ABSTRACT:

Transportation of wet sour gas, produced offshore, to onshore terminals, poses severe corrosion problems. Formations enveloping 25% H2S & C02 at high pressures and temperatures of 20,000 psi & 200°C respectively are not uncommon. Treatment of sour gas being prohibitive offshore due to unfavourable economics, the pipeline option IS indispensable. Presence of water vapour In sour gas results In Internal pipeline corrosion mainly In the form of Hydrogen Embrittlement & Sulphide S tress Cracking and also General weightloss, Hydrogen Blistering and Hydrogen - Induced Cracking. Material selection for such environments IS determined by trade-off In economics between greater strength and thicker walled pipelines. However, recent developments In coating technology, cathodic protection systems and new design concepts like Pipe-within- Pipe type transportation a designer.

INTRODUCTION

As shallow reserves are depleted, the worldwide search for new sources of hydrocarbon IS turning to deeper reservoirs. Drilling and producing these reservoirs require the use of new materials not used previously. Deeper drilling means that the higher pressures will be encountered and that, the reservoir fluids Will be at a higher temperature than normal. The like hood of acid gases (CO2 and H2S) as a reservoir component IS also Increased. The transportation of these sour gases to onshore terminals poses some interesting pipeline design problems, particularly those pertaining to corrosion prevention. Pipeline transportation being the only answer, the presence of water vapour In the sour gas results In the formation of atomic hydrogen In the pipeline from the oxygen accelerated dissociation of hydrogen sulphide gas molecules in presence of water. This ultimately leads to hydrogen Induced corrosion (HIC) In the pipeline. Typically, hydrates In the sour gas form at 70-80° F and hence design considerations demand some form of insulation or heating to prevent blocking.

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