Preferential corrosion of weld seam is common for electric-resistance welded steel pipe in fire protection sprinkler systems (FPS). For many field installed FPS, the weld seam is commonly orientated toward pipe bottom or at the 6 o’clock position, which can lead to severe localized pitting (often following the direction of gravity) and weld seam corrosion under corrosion scale/tubercles or the eventual pipe leakage. Therefore, it has been recommended to orient pipe weld seam toward the building roof, in order to reduce grooving corrosion type leakage by preventing the weld from being located underneath corrosion scale/tubercles for active localized corrosion.
Laboratory testing apparatus and techniques such as static and dynamic pipe test racks, salt fog corrosion chamber, and electrochemical techniques were built and utilized to evaluate the corrosion resistance of pipe weld sections oriented at different positions (i.e., bottom "6 o’clock" and side "9 o’clock" positions). After 12 months of dynamic testing, the corrosion (metal loss) of weld located at 6 o’clock position is 2.7 times higher than that of weld located at 9 o’clock position (77.7% vs. 29.1 %).
To mitigate pipe weld corrosion in FPS, it is recommended to (A) orient pipe weld seam above 9 o’clock position (side) toward the building roof; (B) select steel sprinkler pipe without irregularly shaped finger-type pipe weld for better corrosion resistance of the weld seam area; and (C) reduce the frequency of introducing oxygen rich water into the steel sprinkler piping system to decrease the corrosion rate of steel piping system.
