Practical Failure Analysis

, Volume 3, Issue 5, pp 58–68 | Cite as

Effect of ammonia concentration on environment-assisted failures in a low-nickel copper alloy

  • D. C. Agarwal
Peer Reviewed Articles

Abstract

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.

Keywords

ammonia copper nickel environmental failures failure analysis fractography SSRT stress corrosion 

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. 1.
    A. Turnbull: “Environmental Assisted Cracking,” Conference Report,Brit. Corros. J., 2002,37(2), p. 91.Google Scholar
  2. 2.
    S.A. Avner:Introduction to Physical Metallurgy, McGraw-Hill, 1974, pp. 583–604.Google Scholar
  3. 3.
    R. Francis: “Effect of Pollutants on Corrosion of Copper Alloys in Seawater (Ammonia and Chlorine),”Brit. Corros. J., 1985,20(4), p. 167.Google Scholar
  4. 4.
    R. Francis: “Effect of Pollutants on Corrosion of Copper Alloys in Seawater (Sulphide and Chlorine),”Brit. Corros. J., 1985,20(4), p. 175.Google Scholar
  5. 5.
    D.P. Harvey, T.S. Sudarshan, and M.R. Louthan: “Effect of pH on Corrosion and Monotonic Loading Behaviour of 90Cu-10Ni in 3.5% Sodium Chloride Solution,”Brit. Corros. J., 1988,23(1), p. 61.Google Scholar
  6. 6.
    M. Islam, W.T. Riad, S. AlKharaaz, and S. Abo Namous: “Stress Corrosion Cracking Behavior of 90/10 Cu-Ni Alloy in Sodium Sulphide Solutions,”Corrosion Journal, 1991,47(4), p. 260.Google Scholar
  7. 7.
    J.N. Alhajji and M.R. Reda: “Effects of Sulphides on Corrosion of Cupro Nickel Alloys,”J. Electrochem. Soc., 1995,142(9).Google Scholar
  8. 8.
    P.T. Gilbert: “Corrosion Resisting Properties of 90/10 Copper-Nickel Iron Alloy with Particular Reference to Offshore Oil and Gas Applications,”Brit. Corros. J., 1992,14(1), p. 20.Google Scholar
  9. 9.
    D.C. Agarwal: “Effect of Ammonical Seawater on Material Properties of Copper-Nickel Alloy,”Brit. Corros. J., 2002,37(2), p. 105.CrossRefGoogle Scholar
  10. 10.
    D.C. Agarwal: “Stress Corrosion In Copper-Nickel Alloys—Influence of Ammonia,”Brit. Corros. J., 2002,37(4), p. 267.CrossRefGoogle Scholar
  11. 11.
    ISO 7539-7: 1989(E).Google Scholar
  12. 12.
    D.C. Agarwal and S. Kurian: “Effect of Harbour Environment on Copper Nickel-Alloy,” International Seminar on Ship and Ocean Technology (SHOT-2002), IIT Kharagpur, India, 18–20 Dec 2002.Google Scholar
  13. 13.
    Standard E-8, ASTM, Philadelphia, PA, 1992.Google Scholar

Copyright information

© ASM International - The Materials Information Society 2003

Authors and Affiliations

  • D. C. Agarwal
    • 1
  1. 1.Indian Navy, Naval WingInstitute of Armament Technology, GirinagarPuneIndia

Personalised recommendations