A cooler of an ammonia synthesis plant was destroyed after three years of service due to the rupture of a distribution manifold. Synthesis gas under high pressure and at about 300 deg C, consisting of 10% NH3 and unconverted gas of 25% N2 and 75% H2 content, was water-cooled externally to room temperature in this unit. The fracture had the typical flat-gray fibrous structure of a material destroyed by hydrogen. Specimens for the metallographic investigation showed that the structure appeared to have been loosened by intergranular separations. DVM notched impact specimens from the affected area yielded low specific impact...