Nondestructive Residual Stress Assessment of Pipeline Dents and Other Damage

G2MT was recently awarded an SBIR from the US Department of Transportation to develop the next-generation of pipeline inspection tools that will assess the residual stress, rather than the geometry, to determine the susceptibility of pipeline damage to failure. The technologies we are developing will provide much more insight into the nature and severity of the stresses near dents and damage regions. These new nondestructive testing technologies will be coupled with advanced modeling techniques to dramatically improve the capability to not just determine the difference between good and bad amounts of stress but to quantitatively measure the local stress and map the stress around the entire area. Many years of metallurgical research have shown that stress is the most important influence on the potential for failure of a damaged area.

In fact, dents and damaged regions in pipelines form one of the primary areas of concern for pipeline failures. Mechanical damage by third-parties, seismic activity, damage during installation, errors during welding, and many other sources can put residual stresses into pipelines and increase their susceptibility to failure. In fact, Residual stress is the silent killer of many pipelines. It can be introduced in so many ways but may not result in a failure for many years down the road. The reason for the danger is that regions of high residual stress actively draw soluble hydrogen atoms into themselves, ultimately resulting in extremely high levels of hydrogen that then contribute to hydrogen embrittlement. When assisted by the everyday fatigue that pipelines regularly experience, the results can be catastrophic.

The best existing technology for pipeline inspection combines both interior (in-line inspection via a “smart pig) and exterior pipeline inspection methods that are used following the pigging run. The exterior inspections usually require the pipeline to be uncovered and the coating removed for inspection of each pigging indication above a specified size; anything larger than a selected percentage of the pipeline diameter may be chosen for inspection. Magnetic particle inspection, ultrasound, and automated ultrasound testing (AUT) are typically used to assess the severity of the damage, and damage regions exceeding the contractor’s selected specification or the national codes and standards are required to be removed or repaired. The most common specification for dent removal is determined using a caliper gauge, and dents above six degrees, for example, are all removed or repaired. This rather arbitrary number is intended to be conservative but ultimately pipeline operators regularly report that the cracks and failures simply move to other regions that passed the existing dent testing standards.

G2MT Labs 2011 DOT SBIR Main Objective

The project main objective is to develop an advanced residual stress measurement technique to evaluate the damage severity through the coating on coated steels as regulated by Pipeline Safety Regulations 49 CFR Parts 190-195. This nondestructive testing technology will dramatically improve pipeline integrity assessment and reduce the number of unnecessary pipeline replacement and removal actives. During this Phase I part of the investigation, G2MT Labs is developing and will demonstrate the residual stress mapping technique for pipeline dent assessment. In Phase II, the system will be calibrated for a wide range of pipeline types and damage types.


Along with the DOT SBIR project funding, we are proud to announce the support of several excellent industrial and academic partners who are contributing time, materials, effort, and money to the
residual stress testing project. Are you in the pipeline industry and would like to contribute?

– Please contact us today, we welcome other interested parties to join in this research effort.

Other Nondestructive Residual Stress Assessment Tools

Residual stress assessment should be of interest to many industries and applications. Is yours one?

– If you have a need, a great idea, or an interesting application for a nondestructive residual stress sensor for metals, contact us today. We would love to hear about it and see if we can work with you!