SOHIC Resistance of C-Mn Plate Steels Used in Refinery Service

Cayard, Michael S. (InterCorr International Inc.) | Kane, Russell D. (InterCorr International Inc) | Horvath, Richard J. (Equilon Enterprises LLC)

OnePetro 

ABSTRACT
This research effort was designed to evaluate stress-oriented hydrogen-induced cracking (SOHIC) behavior of a broad range of advanced plate steels (<0.002 wt% sulfur) with various microstructures, compositions, types of metallurgical processing, welding and postweld heat treatment (PWHT). This behavior was examined in terms of apparent threshold stresses as a function of the above mentioned variables. These data were compared and contrasted to the performance of conventional plate steels (>0.002 wt% sulfur) that were not produced to enhance resistance to cracking in wet H2S environments. Test results indicated that SOHIC resistance was adversely affected by microstructural (ferrite/pearlite) banding. However, additional factors also played a role in determining SOHIC behavior . A relationship was developed for the predicted average cracking ratio (PACR) that included the influence of banding index, carbide microhardness and calcium treatment.

INTRODUCTION
This study was conducted by InterCorr International, Inc. over the period October 1994 through October 1996, as part of a Phase II Hydrogen-Induced Cracking (HIC) Research Joint Industry Program organized by The Materials Properties Council, Inc (MPC). The purpose of the study was to produce a 1 Copyright .2002 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole must be in writing to NACE International, Publications Division, 1440 South Creek Drive, Houston, Texas 77084-4906. The material presented and the views expressed in this paper are solely those of the author(s) and not necessarily endorsed by the Association. Printed in U.S.A. more quantitative assessment of the role of microstructure, section size, applied stress, welding, postweld heat treatment (PWHT) and other important variables on the resistance of advanced plate steels to stress-oriented hydrogen-induced cracking (SOHIC) in wet H2S environments.

In a previous study it was found that steels could be processed to produce increased resistance to HIC (i.e., planar, blister crack formation) resulting from hydrogen charging in wet H2S environments [1]. However, it was also observed that these steels varied substantially in their resistance to SOHIC (i.e., through-thickness crack propagation) resulting from hydrogen charging in wet H2S environments under conditions of applied tensile stress. In some cases, steels that had little to no HIC susceptibility exhibited particularly high susceptibility to SOHIC.

In this same work, it was found that microstructure was an important variable affecting SOHIC susceptibility of advanced steels. Furthermore, this work showed that a microstructural ranking system might be possible for use in the prediction of SOHIC susceptibility in advanced steels. In this regard, ferrite/pearlite banding was found to be a major microstructural factor (i.e., steels with little or no banding appeared to have higher SOHIC resistance).