How to Determine the Gas Pipeline Pigging Cycle
Authors: Li Daquan , Ai Muyang , Zhang Peng , Miao Qing , Wang Yubin 
Published: March 2015

Abstract
Many gas pipeline companies in China is always puzzled by the problem that how to determine the gas pipeline pigging cycle. They are often in a dilemma. On the one hand, If the pipeline pigging work is done timely, the efficiency of pipeline can be improved and the economic benefit can be increased. Except that, all kinds of impurities, liquid and dirt in the pipeline are removed timely, and some pipeline accidents such as ice blocks, corrosion of pipes can be prevented. On the other hand, In order to ensure the pipeline pigging safety and effectiveness, the pipeline operating pressure is reduced than normal. Pipeline flow rate will be greatly affected. And in the process of pipeline pigging operations may also cause the pipe is worn, or even cause pipeline rupture accident.
Therefore, if a reasonable pipeline pigging cycle will be determined, the security, economic, social impact and other factors must be considered. Basing on the analysis of relevant laws and regulations or standards, and analyzing the influence of gas supply is can be accepted or not when the pipeline is pigging, except that, including calculated the efficiency of pipeline and condensing liquid volume, some technical methods which are used to determine the pipeline pigging cycle have been discussed. And the application of these methods in the SeBei-XiNing-Lanzhou Gas Transmission Pipeline in China is introduced. It provides reference for the Chinese gas pipeline companies to determine pipeline pigging cycle.

1. Introduction
The pipeline pigging operation has been done timely, the pipeline transportation efficiency will be improved and the economic benefit of Pipeline Operation Company will be increased too. Meanwhile, a variety of impurities, water or dirt liquid which are accumulated in the pipeline have been removed timely, that is propitious to prevent pipe corrosion and natural gas hydrate or other accidents. Since the pipeline pigging operations can bring so much benefit. Is the higher pigging operation frequency, the better? Certainly, it is not the case.
On the other hand, it has a great influence on the process of pipeline production when the pipeline pigging operation has been done. For example, In order to ensure the pigging effectiveness, it is necessary to control the pig's speed in pigging process, so the pipeline operating pressure should be reduced in pigging process. Therefore, operating parameters and pipeline transmission capacity will change. Furthermore, Pigging operation itself may cause damage to the pipeline system, if the pigging operation process is improper, easily lead to pig is stuck, and pipeline is plugged or even cause pipeline rupture accident.
Therefore, how to determine the pipeline pigging cycle reasonably is a question which must be answered before the pipeline system pigging operation has been done. The comprehensive analysis approach of many technical indicators to determine the gas pipeline pigging cycle will be introduced as following. It can be used to guide that the pipeline pigging operation timing is determined.

2. Pipeline Pigging Operation Cycle Determined Methods
In the pipeline operation process, there are some water, impurities, corrosion products and other dirt liquids maybe will gradually increasing in the pipeline with the increase of time. Accordingly, gas pipeline operating parameters will change too. Analyzing the changed situation of pipeline operating parameters, whether the transmission efficiency of gas pipeline is meeting the needs of transportation project has been judged.