Hi! Everyone,

I have a question for above subject. Now we often use spring at first support of pump suction nozzle which has very small nozzle allowable load like ANSI pump (not API) to satisfy nozzle load. In this case, the reasons to use spring are to be reduced Y force occurred by using eccentric reducer, to be reduced X or Z moment occurred from other factors, and to be reduced reaction force occurred by friction. But spring travel will be very small like 1 or 0.5mm only. According to CAESARII, there is shown that the Rigid Support Displacement option is able to be used to save cost if spring hanger travels are very small (A typical value to be used is 0.1 in). Therefore I intend to use Y support instead of Spring caused by above reasons. And also first support of pump must be adjustable type to adjust alignment of pump shaft. So now I'm asking what means of use spring is.
And I would like ask to use Y support instead of Spring carefully.

May I use Rigid Y support instead of Spring......?

Anybody know that, please let me know......

Best regards,

In case the discharge/suction pipes and/or the pump have thermal loads, the +Y support will not work under the elbow/short straight.

It is better not to use immediate support under the elbow/short straight in suction/discharge sides with thermal load in case the nozzle loads are satisfactory. Otherwise you may need to use spring can.

Be carefull! Very small vertical displacement can overload the pump nozzzles.

Hope it help.

Ibrahim Demir

Thanks for your reply.

And I think so that very small vertical displacement can overload the pump nozzles.

But I want to apply that adjustable support will be adjusted at field to set alignment of pump shaft with sustain case. In other words, this method is same as giving initial displacement (e.g. +0.5 mm or -0.5 mm which can be acceptable for nozzle allowable loads) at support point instead of spring support if spring travel is very small and actual loads are over than allowable a little bits.

However we don't know how much displacement will be needed to set alignment.
In my experience, that displacement is not so much big. And in my opinion, we can give initial displacement at adjustable support point instead of spring support if overloads due to Y displacement with expansion case are not so much big as follow example, spring travels are less than 1 mm, and finally stress chief engineer judge that it is possible.

e.g.) EXTERNAL PIPING LOADS (ACTIONS)

FORCE (Kgf) MOMENT (Kgf·m)

FX FY FZ MX MY MZ

OPE 334 319 63 251 6 75
SUS -17 -128 28 17 9 28
MAX 334 319 63 251 9 75
ALLOWABLE 150 271 279 165 126 90
RATIO 2.223 1.175 0.227 1.519 0.073 0.831

If anybody apply above method, and can be judged by someone who is senior stress engineer, please let me know.

Thank you,
Best regards,

Seok

- Did you check your alignment in WNC SUS case?
- Did you set your spring as rigid when you checked the alignment?

Read Welding Research Council (WRC) Bulletin # 449 before you do anything else....

Seok,

I'm not so sure with the idea of using an adjustable base support
with an offset in replace for the spring support. Will it work
at site? (i dont know also but my heart says it won't or it's difficult)...others may comment..
Can you give more details of your piping...size,line conditions,how
far is it from the nozzle?,...In this we can have also an idea, if it
really requires spring support.

Maybe you might ask other respected people in this community like
John Breen, "Anindya", "Superpiper", and many more...Definitely,
they can help.

Regards,
Freon-phil

liam,

Yes, of course I know how to check alignment and lock nuts of spring must be fixed as rigid when checked alignment.
Maybe, you don't understand what i wrote.

Once again, What I explain is that i want to delete spring when spring is selected to satisfy nozzle loads at the first support of pump suction.
Because very small displacement will be occurred when alignment work done. So I think this is same as a very small spring travel.

So I want to use the method as follows

1. Check nozzle loads without spring as rigid +Y support
2. If over, use spring and then check whether nozzle loads are ok or not
3. Change spring to rigid +Y support and input small spring displacement
4. Check nozzle is acceptable or not

I believe that above method is very useful for cost saving and prevention of mechnical vibration.

But I have never been used like above method. So I'm really hoping somebody will verify this method.

Best regards,

Freon,

Thanks for your considering.

Could you give me more information about who John Breen, "Anindya", "Superpiper" is.

I think 1 or 2mm is negligible at field if adjustable type is available, isn't it? However 1 or 2mm caused by thermal expansion excepting adjustable support shall not be negligible.

Anybody has an idea, please let me know.

Regards,

John Breen is a fellow member of the ASME B31.3 committee as well as B31MDC and is far older than myself. Superpiper is a design engineer in Europe....

And if you read the WRC I told you about you would become enlightened.

So the end result of your analysis is that you want to avoid spending a few hundred dollars for a spring support and are willing to risk instead damage to a pump that costs a great deal more, and whose failure may lead to the shutdown of an entire process facility? This seems like a misguided priority.

You also suggest that using a rigid support will reduce vibration problems. This is also not necessarily the case, depending on the location of the rigid support with relation to the mode shapes of the piping at the excitation frequency.

Finally, if I understand your proposed "solution," you are planning to model the rigid support with an imposed displacement in the operating case to get the loads into compliance for your report. This is analytical fraud of the worst kind - you can't build a rigid support that way, and even if you could, the operators would forget how to make it work six weeks after you commissioned the plant. So you would be putting a bogus construct into your model for the sole purpose of forcing the numbers in your analysis report to conform to your requirements.

The purpose of what we do, in case you have either forgotten or have not been taught properly, is to attempt to create mathematical models the accurately reflect the behavior of the hardware we have available to us. We then use those models to determine whether we violate various design criteria.

You, on the other hand, appear to want to use mathematical tricks to produce a report that shows compliance to these criteria, even though your mathematical trick cannot be implemented with hardware. Wrong answer!

hi
my quary is regarding to caesarii
when wetry to batchrun in caesar we found one problem called:"covergence"problems.can we remove that support friction or we can put a rigid Y INSTEAD OF +Y
WHICH ONE IS BETTER IDEA?

CraigB,

I would make a problem.
There is not spring, only +y support at first support of pump suction with satisfied nozzle load(actual: 50kg, allowable: 60kg for y force of non API pump 6"x4").
This system will be perfect for report mathematically maybe.

However, allignment, that is problem. The +y support with adjustable type can be moved(up or down) when alignment is done. After finish alignment, I guess that support loaction might has been changed. In this case, do I have to use INITIAL DISPLACEMENT when SUS case? maybe, the answer is "no"
then, why? I don't understand why we have to ignore it at sus case. If I consider initial displacement like offset when SUS case, nozzle load may be over than allowable load of 60kg. Shall I use this method?

I want to apply realistic analysis between CAESAR II and field.
And also, I think Judgement can be done case by case if a few of displacement is occured and pump has a small allowable load like above example.
How do you think about that?

Best regards,

When you say "I want to apply realistic analysis between CAESAR II and field" and you are still using such support, you must keep in mind… it's not possible.
You try to guess something based on possible scenario by ignoring many others. The above posed answers are very clear. And you are going to take the responsibility for something you are not sure.
The mechanical engineering is mainly focused on "how to avoid something" (there are exceptions, of course). It's also true Caesar II and FEA are exceeding this target, but basically "allowable loads on nozzles" method remains dedicated to "how to avoid". And the answer is … by rethinking the configuration or by using spring supports... for sure not by mathematics.

Dear Seok,

It is not correct to model the changes due to allignment as displacements imposed on the piping because they are not.
The piping system after the allignment procedure has been carried out should represent your CAESAR model.
Also, you are implying that allignment-related changes may equal the small spring travel, that is why you are saying that an adjustable support may be used instead of a spring.
I think you should remember that,
1. Small changes due to allignment is done while the pump is not running.
2. Small spring travel is required when the pump is running.
Are you willing to monitor and adjust the adjustable support as the pump piping goes through temperature changes? If yes, how are you going to make the adjustment at the exact moment the adjustment is needed?
Just my opinion.

Seok,

friend.. before doing anything else, the advice of Sir John Luf(whom i think one of the commitee member)who's equally compettative like those person mention above, is enough or more for your concern. It works for me and I hope you'll try.

And I think your mis guided... So what sustain case for? To calculate loads??? ! Maybe its (OPE) rather than (SUS) for load calculation.

Answer given are not as bold as we will expect here, specially from our senior's advice.

Thank you.

Regards!

My comment regards operating CAESAR II only; not the practicality or reliability of the installation...

If you add a CNode to that +Y restraint and add a Y displacement for that CNode, you can "adjust" that support in your CAESAR II model. Guess a displacement and analyze. Improve your guess until you get your best pump load. I would run the cold case with the proper pipe loads and include the displacement set - as in W+D1. Once you get this D1, use it in all load cases.

But remember, building a reliable piping system and getting numbers out of CAESAR II are two different things.

Seok,

Dave has made my point, from the software side. You can do anything you want with the software input, and eventually get a report that satisfies all the design criteria. But then you have to build what you have modeled. That's not always so easy.

The flaw in your plan is that, by imposing a displacement on a rigid support, you are in effect assuming that you have a "smart" rigid support that readjusts itself between the sustained and operating load cases. We have such "smart" supports, that readjust themselves as displacements are imposed, but they're called spring supports. And your avowed goal is to avoid using a spring support.

The problem with rigid supports on piping near pumps is that pump nozzles have thermal growth associated with them, while rigid supports generally are "cold" since they have very little surface contact area with the hot pipe compared to their surface contact area with air. Yes, I know the heat transfer coefficients are miles apart to, but in general they are not considered to be "hot." And they would often expand in the opposite direction from your desires anyway. Most pump nozzles are in the bottom half of the casing, and most pumps are supported so that the shaft centerline remains at a relatively constant elevation. Most rigid supports, if they expanded, would causer the pipe to rise.

There are things you can do analytically. The rigid support usually bears on the bottom of the pipe. It's possible to use Roark (or other general solid mechanics texts or procedures) to estimate a stiffness for the pipe that considers its tendency to ovalize under such a load, but in general (1) the pipe is awfully stiff, and (2) this calculation is highly dependent on the actual wall thickness [try running the calc with nominal wall thickness, then with wall thickness +12.5% and -12.5% and you'll see what I mean].

Usually the best practical solution is to move the rigid support far enough away from the pump nozzle so that the displacement of the pump relative to the support point becomes "insignificant." It's up to you, as the anaalyst, to define "insignificant." Then, to minimize the forces on the pump nozzle, you probably want to reconfigure the geometry of the piping system so that the first support, at its new location, has "sufficient" weight of pipe on the side away from the pump so that the net vertical force on the pump is minimized in both load cases. Again, "sufficient" is your call. That's what we get paid the big bucks for! (LOL)

This is not as difficult as I have made it sound. Usually, if the first pipe support is 4-6 pipe diameters away, the relatively small thermal displacements of the pump nozzle become bearable. And pipe is rigid enough that most of the time, it's not necessary to jump through hoops to balance off the weight loads on the inboard (pump) and outboard (pipe) side of the first support. And usually, models are linear enough that you can predict what the final geometry needs to be as soon as you do two or three runs and one of them is remotely close to being acceptable.

It is often wise not to argue with people who think they have the answer.... let them test their skills and see what happens,,, it may mean the work will go to those who are more competent in the end.

And whatever anybody does don't ever ever pay for or read a WRC or PVRC paper on the subject matter! Its far better to cook up one owns conclusions....

in reply to the OP,

(excluding very hot pipework)

Horses for courses but i have been known to disagree here.

I think the removal of springs close to pumps is within reason a good idea.
Springs are primeval devices at the best of times and the less used the better. the variance of springs will in most cases negate the analysist origial intention of removing overstresses from the pump. (IMHO)

(In my opinion)Most pump codes are designed so that the pump nozzle is capable of bending an elbow one size bigger than the the nozzle and hence with these configurations, solutions are possible.

I normally place a support nearest the first elbow, so as to eliminate bending moments on the pump, i study the effects of heat transfer in the supports and the baseplates and things (usually work out) without the use of springs.


I feel its much better to let the pipework and support design deal with the nozzle forces, rather than stick in gizmos and gadgets.

Dont forget also that during alignment, both the pumps and the supports can be trimmed to suit.

WRT numbers, only a fool will massage the results to suit, your best accepting what you see and adjusting your design to suit. fidling with caesar will lead down a dark alley, after all pump calcs are about prolonging the life of the pump and are not in the majority, about stress.


Non API pumps can be a swine to pass though......