ISO/TC 156/WG 2 - Environmentally assisted cracking

This document establishes requirements for designing tests and test specimens and conducting tests to assess susceptibility of additively manufactured metals and alloys to localized corrosion and environmentally assisted cracking in aqueous solutions.

1.1 This document specifies procedures for designing, preparing and using pre-cracked specimens for investigating the susceptibility of metal to stress corrosion cracking (SCC) by means of tests conducted under rising load or rising displacement. Tests conducted under constant load or constant displacement are dealt with in ISO 7539-6. The term “metal” as used in this document includes alloys. 1.2 Because of the need to confine plasticity at the crack tip, pre-cracked specimens are not suitable for the evaluation of thin products such as sheet or wire and are generally used for thicker products including plate, bar, and forgings. They can also be used for parts joined by welding. 1.3 Pre-cracked specimens can be stressed quantitatively with equipment for application of a monotonically increasing load or displacement at the loading points. 1.4 A particular advantage of pre-cracked specimens is that they allow data to be acquired from which critical defect sizes, above which stress corrosion cracking can occur, can be estimated for components of known geometry subjected to known stresses. They also enable rates of stress corrosion crack propagation to be determined. 1.5 A principal advantage of the test is that it takes account of the potential impact of dynamic straining on the threshold for stress corrosion cracking. 1.6 At sufficiently low loading rates, the threshold stress intensity factor for susceptibility to stress corrosion cracking, KISCC, determined by this method can be less than or equal to that obtained by constant load or displacement methods and can be determined more rapidly.

This document specifies a method for determining the growth rate of small surface cracks in an aqueous environment (including atmospheric exposure) based on measurement of the change in size of the crack with exposure time. The methodology can be applied to stress corrosion and corrosion fatigue crack propagation. It also describes the varied methodologies for the generation of crack precursors including accelerated generation of single pits. Industries for whom this document is relevant include power generation (including nuclear), oil and gas, aerospace and automotive.

This document specifies a method for the determination of resistance to stress corrosion cracking (SCC) of magnesium alloys intended for use in structural applications (such as magnesium front end, gearbox and clutch housing units, steering column parts, shift actuators, valve covers and housings, brackets and intake manifold blades, electronic devices, power tools and medical equipment). The method allows determination of the resistance to SCC as a function of the chemical composition, the method of manufacture and heat treatment of magnesium alloys. The document is applicable to cast and wrought magnesium alloys in the form of castings, semi-finished products, parts and weldments and covers the method of sampling, the types of specimens, the loading procedure, the type of environment and the interpretation of results. The document allows assessment of the relative performance of materials and products in environments containing chlorides or sulphates, provided that the failure mechanism is not changed, but does not qualify a material or product for service application.

This document specifies procedures for designing, preparing and using precracked specimens for investigating susceptibility to stress corrosion. It gives recommendations for the design, preparation and use of precracked specimens for investigating susceptibility to stress corrosion. Recommendations concerning notched specimens are given in Annex A. The term "metal" as used in this document includes alloys. Because of the need to confine plasticity at the crack tip, precracked specimens are not suitable for the evaluation of thin products, such as sheet or wire, and are generally used for thicker products including plate bar and forgings. They can also be used for parts joined by welding. Precracked specimens can be loaded with equipment for application of a constant load or can incorporate a device to produce a constant displacement at the loading points. Tests conducted under increasing displacement or increasing load are dealt with in ISO 7539-9. A particular advantage of precracked specimens is that they allow data to be acquired, from which critical defect sizes, above which stress corrosion cracking can occur, can be estimated for components of known geometry subjected to known stresses. They also enable rates of stress corrosion crack propagation to be determined. The latter data can be taken into account when monitoring parts containing defects during service.

ISO 6509-2:2017 specifies assessment criteria and provides guidance related to the corrosion type dezincification for the selection of copper alloys with a mass fraction of zinc of more than 15 %, exposed to fresh, saline waters or drinking water. The assessment criteria are based on the exposure tests in ISO 6509‑1. The materials can be in the form of a semi-finished product or in the form of a final product (fittings, valves, etc.). ISO 6509-2:2017 is not applicable to complex products like flow-meters or pump-parts. In addition, other properties of the material might need to be taken into account for the intended application. This document is not intended to validate dezincification in case of failure in the application.

ISO 16540:2015 provides guidelines for the use of four-point bend testing to evaluate the resistance of metals including carbon steel, low alloy steels, and corrosion resistant alloys (CRAs) to stress corrosion cracking. The method gives guidance on testing of both parent plate and welds and includes procedures for metals that have no distinct yield point in their stress-strain behaviour as well as metals with a distinct yield point. The emphasis in this International Standard is on the generic methodology of the four-point bend test. Service application will be varied and the relevant industry standard is to be consulted where appropriate.

ISO 17081:2014 specifies a laboratory method for the measurement of hydrogen permeation and for the determination of hydrogen atom uptake and transport in metals, using an electrochemical technique. The term "metal" as used in ISO 17081:2014 includes alloys. ISO 17081:2014 describes a method for evaluating hydrogen uptake in metals, based on measurement of steady-state hydrogen flux. It also describes a method for determining effective diffusivity of hydrogen atoms in a metal and for distinguishing reversible and irreversible trapping. ISO 17081:2014 gives requirements for the preparation of specimens, control and monitoring of the environmental variables, test procedures and analysis of results. ISO 17081:2014 may be applied, in principle, to all metals for which hydrogen permeation is measurable and the method can be used to rank the relative aggressivity of different environments in terms of the hydrogen uptake of the exposed metal.

ISO 6509-1:2014 specifies a method for the determination of dezincification depth of copper alloys with zinc exposed to fresh, saline waters or drinking water. The method is intended for copper alloys with a mass fraction of zinc more than 15 %. ISO 6509-1:2014 describes only the test methodology and does not set out criteria for acceptability of materials for a specific application. Acceptance criteria are described in ISO 6509‑2.

ISO 7539-11:2013 gives guidance on the key features that should be accounted for in designing and conducting tests to evaluate the resistance of a metal or its alloy to hydrogen embrittlement and hydrogen-assisted cracking.

ISO 21601:2013 provides guidelines on the appropriate steps to take when a stress corrosion crack has been detected in service and an assessment has to be made of the implications for structural integrity. Such an evaluation should be made in the context of the perceived consequences of failure using appropriate risk-based management methodologies. Since this is application-specific, it is beyond the scope of ISO 21601:2013.

ISO 7539-1:2012 describes the general considerations that apply when designing and conducting tests to assess susceptibility of metals to stress corrosion. ISO 7539-1:2012 also gives some general guidance on the selection of test methods.

ISO 7539-7:2005 covers procedures for conducting slow strain rate tests for investigating susceptibility of a metal to stress corrosion cracking, including hydrogen-induced failure. The term "metal" as used in this part of ISO 7539 includes alloys. Slow strain rate tests are adaptable for testing a wide variety of product forms, including plate, rod, wire, sheet and tubes, as well as composites of these and parts joined by welding. Notched specimens may be used, as well as initially plain specimens. The principal advantage of the test is the rapidity with which susceptibility to stress corrosion cracking of a particular metal/environment combination can be assessed.

ISO 9591:2004 specifies a method for the determination of resistance to stress corrosion cracking (SCC) of aluminium alloys. It covers the method of sampling, the types of specimens, the loading procedure, the type of environment and the interpretation of results. This International Standard is aimed at determining resistance to SCC as a function of the chemical composition, the method of manufacture and heat treatment of aluminium alloys. It applies to cast and wrought aluminium alloys in the form of castings, semi-finished products, parts and weldments. Since most natural and many artificial environments contain chlorides, ISO 9591:2004 can be used to compare the performance of products employed under marine atmospheres and in environments containing chlorides, providing that the failure mechanism is not changed.

1.1 This International Standard specifies the procedure for determining the relative resistance of stainless steels and nickel-base alloys to stress corrosion cracking in a sodium chloride drop evaporation system. 1.2 The method results in a threshold stress to fracture, the magnitude of which can be used to rank the relative performance of different alloys for this environment.

Covers procedures for designing, preparing and using U-bend test specimens. These specimens may be used to test a variety of product forms (for example sheet, plate, flat extruded material, wire or rod). The principal acvantages of the U-bend test are its simplicity and its adaptability for use in plants. A disadvantage is that stesses cannot be quantified with accuracy. U-bend specimens made from high strength materials may fracture rapidly and can be dangerous.

Covers procedures for designing, preparing, stressing, exposing and inspecting C-ring specimens. These versatile, economical specimens may be used to test a variety of product forms including parts joined by welding. C-ring specimens may be stressed to predeterminded levels, using simple equipment for application of either constant load or constant strain.

Covers procedures for designing, preparing and using uniaxially loaded tension specimens. These specimens may be used to test a variety of product forms (for example sheet, plate, tubes, wire or rod as well as parts joined by welding, riveting, or other methods). Uniaxially loaded tensile specimens may be stressed quantitatively with equipment for application of either a constant load, a constant strain or an increasing load or strain.

Covers procedures for designing, preparing and using bent-beam test specimens. These specimens may be used to test a variety of product forms (i. e. sheet, plate, flat extruded material, wire or rod). They are espesially suitable for multiple testing and for atmospheric stress corrosion tests; they are usually tested under nominally constant strain conditions. Bent-beam specimens made from high strength materials may fracture rapidly and can be dangerous.

ISO 7539-6:2011 covers procedures for designing, preparing and using precracked specimens for investigating susceptibility to stress corrosion. It gives recommendations for the design, preparation and use of precracked specimens for investigating susceptibility to stress corrosion. The term "metal" as used in ISO 7539-6:2011 includes alloys. Because of the need to confine plasticity at the crack tip, precracked specimens are not suitable for the evaluation of thin products, such as sheet or wire, and are generally used for thicker products including plate bar and forgings. They can also be used for parts joined by welding. Precracked specimens can be loaded with equipment for application of a constant load or can incorporate a device to produce a constant displacement at the loading points. Tests conducted under increasing displacement or increasing load are dealt with in ISO 7539-9. A particular advantage of precracked specimens is that they allow data to be acquired from which critical defect sizes, above which stress corrosion cracking can occur, can be estimated for components of known geometry subjected to known stresses. They also enable rates of stress corrosion crack propagation to be determined. The latter data can be taken into account when monitoring parts containing defects during service.

ISO 17081:2004 specifies a laboratory method for the measurement of hydrogen permeation and for the determination of hydrogen atom uptake and transport in metals, using an electrochemical technique. The term "metal" as used in this International Standard includes alloys. This International Standard describes a method for evaluating hydrogen uptake in metals, based on measurement of steady-state hydrogen flux. It also describes a method for determining effective diffusivity of hydrogen atoms in a metal and for distinguishing reversible and irreversible trapping. ISO 17081:2004 gives requirements for the preparation of specimens, control and monitoring of the environmental variables, test procedures and analysis of results. This International Standard may be applied, in principle, to all metals for which hydrogen permeation is measurable and the method can be used to rank the relative aggressivity of different environments in terms of the hydrogen uptake of the exposed metal.

ISO 7539-9:2003 covers procedures for designing, preparing and using pre-cracked specimens for investigating the susceptibility of metal to stress corrosion cracking by means of tests conducted under rising load or rising displacement. The term "metal" includes alloys. Because of the need to confine plasticity to the crack tip, pre-cracked specimens are not suitable for the evaluation of thin products such as sheet or wire and are generally used for thicker products including plate, bar and forgings. They can also be used for parts joined by welding. A particular advantage of pre-cracked specimens is that they allow data to be acquired from which critical defect sizes, above which stress corrosion cracking may occur, can be estimated for components of known geometry subjected to known stresses. They also enable rates of stress corrosion crack propagation to be determined. A principal advantage of the test is that it takes into account the potential impact of dynamic straining on the threshold for stress corrosion cracking.

ISO 7539-6:2002 covers procedures for designing, preparing and using pre-cracked specimens for investigating susceptibility to stress corrosion. It gives recommendations for the design, preparation and use of pre-cracked specimens for investigating susceptibility to stress corrosion. The term "metal" as used in this part of ISO 7539 includes alloys. Because of the need to confine plasticity at the crack tip, pre-cracked specimens are not suitable for the evaluation of thin products such as sheet or wire and are generally used for thicker products including plate bar and forgings. They can also be used for parts joined by welding.

Specifies the general principles, the apparatus and materials, the sampling, the specimens, the procedure, the assessment of results and the test report. Describes the grain orientation examination.

Covers procedures for designing, preparing and using pre cracked specimens . Recommendations concerning notched specimens are given in annex A. These specimens are not suitable for the evaluation of thin product (sheet or wire); they are generally used for plate, bar and forgings. Their advantage is that they allow date to be acquired from which critical defect sizes, above which stress corrosion cracking may occur, can be estimated.

Covers procedures for conducting slow strain rate tests for investigating susceptibility to stress corrosion cracking, including hydrogen-induced failure. They are adaptable for testing a wide variety of product forms. Their advantage is the rapidity with which susceptibility to stress corrosion cracking of a particular metal/environment combination can be assessed.

Descsribes the general considerations which apply when designing and conducting tests to assess susceptibility of metals to stress corrosion. Particular methods of test are not treated in detail in this document. These are specified in the additional parts of ISO 7539.

The method applies to brass exposed to frech or saline waters. May be used for control or research purposes, but the field of application is not specified. The method consists of exposure of test pieces to copper(II) chloride solution followed by microscopic examination.