Page 399 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

CORROSION DAMAGE, DEFECTS, AND FAILURES 377

Figure 5.72 Cast iron pipe with large hole (19).

Failure of ductile iron piping was solely because of pitting corrosion resulting in pipe
wall perforation.
There was no indication of pipe failure because of defects in the pipe material. In
the majority of cases, corrosion of both ductile iron and cast iron pipes from the water
side was negligible.
Deterioration of water pipe fittings such as service saddles contributes to water
main failures. This type of failure may be because of galvanic corrosion as the pipe is
cast or ductile iron, saddle is bronze, steel, or cast iron, and the service line is made
of copper.
Chemical analysis of the soils where failures of pipe occurred showed the soils to
be corrosive. The soils consisted of wet salty clay containing iron and resistivity in
the range 820–4200 Ω cm. A strong relationship between the corrosion rate of buried
cast and ductile iron pipes and soil resistivity was found.
Thin bituminous coatings on the ductile and cast iron pipes peeled and flaked. In
addition, rust spots were present.
Figures 5.72 and 5.73 show the corrosive attack on samples of cast iron pipe and
ductile iron pipe buried under the soil for 20 and 9 years, respectively. The large hole
in cast iron pipe (Fig. 5.72) and the corrosion pit and perforation in ductile iron pipe
(Fig. 5.73) show the severity of soil corrosion. It is suggested that cathodic protection
can reduce the extent of corrosion of iron pipes.

5.3.7.4.16 Corrosion in Drilling and Well Stimulation Acidizing is the most com-
monly used procedure for stimulating oil and gas wells. The main purpose of acid
treatment is to dissolve rock or other plugging solids. The choice of the acid depends
on the following:

1. Rock-dissolving capacity
2. Contact time
3. Solubility of the reaction products