Load combination?

[SMiK21]

Hi,

I'm designing a flange for a piping with ASME Sec. 8 Div. 1 Appendix 2.

I have to combine force due to Poisson + force due to temperature. My question is: do I combine them 1 x Poisson + 1 x Temperature or there are reducing coefficients?

I thank you in advance.

 

[DSB123]

SMik21,
If you are unsure to what loadings you apply then I would either :-

a) Ask someone else in the Company who has performed these calculations before

or

b) Engage a Consultant with the competence to perform the calculations in accordance with the Code.

 

[TomBarsh]

I'll admit to being dumb here. What is this force due to Poisson? Is this a force that results from Poisson's ratio, the material property? I've never seen this applied to an Appendix 2 flange. Is this common for piping (not my field)?

 

[SMiK21]

Yes. Due to Poisson's ratio, internal pressure becomes also an axial force. That, along with the temperature variations, give a very high value for axial force.

I am not sure if I should consider them or not. According to Appendix 2, bolt load is H + Hp, where H is the total hydrostatic end force. Shouldn't I use force due to Poisson + force due to temperature here?

Hiring a consultant is out of the question.

 

[TGS4]

H+Hp are external loads. Any "load" that would be due to the Poisson effect is not external. Also, how exactly is temperature causing a load? Differential thermal expansion is not considered in Appendix 2, and would fall under U-2(g).

You need to provide more details to your question. Exactly which equations are you talking about here? What exactly is your situation? Specificity will help us to help you.

 

[SMiK21]

It's a steel piping, 900 mm diameter, 5 mm thick (changeable), 18 m long and with 0,22MPa of internal pressure. The piping is divided into 3 parts, each of them flanged at both ends and those flanges are the ones that I am trying to calculate.

It is fixed at both ends, so any temperature variations (say, 20ºC) will produce a load on the flange (piping wants to stretch/shrink, but it cannot, so stress occurs) - am I right so far?

Also, due to the internal pressure, Poisson's effect will occur and the piping will tend to shrink on the longitudinal direction, causing stress.

I think that Appendix 2 is only for hydrostatic loads, but I really don't see what other appendix/code I could use for this

 

[TGS4]

Thanks for the additional information. Just so you understand, there are two parts to designing a flange. The first part is designing the actual metal part of the flange to ensure that it won't break or deform excessively: that's ASME Section VIII, Division 1, Appendix 2. The second part is designing for sealing performance: that involves the gasket selection, assembly (including bolting), and maintenance.

So, you have a pipe that is 18m long, straight, with fixed ends, that may experience temperature variations of upwards of 20°C. Sorry - that's just bad design. Over the 18m length of the pipe, you may see as much as 4mm of thermal expansion/contraction. And you want to design a flange that will accommodate that?!?

Yes, you need to consider external loads. Yes thermal expansion should be considered. I have to think a little bit more about the Poisson effect, but that doesn't matter - you have bigger issues here. Although Appendix 2 does not explicitly describe how to include for external axial loads, it would be reasonable to add them hydrostatic loads. But just because you can, doesn't mean that you should. This is a bad idea, and although you have stated before that hiring a consultant is out of the question, it appears that you and your design are out of your league, and some expert assistance is required.

 

[SMiK21]

Indeed I am, but I'll have to manage it somehow =)

I have uploaded a sketch of the piping.

I have omitted some information (and have forgotten to consider it on my calculations as well): most of the piping, as you can see on the sketch, is embedded in concrete. The very end of it is attached to a valve, then a dismantling joint, another valve, and some more piping.

What I have to design are the flanges that connect the 5,9m sections of steel piping to each other.

 

[TGS4]

I think that we have reached the limit of what you can get for free from an anonymous person on the internet. To reiterate:

This is a bad idea, and although you have stated before that hiring a consultant is out of the question, it appears that you and your design are out of your league, and some expert assistance is required.

 

[SMiK21]

OK, fair enough.

Thank you.