Analytical Parameters For Determining The Integrity Of A Gas Pipeline System
Authors: Falabella D. , Espineira E. , Patitucci H. , Rio S. 
Published: December 2007

This presentation is intended to illustrate the parameters and risk variables which impact the integrity of a gas pipeline system, and the corrective measures implemented by Transportadora de Gas del Sur.

Introduction

Transportadora de Gas del Sur ("TGS") is one of two companies organized as a result of the Argentine Republic's gas pipeline system privatization. Since late 1992, TGS has been responsible for operating and maintaining approximately 6,600 km. of transmission lines, which transport natural gas from the production areas to the distribution centers.

Since its inception, the company has made extraordinary efforts to bring the pipeline system up to a level of safety commensurate with international standards. One of the main problems associated with pipeline maintenance is that of structural anomalies caused by events difficult to predict because of the varied nature of each event.

The challenge is to determine the origin and its evolution in order to institute appropriate corrective measures at the opportune moment.

Parameters Considered in the Integrity Analysis

The primary causes of failures in a gas transmission system, according to worldwide statistics for comparable systems, are: - External corrosion–Internal corrosion–Third party damage–Ground movement–Design and materials–Operating procedures.

Limiting the focus to transmission systems in Argentina, and, more specifically, to the lines operated by TGS, we can describe the causes of failures on TGS pipelines (highlighted in Figures 1 and 2.) Contrary to what happens in other countries of the world, where the main cause of failures is third party damage, in our case the main cause of failures is external corrosion.

The causes of failures for TGS pipelines, listed in order of priority, are:External corrosionManufacturing defectsThird party damageGround movement.

Description of Primary Causes of Failure

External Corrosion. There are several causes which may give rise to this kind of corrosion, among them are the following:

Coating. Our gas pipeline system is in excess of 25 years old, and is typically coated with asphalt coating. This type of coating deteriorates rapidly with age, and, if not properly maintained, allows the corrosion process to progress unabated. This problem was inherited because of the lack of continuity of investments prior to acquisition of the system.

Type of Soils. The great variety of soils traversed by our system, and the condition of the coating, combine to facilitate the formation of corrosion cells.

Cathodic Protection. When adequate cathodic protection levels are not achieved in some locations. the corrosion process continues unabated.

Pipeline Temperatures. The discharge temperatures at compressor stations contribute to the degradation of the pipeline coating immediately downstream.

Bacteria. Natural microorganism as well as those created by man, occur in sufficient quantity to cause, to a greater or lesser extent, bacterial activity. which has been demonstrated to have a cause and effect impact on the corrosion process.