07111 Correlation of Half-Inch Diameter, Mini-Pipe Tests with API Full Size Tests of Casing with Internal Pressure in H2S Environment

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Product Number: 51300-07111-SG

ISBN: 07111 2007 CP

Author: Paul Cernocky, Pete Moore, and Leslie Cernocky

Publication Date: 2007

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Testing using miniature pipe specimens called mini-pipes has been introduced previously as a means to evaluate casing materials loaded with three-dimensional, pressure-induced stresses and one-sided or two-sided H2S exposure.1-3 Hollow mini-pipe specimens are able to expose the material to the type of stresses it can see in well service, and this type of testing can be used to determine combinations of three-dimensional (triaxial) stresses and through-wall hydrogen gradients which lead to pipe failure.2 Likewise, full-scale tests by API have been reported4-6 of casing subjected to internal pressures with ID and OD H2S exposure. This paper reports tests of mini-pipes machined out of the same parent casing-joint material as the API full-scale H2S tests and subjected to similar internal pressures and H2S exposure. The mini-pipe pass and fail tests are shown to correlate with the full-scale API tests. Scaling of the mini-pipes in terms of the diameter-to-wall ratio is explained. Mini-pipes exposed to H2S and loaded to the same percentage of the yield pressure as the full-size casing are shown to fail, while mini-pipes loaded to a lower percentage of yield are shown not to fail. Then mini-pipe tests of the same material are used to demonstrate how the pipe performed significantly better under one-sided, internal H2S exposure than under combined internal-external H2S exposure.