How to measure the Creep Characteristic of Pipes 1

[ATsampalas]

In order to estimate the residual life of pipes operated at high temperature, we are asked to measure the creep evolution.
How can we proceed to take these measures ?

Sincerely,

A. Tsampalas

 

[metengr]

There are several approaches to evaluating the extent of creep damage in high temperature piping. Here are some suggested methods;

1. You can evaluate the extent of creep deformation by tracking changes in the outer diameter of several representative pipe spools. This requires rather accurate measuring and duplicating the measurements to monitor creep deformation (i.e., swell). The drawback is finding the exact spot where you measured the outer diameter to assure consistent readings.

2. A second method is to measure the oxide thickness on the ID surface of the pipe spools using a specialized method of ultrasonic testing (UT). The oxide thickness and measured wall thickness are plugged into an algorithm that will calculate the remaining creep life, knowing the base material. This will most likely require outside expertise in determining the oxide thickness and having the software to calculate remaining creep life.

3. The third method is to perform surface replication of several pipe spools to evaluate creep voids in the microstructure. This will require outside expertise in surface replication and evaluating creep voids to determine the percentage of creep rupture life. In addition, I would recommend surface nondestructive testing to supplement the surface replication.

4. Remove a trepan or plug sample from several pipe spools and have actual creep rupture tests performed to evaluate the creep properties of the pipe spool. This is costly and will require expertise to machine and run the creep rupture tests.

 

[DSB123]

metengr,
In your method 1 you mention the drawback as being finding the exact spot where you measured the outer diameter to assure consistent readings. In reality that's why creep pips are installed such that the dimension over the pips is measured on each and every occasion so there's no doubt about the location.

 

[andyenergy]

the problem with creep pips is they get damaged by idiots wielding grinders to remove the creep pip covers!!

 

[athomas236]

As far as I can see metengr has listed the methods in a way that the methods appearing later in his list give improving accuracy.

There is another method which involves looking at the operating records for temperatures and operating times and estimating the creeep life useage based on standard creep data with a factor of safety.

athomas236