Quality analysis of galvanized pipes applied to natural gas installations in civil construction

Résumé

Some natural gas distributors for residential and commercial buildings in Brazil use galvanized steel tubes
and fittings manufactured by the hot-dip zinc process that are supported by the specifications contained in the
Brazilian Standards. Zinc coating is one of the most widely used methods to provide protection against
corrosion. It is therefore essential that national and international tube manufacturers and installation and
maintenance companies in civil construction also meet the defined national and international standards,
especially when the tubes and fittings are used for natural gas in residential buildings. This two-way
communication could eliminate most issues that delay or prevent superior galvanizing quality. Low standards
lead to the deterioration of the zinc coating and the metal base of the pipes, which may lead to leaks, such as
fluids, flammable gases, and other toxic products, and potentially jeopardise residential and commercial
buildings. Here the importance of ensuring the quality of zinc-coated pipes is demonstrated through a series
of analyses on natural gas pipe corrosion used in civil construction in Brazil. Based on Brazilian standards,
the zinc mass determination per square meter, uniformity tests (Preece test) and metallographic evaluation of
the deposited zinc layer were carried out on samples of galvanized tubes for natural gas. An experiment was
also developed to reproduce the same conditions of subfloors (mortar beds) where there is penetration of
water and humidity reaching the galvanized pipes. Metallographic analysis showed that samples of galvanized
tubes by the hot-dip zinc galvanizing can have discontinuities and defects in zinc layer. Such defects
associated with penetration and/or permeation of the water and humidity in the subfloor favor the corrosive
process and consequently can cause gas leaks and probable accidents in residential buildings.
Keywords: Corrosion, galvanized steel, zinc coating, quality, natural gas pipes, civil construction.