"Self Springing" in "High Energy Piping" systems

[Jake52]

Question on "Self-Springing" of High Energy Piping (HEP).
Ref: B31.1 Power Piping Code, Sec. 119.2 "Stress Range".

Given the following scenario:
-HEP Steam System on new combined cycle power plant.
-Chrome-Moly Piping Material (P91 & P22).
-Max Operating Temperature of 1065 degrees F
-Design Pressure 400 PSIG
-Runs at max temp for 6 wks, (1008 hrs) before 1st shutdown.
-System initially fabricated correctly.
[Zero gap @ Final Field Weld, (FFW) during installation].
-All System stresses well within Code allowables.

Q1. How soon does the self-springing process begin?

Q2. If pipe is cooled/cut @ FFW after 1080 hrs of operation:
Would a gap be present at the FFW after the cut?

Q3. Suggested references for further investigation?

 

[prex]

As the elastically calculated stress in the pipe due to expansion and pressure is allowed to go well beyond the yield stress (it might be close and even beyond 2 times the minimum yield stress at temperature) and unless you have quite low calculated stresses with respect to allowables in your piping (and of course you are not in this situation), the piping will immediately yield at some bends. So:
A1. Almost immediately (after reaching a sufficiently high temperature)
A2. Yes, and the initial gap is likely to increase in time due to creep effects.
A3. There are certainly many references treating this subject, but have none to propose. If your intention is to evaluate the gap at FFW, then be careful, it won't be simple, as it will largely depend on the actual yield and creep properties at temperature of the individual heats of piping materials used.

prex

http://www.xcalcs.com

Online tools for structural design

 

[LSThill]

Jake52 (Mechanical)and prex (Structural)

I agree with prex (Structural); Also, for the Piping Stress Engineer (ASME B31.1 analysis): Main Steam & Boot Drain to the Condenser use P91 to pass the: (required condition for all of the 209 stress cases). Use the lesser material P22 after the first and or the second valve.

Leonard Stephne Thill
Leonard@thill.biz

http://www.thill.biz