Hi All!

I have nozzle load of 11,000#s (OPE) and 13,000# (SUS). This is a barrel type (self re-inforced) nozzle connected to a thick Ellipsoidal Head tank about 3.75" thk. This is just a 12" line and I have 1 spring and if I add another spring downstream I can bring both loads to about a half. However, the above mentioned loads are within allowable per PRG's Nozzle Pro under ASME Section VIII Div. 1 category. I can jack up more load on the closest springs to the nozzle on the operating loads to lower the sustained loads but my question is: Is there any rule of thumb with regards to how much shall we set on the sustained load for a nozzle? To me it is plain and straight forward that it passed the Nozzle Pro and so it can handle the sustained load. In fact the operating load would be present for as much as the system is operating and the magnitude are close.

I really appreciate if somebody or any of you in this forum can strengthen my decision.

Regards,
EddieB

Dear EddieB

Consideration for using spring as follows

1) Try to avoid any spring if possible. because it is costly, & need maintenance & have adverse effect on dynamic analysis..

2) If only one spring stress is OK & nozzle load is ok , don't try to use two spring.

3) you can manually select the spring by putting more load ( & suitable stiffness) on spring until nozzle load is close to zero in sustain case. It will improve the system as far as nozzle load is concern.



Regards

Habib

Also do check the spring variability!!

Lesser it is , the better it is!!

Hi EddieB

The last step of the installation for a single pipe line is always to hook up the last spool with the nozzle. As the result the nozzle loads at this time is zero or fairly small. Before the operation the liquid is filled with pressure, the temporary support is removed and the spring is unlocked and therefore there is the load on the nozzle, so called SUS case.

I don't know any rule of thumb regarding to the SUS loads on nozzle. As long as it is within the allowable, it is OK.

Hope this helps you.

Thanks guys for your input. I really appreciate each and everyone's effort to help me. Actaully I tried to jack up the spring to a higher operating load to relieve susutained load but the pipe where the spring is attached to is failing in a sustained stress when pulled too much. I was feeling better when I was able to get about 50% less in sustained load (7000Lbs) however my sustained stress goes up to about 89% as the result of pulling higher the pipe. Most Old timer engineers I met before never wanted to have sustained stresses higher than 70% (this being the max if possible) - meaning that the lesser it is the better they say. I sure do the understand it is better but as an additional question to this thread:
can any of you guys (and the rest) tell me the most valuable reason why some limit the susutained stress to 70% or what is the futuristic destructive impact of getting into a higher than 70% sustained stresses?

Thanks again for all your helpful tips!

EddieB

Dear EddieB

Technically it is allowed to use 100% sustain stress & 100% expansion stress.
I personally use 98% stress each for fire heater inlet.

In general people try to restrict sustain stress up to 70%.
Because sustain stress is a primary stress. It will always present in the system. Creep/ stress relaxation will not be applicable for sustain case. Hence people use thumb rule like that.

Regards

Habib

Hi Habib,

Thanks a lot for your advice. It helped me strengthen my decision. Thanks all, I really appreciate all your input.

EddieB