Temperature and Allowable Stress Basis

You have answered yourself in the second statement. Note the YS is the basis for allowable even at lower temps (except cryo under some circumstances)

Please give a specific example showing your numbers -

It could be because the high temperature has gone into the "creep" range where the allowable basis is different.

Hello paresh,

Are you talking of stress in metal in general? or is it pipes? In you are talk of less extreme situations, Not inside an internal combustion engine, A system can handle heat better than cold often times. If it gets much below freezing metals tend to get fragile. Though they can easily take several hundred deg' heat.

Take care. If you can give us more details of specific materials than we can work from there.

In any design a Maximum temperature is established. It is the highest temperature at which the item being designed is expected to operate. This temperature dictates what stress is used in design calculations. Higher tempeerature, lower allowable stress.

Hello Abdel Halim Galala:

GA to you Abdel. Nice example.

Hope you are well and stay that way!............

Yes - good example,

But I interpret the question to ask why does the stress basis, that is, the stress 'basis' for AMSE Div 2 is the lower of Ultimate strength divided by 2.4 (at room temperature) or YS (at temperature or room temperature) divided by 1.5 UNTIL you get into the creep range where the 'basis' changes.

The difference in stresses arised due to using a different factors of safety^*. So,for every code/standard there is a factor of safety used in design to be fellow by the users. For this reason, the pressure vessels designed and constructed in accordance with DIN have a thinner shell wall thickness than those designed by the ASME code. And when you apply ASME equations to those vessels designed under DIN, you will find it unacceptable per ASME code. And this "unacceptability" doesn't means that these vessels are refused or can not be used in practical.

* The factor of safety used in ASME code itself is vary from section to another, as that is clear from the Allowable Tensile Strength stated by B31.1 Power Piping which is differ from that used in ASME B31.3 Process Piping. And I can proceed an example I used to demonstrate in my lecturers to my trainee allover the world for a piping system which is designed using the both codes: B31.1 and B31.3, where you can easily find that the pipe Schedule No. by using the rules of B31.1 is higher than that one if we apply the rules of B31.3.

• Data Given:

- Pipe Material : ASME SA 106 Grade B (seamless)

- Pipe Size : NPS 10"

- Design Pressure 1200 psi

- Design Temp. : 680 ^oF

- Corrosion Allowance : 0.0625 in.

• Results of calculations:

- By using the rules and equations of ASME B31.3 : Pipe Schedule No. 60 (XS)

- By using the rules and equations of ASME B31.1 : Pipe Schedule No. 80

The two different results arised due to using two different factors of safety in design which determine the values of allowable stresses.

So, I think that there is no conflict between the both codes, only you have to select the code which will adapt your requirements, factor of safety, specifications and the contractual obligations.

Please see CR4 Thread Threadolet Rating for Refinery Appliction.

Dear Sir

I am continues reading your tips. I am a students. I want to know about Metallic Expansion Joints.

1) How could calculate Plie thickness and No of plies in Exp. joints.

2) How could calculate tie rods dia & No of tie rods in Expansion Joints.

If you have any easy formulas so please reply.

Amit Sharma