Analysis of Cement Mortar Lining in the Presence of Hydrodynamic Loading

Abstract

Cement mortar, used as a lining on the interior wall of metallic pipe, has proven to be beneficial in the passivation of metal corrosion in the presence of water. For many owners/agencies the use of cement mortar lining has become a standard when ductile iron or steel pipe is specified. The lining is traditionally applied with a minimum thickness of 0.25 in. by centrifugally casting the cement to the interior wall or, in larger diameters and at joints, field applied. The lining's performance in operation has proven its benefit over time. However, in large-diameter systems that have been in the presence of persistent hydrodynamic loads there have been recorded failures of cement mortar lining. The failure of the cement mortar lining leaves the pipeline exposed to corrosion and potentially exacerbates the problem. In larger-diameter pipelines with aggressive water, it has become common to specify thicker cement lining (>0.25 in.). The concept of the greater lining thickness is to allow erosion of the lining to occur over time while remaining lining continues to passivate the corrosive environment. This is intended to result in an extension of the pipeline's service life. This paper summarizes the development of an analytical approach to evaluate the sensitivity of cement mortar lining in the presence of hydrodynamic (i.e., hydraulic transient) loads. The equation represented in the paper allows a designer to assess the thickness of the lining and the potential of the lining to fail in the presence of a differential pressure caused by a downsurge or negative transient pressure condition. This analytical approach will help refine the evaluation of using a thicker cement mortar lining in lieu of treating the aggressive fluid, assess the sensitivity of the thicker lining in the presence of dynamic loading, identify what transient controls may be required if thicker linings are specified, and better define the extension or potential reduction of a system's operating life through the use of a thicker cement mortar lining.