WRC 537 Radial Load Sign (+/-)

[MechStruct1]

In WRC 537, Table 5 (Local Stresses in Cylindrical Shells), the corresponding image (see below) shows the positive radial load as acting inward towards the vessel.

I am using a pipe stress program to calculate worst-case nozzle loads and have both positive and negative radial force values for a particular nozzle. Is there anything that prevents me from using the worst-case positive (say 100# inward) or worst-case negative (say 500# outward) radial load instead of conservatively taking the max of the absolute value of the positive or negative and applying it both ways (i.e. +/-500#)?

I am trying to sharpen the pencil to get a nozzle to pass the WRC 537 evals, otherwise I would use the conservative +/-500#.

Any insight is much appreciated. Please let me know if I need to clarify anything. Thank you!

 

[Morcuse]

WRC 537 evaluates a stress state, that is three forces and three moments with their respective signs, and their impact on 4 points (0, 90, 180 and 270 degrees) at the junction between the vessel and the nozzle (or its reinforcing pad, if applicable).

Now - what are the actual stress states that you are required to guarantee?

 

[MechStruct1]

(If I understand your question correctly...) We are required to guarantee the stress state with all 6 loads acting concurrently.

Also, there is no cyclic loading expected, so no fatigue considerations.

The key to success is dedication to life-long learning. -Stephen Covey-

 

[SnTMan]

MechStruct1, it is likely but not certain that the worst case will be with the radial load directed outward.

What you should do is evaluate each set of loads as given, to be sure.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[DriveMeNuts]

WRC 537 conducts six independent stress analyses (for each load) and then superimposes all of the six results on top of each other to get a total stress at each of the four quarter points.
An inwards radial load causes compressive stress, reducing the magnitude of Tensile stresses caused by Moments.
An outwards radial load causes tensile stress, reducing the magnitude of Compressive stresses caused by Moments.
To do a complete and accurate job, you need to assess each design case. Sometimes you can think really hard and use logic to reduce the number of design cases, however if a report needs writing then other people will not be interested in reading your mind or repeating all of the really hard thinking to re-learn your simplification logic.

 

[NRP99]

I would use (conservative) algebraically higher number for nozzle assessment with +/- both directions.

That way "I" am covered. If nozzle is not passing, then there must be conservative parameters which are used in estimating nozzle loads from pipe stress analysis which needs to be questioned for "how much conservatism is good enough for these higher loads?"

GENERAL NOTE: Loads listed herein shall be considered to act in the combinations described above; whichever produces the most unfavorable effect in the component being considered. Effects of one or more loads not acting shall be considered.

 

[MechStruct1]

Good thoughts. It sounds like some would say to apply separately the worst-case radial loads in their given directions or to simply apply the higher (magnitude) radial load in the +/- directions to be conservative.

Thank you for the responses! Happy Friday!

The key to success is dedication to life-long learning. -Stephen Covey-