Hello,

In case of recalculating an existing pipe system with several years of operation, is it correct to consider the allowable stresses from B31.1?

In my opinion the answer is no but Im not sure if applying again the code as brand new pipe the result should be conservative or not.

I haven´t found anything regarding that issue on the code. Any light would be appreciated!

thanks!

I did some analysis for existing systems by using the allowable stresses from the code used for installating the systems. The allowable stresses should not have to meet current code values, but they met or had to meet the old code values.

Also it is good to check the loacal regulations and registration requirements. If the system is required to re-rate, check the related codes, such as ASME FFs-1.

Carter

API 579 should be referenced as B31.3/B31.1 are for brand new piping. However it is upto the owner to decide.

Regards

What is the purpose of the new calculation?

Your Client was asking you to check the original project and the result is negative?

Or maybe some piping components have been replaced after several years of operations and your Client wants to reevaluate the system? I think in this case you may try to "recalibrate" the number of cycles for your (EXP) load cases and you also may try to change "actual" thk/new CA for components still maintained in system (however this approach may be not realistic if the corrosion is not uniform, so it is better to evaluate carefully if it is the case to proceed in this way). In addition such rerating procedures are not qualified by any standard (rather there are more realistic but complex methods -as it was mentioned- which are not addressed by Caesar) so the only recommendation I have is to discuss with your Client the approach.

Hi,

the purpose is to improve the actual pipe supporting, some components shall be replaced so a new calculation has to be done.

As I have no information regarding the realistic situation of the pipes (permanent strain, corrosion...) I aggre with you mariog that It would be correct to assume some conservative hypothesis like increasing number of cycles, or reducing the pipe thickness, corrosion allowance...

Anyway, I will check ASME FFs1 and API 579.

Thanks to everyone for your support.

Regards

I have a related question.

We are involved in a piping project where some portion of a high pressure (1500 Psig) high temperature (1000ºF) steam piping in ASTM A335 P22 material will have to be removed and a heavy weight (20,000 Lbs) new steam control valve, along with new A335 P22 material piping and associated new pipe supports (hangers)and restraints will be welded to the existing remaining piping. The piping has a nominal diameter of 12", extra heavy wall thickness (1.3" minimum) and is in operation for last 15 years, at reasonably steady load.

As the piping is in operation for so many years in the creep zone, it must have self sprung and therefore a considerable portion of expansion stress, equipment terminal reactions and movements have reappeared in the cold condition. The pipe was erected with no cold pull up gap.

Can Caesar-II be used to simulate the configuration (that is movements), residual stress and moments and forces in the cold shutdown condition at all node points? Please advise.

Regards (2011-02-21)