Pipe and fittings pressure rating 1

[Brough]

Brough (Mining) 18 May 06 8:59
Can someone help me to understand the relationship of pipe schedule designations and respective pressure ratings. I think I understand that the formula for calculating bursting pressure for a given pipe schedule wall thickness is Barlow's formula...P= t * 2S/OD....and to determine working pressure, the bursting pressure is divided by a selected safety factor. Is this correct?....but doesn't temperature of the fluid in the pipe have a bearing on bursting pressure value?

Is it correct that to determine the selection of a particular pipe schedule you calculate the schedule required with the formula: Schedule = 1000 * P/Sh...where P = pipe system pressure and Sh is ultimate tensile strength at a given temperatutre?

Also can someone explain to me what a pipe fitting with, let's say a 150 class rating actually means with regard to pressure rating? Sometimes I see fittings designations as 150 lb and sometimes as 150 class...do both designations mean the same thing? Does 150 lb fitting mean that the working pressure of the fitting is 150 PSI at 150 degrees C?

Thank you for any information on this. Tim Brough

 

[Cockroach]

Barlow's formula is simplistic, probably the most misunderstood equation in pressure vessels. It applies only to thin walled pressure vessels, wall thickness less than one-tenth the bore diameter.

Typically you need to review a tri-axial state of stress model like Von Mises-Hencky or various API models. Working pressure is something like you've defined, but it is material yield divided by factor of safety. Burst pressure is completely different, we're in the plastic zone here and are talking rupture.

Temperature effects the yield strength of the material, which alters the above mentioned models. In civil for example, building fires contribute to collapse since the applied heat to beams relaxes the steel and makes it incapable of taking on tranverse loading.

ANSI Class 150 designates a maximum operating pressure of 275 psi between -20/+100 F. Additional information can be found in valve manuals or API 6D. The "pound" thing to "class" thing is the same thing, it's typical of jargon in the oilfield for example. The "150" categorizes ratings of pressure retaining devices to a standard recognized on a global scale. The European or metric conversion is PN 20, "PN" for "pressure nominal". The pressure conversion imperal/metric are identical loading situations but in differing units.

You have several questions here not intended for this forum. I would recommend a valve handbook or the API 6D manual which would cover definitions. Good luck with it.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[Brough]

Your information concerning pipe fittings class definitions is very helpful, Mr. Hueston. I have not been succesful in finding germane posts on this site concerning pipe fittings class definition and I have researched other resources immediately available.

Thank you.

 

[rorschach]

Brough, also remember that the larger the pipe, the lower the pressure capability, with the wall thickness remaining the same. you have to calculate the hoop stress on the tube.

 

[LarryTaylor]

If I manufacture a sensor for petroleum pipelines, what is the preferred methodology for certifying a pressure rating (Class 600) for my sensor? I already have electrical safety approval (EExia) through CSA.

 

[handleman]

Larry,
Please start a new thread for this question.

Thanks!