INTRODUCTION
Corrosion remains a key issue in petroleum production. Its continued occurrence has consequences on the safety of people and environment and the integrity of facilities and affects the economy of the oil or gas field. Particularly the presence of severe environments containing corrosive components such as carbon dioxide and hydrogen sulphide poses serious problems. A central element in the design of facilities and the corrosion control is therefore the proper choice of materials which are both, economical and provide a satisfactory performance over the entire service life with respect to the given environment. Prior to the production phase, reliable corrosion monitoring programmes have to be selected, established, and implemented, as necessary.
This paper gives a comprehensive overview of the long time experience of the authors' company regarding these considerations: one large oil field developed about 50 years ago in Austria and 4 gas fields, two of them in Austria and two in Pakistan are described. The different gas fields have been successfully developed and brought on stream between 1967 and 2003. These gas fields do not only vary in their geographical position, but also in gas compositions, the dates of production start, and the location of gas dehydration units.
One major aspect dealt with in each of these cases is the material selection with respect to the given environment, the implementation in the field and the corrosion monitoring. Where the initial decision has been made in favour of carbon steel, the inhibitor selection in the laboratory and the inhibitor application and optimization in the field are described. Furthermore, for the oil field a lot of technical measures are described, some of them having derived from R&D projects. These measures have led to a tremendous decrease in workovers and linepipe failures und thus to huge cost reductions. The corrosion monitoring results which are presented in this paper give evidence of the experience gained in more than five decades of the production and transportation of oil and more than three decades of the production and transportation of wet corrosive natural gas.
The production and the transport of wet corrosive natural gas and oil demand for thorough selection of suitable material and measures for combating corrosion to obtain long lifetime of the production facilities. In addition to the liquid phase which may show a low pH value and some amount of chlorides the existence of the corrosives CO2 and H2S in the gaseous phase can pose serious problems to the corrosion engineer. Carbon dioxide sweet corrosion is a well known problem in gas production. CO2 dissolves in brine to form carbonic acid that ionizes to yield a low pH value. The resulting acidic solution strongly enhances the corrosion in carbon steel pipes and facilities. The presence of CO2 would lead to corrosion rates of several mm/year if no proper corrosion protection methods were taken. The major concern - besides general corrosion - with the presence of H2S is the likelihood of stress corrosion cracking (SCC), if the materials are not properly selected.