Effect of Gaseous Hydrogen on Strain Gage Based Instrumentation

Material qualification testing such as tensile and fracture mechanics testing often relies on the use of strain gage or strain gage based instrumentation. This work presents observation of gaseous Hydrogen effect on strain gages in pressure range between 10-12 MPa (1500-1700 PSI) and its potential effect on testing data. In high pressure gaseous Hydrogen environment, anomalous reading from instrumentation such as clip gage and load cells have been observed. These test instrumentations are based on strain gage. Foil strain gage is commonly composed of metal foil that is insulated by a flexible substrate. It is known that Hydrogen might change the electrical properties of metallic materials and therefore the metallic foil of the strain gage might be affected by it. Since off the shelf instrumentation manufacturers of clip gage, extensometer, and load cell do not divulge their type of strain gage, we decided to test two of the most common strain gage material: Ni-Cr and constantan (Cu-Ni alloy). Additionally, a specially marketed Hydrogen gage was also tested in conjunction with the other gages. A steady state measurement condition defined as constant strain, pressure, and temperature was used to perform the test in quarter and half bridge configuration. The effect of post-test environments was also investigated.