How to reduce Forces and Moments around Nozzle Connection?

Could you tell me how to reduce Forces and Moments at Nozzle when pipe is connected to Turbine. Pipe size is 400NB, temperature is 177 Deg. C and Pressure is 9.687 kg/cm2.

In Thermal case forces and moments are within Allowable Values. But in Earthquake and Wind Case it is many times higher than Allowable Values.


Regards
Daman

Daman,

You could try reading the post from a few days back entitled ... "How to reduce moments around nozzle connection ?"

Have someone experienced and competent do the work for you and learn from them otherwise PXL= M

Reduce P or L and M decreases....

Typically, you add system flexibilty to reduce strain-based loads and increase stiffness (e.g. add supports) to reduce response due to loads that must satisfy equilibrium - the force-based loads. Since your issue is with the wind & seismic loads, I guess you should be looking at adding supports in the horizontal direction.

This has all been said before. I add it again here to take the opportunity to ask how you established your turbine load limits for those wind and seismic loads.

Sir what ever you said is Right.

In this case there are two Wind Loads.
One is in X- Direction (Case-W1) and second is in Z-Direction (Case-W2).
Speed of wind is 180 km/hr.

Equation P x L = M. I reduce the Length it further help me in Thermal Case not in Wind case.
If I am trying to reduce force and moment in Wind Case. Then Thermal Force and moment get increased. The response of Case-W1 is entirely different from Thermal response.
Adding support cannot solve my problem. The way which I had found is to restrict pipe in X & Z Direction (means Stiffen the pipe). Then flexibility of the pipe will come down and causing High Thermal force and moment.

Regards
Daman

Daman,

You should consider, as Dave Diehl has mentioned .... what allowable loads should apply to earthquake and design wind load ? And what are allowable load limits intended to protect ?

Earthquake is a survival situation and not an operational one. Surely the plant would shut down due to all manner of detectors in that event. Thus I would suggest, aim for stresses in piping below yield and leave it at that. Maybe the turbine vendor could help you out too. You should be aware that you can make the real situation of earthquake damage far worse by adding restraints and stiffening the pipe. Flexibility often means ability to survive.

So far as wind is concerned .... is the piping really exposed to direct wind at 180km/h ? It is common practice in refinery work to exclude piping less than 10m from the ground from wind loads, due to shielding of adjacent plant, unless it is an OSBL rack or similar. Worth a thought ?

First of all Thanks for your Contribution.

Sir the main problem is the Turbine at Open Place. there is no building to cover the turbine and the pipe is at 14mt Elevation. I am agree with ur point that Earthquake is a survival situation and not an operational one. Surely the plant would shut down due to all manner of detectors in that event.

As far as wind is concerned .... i am getting forces 5 times higher than the allowable. Allowable Forces are 1000N and Moments are 10000N.
I already foward my analysis report to Client. If there is any additional allowable limit for Wind than its ok otherwise i have to seach for some alternative.

Regards
Daman

1000 N is a very small load for this pipe size. Turbines generally have robust casings. Are the units OK?

Siv

Unit is right. In Thermal case Forces are less than 800 N and Moments are less than 6000 N. Problem only in Wind Case.

I am using Auto pipe software. I dont know how to use Snubber in this software. I used damper instead of Snubber but it doesnot take Wind Load.

I agree with Siv, 1000N is a pathetically small allowable for 400nb pipe. Just not realistic.

A snubber is not designed to deal with wind loads, they resist shock loads and usually need a sudden movement to lock, something like 250mm/min.

Submit your loads to the vendor with supporting data, particularly wind speed and duration, ask for approval or calculations to prove they are unacceptable.

Autopipe .... ??? !!!!

MoverZ

I already submit my Report to the Vendor.
Wheneve i will get reply. i will let you know.

But Sir this is really a good exercise i learned so many things from it.

Regards

Daman

MoverZ is 100% correct as far as Snubbers used for wind loads is concerned. They require a sudden acceleration such as steam / water hammer, seismic loads or PSV firing loads in order to lock.

In lieu of these expensive devices (Snubbers) boxed guides designed and placed strategically are always a better solution though more difficult to achieve from the designers view point.

As for Mover Zs reference to Autopipe I am unsure what the intent is to that reference. Ahh I see now MoverZ is not the source of the Autopipe reference its the user above who apparently is visiting this forum for general non CAESAR II commentary.....

My suggestion for getting the benefit of learning from an experienced competent designer still stands as well.

Damanpreet,

You are dealing with High temperature Turbine piping and routing should be such that you will have a point in the piping system, where the thermal displacements will be close to zero. Add a guide or axial stop based on this and this will take care of your wind problem. Dont use special supports like snubbers as they require maintenance and snubbers are additional cost to the client. In this way, you can increase ur piping stiffness without affecting your Nozzle. Check NEMA SM23 for the allowable loads for 400 NB pipe in operating condition.

Regards

SSK,

Sir i am using AUTOPIPE Software for this LP STEAM Piping problem. I already used Guide through which my Thermal Forces and Moments are below 1000 N. There is one Damper Support is in Autopipe software that is not taking any Wind Load.

More Guide cause High Thermal Forces. I tried all possible way. But i am not getting any solution.

I already foward my Repory to Vendor. Whenever i will get any Reply. i will let you know.

Regards
Daman

Damanpreet,

Also make sure that you do a WNC case with anchor free at the nozzle and checked for sustained deflection at the free end. This should be as close to zero as possible. Check this with springs both in locked and unlocked condition.

Regards

WNC case(for steam piping - any differance?) with anchor free at turbine nozzle with springs locked I understand, but why with springs unlocked?
Moreover, this we do with as-built ISO with actual weights of valves, flanges & insulation etc when cold setting method of springs is adopted.

In turbine piping, many times failure to meet the allowables with feasible piping layout is a reality & a compromise of higher nozzle allowable is very often worked out between A/E firm & turbine vendor.

How practical it is to keep the steam turbine in a high wind load & consequently meet the low turbine vendor nozzle allowable is to be seen with the big picture of sound operability of the steam turbine in view!

I am totally in agreement with LufSir - these are too involved areas
requiring experienced competent designers; this may not be a rocket science, but use of software by too young is risky for the owner of the plant like giving a gun in the hand of a student!

regards,

sam

Sam,

The only reason why I suggested "with springs in unlocked condition also" is based on the fact the Turbines are extremely strain sensitive ( that is what my understanding is based on the extremely low allowables offered by NEMA)and more than that of pumps( where we do it with springs in locked condition only).

I agree with you that this is preferably done with as built iso and actual wts. of insulation, flanges , valves etc, but even in the design stage, the adequacy of supporting can be checked ( and better be) in the WNC, Anchor Free case. This I find is mostly not done and the align ment problem is overlooked.

I also fully agree with you that such analysis requires years of practical experience and young engineers should perform such analysis only under the guidance of an experienced one.

Regards

Sir, I already done WNC-Case with anchor free at the Nozzle and checked for sustained displacement at free end. In which I am getting some displacement which is acceptable by vendor because after the Control Valve, pipe is inside the Turbine Casing so there is no provision to provide support.

Checking this with spring in locked condition that I understand. But in Unlocked condition???

Finally, I had changed the pipe routing after consulting with vendor. Through which I reduced Wind forces and moments to some extent. But problem is still there.

Damanpreet,

I have used snubber in the Autopipe software for the slug flow application.
We have to use Damper option to simulate the snubber.

If damper is not helping in reducing the wind/seismic load, this means the point where damper is modeled in Autopipe is not right. The point where damper is to be simulated should be close to the nozzle & there should not be any change of direction before the turbine nozzle.

Hope it will help you.

Regards
Saneh

try sway braces.these are supports where you can vary the stiffness.

Damanpreet,

Regarding checking with springs in unlocked condition, pl. read my response carefuly.

Regards