During the past 50 years, the 90–10 iron modified cupronickel alloy (CA706) has been developed extensively for marine and offshore applications It has proved to have good corrosion, erosion–corrosion, and fouling resistance to sea water The behaviour and protection mechanism of the alloy in these environments has been the subject of many detailed studies under various conditions, ie differing flow velocities, temperatures, pH values, compositions of sea water, and many other factors This review has been compiled by consulting hundreds of references on the properties and behaviour of this alloy It provides a sufficient and unique guide for materials specialists, corrosion technologists, and engineers in the evaluation and use of this alloy in marine environments: it is fully referenced to allow a quick access to the relevant literature

Behaviour of 90–10 cupronickel in sea water

Stress corrosion cracking of a copper elbow fitting

The electrochemical behaviour and stress corrosion cracking (SCC) susceptibility of 70 : 30 Cu–Ni alloy were investigated in 18% monoethanolamine (MEA) solutions at 60 and 90°C. The MEA solutions were used under the deaerated, aerated and H2S saturated conditions. Potentiodynamic polarisation experiments showed that the alloy exhibits an active–passive transition in both the deaerated and aerated solutions at pH 9. On the other hand, it underwent active anodic dissolution in the absence of passivity in the same solutions when the pH was increased to 12, and also in the H2S saturated solution. Open circuit potential measurements showed that the corrosion potentials reached steady state values relatively quickly and that the alloy remained active under all conditions of test. Linear polarisation measurements revealed that the corrosion rates were generally higher in the aerated solutions than in the deaerated ones and tended to be higher in solutions of pH 12 than at pH 9. The corrosion rates were s...

Electrochemical behaviour and stress corrosion cracking of 70 : 30 copper–nickel alloy in monoethanolamine solutions

The common alloys used for tubing in power plant feedwater heaters and condensers are identified and the major corrosion problems encountered in these components are described. The frequency of failure and failure modes in both components are shown to be alloy specific. Some corrosion problems are shown to be controllable through minor design modifications in the equipment and others through judicious selection of alloys. In condensers, alloy selection is most effective when based on tube location. In feedwater heaters, strict control of water quality is shown to be necessary with most alloys to minimize corrosion problems. Benefits of some auxiliary techniques for preventing corrosion attack on condenser tubes also are discussed. These include coating and cathodic protection of the tube sheet and cooling water intake screens.

Prevention of corrosion-related failures in condensers and feedwater heaters

The copper-nickel alloys have found extensive application in steam generation systems. In general, these materials have excellent resistance to corrosion-erosion and stress corrosion cracking (SCC). However, service failures, characterized by intergranular cracking and believed to be the consequence of stress corrosion, have occurred. The use of harder tempers to meet the demands of higher operating temperatures and pressures has increased susceptibility to SCC. Further, the treatment of feedwater with organic amines or hydrazine, which produce ammonia upon breakdown, enhances corrosion and stress corrosion of these materials.1,2 Accelerated stress corrosion cracking (SCC) was induced in copper alloy 720 (40–43 Ni, 1.5–2.5 Fe, 0.5–1.7 Mn, balance Cu) by exposing stressed c-ring specimens to the vapor over ammoniacal solutions in autoclaves at 500 F (260 C). The scanning electron microscope (SEM) was employed for fractographic analysis of the resultant intergranular cracking and for micro-chemical...

G. A. Wilkinson

Papers

Stress Corrosion Cracking of 60/40 Cupro-Nickel Alloy: Fractography and Chemical Analysis