Hello everyone. Still new in this field, and hope you could have much much time to answer (or give comments) on my queries below

1. "Since most of the cyclic loading events comprise much fewer than 50,000 cycles, the effect of mean stress in fatugue life are neglible for pipe materials with ultimate strengths below 100,000 psi"

QUESTION: Could you please provide me (at least) a table or any information to how I can estimate the number of cycles for a particular condition experienced by the piping system?

2. "If the stress analyst has an estimate of the pressure thrust, then a feasible option is to use the PD/2t + PT(107) method and instead of the full thrust load, enter the estimated value in the radial load input (with proper sign)

QUESTION:
a. as what you've probably expected, how can I possibly determine the "estimated value" of the pressure thrust in order for me to at least get the "closest" result in WRC 107?
b. Can CAESAR II provide us the "estimated value"? (CAESAR II may provide an option in WRC 107 of this "estimated value" that we can use in this analysis... hope this could mean something to COADE)

3. "Disabling this directive causes CAESAR II to strictly follow the piping code recommendations, i.e. depending on the active piping code, some load cases will consider corrosion and some will not"

QUESTION: What are these "some load cases" which will consider the corrosion allowance (or will consider a corroded pipe)?

thank you in advance!

regards,

NYX,

You should be able to estimate the number of cycles of your system according to the process information that you have. I don't know of any tables to do this. Talk to your process engineering people.

In Caesar II it is customary to use the full pressure in computing pressure thrust. Whether you should turn on this directive or not in the WRC-107 module depends on how your piping is restrained. If you have an anchor or axial stop in the line leaving the nozzle before or at the first bend or tee encountered then you do not need to consider pressure thrust as the nozzle will not be able to pull away from the vessel. Of course, this may cause expansion load problems. If your system has no axial restraint between the nozzle and a pipe bend or tee then you should include the full pressure for determination of pressure thrust.

When the straight run of pipe leading out of the nozzle is of sufficiently long length (I cannot be specific here) then the pipe flexibility may absorb some of the pressure thrust effect, thereby lowering the radial load at the vessel/nozzle interface. I think this is what you are referring to above, but I don't know of a method to calculate this. Perhaps one of our esteemed experts who often post to this forum will have some ideas for you.

Another instance where the vessel shell only sees a portion of the pressure thrust is where you have an axial stop with a gap that is less than the movement the pipe would experience due to pressure at a tee or bend. You could probably estimate the equivalent pressure with Caesar II by calculating the pressure thrust force (P*A), inputting this force for different values of P as an axial force at the first bend or tee, and then running a F1 (OPE) load case and look at your axial displacement at the stop location. Of course, when you do this you should not be modeling the stop. You could then graph your axial displacement against pressure thrust to determine what axial force corresponds to the gap to be modeled in your axial stop. Divide by the internal area of the pipe to obtain the corresponding equivalent pressure. It would not be conservative, but you could use this pressure in your WRC-107 analysis. However, do not use this reduced pressure in your actual static analysis! Use your actual operating conditions and put the stop with gap into the model for the static analysis.

As for which load cases consider corrosion allowance and which do not this depends entirely on which piping code you are considering. Read the specific code you are designing to for the answer to this question.

NYX,

Regarding pressure thrust :

This is created due to change in flow direction and the magnitude of the P*A load that actually comes to the equipment connections depends on how the line is supported and the relative stiffness of te different components of the system.B31.3 does not tell specifically how this thrust load has to be used in the system , only thing ie tells that the longitudinal pressure stress due to this P*A has to be combined with the Lonitudinal bending stress and checkd against the primary stress allowable. For most equipments, if you go by the "allowable load" method of qualification, inclusion of this P*A will definitely pose to be a problem but it is not actually so, as the equipment is always qualified for the pressure loading at the design stage.B31.3 rules for area replacement is also based on the membrane effect of this pressure thrust and not on bending ( Read WRC Bulletin 368 for detail).Hence even when you are using WRC Bulletin 107, I would recommend you not to consider pressure thrust as it will be overly conservative and not accurate also(Read a paper by Mandeep Singh and Dave Diehl in one of COADE' s newsletter).

The code is also silent on the issue of "pressure induced" or Bourdon effect strain. This is very similar to thermal displcements and in analysis is treated as "initial strain" to develop [P]=[K][D] eqn., similar to thermal strain.

Pressure can also affect the stiffness matrix by the K-Delta or "stress stiffening" effect.

The last two points are mostly valid for FRP or for high pressure systems .

Regards