Equipment Nozzle loads in +Y direction Acceptable or not

Dear memebrs:

We do an analysis of Water refrigerator - steam line for a temperature of 455°F pipe material carbon steel. In which the nozzle load for 8” flange is +676 lb at node 630 and +192 lb at node 970 which is less than the allowable load 787 lb but the force acts in the +Y direction.

But the doubt is, as per COADE Pipe stress analysis Seminar notes, Chapter-2 page 2-19, section 2.2.3-Consideration of Nozzle loads – It is specified that for a nozzle load in +Y direction (237 lb) seems to be unnatural for a gravity load and therefore it is not an optimally supported system. By re-analyzing the piping system the nozzle load has been changed to –Y direction (-495 lb) and it seems to be accepted compared to the above case even if the magnitude of the force is increased.

Why is it so? Can someone clarify this?

The same kind of situation occurs in our case as specified in first paragraph. The above discussed details are attached with this topic.

If the nozzle load must or (for optimal system) always be in the –Y direction, the following are the queries of the same,

1.Usually the allowable nozzle loads provided by the vendor is for both the +/- directions, so that the nozzle load in the +Y direction shall be accepted and the piping support system shall said to be optimal. If not please clarify.

2.But our Contractor says that if the actual value of nozzle load is within the allowable value then we need not to consider the directions. Is his suggestion is accepted?

1. yes
2. yes (acceptable)

That example was built to show how deadweight load can be shifted.

I would agree that a positive deadweight load on a restraint would not be optimal. If I have three supports - A, B, C - the sum of their deadweight loads would be equal to the total system deadweight. If A=-500, B=-250 & C=-1000, the total weight of the system is 1750. Now if B was +250, then A+C=-2000. So the remaining supports must also include the extra weight. A or C or both will be a bigger support than in the "optimal" configuration.

Yes, the initial +237 is smaller in magnitude but the -495 has a better looking sign.

I would check if the system is stable if the nozzle is disconnected.

A positive load may mean that your last support before the nozzle is functioning as a pivot point and if the nozzle is disconnected the pipe will displace upwards sometimes signifcantly. If the Nozzle Load is positive Y in the sustained case then I would say that it is poorly desinged. If it is only positive in the operating cases then it may not be optimally designed but it may be adequately designed.

Paldex,

Take note that forces (axial, longitudinal, circumferential) are not the only loads you need to check and review on the equipments nozzles. Applied moments (torsional and bending) due to sustained, operating, and occasional loads also needs to conform with your equipments allowable loads.

Moment loads are also obtained from maximum absolute value of sustained, operating, and/or combined load of operating+occ.
In other words, select the maximum value with respect to the loads acting on the nozzle's local direction (axial, longitudinal, or circumferential), not the signed values.

Dear Dave, Greg and Flexy,

None of them have gave a clear solution on my clarification.

But the doubt is, as per COADE Pipe stress analysis Seminar notes, Chapter-2 page 2-19, section 2.2.3-Consideration of Nozzle loads – It is specified that for a nozzle load in +Y direction (237 lb) seems to be unnatural for a gravity load and therefore it is not an optimally supported system. What is meant by "unnatural for a gravity load"

Is nozzle load must always be in the –Y direction ?

The answer is, no, the nozzle load does not always have to be in the -Y direction. However, if it isn't, you better have a really good understanding of why it is +Y in your SUS case.

It's true that the nozzle itself doesn't care if the load is +Y or -Y (same for the other force and moments as well). If the vendor has been given a design load of X,Y, and Z lbs and MX, MY, and MZ ft-lbs, then signs should not really matter to the equipment at that point.

The point that you missed in the responses, Paldex, is that, if you are getting a +Y on a nozzle in your sustained case, it can be an indication of a poor support arrangement. If you disconnect that nozzle connection (or change the anchor restraint stiffness to 0), you are likely to see a +Y displacement at that node. If you see something like 1/16" of movement, you probably don't have a big concern. If you see the node lift a couple of inches when you disconnect the equipment anchor, you have a very poorly supported pipe system.

On the other hand, I've ended up numerous times with a +Y load on a pump discharge in particular where I have a spring over the discharge nozzle. When a hot pump system heats up, it's going to shift load from other supports to the nozzle. To compensate, I have on occasion set the spring load to higher than what Caesar calls for, resulting in a +Y load on the pump nozzle in SUS. The reason for this is that in OPE, the final -Y that ends up on the pump nozzle is still within the allowable range. So, this would be a case where I would expect to have a +Y load in the SUS case and not be concerned.

There is rarely such a thing as "Always" in our business.

"...you better have a really good understanding of why..."

"There is rarely such a thing as "Always" in our business."

Well said Mr. Klein.

Dear All Members,

Thankyou very much for your solutions and suggestions. Finally, the doubt has been clarified.