We take care from the start of engineering by providing owners requirement of steam turbine and rotating equipment connected piping alignment with springs unlocked.

After coducting WNC analysis with user springs unlocked & nozzle free,
at site we find the need to change the nearest spring to nozzle to higher size at the time of commissioning.

To avoid such a situation, what is the way out:

1) realistic weight consideration of all accessories/specialties - clamps, shoes, flange, valve, insulation
2) consider spring nearby the nozzle selected not to the middle of range as it is the usual practice, but in the top side.

Try changing the hanger stiffness setting on the 2nd HGR load case from "Ignore" to "As Designed". This can provide a more optimized design.

Sir,

We consider the cold balance method of spring selection in order to achieve alignment at flange of steam turbine connection with "As designed" user spring stiffness.

But, due to imperfection in load estimation of support auxiliaries - viz. shoe, welded attachment etc and high frictions at precisely designed small gap restraints - say 0 mm or 2 mm gap, our Caesar -II WNC run with nozzle free does not match with reality very often!

Our weight values of valves, flanges etc are taken from catalog, not as-built data - so, we estimate mostly in the lower side of real weights!

That is why I thought that it is wiser to have such near equipment nozzle spring size be chosen, not load centered, but on the upper side of the working range!

How many times will we try to change such springs at the last moment with higher size!

reg,
sam

For such supercritical systems, one should use final (installed) weight data for all inline items from vendor and then perform final analysis. Also, weights of fasteners, cladding for insulation and all weights that you mention above must be considered to have more realistic design/spring sizing.
Spring support datasheets to be kept under hold until final vendor data is available.

Dear Sigma,

Thanks for the right approach you are taking!

In earlier days of nuclear plants and very large size power plants we were taking such care. All supports with civil structure were simulated with stiffness from previous unit design and spring hangers, snubbers were very carefully designed.

reg,
sam

In my opinion Sigma wrote a perfect case
But in live we as stresser know that everything go parallel:
Design, maufacturers, procurments so it hard to say sorry but we don't have a final data so we can not give what type of support You need.

I have simmilar situaltion that we have in free end case a movement 40 mm and should be 3 mm. It was caused by different type of valve and different isnulation but we assume at first with spring manufacturer that we want to used a spring that in cold case they will be not in the middle point of possible range but near the one of extrime.
We always know whether the spring will be loaded or unloaded so You can assume on in which direction will be movement.

I make my instalation like Sam wrote in Point 2.

And the installation work

One more caution in design stage:

3) When we are not very sure of weight of special items like valve, strainer, flange, it is better to opt for stiffer springs say DV35, at best DV70 instead of DV140 C&P varible or constant effort springs.

It may make sustained load case nozzle load conformance a bit difficult, but spring unlocked nozzle alignment through spring load adjustment very easy!

i saw problem mostly the cases where we used constant spring or C&P DV140 soft springs near nozzles1

It is our wrong choice for which we delay plant start up by weeks, but blame construction and operating staff!

reg,
sam

Our general practice is to set springs in a way to get the alignment in disconnected condition (springs locked and unlocked) as well as to qualify nozzle loads with respect to allowable.

This is tedious task but we have been able to achieve this for so many years.

Also, the calc needs to be re-run with final vendor weight data to ensure there are no flaws.

But all said, the site always have ways to create issues during construction and this needs to be resolved on case to case basis.

Some users will use CAESAR II to select springs for hot load design AND cold load design to assure that the same spring can be balanced in both cases. But I agree, those weights are very important.