|Publisher||Society of Petroleum Engineers||Language||English|
|Content Type||Conference Paper|
|Title||Accelerated Sulfide Stress Cracking Tests for Threaded Tubular Components|
|Authors||Lee, K.A., Hughes Tool Co.|
SPE/IADC Drilling Conference, 5-8 March 1985, New Orleans, Louisiana
|Copyright||Copyright 1985, SPE/IADC 1985 Drilling Conference|
Two new sulfide stress cracking (SSC) tests have been developed which can be used to evaluate materials for use in threaded tubular components. A modified tensile specimen, used with the test guidelines outlined in National Association of Corrosion Engineers (NACE document TM-01-77, produces data in short testing times which can be easily evaluated to determine SSC resistance of materials at various hardness and loading levels. A dynamic SSC test for full size tool joint assemblies has been developed which produces brittle failures in the area of the last engaged thread of the tool joint pin. These two tests coupled together can be used for evaluation of materials for use in hostile drilling environments.
Increased drilling activity in deep, sour gas wells results in an increased incidence of brittle failures in standard API approved tool joints. In an effort to produce a more sour gas resistant threaded connection, produce a more sour gas resistant threaded connection, many manufacturers are aggressively testing new alloy modifications. The most common "accelerated" sulfide stress cracking test used for alloy evaluation is the NACE TM-01-77 procedure which makes use of a smooth tensile specimen. Use of this test presents problems for manufacturers of threaded components problems for manufacturers of threaded components such as tool joints, because of an inherent vagueness in the way data in this test is generated, presented and evaluated. In addition, the NACE smooth tensile specimen can require test times up to 720 hours. A modification of the test specimen used with TM-01-77 has been developed and extensively tested at Hughes Tool Company. The specimen incorporates a rounded notch, designed to simulate the last engaged thread (LET) area of a tool joint pin. The test data is much more rapidly obtained and can be readily evaluated to determine a material's resistance to SSC at any hardness level and loading condition.
A fixture for testing of full size tool joint assemblies has been developed which produces a brittle fracture that is very similar to H2S induced tool joint failures experienced in the field. The test involves rotation of the assembly were immersed in the NACE solution. Provision for removal of iron sulfide film from be en Provision for removal of iron sulfide film from be en 01) surface has been made and the data indicates that this test is viable for evaluation of full size assemblies.
NACE Task Force T-1F-9 developed an "accelerated" sulfide stress cracking (SSC) test for use with smooth tensile specimens in 1977. This test was designed to allow analysis of sulfide stress cracking susceptibility of ferrous and non-ferrous alloys for use in hostile oil field environments. The test method was designed to test materials subjected to an aqueous environment containing hydrogen sulfide (H2S) while under the influence of a tensile load. As stated in document TM-01-77, the test was designed to introduce hydrogen atoms into the steel which then diffuse to regions of high triaxial stress where they become trapped and induce delayed brittle fracture. The specimen configuration for use with TM-01-77 is a smooth tensile specimen as shown in Figure 1. This specimen is the same as the tensile specimen called for in ASTM A-370. The specimen has no external stress raisers and relies on internal stresses at defects to produce the triaxial stress effect. produce the triaxial stress effect. The NACE test procedure calls for testing the specimen at incremental levels of applied stress which correspond to specific yield strength percentages of the material. The data is reported as a semilogarithmic plot of percent of yield strength (applied stress) versus time to failure. The data can be used to determine an applied stress level at which failure will not occur for a specified length of time. The NACE criteria of no failure in 720 hours defines this threshold stress level. In oil field applications of tubular components, API Specification 7 for Drilling Equipment requires a specific minimum yield strength of 120 ksi (827 MPa).
|File Size||725 KB||8|