Predicting the fatigue life of pipelines

The Paris Equation should be familiar to those who’ve taken fracture mechanics in school. It’s an equation used to calculate the fatigue life of a cracked component as it undergoes continuous loading and unloading situations. Now you may think, why would a cracked component continue to be in service? Two practical reasons—one, cracks can develop overtime (period of years) without anyone noticing. So the crack(s), in an oil/gas pipeline for example, will likely go unnoticed until someone comes by for routine maintenance/inspection. Two, it may be very expensive or technically challenge to replace the cracked segment of pipeline right away. Pipelines extend into remote areas and may be difficult to reach in the winter time.

This is where researchers like the University of Windsor’s Dr. Sreekanta Das can help. Dr. Das and his research team have been developing a model based on the Paris Equation to estimate how long a cracked pipeline can be used  in service without causing any dangers of leaking or bursting.

In the school context, the Paris Equation represents a very simple situation—you’re given various values and constants and it’s simply just “plug-and-play”. The only challenge to getting the correct fatigue life estimate is making sure all of the numbers are entered in the same units of measurement.

But using this equation correctly to predict real-life situations (like the fatigue life of an oil/gas pipeline) is more complicated that you may think. “[The Paris Equation] has lots of parameters that will depend on specific applications, materials, load history, and crack shape,” says Das. “It’s your job to figure the parameters to fit into the equation.”

Here’s a link to my latest article in EPCM World where I spoke to Dr. Das about his model on assessing the fatigue life of pipelines.

A photo of  the Trans-Alaska Pipeline system. (Source: Wikipedia)