Let me modify Steven's response.

3. Code Stresses - no. Stress Range - no. Actual stresses - yes.

Cold springing (or cold pull) has no effect on sustained loads - the pipe weighs the same whether or not you cold spring it.

Cold springing has no effect on the thermal stress range, which is defined as the algebraic difference between the system's hot and cold state of stress.

Cold springing DOES affect the state of stress within the system in both the hot and cold load cases - its effect on the terminal equipment loads is caused by the deformation created by the cold springing. This deformation, in turn, imposes a state of stress within the pipe that is different than one would find if the system had been installed with no cold spring.

BUT (to emphasize the Code rules once more) the cold spring has no measurable effect (since we assume linear behavior of the piping system) on the algebraic difference between the hot and cold stresses.

Think of it using this analogy.

I get up in the morning to go to work. I get in my car, and set the trip odometer to 0. I drive to work, note the trip odometer reading, put in a full day, and go home. When I get home, the trip odometer records how many miles I have driven, and the difference between the reading when I got into my car after work is X. The next day, I am driving to work, and I stop for gas 1/3 of the way there. I reset my trip odometer to 0. When I get to work, I note the trip odometer reading. It is different than on the previous day. I work a full day, get in my car, and drive home. The difference between the reading when I left work and the reading in my driveway is the same as the day before, but the absolute trip odometer readings are different.

That's what cold spring does - it changes the minimum state of stress within the piping system from the installed temperature to some temperature intermediate between the installed and operating temperatures. By making this change, the absolute magnitude of the larger thermal load imposed on the terminal nozzle is decreased, at the expense of increasing the magintude of the nozzle load at the other end of the operating thermal cycle.

That's ALL it does, when only Code stresses are considered. For those of you paying attention to the "hot operating load case," cold spring will change that, too.

I think your understanding was correct, Sanjay, but I hope this discussion increases your understanding of how the B31 Codes look at fatigue stresses.