The interior of a cylindrical tank used for the road transport of concentrated sulfuric acid revealed severe blistering of the plates, mainly over the crown and more particularly on the first ring. The tank, made in 1958, was of welded construction, the material being mild steel plate. Some of the blisters were pierced by drilling a hole in the center and at the same time applying a small flame. In several cases combustion of the escaping gas caused minor explosions, a result characteristic of hydrogen. Etching showed the material to be a low-carbon steel in the partly spheroidized condition....