A methodology was developed to improve the integrity management of pipelines, taking account of internal corrosion, external corrosion and third party damage. The system can be used to define the corrosion control and monitoring needs of new and existing lines. It also serves to determine the integrity, optimize inspection and manage repair and rehabilitation of existing lines. The approach to the evaluation of the degradation rate and fitness for purpose of the pipeline is deterministic. The methodology considers the relative contribution of all relevant factors, such as CO2, H2S, 02, organic acids and bacteria on internal corrosion, soil corrosivity, coating condition and cathodic protection on external corrosion and operating environment on third party damage. The inspection planning follows a risk-based approach. The system has been applied to a large number of pipelines all over the world and shown to add value to the business of operators.
INTRODUCTION
Pipeline integrity management historically has been based primarily on the composition of the produced fluids (internal protection) and the soil conditions (external protection). This approach has resulted in excellent designs from the point of view of the pipeline project engineer. For example, CO2 corrosion is usually accounted for in much detail and the use of alternative materials or corrosion inhibition is selected on the basis of accurate models to cope with internal corrosion. In a similar manner, suitable coatings and cathodic protection systems are designed to prevent external corrosion.
Once the pipeline is in service, it often turns out that other factors, usually of an operational nature, pose a serious threat to the integrity. In many cases oxygen ingress and the presence of bacteria, or the reliability of the inhibitor pump are determining the internal corrosion rate and hence the related operating expenditures. The correct operation of cathodic protection systems and timely coating repairs tend to determine the costs of external corrosion.
Another major class of threats is that of third party damage, which can vary from accidental damage due to digging or trawler boards, to sabotage and theft of product. Historical data on pipeline failures are used to determine the main exposures to pipeline integrity, hence enabling measures to be taken on failure prevention. It should be realized that the failure frequencies are highly dependent on the local circumstances. E.g., Table 1 shows that the main causes of failure in Europe and the US are external damage, mechanical damage (manufacturing and construction defects) and corrosion .
