Pipeline Pigging And Cleaning: What Do We Really Know About It? Part 2

In a previous P&GJ issue Part 1 discussed: Paradigms, Polyurethanes, Durometer, All Cleaning Pig Types, How to Get Started Pigging, Types of Cleaning, What is Clean, and False Paradigms. This conclusion will discuss: “Cleaning a Pipeline, Types of Cleaners, and Pipeline Efficiency, an added benefit in preparation for running an ILI tool.

Cleaning A Pipeline
There are two types of pipeline cleaning programs available. One type is referred to as mechanical cleaning (the running of mechanical pigs dry) and is the answer most mentioned when asked, “Do you clean your pipelines?” Most debris in a pipeline is in the 4 to 7 o’clock position due to gravity. In most cases, if a pipeline is mechanically dry pigged, this type of cleaning will only displace the debris from the 6 o’clock position to 360 degrees around the pipe wall. Even if more mechanical pigs are run, the solids (i.e., black powder), iron compounds, and other organic and inorganic compounds can be broken-down to sub-micro particles causing down stream nuisances. For example: plugged meters, fouled turbine/compressor filter elements, customer’s treating equipment, etc. Again, the more one mechanically dry pigs, the smaller the particles can become. If the solids are iron compounds (iron sulfides, iron carbonate, iron oxides, etc.) these particles and sub micro-particles will be pressed by the pig’s disc and cups, at pipeline pressure, into any pipe wall anomalies and/or pitting which may interfere with the magna-flux readability of actual pipe wall metal loss areas especially if these compounds are magnetite.

Liquid Cleaning With Surfactant Base Cleaners
Achieving greater solids removal from pipelines with fewer pig runs requires liquid cleaning, referred more commonly to as chemical cleaning. This type is becoming more popular in the industry . Liquid cleaning in tandem with mechanical pigs will remove a greater volume of debris with fewer runs. Liquid cleaning by definition means the use of liquid cleaners mixed in a diluent (water, diesel, methanol, IPA, MEK, etc.), to form a cleaning solution, pushed through a pipeline using mechanical pigs. Most cleaning companies will use a calculated volume (2 to 3-mils) of liquid solution to coat the interior walls based on a given diameter and length of pipeline, using 10 to 20% of that volume as pipeline cleaner. A minimum of 10% by volume of pipeline cleaner is suggested to not only allow the cleaner to penetrate and permeate the solids but also enough percent to be able to carry the solids out of the pipeline. The cleaner mixed with a diluent should be enough in volume to form a froth to keep the solids in suspension so as not to allow them to settle before being expelled from the pipeline.

There are various manufacturers of cleaners. However, a careful choice of designed pipeline cleaners should be based upon the following characteristics: