Optimization of Side-Groove Configuration of NACE Method D Testing

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Corrosion resistance of low alloy steels for oil country tubular goods (OCTG) is a key point in order to select the suitable material. Among the corrosion test defined in NACE TM0177-2016, Double Cantilever Beam (DCB) testing in accordance with NACE TM0177-2016 Method D can be evaluated corrosion resistance as fracture toughness (K1ssc).

In this methodology, testing operators check the validity of the fracture surface to determine K1ssc in accordance with NACE TM0177 Method D 11.6. Edge cracking has been a big issue for industries.

Product Number: 51323-19218-SG

Author: Hiroki Kamitani, Hisashi Amaya, Keiichi Kondo, Yuji Arai

Publication Date: 2023

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NACE TM0177-2016 Method D testing is a common methodology to evaluate sulfide stress cracking performance in a sour environment. In this methodology, fracture surfaces are evaluated and some invalid cases are documented in accordance to TM0177 Method D 11.6.1. Specifically, edge cracks which occur from the bottom of side groove and prevents crack propagation is a key issue for this methodology and the optimization of side-groove configuration from V shaped side groove to U shaped side groove has been studied to prevent the occurrence.

It was revealed that U shaped side groove can reduce the occurrence of edge cracks by former FEA analysis and Method D test using test specimens in a certain machine shop. On the other hand, there would be some effect of machining of side groove in terms of crack propagation. In this study, we prepared Method D test specimens from API 5CT C110 with V and U shaped side-groove machined by machining company A and B. Afterwards, corrosion tests in 1 bar H2S, pH 2.7 (standard condition for API 5CT C110) were performed. As a result, edge crack was reduced by applying U shaped side groove prepared by both machining shops. It can be concluded that U shaped side groove is generally effective to prevent the occurrence of edge crack.