Stress Corrosion Cracking of CRAs in Completion Brines
Authors: Bybee Karen 
Published: February 2015

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 90188, "Oilfield Environment-Induced Stress Corrosion Cracking of CRAs in Completion Brines," by Richard Stevens, SPE, Mingjie Ke, SPE, Paul H. Javora, SPE, and Qi Qu, SPE, BJ Services Co., prepared for the 2004 SPE Annual Technical Conference and Exhibition, Houston, 26-29 September.

Failures, caused by stress corrosion cracking (SCC), of corrosion-resistant-alloy (CRA) production tubing and sand-control screens have been reported in recent years. Increased use of CRA materials for downhole applications is the result of requirements for high-pressure/high-temperature and sour-production environments. The full-length paper presents comprehensive results from SCC evaluations of various CRA materials in different oilfield environments.

Introduction

Recent failures of high-strength CRAs have been reported for high-temperature applications involving low-density calcium chloride (CaCl2) packer fluids. One failure was reported for super 13Cr 95 ksi in an 11.0-lbm/gal CaCl2 brine inhibited with ammonium bisulfite (NH4HSO3), a morphorline-based corrosion inhibitor, and glutaraldehyde in a well with a bottomhole temperature of approximately 300°F. Failure analysis concluded that the presence of oxygen, CO2, and hydrogen sulfide (H2S) in the CaCl2 brine was the most likely cause of the cracking. Extensive laboratory evaluation demonstrated that similar SCC susceptibility could occur in CaCl2 brine by lowering the pH or by not adding an inhibitor package. Comparative testing demonstrated that cracking did not occur when calcium bromide (CaBr2) or sodium bromide (NaBr) brine environments were used.

Another failure in 11.3-lbm/gal CaCl2 inhibited with NH4HSO3, sodium thiocyanate (NaSCN), and glutaraldehyde was reported for 25Cr 130 ksi at approximately 350°F. The tubing failed by chloride SCC from the CaCl2 packer fluid, most probably as the result of an air ingress into the annulus.

Since the failures of high-strength CRAs have been reported, massive efforts have been mobilized to understand the problem, identify the controlling factors, determine operational limits for brine/metal combinations, and supply safe brines for packer-fluid applications. The full-length paper is the continuation of an ongoing extensive research-and-development effort to better understand cracking issues, and it presents additional data to further identify and provide safe packer fluids.

Experiments

SCC Tests. C-ring coupons were cut from tubular samples of 22Cr 140-ksi duplex stainless steel, HP1 13Cr 110 ksi, super 13Cr 110 ksi, super 13Cr 95 ksi, modified 13Cr 110 ksi, 13Cr 95 ksi, and 13Cr 85 ksi. Specimens were stressed to 90 or 100% of the actual yield strength of the material using the 0.2% offset calculation as specified by the Natl. Assn. of Corrosion Engineers. Immediately after a specimen was stressed, it was immersed into the test brine and was inserted into a 1-L pressure cell. The test brine was pretreated with the inhibitor package if used, but was not degassed or purged to remove dissolved oxygen. This procedure was used to reflect prevailing field operations. The pressure cell then was sealed.