Nondestructive Onsite Grade Verification for Trenchless Applications

Trenchless methodologies represent an innovative and critical approach for the safe and effective management of pipeline infrastructure. The uptake has required collaboration between research firms, contractors and pipeline operators working together to advance a multitude of technologies.

In the material verification space, with the Pipeline and Hazardous Materials Safety Administration (PHMSA) Mega Rule taking effect in 2021, there has been tremendous pressure to develop industry solutions to nondestructively assess pipe grade and safe operating pressure. In-line inspection tools have proven invaluable for corrosion assessment, and currently, there are a handful of available methods to assess material strength and toughness.

The technology is now commonly known by its non-destructive test technique as Automated Ball Indentation (ABI®) and has been used in NRC-regulated programs, by pipeline operators, water companies, and aerospace firms to nondestructively verify their assets.

ABI is a nondestructive mechanical testing technique for determining tensile and fracture toughness properties. It is based on progressive indentation with intermediate partial unloadings until the maximum depth (maximum strain) is reached, and then the indenter is fully unloaded. The ABI® test is a macroscopic (bulk) technique that measures the properties on a small volume of metallic materials.

During an excavation, particularly in high density areas, speed to test and concurrently assess pipe grade can prove critical to cost control, savings, traffic control on paved streets and site management. Both the ABI® test method and overall speed of the technology allows operators to realize significant savings and safety advantages over conventional destructive testing costs.

ABI provides a nondestructive measurement of tensile properties and fracture toughness that eliminates the need to cut any samples. The ball indentations are shallow, with smooth edges and produce compressive stresses in the material that retard crack initiation. Each test is performed in under five minutes (three tests per location are recommended to determine average values and their standard deviations) and measure the following key mechanical properties: yield strength, true-stress/true-plastic strain curve, strain-hardening exponent, strength coefficient, uniform ductility, ultimate strength, and initiation fracture toughness.

ABI is an ideal technique for measuring material properties quickly and nondestructively. The testing system can be lowered into and pulled out of the keyhole in less than an hour and immediately provide the data and results needed.

Smart-pig MFL tools and nondestructive ABI® testing are complementary. A salient example is a run that discovered a 50-foot pipe joint (12-inch outer diameter) with a reported wall thickness of 0.281 inches while the rest of the pipeline had a wall thickness of 0.312 inches of Grade X52. The ABI® tests determined and confirmed that the joint met Grade X65, so the maximum allowable operating pressure (MAOP) of the line did not need to be lowered since the increased grade compensated for the reduced thickness.

As operators assemble their plans for the coming decade, technology adoption will be critical for the industry. ABI® satisfies NDT requirements of 49 CFR §192.607, and the technology has been used and validated numerous times across multiple industries and countries.