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Copper nickel alloys 90/10 and 70/30 are used extensively in saltwater systems operating on marine platforms and offer high corrosion and biofouling resistance. However, systems using these materials were reported to fail prematurely. Preliminary investigations revealed pollution of harbor waters with tangible levels of ammonia and sulphides which was reported to be the primary cause of failure. The present author(s) have performed laboratory and field investigations to identify the stress-material-environment interaction of the copper nickel alloys extensively in use on seawater system of marine platforms. Results obtained point to the fact that polluted seawaters can affect the material properties of the alloy leading to premature failure(s) of systems at stresses well below the designed stress. The paper presents the correlation of the results of the laboratory and field tests of 90/10 and 70/30 copper–nickel alloys in seawaters polluted with ammonia and sulphide pollutants.

The authors carried out failure analysis of bent and branched copper-nickel alloy pipelines that had failed in marine environments. These failures were almost always dominated by a brittle stress-corrosion cracking (SCC) mode and could often be attributed to the presence of ammoniacal byproducts in the operating environment. Attempts were made to reproduce the marine-type field failures in the laboratory by testing a Cu-5.37%Ni alloy, similar to the material used in failed pipelines. The tests were performed under slow strain rate test (SSRT) conditions in aqueous ammonia and ammoniacal seawater. Results revealed that the ammonia-induced brittle SCC failures were predominant and reduced the load-bearing capacity of the alloy. The real-life failures are not simple SSRT-type failures. The operating conditions, in addition to the induced residual stresses from manufacturing/processing, subject the system pipes to external forces and widely varying pressures and fluid flow rates. This combination of stresses can produce both static and cyclic stress conditions, similar to a static load coupled with a low-amplitude cyclic load. Tests conducted under superimposed cyclic stresses on prestressed specimens were found to accelerate the stress-corrosion failures in the present copper-nickel alloy in an ammoniacal environment.

The author has studied several failures in the field of bent and branched copper-nickel pipelines exposed to marine environments contaminated by ammoniacal byproducts. The cause of the failures was investigated by laboratory tests on the Cu-5.37 wt-%Ni alloy used for the failed pipes. The tests were conducted under slow strain rate testing (SSRT) conditions, in aqueous ammonia and ammoniacal sea water environments. These studies revealed that the presence of ammonia in sea water impairs the load bearing capacity of the alloy, and the aqueous ammonia environments tend to cause brittle stress corrosion cracking failures, which are often premature and/or catastrophic. However, in addition to induced residual stresses from manufacturing/processing, the operating conditions in marine environments subject these pipes to external forces and widely varying pressures and fluid flow rates, which can cause both static and cyclic stresses. Experiments conducted under SSRT conditions, however, could not predic...

Copper-nickel (Cu-Ni) alloys are the materials of choice for many piping applications; however, a number of premature field failures in copper-nickel pipes exposed to the marine environment have been observed by the author. A majority of these failures occurred at the bends in long-span and branched pipes located near water closets and/or bilges that were frequently filled with stagnated water. Failure analysis investigation revealed that the nickel content of the failed pipes was typically less than the specified value. The operative mechanism(s) causing the premature field failures invariably involved corrosion-assisted material cracking. The environment to which the failed pipes were exposed contained magnesium chloride (MgCl2) and sodium chloride (NaCl), along with biodegradable materials capable of releasing ammoniacal byproducts. Many complex material-environment interactions are possible in marine piping systems, and the operative interaction depends on the stresses encountered and the chemistry and temperature of the exposure environment. While a failure analysis can usually identify the overall operative modes and mechanisms that cause the failures, an understanding of the material-environment interactions is needed to develop the corrective measures necessary to avoid premature field failures in real life applications. A commercial Cu-5.37% Ni alloy very similar to the composition of the field failure pipes was studied under slow strain conditions in air and in solutions containing 3.5 wt.% NaCl + 10.0 wt.% MgCl2 + either 1.0 wt.% ammonia or no ammonia additions. No deterioration of the mechanical properties of the alloy was observed in the tests conducted in the NaCl/MgCl2 solution without ammonia. However, with the introduction of 1.0% ammonia, there was a reduction in the mechanical strength of the alloy, and the mode of failure changed from ductile rupture to brittle fracture. The slow strain rate tests of the alloy were conducted in aqueous ammonia at various concentration levels. The failures observed in aqueous ammonia showed a significant loss of strength with increasing ammonia concentration. The failures were predominantly brittle, exhibiting both intergranular and transgranular fracture paths. In general, the propensity for crack formation increased with increasing ammonia. The failures observed in aqueous ammonia were more severe and different than those observed previously in samples tested in ammonia containing 3.5% NaCl + 10.0% MgCl2 solutions. This paper discusses the aqueous ammonia failures in detail.

The test results from an earlier investigation by the author on the mechanical behaviour of a low nickel nickel-copper alloy exposed to a solution of 3·5%NaCl + 10%MgCl2 with and without ammonia indicated that the presence of 1% ammonia alters the failure mode and affects the load bearing capacity of the material. In the present investigation, further tests have been conducted on the same alloy to study its mechanical/corrosion behaviour on exposure to an aqueous solution of ammonia in comparison with exposure to a similar solution of ammonia containing 3·5%NaCl + 10%MgCl2. A constant displacement rate of 9·6 × 10-3 μ m s-1 was used and the concentration of ammonia was maintained at 5%. On exposure to the 5% aqueous ammonia solution, the mechanical properties of the alloy were degraded significantly and the material exhibited a brittle stress corrosion type of failure. However, on exposure to 5% ammonia in the presence of 3·5%NaCl + 10%MgCl2, there was less change in failure mode relative to that ...

A low nickel copper alloy commonly used in the plumbing/drainage pipelines on ships was investigated under slow strain rate conditions in air, and in solution containing 3·5%NaCl + 10%MgCl2, with and without 1% ammonia. The tests were conducted at ambient temperature (28 ± 1°C) at strain rates corresponding to a crosshead speed of 5·76 × 10-5cm min-1, without a passivation current. The results obtained did not show any significant deterioration in the mechanical properties of the alloy in the tests conducted in air or in solution without ammonia. However, with the introduction of 1% ammonia, a reduction in the material strength and a change in the mode of failure were observed. This paper discusses the results obtained in the present investigation and in particular the load bearing capacity of the material and the modes of failure in Cu–Ni alloys exposed to sea water.