Piping Stress Analysis 12

[ChrisProcess]

Hello, first time poster with a query regarding piping stress analysis.

At the moment I work in plant design Process Engineer. Before issuing drawings we send selected lines out for Stress Analysis (our somewhat simplified criteria for Stress Analysis is D>2", dT>100 Deg C). It is now desired to do this analysis in-house.

I've taken it upon myself to research this.
I've assembled numerous guides (including the CASTI guidebook to ASME B31.3 & Process Piping the Complete Guide by Charles Becht).

I know that Caesar, Autopipe and others are used, but for various reasons they don't want to go this route. Instead they want to establish either a guideline or program that will cover the stress analysis.

We can characterise out piping networks quite easily, in terms of fittings, equipments dimensions, operating conditions etc. via our database system and 3d model.

So what I'm really looking for is somebody that works at this day to day, to give some pointers. I've spoken to my former mechanical engineering lecturer who thinks developing it from the ground up is a bad idea (i.e. go the Caesar route). I would like to get some other opinions on this. If it really is a bad idea, its best to find out at this early stage.

From reading the guides, a lot of it seems pretty vague, or at least up to the designers dicretion.
I would like to know how those working at it proceed and if to develop our own properitary procedures/software is feasible.

I'm assuming for all this that ASME B31.3 is the main guideline to consider regarding Stress Analysis for Process Piping.

Thanks for getting this far!

 

[pepeuy]

Hi, everyone. I have graduated of mechanical engineering last december. I now work on a company that designs and builds power plants burning biomass.

I'm having some trouble designing the steam pipe from the boiler to the turbine, on my college the subject about stress analysis of piping systems doesn't exist.

So i have read this and other posts looking for answers but so far no results.

I have the kellog book and the bentley autopipe software. I have some questions about them.

When i use the guided cantilever method on a simple L, i get some numbers different to those that the autopipe finds. I'm not using an elbow on the guided cantilever, but the results are somewhat 10 times as bigger than of autopipe.

Can some one tell me why?

Thanks to all.
José M. Roca

 

[DSB123]

pepeuy,
It sounds like you have some data wrong somewhere. Also it sounds like you are in-experienced in performing pipe stress analysis. I would suggest you contact a competent pipe stress engineer to analyse your line between the boiler and turbine so you do not end up damaging the turbine or boiler. These lines need to be analysed/designed correctly - not by a newcomer to the pipe stress field.

 

[pepeuy]

Dear DSB123, i totally agree in what you say. I'm telling this to my employer but he thinks this is an easy task.

I'm totally in-experienced in this subject but i teach strenght of materialsat the state university, so i think that with some good reading i will be getting the basics pretty soon.

The other thing is that in my country (Uruguay) i don't recognize any specialized company or engineer on the subject.

Thank you very much.

 

[BigInch]

pepeuy,

I would suspect just as dsb, that there is an input or calculation error. You should not be getting answers with an order of magnitude difference. Autopipe has developed a pretty good reputation in accuracy of its results, so based on the evidence provided and without further details, we would have to conclude the possibility of an error in your calculations is, shall we say, slightly higher.

I would suggest you start a new thread and post a diagram of your piping configuration and both your hand calculations and computer analysis input data and results. And be sure to state the design code you are using. Than somebody might take the time to review them and suggest a meaningful answer to your question.

"If everything seems under control, you're just not moving fast enough."
- Mario Andretti- When asked about transient hydraulics

http://virtualpipeline.spaces.msn.com

 

[PCGUSA]

I need help getting back into Pipe Stress Analysis field. I am a licensed PE in the state of Michigan.
I worked for Sargent & Lundy Engineers and Bechtel Corp., performing Nuclear and Fossil Power Plant Pipe Stress Analysis for 8+ years.
I switched my career to automotive component design/analysis in 1985. I am currently working for one of the Big 3 in Detroit. I plan to take an early retirement. I would like to get back in the Pipe Stress Analysis field.
While at Sargent & Lundy Engineers and Bechtel Corp., I used PIPSYS and ME101 programs to analyze Piping and determine support loads for thermal, deadweight, seismic and fluid dynamics conditions.
My questions are as follows.
Have the codes changed a lot in the last 24 years?
How do you combine stresses/loads from different static and dynamic events for piping qualification?
What else can I do to transition back into Power Plant field? Appreciate any help!

 

[JohnBreen]

Hello,

Have the codes changed a lot in the last 24 years?

Since 1984, I hope so.

The ASME B31 Piping Codes still incorporate a lot of what you remember but ASME B31.3, Process Piping has really taken the lead in changing things. Quite a lot of the piping being done now is Process Piping so if you can get into an ASME B31.3 seminar preferably one that has Glynn Woods or Ron Haupt as an instructor, you will pick that up quickly. Also read the books by Glynn Wood and Dr. Charles Becht IV.

How do you combine stresses/loads from different static and dynamic events for piping qualification?

Pretty much the way it was done in 1984. Stresses are still combined in accordance with Tresca failure theory with the exception of a minimum wall calculation that we put into the B31.3 High Pressure Chapter. The ASME Codes have you look at the primary stresses (stresses due to sustained pressure and weight) and compare them to the allowable stresses (as shown at temperature in Appendix A). You will find that we have now included an equation for calculating sustained stresses that we did not have in 1984. The secondary stress ranges (due to the displacement of thermal expansion/contraction and other cyclic loadings) are compared to a calculated allowable stress range in accordance with B31.3 - however NOW we consider values for "f" in that equation that are greater than 1.0 (low cycles in the life of the system).

Have a look at this:

http://www.becht.com/Content.aspx?cid=180&lvl=3

What else can I do to transition back into Power Plant field?

Learn the software. You will find that the software has greatly improved and the Internet had provides a lot of discussion forums where you can go to learn the "tricks of the trade". The Internet is REALLY great for sharing the knowledge. Then of course you will have to know the ASME Codes for Pressure Piping and what changes have been incorporated since 1984. Not too bad as the basics still apply - Pi is still approximately 3.2415926 (give or take).

Appreciate any help!

You are welcome.

Regards, John

 

[JohnBreen]

Uhhhhhhhhhhhhhh well,

Pi has not change THAT much - it is approximately 3.1415927... and some change. Sorry 'bout the dyslexic fingers.

John