule lower . for example calculation shows we can use schedule 40 for pipe ½ and 1 ½ but our general specification mentioned we have to use schedule 80 for these size pipe . Also for valve show as well. we have to use higher rate for size smaller. I guess, the reason should be in the line classes but I don’t get it in the standard .I will be appreciate if some body answer my question.

regard
farhad

 

[C2it]

Mechanical strength is the usual reason for a higher schedule than required for pressure being used in small bore piping.

 

[BigInch]

Things smashing into < 2" pipe can cause a lot of damage, if that pipe was designed for pressure stress alone.

http://virtualpipeline.spaces.msn.com

 

[moltenmetal]

Yes, mechanical strength is the usual reason for doing this- particularly on nozzle necks on vessels etc. Corrosion allowance is the other. 1/16" is a significant fraction of the wall thickness of pipe at < 2". But that doesn't make it right to specify sch80 or sch160 pipe below 2" under all circumstances. Specifications have to be application specific: if the largest pipe on a particular unit is 2" but there's a lot of complexity, you may want to make an application-specific specification to save yourself some money.

 

[C2it]

DOn't forget the 240# hairy ar$ed fitter / rigger, climbing all over your delicate 2" pipes.

 

[JLSeagull]

Also, at that size the cost for higher schedule is not significant.

 

[GSTeng]

Vibration stresses can also be a factor when dealing with rotating machinery. Small lubrticatng lines and similar small pipes need to be able to put up with various types of vibration.

 

[itdepends]

Do you use threaded fittings on the smaller pipe sizes and welded flanges on the larger? If so- do your pipe thickness calculations allow for the loss in pipe thickness due to the threading?

 

[farhad2474]

Thank you for your answer.

But I looking for standard ,that tell me when should I use schedule higher .

 

[JLSeagull]

Instead of industry standard concensus organizations such as ASME for minimum requirements, consider the operating company standards. Most oil, gas and petrochemical companies have company standards that apply the engineering group experience in addition to the minimum standards. Also, consider engineering judgement as another supplement to standards.

 

[11echo]

"itdepends" ...touched on it. When you try to thread smaller pipe at sch40 and below you do-or-almost end up with a spring at the end of your pipe at the end of the threading process. Hence the use of sch.80 in these sizes for threaded connections.