Investigation of causes of failure for a brass nipple pipe

Brass is commonly used in water distribution systems as fittings or connector pipes. Brass provides cost effectiveness and durability, but brass plumbing components are also known to be susceptible to failure mechanisms such as dezincification, oxidation, stress corrosion cracking (SCC). While the failure mode is often identified and studied rigorously, the causes may or may not be obvious and could originate from one individual or combination of factors.

In this study, a field-failed brass nipple pipe, surviving in the field for less than a year before cracking and causing a leak, was analyzed to determine the cause(s) of the failure. Some of the causes to be considered for the initiation of failure include (1) stress corrosion cracking resulting from residual stress from drawing/extrusion/machining process & installation to localized dealloying, (2) stress corrosion cracking due to water quality – impact of the presence of minerals, organic matters, sediments in the pond/underground water the brass component was used for distributing, (3) chemical-induced stress fracture – possible presence of nitrogen-based compounds in the service environment, i.e. fertilizers used in farming communities.

ASTM B858 protocol was used to evaluate and compare the propensity for chemical-induced stress cracking for components produced with different manufacturing processes. Digital microscopy as well as SEM/EDS were used for fracture surface examination and elemental analysis. Metallography samples were prepared, and optical microscopy was used to characterize grain structure and to investigate localized dealloying behavior. Findings on the causes of the failure and corresponding failure mechanisms will be reported.