Session: 05-04-01 Fittings and Testing Methods

Paper Number: 86927

86927 - Improved Fracture Toughness Test Method for Single Edge Notched Tension Specimens in Clamped-End Conditions 

In the oil and gas industry, the strain-based design and the pipeline integrity assessment prefer to use the low-constraint fracture toughness that is often measured experimentally using the single edge notched tension (SENT) specimens in the clamped-end conditions. Since 2006 when DNV in Norway published the first SENT fracture toughness test practice, extensive investigations have been performed analytically, numerically and experimentally for developing an effective fracture toughness test method using the clamped SENT specimens, and different SENT test methods were developed, including CANMET and ExxonMobil methods in terms of the J-integral and the crack-tip opening displacement (CTOD). Those efforts led to the first SENT fracture toughness test standard BS 8571 being published in 2014 and updated in 2018.

However, the existing SENT test methods may determine inconsistent test results on fracture toughness for the same specimen due to different equations used for the experimental evaluation. And thus, the SENT experimental evaluation methods need to be further studied and improved for determining reliable fracture toughness data using the clamped SENT specimens. For this reason, this paper performs a comparative study of existing fracture toughness test methods using the clamped SENT specimens with an aim to develop an improved SENT fracture toughness test method. The comparisons are made for the available solutions of the stress intensity factor K, the geometrical eta factors, the elastic compliance equation, and the constraint m factor for converting the J-integral to CTOD that were obtained for the clamped SENT specimens. From the comparisons, the more accurate solutions of the K factor, eta factor, compliance equation and the m factor will be identified. The difference between the J-converted CTOD and double clip gage measured CTOD is also discussed. On those bases, an improved SENT test method is proposed, and the resulting experimental data are compared and evaluated with those from other existing SENT test methods for a pipeline steel and a structural steel.

Presenting Author: Bruce Wiersma Savannah River National Lab

Presenting Author Biography: Dr. Bruce Wiersma is an advisor engineer at SRNL and has been performing the consulting service of corrosion mechanism and corrosion assessment of pressure vessels and storage tanks for more than 30 years.