Accurate Estimation of Yield Strength and Ultimate Tensile Strength through Instrumented Indentation Testing and Chemical Composition Testing

Abstract

Federal rule changes governing natural gas pipelines have made non-destructive techniques, such as instrumented indentation testing (IIT), an attractive alternative to destructive tests for verifying properties of steel pipeline segments that lack traceable records. Ongoing work from Pacific Gas and Electric Company’s (PG&E) materials verification program indicates that IIT measurements may be enhanced by incorporating chemical composition data. This paper presents data from PG&E’s large-scale IIT program that demonstrates the predictive capabilities of IIT and chemical composition data, with particular emphasis given to differences between ultimate tensile strength (UTS) and yield strength (YS). For this study, over 80 segments of line pipe were evaluated through tensile testing, IIT, and compositional testing by optical emission spectroscopy (OES) and laboratory combustion. IIT measurements of UTS were, generally, in better agreement with destructive tensile data than YS and exhibited about half as much variability as YS measurements on the same sample. The root-mean squared error for IIT measurements of UTS and YS, respectively, were 27 MPa (3.9 ksi) and 43 MPa (6.2 ksi). Next, a machine learning model was trained to estimate YS and UTS by combining IIT with chemical composition data. The agreement between the model’s estimated UTS and tensile UTS values was only slightly better than the IIT-only measurements, with an RMSE of 21 MPa (3.1 ksi). However, the YS estimates showed much greater improvement with an improved RMSE of 27 MPa (3.9 ksi). The experimental, mechanical, and metallurgical factors that contributed to IIT’s ability to consistently determine destructive UTS, and the differences in its interaction with composition as compared to YS, are discussed herein.

Hot Deformation Behavior of C-Mn Steel with Incomplete Recrystallization during Roughing Phase with and without Nb Addition

“…For quantitative pearlite determination and estimation of potential changes in the R m , the equation by Pickering was taken from [29]. The FG size distribution was determined using ImageJ software (ImageJ 1.53k, open source software, NIH, Bethesda, MD, USA) by manually outlining the FG crystal boundaries on FE-SEM micro-photographs and the results are presented by Feret's diameter.…”

“…The relatively high Nb content in 240 Nb allows a sufficient phase fraction of Nb(C,N) needed for the Zener pressure for MFS comparison. An equation for ferrite-pearlite steels provided by Pickering was taken from [5,29,32] and used for strength estimation. Similar compositions are found for flat structural products as they are common for so-called commodity grades as presented in [33]; if needed, they are modified by introducing V for controlled post-rolling precipitation for additional strength increase.…”

Ensuring natural gas infrastructure is suitable for hydrogen service

“…52 Specialized inspection techniques such as instrumented indentation testing to determine hardness may assist in identifying sections of piping that are out of specification for HCNG service. 53 Additionally, establishing the API pipe classification of each segment of the piping may assist with setting appropriate inspection frequencies. 54…”

“…A positive materials identification (PMI) program may be required to identify the pipeline metallurgy and determine its compatibility with the intended HCNG service 52 . Specialized inspection techniques such as instrumented indentation testing to determine hardness may assist in identifying sections of piping that are out of specification for HCNG service 53 . Additionally, establishing the API pipe classification of each segment of the piping may assist with setting appropriate inspection frequencies 54…”

Mechanical characterization of FDM parts through instrumented flat indentation

“…Alternatively, non-destructive characterization tests (such as hardness tests) are performed through a technological test that does not directly measure a mechanical characteristic. On the other hand, the measurements from these tests can be correlated to the mechanical behavior [37][38][39][40][41][42][43]. Compared to conventional tests (e.g., tensile tests, compression tests, etc.…”