Session: 05-02-3: Experimental Testing - Session three

Paper Number: 121395

121395 - Transition Curve Fitting of Charpy Test 

Abstract: 

The Charpy V-notch (CVN) impact test is a typical method to evaluate steel pipe toughness and resistance to fracture propagation.  The CVN tests are generally conducted at multiple temperatures to capture the transition from low impact energy nonductile regime to the high impact energy ductile regime.  This transition behavior is represented by the variation along temperature in either measured impact energy or observed shear area percentage at the fracture cross section.  Transition curves fitted from raw test data are used to derive key parameters, such as upper shelf impact energy (EUS) and Shear Area Transition Temperature (SATT).  There are multiple procedures to derive the transition curves, among which two are widely used.  One is developed by M. Rosenfeld in 1996 by proposing the shear area as a Sigmoidal function of temperature.  The other one is recorded in Section 9F.2.3 in API 579/ASME FFS-1 (2021) where impact energy is expressed by a hyperbolic tangent function of temperature.  The selection of fitting approach consequently results in difference in the derived SATT and even EUS, which can generate unnecessary barrier for an operator when compares pipes properties or builds up toughness distribution within their system based on tests from multiple labs.  For consistency purpose, it may be necessary to repeat the transition curve fitting process with consistent approach from raw test data instead of using lab reported SATT and EUS.  The derived SATT and EUS at tested specimen size can then be converted to the equivalent full size values following Zhang and Rosenfeld (2022) approach for comparison, built up databased and distribution, or any other integrity assessment tasks.  In this paper, it first demonstrates that Rosenfeld’s Sigmoidal equation and API 579/ASME FFS-1’s hyperbolic tangent equation can be transferred into the same equation.  Based on it, a simplified fitting procedure is recommended for fitting the transition curves of shear area and impact energy.  This recommended approach takes the advantage in simplicity from Rosenfeld’s approach while maintain certain level of flexibility and robustness from API 579/ASME FFS-1 approaches.  The mathematically detail of the fitting process are discussed for implementation purpose.  Finally, the performance of the procedure is demonstrated through working examples. 

Presenting Author: Fan Zhang Phillips 66

Presenting Author Biography: Dr. Zhang is an Integrity Tech Service engineer at Phillips 66. Before joining the operation company in 2019, he worked as a consultant at Kiefner and Associates. He has published 30 technical papers on pipelines and served in multiple API/ASME standard committees and technical panels for industry conferences.

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