ASME B31.3 - Cold sping

[Fran67]

Hello everybody,

I understand that the ASME B31.3 code defines the "cold spring" as a desired pipe initial displacement during pipe assembly/erection.
As "desired", I understand that the initial displacement and pre-load is under engineering control (calculated, alignent offset controled..etc)

Do you know what speak the code about the pre-stress which appears during pipe assembly, corresponding to the non desired cold spring?
For example: Imagine a 3mm offset between the pipe and the support during erection -> To let the mounting, a load is applied on the pipe to correct the offset -> This load is corresponding to a pre-load which should be considered in the pipe design calculation.
The problem is that the value of this load is not easy to be determined.

Do you know what the ASME B31.3 code speak about this?
- Is this undesired and random pre-load included in the safety factor used in the chapter II for piping design?
- Else, how to include this load?
- Is there any requirement in the code which impose to limit the acceptable offset or impose a pre-mounting of the pipe before final welding to limit the offsets??

Thank you for your responses,
F67

 

[KevinNZ]

Undesired and random pre-load would a one off displacement load. This could be considered like earth settlement for the piping design.

Movement due to earth settlement, since it is a single
cycle effect, will not significantly influence fatigue life.
A displacement stress range greater than that permitted
by para. 302.3.5(d) may be allowable if due consideration
is given to avoidance of excessive localized strain and
end reactions.

B31.1 Also covers Noncyclic Displacement Stress. You could use this make a judgment call about B31.3 piping.

(2) Noncyclic Displacement Stress Ranges. Stress
ranges caused by noncyclic movements such as those
due to settlement or uplift of pipe-supporting structures
or components such as buildings, pipe racks, pipe anchors,
or rigid supports will not significantly influence fatigue
life. Stress ranges caused by such movements may be
calculated using Figure 104.8-1, eq. (17), replacing SA
with an allowable stress range of 3.0SC and replacing
MC with the moment range due to the noncyclic movement.
The stress ranges due to noncyclic displacements
need not be combined with cyclic stress ranges in accordance
with (1).