The new Standard Test Method NACE TM0316 “Four-Point Bend Testing of Materials for Oil and Gas Applications” was published last year in 2016. NACE TM0316 addresses the four point bend testing which is extensively used in the oil and gas industry to qualify materials for sour service.
The four point bend (FPB) test is used to evaluate the resistance of metals to sulphide stress cracking and to stress corrosion cracking. FPB testing is mentioned in the European Federation of Corrosion publication 16 (EFC 16) and EFC 17 as a statically loaded test with referenced to ASTM G38 and ISO 7539-2; these two standards address the specimen preparation and loading. EFC 16 and EFC 17 only provide references to the loading and to the testing solution.
ASTM G39 and ISO 7539-2 provide details on sample preparation and loading. Other ASTM documents such as ASTM G30, G36, G44, G50 provide further on the specific corrosive environments.
NACE MR0175 identified FPB as per EFC 16 guidelines and recommends them. NACE MR0175 also provides some basic guidance for the FPB testing. EFC 16 and EFC 17 as well as NACE MR0175 make reference to NACE TM0177, however NACE TM0177 does not list FPB as one of the testing methods. The new NACE TM0316 closes the gap and provides, in one single document, the necessary information, method and most important failure appraisal.
The new NACE TM0316 provides a general introduction and describes the principle of the test. In section 3 a description of the loading jig design is presented. This is aligned with ASTM G39
Specimen preparation is of utmost importance and is presented in Section 4. In this section the sample preparation of welded specimens provides more detail than any other previous standard. Stain gauging is address in section 5 and loading in section 6.
The test solution and listed ion section 7, the test solutions are A, B or C as per NACE TM0177. Reference is made to the non-mandatory appendix C. Appendix C is extremely useful as a comparison between the requirements of different standards such as NACE MR0175,. NACE TM0177 and EFC 16
The test procedure is detailed in section 8. Failure appraisal is presented in Section 9 and the requirements for the test report are shown in section 10.
This new standard is already being used by several laboratories and being incorporated in several specification for oil and gas operators. The use of this standard will not disrupt current testing programmes and it is already providing clear guidance for testing.
At Oil & Gas Corrosion we can assist you in the following areas:
Reviewing previous Four Point Bend testing against the requirements of NACE TM0316
Specifying a testing programme that covers FPB testing and managing the testing laboratories
Defining the requirements for FPB