An appraisal is made of special conditions contributing to the severe corrosion experienced on buried pipelines in the arid desert soils of Syria and Iraq. The effectiveness of cathodic protection in reducing corrosion in such areas is discussed in detail.
Generally cathodic protection is difficult in desert soils and results are less satisfactory than in moist low resistivity soils. Potentials are notably erratic and are subject to variations of 0.5v within a distance of a few feet. General potential checks at intervals of 200 ft show many points with low potential on pipelines which are polarized (—0.85v or more). In practice the amount of current which can be drained from an element of bare surface is controlled in desert soils by the resistivity of the matrix. Where the bare element is in contact with the high resistivity matrix only, it is possible to drain sufficient current to polarize the pipe surface, provided that the bare element is not too large. Where the bare element is in contact with a lower resistivity salty patch, which is itself enclosed in an envelope of the high resistivity matrix, then it may be a practical impossibility to drain sufficient current through the envelope to polarize the pipe surface. This results in low potential locally.
In unfavorable conditions the general polarization of pipe surfaces in desert soils may be very difficult unless the pipe has first class coating surrounded by substantial thickness of soil or selected ditch padding. Even so, areas of locally low potential may exist. 5.2.2, 4.5.2
