Page 56 - Reliability and Maintainability of In service Pipelines

Introduction 45

change this effect, however the resulting deterioration may occur in a longer time-
frame, in comparison to effects observed with a combined action of these gradi-
ents and applied stresses, which can enhance or reduce the level of diffusion and
osmosis and thereby the resulting degree of deterioration.
Applied stresses alone can also contribute to deterioration of GRE, given that
the capacity to withstand the applied stresses is exceeded, result in swelling,
embrittlement, and microcracking of the structure. The continuous impact of these
factors over a long period of time can cause exhaustion of the structure, and
increase the susceptibility towards various failure modes, ultimately resulting in
deterioration (Owens Corning, 2011).

1.6.4.3 Clay Pipes
The extent of resistivity to the damaging effects of sulfuric acid in piping highly
depends on the pipe material. Pipes derived from cement and metals hold a higher
susceptibility to rapid deterioration when exposed to sulfuric acid. This is especially
common in sewer systems, where concrete piping is typically used and is subject to
corrosion due to the highly acidic nature of the environment. The growth of bacte-
ria and microbes in these pipes, which also generate sulfur, is a component that
adds to the sulfur-based corrosion that occurs inside these concrete pipes. Factors
including acidic soils and temperature changes also accelerate this process and pro-
vide a thriving environment to conditions that favor corrosion.
The usage of vitrified clay pipes in sewer systems have proven to be the only pipe
material to resist sulfur-based corrosion, as well as aggressive soils, solvents, and indus-
trial wastes. Due to this resistivity, no protective coating and linings are necessary.
Vitrified clay pipes are also known for their rigidity and ability to avoid loss
of strength by not deflecting or flattening when loads are applied, in comparison
to plastic pipes which deflect and deform under loads (Gladding McBean, 2017).

References

American Concrete Pipe Association, ACPA, 1993. Concrete pipe technology handbook, Irving,
Texas.
Ahammed, M., Melchers, R.E., 1994. Reliability of underground pipelines subject to corrosion.
J. Transport. Eng. 120 (6), Nov/Dec.
Ahammed, M., Melchers, R.E., 1997. Probabilistic analysis of underground pipelines subject to com-
bined stress and corrosion. Eng. Struct. 19 (12), 988 994.
Alton Materials, 2017. The difference between ferrous and Non Ferrous scrap metal. [online]
Available from: http://www.altonmaterials.com/the-differences-between-ferrous-and-non-ferrous-
scrap-metal/ (Accessed 25 April).
Anon, 2002. Office of Pipeline Safety, websites: www.ntsb.gov and www.ops.dot.gov