Temperature Effects on Equipment Performance
C-FER Technologies’ origins are in evaluating the performance of structures in extreme cold environments that are encountered in developing oil and gas resources in Canada’s Arctic. Low operating temperatures cause most materials to become brittle. This can affect the load and fatigue capacity of structures, such as ice breaker hulls and stationary ice resisting structures.
We can test these cold weather structures under representative operating conditions. This requires not only large loading systems, but also high capacity cooling systems. Instrumenting these tests can also be challenging due to condensation and frost accumulations.
Changes in the temperature also cause thermal expansion and contraction of structures. If the structure is unconstrained, the stress in the structure usually remains unchanged. If the structure is constrained from expanding or contracting, stresses can increase in the structure. For extreme temperature changes, these stresses can exceed the yield strength of the material. This can result in permanent deformation of the structure. If the extreme temperature changes are cyclic, incremental deformations can occur with each cycle. Coupon or full-scale tests can be conducted to determine if the incremental damage caused by thermal cycling will lead to low-cycle/plastic fatigue failure.
If equipment operates at high temperatures for prolonged periods, material creep and stress-relaxation can occur. This can lead to permanent deformations. Upon cooling, the deformed equipment may be subjected to large residual stresses and cracking. The challenge with measuring these high-temperature processes is that they can occur over long periods of time. Advanced material testing methods infer long-term material performance while keeping testing times reasonable.
The rate of temperature change can also have an impact on equipment performance. Rapid changes in temperature can cause temperature gradients in large structures. This can lead to differential thermal expansion and non-uniform stresses in structural components. Thermal shock can occur when systems operating at high temperature are suddenly quenched with cold fluid or gas. In subsea or polar regions applications, where the environment is normally cold, thermal shock can occur when warm oil and gas from deep in the earth are brought to surface.
Structural testing scenarios where high or low temperature conditions need to be considered include:
- Low temperature;
- Fracture propagation in girth welds in Arctic pipelines;
- Fill/empty cycling of composite compressed natural gas storage vessels with cooling due to the Joule-Thomson effect;
- Thermal shock loading of subsea valves;
- High temperature;
- Well casing connection performance in high pressure, high temperature (HPHT), thermal and geothermal wells; and
- Structural performance of downhole tools.