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Differential Diagnostics Episode 2

When plain dents, metal loss and gouging occur in the same area, it increases the possibility of pipeline failure. Is it possible to identify interacting threats?


In our last episode, we discussed the challenges of quantifying mechanical damage. To better understand why this is so critical, let's take a closer look at how mechanical damage can impact a pipeline's integrity. No two pipelines are quite the same, and no two instances of damage are ever identical. Impacts to pipeline integrity as a result of mechanical damage can occur in many ways.

Sometimes the consequences of mechanical damage are delayed and relatively minor. In other cases, they are instantaneous and catastrophic. Mechanical damage can occur when a line is struck from above, possibly during construction, excavation or other above-ground activities. It can also occur from below, possibly from rocks or other debris impacting a line when it is initially installed, or as a result of gradual soil movements. And when a line is decades old, as so many are, the opportunities for mechanical damage during those years are numerous.

But what is mechanical damage? What are its defining characteristics? In many cases, damage causes a dent which changes the shape of the pipeline, compromising its circumference and internal diameter. A dent has length, width, depth and strain; characteristics that are identifiable and measurable. Sometimes coincidental metal loss occurs with a dent, usually resulting from coating damage incurred at the time of a third-party strike or a construction defect. If gouging is present, micro-structural damage to the pipeline material can occur and may even cause cracking.

When impacts occur at pressure, there is a likelihood the dent will re-round. If line pressure fluctuates, pressure cycles result, and dents can be cycled. As this occurs, residual stresses are produced in the dent area. Increasing the potential for cracking and failure, plain dents, metal loss, gouging, residual stresses, cracking, isolated or interacting, these flaws can severely compromise the integrity of a pipeline. So, the question becomes, what technologies exist to help operators better understand these pervasive integrity threats?

Differential diagnostics, the power to know more.