Journal of Failure Analysis and Prevention

, Volume 17, Issue 4, pp 632–641 | Cite as

Corrosion of Thermally Insulated Galvanized Piping in a Low-Temperature Hot Water System

  • D. Ifezue
Case History---Peer-Reviewed


This paper presents the case study of internal oxygen corrosion and corrosion under thermal insulation (CUI) that occurred in a low-temperature hot water (LTHW) system of a nine-storey building. High dissolved oxygen (DO) levels (>4 mg/L) resulted in severe tuberculation and through pitting of thin-walled carbon steel piping. Leachate from the phenolic foam insulation subsequently contacted the galvanized surface, resulting in high corrosion rates of approximately 1 mm/year. Multiple leaks were experienced from the horizontal ceiling pipe runs within 18 months of commissioning. The high DO levels were caused by incorrect pressurization of the system and possible under sizing of the vacuum degassing equipment. Inhibitor levels were also very low, resulting from historic under stocking. Within the building sector, galvanized steel pipe is still widely used under thermal insulation despite non-compliance with Section 4.3.5 of NACE Standard SP0198-2016. The CUI failure experienced in this case study illustrates the consequence of systemic non-compliance. Recommendations are proposed for mitigating the identified causes of failure, with important ramifications for LTHW system piping material selection, in the building industry.


Galvanized Corrosion under insulation Oxygen corrosion Dissolved oxygen Vacuum degasser Tubercules Low-temperature hot water system 


  1. 1.
    C.B. Alvarez, F.C. Porter, Corrosion Resistance of Zinc and Zinc Alloys (1994)Google Scholar
  2. 2.
    SP0198-2016, Control of Corrosion Under Thermal Insulation and Fireproofing Materials—A Systems Approach Google Scholar
  3. 3.
    G.E. Power, Handbook of Industrial Water Treatment. Water—Water & Process Technologies, 1997–2012 Google Scholar
  4. 4.
    Corrosion Manual for Internal Corrosion of Water Distribution Systems (National Service Centre for Environmental Publications (NSCEP), 1984)Google Scholar
  5. 5.
    SSPC-PS Guide 12.00, Guide to Zinc-Rich Coating Systems (SSPC, Pittsburgh, PA)Google Scholar
  6. 6.
    E.G. Haney, The Zinc-Steel Potential Reversal in Cathodic Protection. CORROSION/81, paper no. 216 (NACE, Houston, TX, 1981)Google Scholar

Copyright information

© ASM International 2017

Authors and Affiliations

  1. 1.Global Corrosion Consultancy LtdManchesterUK

Personalised recommendations