The recent introduction of KIAPPLIED to the TM0177 Method D test method is explained and discussed. The reporting of KIAPPLIED allows end users to calculate an equivalent NACE KISSC from DCB results that would be considered “offspec” when considering NACE or API requirements. If the crack path is valid, you can still get some information from the test.
The NACE TM0177 Method D [1] (DCB) test is a test method for specifying the performance of steels for sour service. It has been successfully used as a quality assurance test for many years and is generally accepted as one of the most discriminating tests for sulfide stress cracking resistance of carbon and low alloy steels. This is because the test method is based on fracture mechanics principles that give a real measure of material resistance to cracking mechanisms such as sulfide stress cracking. There have been numerous papers discussing the DCB and its use. Most of these can be found in NACE International publications, with some more recent examples given in references [2 to 10]. Recently, both API and NACE committees have moved to require the test provider provide more information. These changes are explained and the possible applications by the end user of the test method are discussed. This paper is not meant as an exhaustive literature survey but more to help users understand the changes and potential implications that will enhance the use of the test method for material qualification and as a tool for design. The information contained in this paper consists of factual data and technical interpretations and opinions, which, while believed to be accurate, are offered solely for information purposes. No representation or warranty is made concerning the accuracy of such data, interpretations and opinions.
The changes are summarized below at the time of writing based on the 2005 edition of TM0177. Note that the next edition of TM0177 will be balloted and may contain changes in both wording and numbering. Changes are in italics.
Background Equations The NACE TM0177 Method D test is a blend of interactive physical and chemical conditions. See Figure 1 for a schematic of the DCB. It is important to note that the overriding mechanical assumption is that the DCB is properly machined according to the requirements in the test method. I refer to a previous paper [9] for background information. The measured arm displacement is compared to the arm displacement calculated from final results of crack length and lift-off load as per equations 7 and 1. Figure 3 shows the minimum, maximum and average differences for the various target arm displacements from reference [9] and Table 1 summarizes the percentage changes. These indicate the change in the effective arm displacement when cracking arrests. Negative values mean smaller arm displacements. For this data, the loading of the wedge into the DCB was conducted using a vice method. Larger arm displacement relates to greater force to insert the wedge.
