Resistive Force of Wax Deposits During Pigging Operations

Abstract

One of the forces that act on a pig while in operation in a pipeline is that due to the layer of wax deposited on the pipeline wall. Therefore, if the motion of a pig or its cleaning efficiency are to be determined, this resistive force must be known as a function of the relevant parameters. The goal of this paper is to present a procedure for evaluating this force in situations of engineering interest. In essence, the procedure consists of the following steps: (i) determine the wax shear strength according to an experimental procedure developed for this purpose; (ii) from finite-element results, obtain the maximum stress in wax; (iii) with the foregoing information, calculate the pressure required for the pig to cause a maximum stress on wax equal to its shear strength. This pressure value is the threshold below which no wax removed can occur, according to the present simple approach. In this paper, each of these steps is described in detail and exemplified.