Abstract

The paper mentions various factors which influence internal corrosion and how they might be controlled and monitored in submarine pipelines carrying hydro-carbon products. There is a description of factors influencing the choice of inspection areas and of inspection methods. Finally, procedures to estimate the corrosion rate/lifetime and the establishment of the allowable operating pressure are given.

Introduction

Experience has shown that corrosion is one of the main threats to the integrity of submarine pipelines carrying hydrocarbon products, and extensive efforts are made to monitor, control and reduce the corrosion problem. problem. In order that a system operates during the service phase with a minimum of problems, it is important that the corrosion control system is considered problems, it is important that the corrosion control system is considered early in the design stage. During this early consideration it is necessary that all relevant information is available. This might include earlier experience, research work, etc which con be considered as "Know how", ref. Figure 1. The cycle presented in Figure 1 is schematic but indicative of the dynamic interaction between experience gained, research follow up and the use of rules, codes and specifications to give guidance during design.

Ideally, the design stage would eliminate any further consideration of corrosion. In practice, that is not possible. During design certain assumptions must be made about the nature of the corrosive environment. During service, the environment must therefore be monitored to ensure that there is no significant deviation from these. Further, some material loss is almost always experienced. It is then necessary to ensure that this is kept within acceptable limits or to take action of some type if it appears to be unacceptable. Such action can then feedback to the Know how" part of the cycle and hopefully prevent a similar situation arising again.

This paper will discuss some of the above aspects, starting with a brief discussion of the problem itself - CORROSION. Building upon the principles outlined in that discussion, various methods of control will be mentioned including a consideration of the important design stage. This in turn is followed by a section dealing with various monitoring and inspection techniques leading to the concluding sections.

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