Nozzle loadings exceeding exchanger inlet nozzle 6

[MQM90]

Dear

My nozzle loadings are exceeding for exchanger inlet nozzle (drawings attached)

My piping parameters are as follows:

1. Piping material is SA 335 Gr 11 Cl 2 & dia 18 inches
2. Operating Temperature = 350 deg.C
3. Design Pressure = 30 kg/cm2g4.
4. Flange rating is 300 lb (Weld Neck)

Overall flexibility/stress ratio is 0.90 as reported in the software output file.

Can any piping expert or an experienced person tell me how to reduce the stresses on a piping system whose stress ratio are still within the limits but nozzle loading are exceeding.

My idea if i go for higher strength material or high rating flange.

Thanks


Osama Nusrat Ali

 

[SNORGY]

TGS4:

Thank you for that response. I would give you two stars if I could.

In the industry and region where I work, there is always enormous pressure put on the "engineers" (the guys and gals who actually do the math and design stuff) by the "non-engineers" (the MBAs and - worse - "Project Engineers / Managers" and - even still worse - "Clients") to do as little engineering as possible and "finish" things as quickly and cheaply as possible. More than occasionally, the "engineers" are threatened with their jobs or with being excluded from subsequent project involvement because they are perceived to be irritants rather than valued professionals if they are to take the time to do everything right.

That said, if flange calculations, as you suggest, were to be made part of all routine stress analyses, the sad truth is that most "clients" and absolutely no "managers" would be on board with the concept and they would most likely not pay for it. With the prevailing budget, schedule, cost and "minimization of engineering" mentality, pretty much nothing would ever be done if it was to be done correctly. It's sad, but it it's an honest encapsulation of the truth.

Honestly, I don't routinely check for flange opening / closing forces if the service otherwise has a low risk assessment rating due to the consequences of loss of containment. One would hope that an engineering team's collective judgement would identify where such extra design effort is mandated, but, sadly, such is seldom the case. We exist in a business where the stakeholders want fast, cheap answers at little to no engineering cost.

Hitherto, after 27 years, my judgement has served me well and I have not produced anything that has "failed" or "given rise to an incident". I now check the things that I feel are important to check, and do the things that I feel I need to do, irrespective of whatever else I am told. The "superiors" sometimes get anxious and impatient, but so far they haven't fired me. Sometimes just handing them my calculator, pencil, and a pad of paper is enough to make them go away until I am "done".

I wouldn't go so far as to say "weak and impotent", although I am compassionate with respect to that sentiment. I would, rather, suggest that engineers get beaten up to the point to where they begin to believe that maybe all of these things that they thought they were supposed to be doing really don't matter. They are not impotent. They are victims of dangerous propaganda from those who refuse to accept the value - or from their perspective, "cost" - of sound engineering.

I agree with you. However, don't underestimate the power of "The Project Team" or "The Client".

Still...star.

Regards,

SNORGY.

 

[TGS4]

SNORGY - well said. I too have encountered the exact same thing. The intimidation factor can be enormous. (The way you describe it, we may have worked on the same project teams ).

Reminds me of the project where the client wanted a "leak-tight commissioning and start-up". We determined the cost of controlled-bolting for every flange, with a specific procedure for each flange - and there were >6000 flanges. The cost and schedule made him physically gag (good thing I was there to see the reaction!). He then said something to the project manager about wanting a "leak tight start-up, but without all that extra cost those engineers dreamed up". At least our project manager was a decent engineer and told him to basically "bugger off". Pay me now or pay me later, but you WILL pay.

 

[BigInch]

"Please write down what part you don't want me to do." also works quite well.

**********************
"The problem isn't finding the solution, its trying to get to the real question." BigInch

http://virtualpipeline.spaces.live.com/

 

[LSThill]

MQM90 (Mechanical)

Question
What SIF are you using for the Elbows??

 

[MJCronin]

Bravo...!!! SNORGY...!!!!

Describing engineering as an "irritant" is spot on...

Things are getting worse...not better.

Managers perceive engineers as only a necessary "sponge" for responsibility...and never as the only real key for project success.

Your phrase

"to do as little engineering as possible and "finish" things as quickly and cheaply as possible."

is probably written on the back of all MBA certificates awarded today.

-MJC

 

[MQM90]

Thanks

To All

Nice discussions.

Take Care

Osama Nusrat Ali

 

[4Pipes]

Snorgy,

..by what percentage.. If the system analysed was a reasonably practical application of the theoretical basis of the software then the answer is none.
However, if the theoretical basis of the software is not a practical application for the sytem analysed then the answer could be quite a lot. In this OP, I would suspect that the theory is being stretched. Maybe not to its limit but at least to suggest caution.

A factor with Caesar and every other software application is that the writers assume that the users are qualified. They do not include warnings about limitations of scope.
Many years ago, I suggested to Coade that warnings about limitations might be useful - I was very quickly put back in my place. Coade told me in no uncertain terms that the software is intended for users who know the limitations of the theory. For example, you could apply a force to a simple cantilever that has a small bending stiffness at its fixed end. Caesar will (or used to) not object even if the rotation of the cantilever goes past 90 deg. No over stress, no problem. You can just as easily come up with less silly examples that are equally beyond the validity of the software.

 

[SNORGY]

4pipes:

I don't disagree with you. I just work in an environment with a different culture or approach towards "when to do" something and "when not to do" something.

The obviously correct answer from the pure engineer's perspective is to calculate everything in exact accordance with the theory.

The reality is that if you have run a CII analysis - for example - and determined that nozzle loads are within acceptable limits, then in most instances, you will not be afforded the man hours or the liberty to extend that analysis into more detailed calculations related to flange opening / closing / misalignment - or at least such activity will be strongly discouraged. What people seek are quick guidelines: "...if you are within (x)% of *this*, then you don't do *that*...", or so appears to be the culture.

I never said it was right, I just said that that's how it is.

I would like nothing more than to force everyone to accept that EVERYTHING SHALL BE CALCULATED. To accomplish this, though, will require nothing short of a rebellion of monumental proportions. A good place to start would be to ban all MBA's from positions of authority in engineering companies.

Not that I am in any way bitter.

Regards,

SNORGY.

 

[SNORGY]

Further to the above...

Another very sad truth is that, if an engineer undertakes to perform detailed calculations for everything, no matter how correct or elegantly performed, most "employers" that I know will get rid of that engineer at the very first available opportunity, using justification somewhat like:

"Great guy (girl), but made a big technical deal out of everything, slowed us down, hurt our projects, frustrated our clients, and really wasn't any good to us in the overall scheme of things...".

I've seen it too often.

I am not saying it's right...but that it is what it is.

The key is to somehow know when something needs to be flogged rigorously versus when it can be readily judged one way or the other. I am not sure what teaches that other than experience. And, when experience is used towards that end, it is usually supported by a guideline founded upon a rule of thumb or approximate premise similar to the one I described.

Regards,

SNORGY.

 

[4Pipes]

Snorgy,
It's a funny old world. I agree on all your comments but cannot agree that everything must be calculated. It is becoming very much the norm to do lots of calcs. However, oftentimes a comparison, common sense, a fag packet or a chart would be just as good and equally as accurate when appropriate. How accurate is your input? How accurate is wind and friction? A guess to 3 decimal places is still a guess.
I do sometimes have sympathy with project managers complaining about time taken by stress. Doing multiple runs to get a "pass" by moving a support a couple of inches at a time is missing the point. Pipe stress is not watch making. This creates the situation with your great guy. He/she does not do anybody any favours by crying wolf. Real problems then get totally ingored.

 

[SNORGY]

I agree.

I guess it depends on the definition of "calculation".

Referring to a chart or a nomograph (as is frequently done) becomes a calculation when it produces a quantifiable output as a function of a quantifiable input. For example, visual inspection of a Moody diagram for "f" is just as good as a Newton Rhapson iteration of the Colebrook equation. Also, a person with enough experience saying, "...f will be about 0.015..." might be just as good as either. I have done either or all of the above, depending on how accurate an answer the task warranted.

What is *not* a calculation is s statement like, "I dunno...that's what they did on the last job...", or "..We just do it that way because that's what others do...", or "...That's the size that the Client wants...", or other such similar technical justification.

So, I guess it would be more accurate to state, "Everything must be given at least some semblance of coherent engineering thought."

As an aside...

We prefer to call them "cigarette boxes" in Canada.



Regards,

SNORGY.

 

[MQM90]

Special Thanks to SNORGY & BigInch & 4Pipes

Osama Nusrat Ali