Failure Analysis of Firewater Systems

Early failures were observed in firewater systems comprising carbon steel pipes and cast‑iron components, manifesting as (1) corrosion of the piping after 1–2 years in service and (2) cracking of a fitting upon initial pressurization. The investigation combined X‑ray fluorescence (XRF) for material composition, optical metallography for microstructural characterization, and detailed fractography with localized chemical analysis using a scanning electron microscope equipped with energy‑dispersive X‑ray spectroscopy (SEM/EDS). Where appropriate, macro‑ and microhardness measurements were also performed.

Results indicate that corrosion in the steel pipes is attributable to water quality and operating conditions (system parameters and management), which promote early corrosion mechanisms; in particular, suspected microbiologically influenced corrosion (MIC) and poor weld quality locally promoted pitting, notably near the weld seam and heat‑affected zone. The cracking of the cast‑iron fitting stems from an inadequate, fabrication‑induced microstructure that imparts brittleness incompatible with initial pressurization.

These findings highlight the joint importance of (i) upstream quality control for components (material specifications and processes) and (ii) rigorous control of service conditions (water quality and operation) to ensure the durability of firewater systems.