Photo Gallery I5: Improper Galvanizing
Galvanized steel pipe has dramatically transformed over the past 150+ years. Since earliest examples, the quality of galvanized steel has declined to the point where today, it cannot be relied upon for long service under almost any conditions. Old examples of galvanized steel had such a thick coating of zinc that it could often be sliced away in slivers with a sharp blade; providing reliable service since 1896. In another more recent CorrView investigations of one of America’s earliest universities built in 1877, the original galvanized wrought iron pipe was still providing service; only now reaching retirement after 147 years.
In contrast, new galvanized steel pipe appears with such a thin coating of zinc that eye protection must be used when rolling a groove in order to protect against small flying shards of razor sharp zinc. While American made products still exceed the quality of foreign produced galvanized steel, failures of large diameter schedule 40 galvanized steel pipe have occurred in under 5 years.
For dry and pre-action fire sprinkler system, this change in quality has been highly detrimental; finding most such systems to achieve at most 20 years of service before requiring replacement. Many of the failures at fire protection systems are not entirely due to lower quality, but standard fabrication and installation methods. Although thiwall schedule 10 pipe has become the fire industry standard, arguably its limited wall thickness would not be a factor where its internal zinc protective coating stopped all corrosion.
Following improper procedures which further reduce service life, however, is common. Whether installing branch ports to the mains in a fabrication shop, or welding them on at the job site, a fatal flaw of most galvanized steel fire sprinkler installations is the failure to hot dip the entire pipe section after welding.
Typically the fabrication begins with galvanized steel pipe; the steel branch ports then welded on as per its design. Aside from grinding away the zinc finish at the outer area to be welded, necessary for a proper weld, the heat of welding burns off the zinc protective finish at the inside of the pipe, which is of course unseen. After the steel port has been welded on, a “cold galvanizing” compound is applied to the outside of the pipe; satisfying everyone’s belief that they have a galvanized steel system when in fact the inside surface has not been addressed. As exists for any direct connection between carbon steel and galvanized steel, accelerated pitting occurs in the weld affected areas resulting in premature failures.
While cold galvanizing compounds are claimed equal to picking and hot dipping steel into molten zinc, there are no doubt differences. Yet in many examples, standard grey or silver spray paint is often used as a substitute given that its appearance is somewhat similar. For those in the fire protection industry, and to the building owners they serve, the presence of either bare carbon steel ports or any form of coating or paint covering defines a not quite galvanized steel piping system that should be expected to fail prematurely.
