During design, it is important to ensure that alloys being specified are readily available. Just because an alloy is listed in standards does not mean that it is currently manufactured. As an example, it was desired to change from copper to a brass for tanks in instant hot water heaters to reduce cost. In hot water dezincification is very likely with a brass, so a 70/30 arsenical brass to British Standard CZ126 or UNS C26100 was selected. Unfortunately, this is only available as pipe and tubing and not as sheet, which was required to make the heater. Copper-nickel was more expensive than copper, so no material change was made.

It is important to check availability before writing specifications to avoid costly delays.

When specifying alloys it is sometimes thought that simply requesting supply to ASTM standards will be adequate. However, there are potential corrosion problems that can arise due to incorrect manufacturing. One example is copper and copper alloy tubing for heat exchangers, which may contain carbon films from the manufacturing process that cause pitting in service. Only BS2871 Part 3 specifies that tubes must be free of “deleterious films” in the bore, although it does not specify a test.

Nickel aluminium bronze can have undesirable phases in it that can be rapidly attacked in seawater. To combat this, it is common to specify that the nickel content should be 0.5% or more than the iron content. In addition a final heat treatment after all hot working and welding operations is recommended to restore the optimum microstructure. Neither of these recommendations is included in ASTM specifications.

Similarly, the ASTM requirements for duplex stainless steels are very basic and it is common to also require a low temperature impact toughness test, a corrosion test to ASTM G48 and a microsection at X500 to ensure the quality is adequate and there will not be a premature failure.

While it is well known that some copper alloys are susceptible to SCC in ammonia and ammoniacal environments, what is often forgotten is that some copper alloys are also susceptible to SCC in other environments. Below are some of the common environments that can cause SCC of copper alloys.

Mercury - All copper alloys.
Sulphur Dioxide - Brasses over a limited concentration range of SO2.
Nitrites - Brasses, but other copper alloys may be susceptible.
Chlorides - High beta-phase brasses and high tensile brasses.

Note that the order of ranking of susceptible alloys varies with the different media causing SCC.  A high stress is not always required, as some alloys have high resisidual stresses from manufacture.

A failure of a pump or agitator shaft can be an expensive item because of other consequential damage. Corrosion fatigue is something which can particularly affect rotating components, such as pump or agitator shafts, which are operating in corrosive media. Although it has been known for a long time that sharp steps in shafts can act as stress raisers, this is not always properly accounted for in designs. The local stress intensification factor can be high if the step is very sharp. If a radiused change of diameter is introduced, the local stress can be lowered and the greater the radius of curvature, the lower the local stress during operation.

When specifying cast copper alloys, for instance for pump or valve bodies, there is sometimes excessive concern to prevent dezincification by not allowing any alloys containing zinc. This is because an alloy known as manganese bronze is, in fact, a high tensile brass, and it is very susceptible to dezincification in seawater. Gunmetals are alloys of copper, zinc, tin and lead that have given excellent service in both fresh water and seawater for many years without de-alloying. This is because they all contain less than 10% zinc and this is not sufficient to allow dezincification to occur, even in seawater. Zinc-free alloys like phosphor bronze are difficult to make pressure-tight as castings, while the lead in gunmetals ensures good pressure-tight castings.