In-Situ Determination of Pipe Body Fracture Toughness Using Planing-Induced Microfracture Method

Abstract Pipe toughness determination as part of nondestructive evaluation (NDE) has been sought for decades. Material toughness is needed when analyzing the critical crack size that would fail at MAOP and when performing a fitness-for-service evaluation with cracks discovered during an inspection. When toughness data is not available, operators may use conservative values, perform cut-outs for lab testing, or use other industry-accepted data, such as collected by nondestructive testing. This paper presents a new in-situ, minimally invasive technique to provide pipe body toughness data using the method of planing-induced microfracture. This method involves using a specialized blade featuring a central opening where the material is stretched and fractured instead of being cut, leading to standing residual ligaments on the fractured surfaces of the sample. Characteristics of these ligaments, such as their height, are shown to correlate with the material’s fracture toughness. Preliminary proof-of-concept testing from 30 samples showed that the method could predict KIc to within ±20% of the values derived from destructive lab testing [1]. In the work presented in this paper, a portable prototype instrument has been developed which can create “islands” on a pipe surface and perform the planing-induced microfracture test. This paper will give an overview of the planing-induced microfracture method, the prototype field instrument, and recent test results using the tool.