when looking for non-palladium-based alloys for use in hydrogen separation membranes. Fatigue While most failures in practice have been through fast failure, there is experimental evidence that hydrogen also affects the fatigue properties of steels. This is entirely expected given the nature of the embrittlement mechanisms proposed for fast fracture. In general hydrogen embrittlement has a strong effect on high-stress, low-cycle fatigue and very little effect on high-cycle fatigue. Environmental Embrittlement Hydrogen embrittlement is a volume effect: it affects the volume of the material. Environmental embrittlement is a surface effect where molecules from the atmosphere surrounding the material under test are adsorbed onto the fresh crack surface. This is most clearly seen from fatigue measurements where the measured crack growth rates can be an order of magnitude higher in hydrogen than in air. That this effect is due to adsorption, which saturates when the crack surface is completely covered, is understood from the weak dependence of the effect on the pressure of hydrogen. Environmental embrittlement is also observed to reduce fracture toughness in fast fracture tests, but the severity is much reduced compared with the same effect in fatigue Hydrogen embrittlement is the effect where a previously embrittled material has low fracture toughness whatever atmosphere it is tested in. Environmental embrittlement is the effect when the low fracture toughness is only observed when the testing happens in that atmosphere. Sources of hydrogen During manufacture, hydrogen can be dissolved into the component by processes such as phosphating, pickling, electroplating, casting, carbonizing, surface cleaning, electrochemical machining, welding, hot roll forming, and heat treatments. During service use, hydrogen can be dissolved into the metal from wet corrosion or through misapplication of protection measures such as cathodic protection. In one case of failure during construction of the San Francisco–Oakland Bay Bridge galvanized (i.e. zinc-plated) rods were left wet for 5 years before being tensioned. The reaction of the zinc with water introduced hydrogen into the steel. A common case of embrittlement during manufacture is poor arc welding practice, in which hydrogen is released from moisture, such as in the coating of welding electrodes or from damp welding rods. To avoid atomic hydrogen formation in the high temperature plasma of the arc, welding rods have to be perfectly dried in an oven at the appropriate temperature and duration before use. Another way to minimize the formation of hydrogen is to use special low-hydrogen electrodes for