Tygojinn There are two known methods, based on wave propagation theory, for the analysis and interpretation of the dynamic pile load test. The CASE analysis of high strain bearing capacity detection of single pile and tensile stress and compressive stress analysis of piling monitoring can be conducted. Link to Active This link will always route to the current Active version of the standard. The quality of the result produced by this test method is dependent on the competence of the personnel performing it, and the suitability of the equipment and facilities used.
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Mechanisms[ edit ] During hydrogen embrittlement, hydrogen is introduced to the surface of a metal and individual hydrogen atoms[ citation needed ] diffuse through the metal structure. Because the solubility of hydrogen increases at higher temperatures, raising the temperature can increase the diffusion of hydrogen.
When assisted by a concentration gradient where there is significantly more hydrogen outside the metal than inside, hydrogen diffusion can occur even at lower temperatures.
There are a variety of mechanisms that have been proposed:  Internal pressure: Adsorbed hydrogen species recombine to form hydrogen molecules, creating pressure from within the metal. This pressure can increase to levels where the metal has reduced ductility, toughness, and tensile strength, up to the point where it cracks open hydrogen-induced cracking, or HIC. Phase transformations: Phase transformations occur for some materials when hydrogen is present.
Hydrogen enhanced decohesion: Hydrogen enhanced decohesion HEDE where the strength of the atomic bonds of the parent material are reduced.
Hydrogen enhanced localised plasticity: Hydrogen enhanced localised plasticity HELP is the process where the generation and movement of dislocations is enhanced and results in localised deformation such as at the tip of a crack increasing the propagation of the crack with less deformation in surrounding material giving a brittle appearance to the fracture.
Experiments have shown that stationary dislocations begin to move when molecular hydrogen is dissociated and absorbed into pre-strained material. Hydrogen enhanced vacancy formation: Vacancy production can be increased in the presence of hydrogen but since vacancies cannot be readily eliminated this proposal is inconsistent with observations the removal of hydrogen reduces the embrittlement.
Hydrogen enhanced dislocation emission: Hydrogen enhanced dislocation emission proposes that hydrogen is adsorbed onto to the surface and allows dislocations to be generated at lower stress levels thus increasing the level of localised plasticity at the tip of a crack allowing it to propagate more freely.
Material susceptibility[ edit ] Hydrogen embrittles a variety of substances including steel,    aluminium at high temperatures only  , and titanium. This methane does not diffuse out of the metal, and collects in the voids at high pressure and initiates cracks in the steel. This selective leaching process is known as hydrogen attack , or high temperature hydrogen attack, and leads to decarburization of the steel and loss of strength and ductility.
As the strength of steels increases, the susceptibility to hydrogen embrittlement increases. In high-strength steels, anything above a hardness of HRC 32 may be susceptible to early hydrogen cracking after plating processes that introduce hydrogen.
They may also experience long-term failures anytime from weeks to decades after being placed in service due to accumulation of hydrogen over time from cathodic protection and other sources. Numerous failures have been reported in the hardness range from HRC and more above; therefore, parts in this range should be checked during quality control to ensure they are not susceptible.
Copper[ edit ] Copper alloys which contain oxygen can be embrittled if exposed to hot hydrogen. The hydrogen diffuses through the copper and reacts with inclusions of Cu2O, forming H2O water , which then forms pressurized bubbles at the grain boundaries.
This process can cause the grains to literally be forced away from each other, and is known as steam embrittlement because steam is produced, not because exposure to steam causes the problem. Vanadium, nickel, and titanium[ edit ] A large number of alloys of vanadium, nickel, and titanium absorb significant amounts of hydrogen.
This can lead to large volume expansion and damage to the crystal structure leading to the alloys becoming very brittle. This is a particular issue when looking for non-palladium based alloys for use in hydrogen separation membranes. The first category is from the preexisting hydrogen already present within the metal from creation and the second category is hydrogen introduced from the environment the metal finds itself in.
Examples of Internal Hydrogen Embrittlement include processes such as casting, carbonizing, surface cleaning, pickling, electroplating, electrochemical machining, welding, roll forming, and heat treatments. Examples of Hydrogen Environmental Embrittlement include generic corrosion from exposure to the environment or through misapplication of various protection measures. Processes that can lead to this include cathodic protection , phosphating , pickling , and electroplating.
A special case is arc welding , in which the hydrogen is released from moisture, such as in the coating of welding electrodes. Other mechanisms of introduction of hydrogen into metal are galvanic corrosion , as well as chemical reactions with acids or other chemicals.
One of these chemical reactions involves hydrogen sulfide in sulfide stress cracking SSC , a significant problem for the oil and gas industries. Embrittling procedures such as acid pickling should be avoided, as should increased contact with elements such as sulfur and phosphate. The use of proper electroplating solution and procedures can also help to prevent hydrogen embrittlement.
Then the same test can be used as a quality control check to evaluate if baking was sufficient on a per-batch basis. In the case of welding, often pre-heating and post-heating the metal is applied to allow the hydrogen to diffuse out before it can cause any damage.
Due to the time needed to re-combine hydrogen atoms into the hydrogen molecules, hydrogen cracking due to welding can occur over 24 hours after the welding operation is completed. Another way of preventing this problem is through materials selection. This will build an inherent resistance to this process and reduce the need of post processing or constant monitoring for failure.
Certain metals or alloys are highly susceptible to this issue so choosing a material that is minimally affected while retaining the desired properties would also provide an optimal solution. Much research has been done to catalog the compatibility of certain metals with hydrogen. Similar tests can also be used during quality control to more effectively qualify materials being produced in a rapid and comparable manner.
For steels, it is important to test specimens in the lab that are at least as hard or harder than the final parts will be. Ideally, specimens should be made of the final material or the nearest possible representative, as fabrication can have a profound impact on resistance to hydrogen-assisted cracking. The test focuses on hydrogen embrittlement of copper alloys, including a metallographic evaluation method A , testing in a hydrogen charged chamber followed by metallography method B , and method C is the same as B but includes a bend test.
The sustained load test is still included in many legacy standards, but the RSL method is increasingly being adopted due to speed, repeatability, and the quantitative nature of the test. The RSL method provides an accurate ranking of the effect of hydrogen from both internal and external sources. The F test is performed by comparing a standard fast-fracture tensile strength to the fracture strength from a rising step load test where the load is held for hour s at each step.
In many cases it can be performed in 30 hours or less. F is based on the F method and is similar to F but with different root radius and stress concentration factors. Catastrophic failures occurred in shear bolts in the span, after only two weeks of service, with the failure attributed to embrittlement, possibly from the environment. Extensive remediation works were initiated.
Looking to qualify new coatings, materials, or cleaners? Rapid Hydrogen Embrittlement Testing per ASTM F, F, and F It g the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. It does so by measuring the threshold for the onset of subcritical crack growth using standard fracture mechanics specimens, irregular-shaped specimens such as notched round bars, or actual product such as fasteners 2 threaded or unthreaded springs or components as identi? For steels less ff 48 HRC, a h step-loading pro? Individual reprints single or multiple copies of aztm standard may be obtained by contacting ASTM at the above address f at phonefax aastm, or service astm. Historically, time-to-failure sustained load tests have been conducted to determine the threshold stress.
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