BS EN ISO 7539-10:2020 pdf – Corrosion of metals and alloys – Stress corrosion testing Part 10: Reverse U-bend method.
1 Scope This document specifies procedures for designing, preparing and using reversed U-bend (RUB) test specimens for investigating the susceptibility of the metal to stress corrosion cracking. The term “metal” as used in this document includes alloys. 2 Normative references The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 7539-1, Corrosion of metals and alloys — Stress corrosion testing — Part 1: General guidance on testing procedures ISO 8407, Corrosion of metals and alloys — Removal of corrosion products from corrosion test specimens 3? Terms? and? definitions For the purposes of this document, the terms and definitions given in ISO 7539-1 apply. ISO and IEC maintain terminological databases for use in standardization at the following addresses: — ISO Online browsing platform: available at https://www.iso.org/obp — IEC Electropedia: available at http://www.electropedia.org/ 4 Principle The RUB test is a particularly severe test for assessing susceptibility to stress corrosion cracking. The test is intended primarily for application to metals with high corrosion resistance, such as Ni- based alloys, with the advantage, compared to methods such as the conventional U-bend test, of having significantly less stress relaxation. It is used primarily as a screening test for tubing, piping, plate, bar and other products including welded materials. It may also be used as an acceptance test for performance in service subject to agreement between the parties.
The test is normally performed in a laboratory by exposing the specimens to simulated service conditions. A further objective of the test is to compare and evaluate the influence of different material parameters. The principal advantages of the test are its simplicity and its ability to provide a rapid screening. If conventional U-bend or C-ring specimens are used for screening tests in a high temperature solution of 573 K or higher, marked stress relaxation occurs and a long testing time is needed for the evaluation. However, the stress relaxation in RUB specimens is smaller than that in conventional U-bend and C-ring specimens, due to the bi-axial stresses in RUB specimens. Therefore, screening tests can be done within a relatively short time through the use of RUB specimens. A disadvantage is that the stress state is complicated and is difficult to quantify with accuracy. If an accurate stress state is desired, an alternative method should be used. Wide variations in test results can be obtained for a given metal and environment even when testing nominally identical specimens and the replication of tests is frequently necessary. If specimens are prepared from tubing of different dimensions or are subjected to different stressing procedures, test results can be even more variable. 5 Specimens 5.1 General RUB specimens are prepared from pieces of production tubing, piping and other hollow cylindrical products cut into half longitudinally or from a plate, bar or other products formed into a semi-circular shape along the axial direction. The specimens should be cut by sawing or other such methods that do not affect the material properties. Then they should be shaped into their dimensions by machining. The side face of the specimens should be deburred and then finished by sequentially coarse-to-fine grinding using abrasive papers or cloths to a surface finish such as P600 (see ISO 3366 or ISO 21948) without increasing the temperature of the specimens.
The tubing shall retain its original surface finish. If heat treatment is added, final heat treatment shall be performed before the reverse U-bending process (and pre-straining, if this is adopted). 5.2.2 Other products A variety of bar stock, plate and other forged or rolled material or welded material can be employed. These materials shall be machined into a plate after final heat treatment and pressed into a semi- circular shape between inner and outer formers. The surface of the specimens shall be finished by sequentially coarse-to-fine grinding using abrasive papers or cloths up to a surface finish such as P600 (see ISO 3366 or ISO 21948) without increasing the temperature of the specimens before the pressing process. Specimen preparation from a plate is shown in Annexes A and B.