Hello Forum Members,

This is my first post though I have been frequently visting the site for the last couple of weeks now.

I hope some of you can give me some honest advice.

I am a 36 year old Chartered Engineer working in the UK. My 15 years in industry has been spent as a CAE/F.E analyst in both the automotive and Aerospace industries.

Within the auto industry, I have been mainly conducting linear-static stress analysis using solvers such as MSC/Nastran and Abaqus. I have also spent many years doing non-linear crashworthiness e.g Front, Rear and Side vehicle Impacts, seat belt and airbag modelling using LS-Dyna and PAM-Crash.

Within the aircraft industry Airbus/Boeing I have mainly spent most of my time doing stress analysis hand calcs : Lug Analysis, Bolt Group stresses, Stringer/Wing spar analysis etc,

A lot of generous advice can be found on this forum - regarding entering the Pipe stressing and the PetroChemical industry. Having taken some advice of members (J. Breen and J Luf etc.)- Having had a look at ASME B31.3 and a few text books recommended by some of you. I can honestly conclude that I have the utmost respect for the incredible detail and knowledge required to design suitable pipes to what appears to be exacting standards.

The shear volume of infomation pre-cludes that simply learning the ins-and-outs of CEASAR II will NOT qualify you as a pipe stresser. A trap that a lot of rookies fall into thinking.

For many it is very difficult to enter a particular industry when you are of a certain age.

So here are the questions that I am seeking honest answers to :

1) Do you think it is possible to make the transition from an Aircraft/Automotive stress analyst to the Petrochemical industry ?

2) Can the transition be made regardess wheather your are applying for a permanent or contract position ?

3) As a proven Stress Enginner - is there anything else you should seek knowledge about neglecting CEASAR II and B31.3.

I hope you can shine some light on the subject. I really enjoy both hand stressing and F.E modelling - but is it too late ? : surely stress is stress whatever the part is. The problem may lie in understanding the loading and boundary conditions of the real world problem or the assumptions made in the hand calc. I am of the opinion that this is something that can only be acquired on-the-job or from somebody with years of specific pipe design experience.

I apologise if this has been answered elsewhere on the forum (though I did try searching the forum with no luck). I can't be the only stress engineer using this site, NOT operating in pipe design.

Thanks in advance.

Although not at age, but more or less directly from school, I made the transition from architectural engineering to pipe/vessel engineering.
I'm working in this field for several years now and I'm still learning. I don't think you should try to become a pipe stress expert for a 6 month job only. You will need these first 6 months to learn the basics of pipe stress analysis itself and the basics of a good piping design.

What I think is the most important (and I experience that with new colleagues too) is that you first have to get your facts together about the basics of pipe stress analysis. Sort out the primary vs. secundary stresses issues, which you (mostly) don't have in other branches.
Then there is the interaction of the piping with the equipment, supports and all other stuff surrounding the piping. This is an often forgotten or overlooked subject.
Also you must get a feeling with piping systems. The most bizarre systems have been designed and calculated (and approved), which are way to stiff (to high nozzle forces), way to flexible (vibrations) or in another way just plain wrong (too many bellows and springs for example).

On the codes part, there are a lot of other codes apart from ASME B31.3. All have their own usage and have their own rules, which can't be compared to those of other codes. And if you want to perform stress analysis for FRP then you'll need a lot of extra knowledge about the material, material properties, material behaviour and specific stress analysis issues.

Pipe and vessel engineering is a very interesting and inspiring matter, but, in my opinion, can only be executed well if you have a lot of experience or if you're tutored by an experienced pipe/vessel engineer. Always start with simple systems and don't get to enthousiast. A wrong design can kill people.

I absolutely don't want to scare you away from this wonderful occupation. It's just that I see too many people (within my company, on this forum and on other forums) that think they can do a good job as pipe stress analyst within a few weeks after having read the CAESAR II tutorial.

Thanks for your reply.

A lots of useful info you have given me regarding, primary/secondary stresses, equipment and support etc.

I am under no illusion that knowing CEASAR II will permit you to being a good pipe stress analyst. It wont. !!!

Equally there is no single software code in the aircraft or automotive industry that will enable you to be a good Automotive/Aerospace stress analyst.

Though it sounds to me that you are implying that the only route into the industry would be to secure a permanent role. As a short term contract will be nigh on impossible. This stands to reason I guess. Though I wonder if it is the case if the contract were to be for 2 years !!!

You also said that "The wrong design can kill people".

This is also true for the Automotive/Aircraft industry. However cars are designed in 3 year programs. Aircrafts are designed in 10-12 year programs. Both are rigourously tested to ensure that failures do not occur.

How much testing are you doing in the pipe industry to minimise these risks?

I would be interested to know the kind of checks you conduct to ensure the numbers calculated by hand or by CEASAR are correct ? In Aircraft the stress checking process is gruelling and exhaustive.


Thanks for your advice Corne

[u][/u]

1 yes
2 yes
3 Working with/under a Senior Pipe Stress Engineer would be the best way to focus your direction while gaining experience.

A growing US/UK firm had COADE teach CAESAR II classes at several company locations. The word in their London office was that they were converting aerospace engineers into piping engineers.

It can be done but, as others say, with supervision.

Thanks for the info Dave.

That does sound promising. In the aircraft industry we do a tremendous amount of hand stressing. We even have large departments setup specifically to "check stress" the work of others.

This is then compared with departments who run similar checks in MathCAD and MS/Excel.

After all this it is further backed up by F.E analysis - through to physical testing.

Can some of you let me know the kind of rigorous checks conducted in the Pipe stressing field.

How much linear-static hand calculations are you conducting in your day-to-day routine as pipe stress engineers ?

By the way Dave : I don't suppose you know the name of the "growing US/UK firm", do you ?

Thanks for your help guys - I really appreciate it. Cheers.

Based on my personal experience, my thoughts

If the engineering fundamentals are strong engineers can switch between different fields.

It is not uncommon for people to take up different roles during their career. as an example even within piping (or pipe stress) there are different areas like power, process, oil and gas, offshore etc. where there are different requirements / std.s etc. which are quite varied and
needs some adjusting while switching.

The best way forward would be to intially involve in the piping design environment for a while, taking up a more general role like checking drawings, MTO etc. and get the hang of project cycle - interdiscipline workflow etc. and slowly graduate to pipe stress which will make the transition easier (this should suit your employer as you'll be contributing while you gain the required experience)

Thanks for the advice sn idea.

There have been quite a few views of this thread.

Though I am somewhat surprised that nobody has come back with an answer regarding the checking of Ceasar II results or the degree of hand calcs undertaken in pipe stressing.

Am I asking a crazy question here. Or am I to believe that there really isn't the sort of checks similar to those that exist in the aircraft/automotive industries.

Please someone clarify. Are the equations in Kannapan and Kellogg books used on a routine basis by the average pipe stressing engineer or not ?

CAESAR II vs hand calculations?

I don't think anybody has had the nerve to check the CII outcome completely. The flexibility analysis itself (3D beam theory) can't be done by hand unless you've unlimited time on your hands. What you can do is check the calculated SIF factors, the calculated maximum allowable stress and the code stress. I think it's good for an engineer to have checked these three values at least once. It will give you a better understanding of the whole code stress check as you had to study it in-depth.

About the equations of Kannappan and Kellogg: I don't use them when checking a network. I have made some copies of these formulas and graphs though which are in use by are piping engineers when determining the routing. It's old-skool stress checking which can be done much faster, better and more precize by computer (CII) nowadays. It is a good and quick help though at the start of a project to determine loop lengths and such.

Thanks Corne,

If the internal beam theory calculations conducted by Ceasar II are too complex/tedious to compare with equivalent hand methods.

Can you tell me what levels of testing is conducted as a fail safe.

Are the pipe installations tested in situ only ? or are there component level tests you conduct on critical areas of the piping design prior to full installation ?

When does the pipe stressing engineer know that the Caesar II simulations have been exhausted and more importantly how can he have full confidence in the results regardless of B31.3 compliance ?

Wow, you want a complete 4-year course in pipe stress engineering here in the forum? :-)

I'll try to give some short answers to the questions above. To explain everything fully will take me way too much time and I'll probably need a new keyboard when I'm halfway. Try searching this forum and the internet (eng-tips.com for example) for posts by John Breen. He has posted a lot of lengthy in-depth posts over the years.

Let me start by saying that even if CAESAR II does its job correctly and if the stresses are within the codes allowables, you can make a disastrous design. As an aircraft stress engineer I don't have to tell you that dynamic loads can cause a lot of damage to structures that are calculated using static loads only.

Piping systems are (almost) always field-tested using an hydrotest. The test pressure is determined according the applicable code and is approx 1.5x the design pressure. At very high temperatures the test pressure may be higher if tested at ambient temperature. Some systems don't have to be hydrotested and sometimes the (local) rules are more strict in comparison with the code (the european PED vs. ASME B31.4 or dutch RToD for example).

Components are often classified, especially if standard ASME components are used. There are extensive tables in which you can find the maximum pressure for pipes, bends, tees, flanges and the like. Keep in mind that this classification is purely based on hoop stress, not on longitudinal stresses.

Phew !!!

Thank goodness for that.

I thought everyone was keeping silent on the forum regarding the testing side of pipe stressing because you guys did'nt do any and was winging it.

I am relieved to say the least.

I kept hearing time and time again that the misuse of the Caesar II and FE/Pipe software could lead to deaths etc - as if that is all you guys believe in.

Thankfully you have re-instilled my confidence Corne.

Really appreciate the "hydrotest" and the safety margin info you work to. Also thanks for the eng-tips website - though I have been a forum member on that website for quite some time.

Don't worry I do not intend to train myself in pipe stressing from a forum. Ive been an Engineer surrounded by mathematics and F.E far too long to know that would be a complete waste of my time. Thanks.

As one who has frequently caustioned people about the possibly disastrous consequences, let me reassure you about a few things.

1. My first job out of engineering school was for a maker of jet engines.

2. The big keys to getting pipe stress analysis right are:

2a. Complying with the design code.

2b. Understanding the boundary conditions and getting them right.

2c. Designing something that is easily constructable.

3. The code rules have been checked repeatedly, hundreds of thousands of times, for about 75 years. The allowable stress limits, materials specifications, welding procedures, and commissioning and testing procedures work, if you follow them. Most of these rules come from the day when stress analysis of piping systems, using simple beam theory, WAS done by hand using the procedures in Kellogg. I have worked on projects where the original stress reports were indeed in that form. But CAESAR II is a lot more cost-effective.

4. CAESAR II (and other programs) are commonly checked by running a set of test problems and comparing the results with known solutions. Search for "program verification" or just "verification" on this site and you will find the discussions. Once this is done, there's no great reason to be concerned about the accuracy of the program output as long as the boundary conditions, materials properties, piping system geometry, and SIF's are correct.

5. Piping components are tested and retested continually, by one organization or the other. Vendors must make test pieces and subject them to many test procedures. See applicable ASTM specifications, WRC bulletins, vendor web sites, and the like for details.

With all this being said, if you have a background in the fundamentals of stress analysis and get yourself into the right situation, with a capable mentor, there's no reason you can't learn to be a capable stress analyst pretty quickly. I have cautioned against all of the following in recent memory.

A. Trying to do a stress analysis when you don't fully understand the material properties (such as fiberglass piping systems).

B. Not understanding how stresses combine.

C. Not understanding fatigue behavior of your material.

D. Using the wrong code.

E. Not understanding the difference between primary and secondary stresses.

F. Thinking that friction can help you.

G. Ignoring the real-world behavior of things we commonly classify as "rigid." One of our posters (Ed Klein, I believe) correctly notes in his signature that "all the world's a spring."

H. Dismissing the importance of getting the boundary conditions right. In many cases, this can be pretty exasperating - the equipment vendors often don't know what the limitations of their own equipment are. But all guesses are on you, and that's a big responsibility to take.

I'm sure there are other things I should be listing here. But if you can handle all of the above, you will be more than adequate.

mr. crashtek, my background is also Aerospace Engineer and I worked for 1 year as aircraft structural stress engineer. now i'm working as piping stress engineer. it's remembering me of creating stress report, FEM report, etc. (is the reference book Michael C. Niu?

I know that you are veteran and have strong fundamental/concept in stress, but it's quite different to understand and comprehend the piping systems. like mr. sn_idea said, you will deal also with piping design, material..so many considerations, etc. it'll take time. anyway, goodluck to you sir.

Interestingly and honestly the first time I got interviewed after graduating from college, they asked me this question "is it possible that Aircraft engineer be a piping stress engineer?"

I said "yes, it is possible since they have the basic of mechanic of material, etc" but they need to understand the each code intend which need time.