Study Of The Strain Gage Used In High Pressrue Hydrogen Gas Environment

Hydrogen energy is going to be widely used in the foreseeable future,while a crucial issue that confronts the use of hydrogen energy is hydrogen embrittlement（HE）.Hydrogen atom reduces ductility and fracture stress and thus degrades the mechanical properties of metals after a long period served in high pressure hydrogen gas environment.It is necessary to measure stress and strain of the components in hydrogen service,thus the strain gage used in high pressure hydrogen gas environment is to be developed urgently.In this paper,Cu-Ni and Fe-Cr-Al strain gages have been studied.The phase structures and compositions were characterized and analyzed by XRD and EDS;the effects of hydrogen on the modulus and hardness of two alloys were characterized by nanoindentation;the hydrogen contents of the specimens were measured by TDS;the hydrogen diffusion coefficients of the alloys were estimated by the experiment of hydrogen permeation;the zero point drift and the creep in hydrogen gas environment were measured by the strain gage apparatus.The main conclusions are shown as follows:（1）After hydrogen-charging,the elastic modulus and hardness of the alloys have changed.The modulus of the Cu-Ni alloy is changed from 142.67GPa to 114.71GPa,which is reduced by 19.6%.The modulus of Fe-Cr-Al alloy is changed from192.35GPa to 219.39GPa,which is increased by 14.1%.The hardness of Cu-Ni alloy is changed from 2.95GPa to 2.78GPa,which is reduced by 5.8%.The hardness of Fe-Cr-Al alloy is changed from 3.62GPa to 3.86GPa,which is increased by 6.6%.Hydrogen promotes the indentation creep in two alloys,while the creep is larger in the Cu-Ni alloy.（2）The hydrogen content of the Cu-Ni alloy is 40wt.ppm,and that of the Fe-Cr-Al alloy is 1.55wt.ppm.The hydrogen diffusion coefficient of the Cu-Ni alloy is 7.4×10^-8mm²/s,and that of the Fe-Cr-Al alloy is 4.1×10^-7mm²/s.（3）The zero point drifts of two alloys increase with the hydrogen gas pressure.In 2MPa,4MPa and 8MPa hydrogen gas,the zero point drifts of the Cu-Ni strain gage are-517.25με,-697.40με,-831.84με,and those of the Fe-Cr-Al strain gage are 2.0με,4.01με,5.20με,respectively.The effect of hydrogen on the Cu-Ni strain gage is much obvious.（5）The creep of the Cu-Ni strain gage in 8MPa hydrogen gas is-915.45με,while that of the Fe-Cr-Ni strain gage is 4.45με.The creep of the Cu-Ni strain gage is more sensitive in high pressure hydrogen gas environment.（6）Compared with the Cu-Ni strain gage,the measurement data of the Fe-Cr-Al strain gage is more accurate,reliable and stable in high pressure hydrogen gas environment.Thus the Fe-Cr-Al strain gage is more suitable than the Cu-Ni strain gage in hydrogen service.