【正文】 essure, and hydrogen purity, as well as material properties including grain size, hardness, and strength. This section explore how hydrogen embrittlement may ect a hydrogen tower. Evidence suggests that, unlike hydrogen attack, hydrogen environment embrittlement may be most severe at ambient temperatures Like hydrogen attack, however, HEE bees more severe with increasing pressure. Test data suggests that the degree of embrittlement is proportional to the square root of hydrogen gas pressure This suggests that designing turbine towers for relatively lowpressure storage may help prevent hydrogen embrittlement. It is fortunate, therefore, that the storage pressures under consideration are only about 10% of hydrogen pipeline operating pressures. Hydrogen gas purity is another major environmental factor controlling HEE. Experimental evidence has shown that crack propagation in a stressed specimen could be controlled by the introduction of oxygen into the hydrogen environment. Investigators demonstrated that a crack propagating in a pure hydrogen environment could be stopped with the introduction of as little as 200 ppm oxygen at atmospheric pressure Because the method of H2production under consideration is via an electrolyzer, gas will be readily available. Al though adding to H2can result in an explosive mixture, adding the necessary levels of is expected to have little ect on safety. This is because the required oxygen con centration (approximately 200 ppm) is far above the upper bustible limit of hydrogen in oxygen (94% by volume). Two hundred ppm oxygen in hydrogen represents % (by volume) of the oxygen required to create an explosive environment. Steel posed of larger grains with precipitates heavily concentrated along grain boundaries can also expedite HEE because they allow for easier diusion of hydrogen through the metal’s lattice structure The Sourcebook for Hydrogen Applications lists proper control of grain size as a successful measure of HEE prevention Grain size is controlled in the steel forming and treatment process. For tunately, selection of steel plate with the appropriate grain size is not anticipated to be diLcult. Increased material hardness can also magnify the ects of hydrogen embrittlement. Typically, hardness is increased by causing residual tensile stresses in a material’s surface through treatments like forging, cold rolling, or welding. Theoretically, when hydrogen adsorbs to a material’s surface, it decreases the energy required to form a surface crack The bination of these two factors facilitates the for mation of surface cracks. Tower welds are therefore particularly susceptible to HEE because rapid cooling of the welds can cause “hard spots” where carbon and other impurities coalesce. However, as a general guideline, troublefree welds can be obtained in lowalloy steels containing up to about % carbon and to a carbon equivalent (C +14Mn) of % Steels ering the strength assumed in this study (such as S355J0 as speci4ed by British Standard EN 10025 and Grade485 steel as speci4ed by ASTM Speci4cation A 516/A) have equivalent carbon contents of % and %, respectively. These steels require preheating of the joint and the use of lowhydrogen electrodes to protect their welds from HE. Alternatively, the tower’s structural requirements could be met with thicker walls made of steels having lower carbon and manganese contents or possibly by the use of steels which meet the American Petroleum Institute speci4 cation 5L such as X70—a 70 ksi steel which is resistant to hydrogen induced cracking. Another possibility which this study does not address is the use of posite reinforcement of the tower walls. Material strength, a property related to both grain size and hardness, is perhaps the most predominant material property inAuencing hydrogen embrittlement. It has been generally observed that higherstrength steels exhibit greater loss of ductility, lower ultimate strengths, and greater propensity for delayed failure than their lowerstrength counterparts when subjected to a hydrogen environment It is for these rea sons that many experts suggest use of lowerstrength steels for hydrogen applications. Some experts have designated an ultimate strength of 700 MPa as a benchmark, below which steels are signi4cantly less susceptible to HEE Steels monly used for tower construction fall within this bench mark。 towers are typically constructed of a lowstrength, lowcarbon structural steel with yield and ultimate strengths at or below 350 and 630 MPa, respectively.Based on the considerations outlined above, the risk of HEE does not exclude the use of wind turbine towers for hydrogen storage. It is, however, diLcult to pare the use of a wind turbine tower as a pressure vessel to more tra ditional hydrogen applications because, unlike conventional pressure vessels, they are subjected to signi4cant dynamic loads inherent in wind turbine structures. The dynamic struc tural loads applied to a turbine tower would serve to repeat edly open micro4ssures, one mechanism by which HEE is theorized to propagate. Due to the potential for catastrophic failure, HEE requires more research and experimentation.. Structural analysisPressurizing the interior of a wind turbine tower creates unique structural demands. A pressurized tower must not only withstand loads caused by normal operation of the wind turbine, but it must also ful4ll the requirements of a pres sure vessel. Tubular towers for modern utilityscale wind turbines are typically limited by the fatigue strength of the horizontal welds. One primary concern, therefore, is the ef fect of pressurizing the tower on the fatigue strength of these welds. In addition, the hydrogen pressure loads must not exceed allowable margins for pressure vessels.. Loads and stressesWind turbines are subjected to widely varying aerodynamicloads. These loads induce large bending moments that, in turn, cause tensile and pressive stresses paral le