The double cantilever beam (DCB) test is being increasingly used in the process of qualifying materials for sour service. Although the DCB test has been standardized in NACE Standard TM0177, Method D,
it is acknowledged that variables such as specimen geometry, test temperature and initial loading can affect Klssc values even when they remain within the tolerances of the test method. This can make it challenging to set uniform acceptance/rejection criteria. Understanding the behaviour of subsize DCBs is particularly important because many components in sour service can only be tested using subsize DCBs. The present work shows that specimen geometry, test temperature and loading conditions are all related. An empirical specimen thickness and test temperature correlation is given for an API 5CT T95 material. An explanation for the observed behaviour for carbon and low alloy steels is given and implications for both performers of the test method and end users of the tested components are discussed. Potential changes to the NACE International TM0177 Method D test are considered.
Keywords: TM0177, double cantilever beam, DCB, testing, hydrogen sulfide, steel, sulfide stress cracking, specimen size, test temperature, specimen compliance, arm displacement, test methodology