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For the last 35 years the American welding industry has placed limits on electrode coating moisture to control the hydrogen content of shielded metal arc (SMA) welds in order to minimize weld cracking in steels. Within the past several years, however, various tests have been proposed or developed for the direct measurement of diffusible hydrogen in welds. This report compares many of these tests with each other and with the coating moisture test.
The methods of measuring diffusible hydrogen that were compared were the International Institute of Welding (IIW) test (collection over mercury), the American Bureau of Shipping test (collection over glycerin), collection over silicone oil, a gas chromatographic technique, and several variations of the above. The gas chromatographic technique produced results that agreed within 15% with the IIW method, while the other test methods produced results that were often 50% smaller than the IIW value. The lower values were attributed to solubility of hydrogen in the collection media. It was therefore concluded that these two methods also produced the most reliable measure of the diffusible hydrogen content. The coating moisture was measured in the electrodes used and had a poor correlation with the diffusible hydrogen content.
coating moisture, diffusible hydrogen, gas chromatograph, glycerin, hydrogen, mercury, shielded metal arc welding, welding electrodes
Siewert, Thomas A.
Metallurgist, National Bureau of Standards, Fracture and Deformation Division, Boulder, CO