Clad Steel: An Engineering Option

Abstract

ABSTRACT Corrosion resistant alloy clad steel has been available in various forms for over 40 years and is being used increasingly in the oil and gas production industries. In the context of the specific requirements of this industrial sector, methods of manufacturing clad plate, pipe and fittings are given along with welding details and information on existing field applications of clad products. 1. INTRODUCTION The use of corrosion resistant alloys (CRAs) for the control of corrosion in oil and gas systems has a number of benefits. Production systems constructed of correctly selected CRAs (based on appropriate laboratory testing or previous field experience in similar enVironments) will provide a safe, leak-free system for the full duration of a project. Whilst the inital capital expenditure often appears to be higher for a CRA system there are great savings to be made in reduced processing requirements through the safe handling of wet corrosive fluids. If well fluids can be transported to shore or to an existing platform without drying then the cost savings in equipment, weight andspace can be more than sufficient to cover the expense involved in the CRAs needed to handle the fluid from the well to the processing facility. Additional savings can be made in operating costs since corrosion inhibitor injection is not required and inspection and maintenance costs are greatly reduced compared to a carbon steel production system (with or without internal organic linings). Thus if a life-time costing approach is taken CRAs can often be show to be an economic corrosion control option for oil and gas production systems. Nevertheless, CRAs contain expensive alloying elements, particularly the more highly alloyed materials required for corrosive sour production systems. Clad steel is a composite product developed to provide effective and economic utilisation of expensive materials. The cladding layer which will be in contact with the corrosive fluids is made of the corrosion resistant alloy whilst the less expensive backing steel providesthe strength and toughness required to maintain the mechanical integrity. Because high strength backing steel can be utilised, wall thicknesses can be reduced relative to solid CRAs thus reducing fabrication time and costs. The cost saving from using clad steel rather than solid CRA is particularly valid when the total thickness increases or when the cladding grade becomes more complex and hence expensive. An indication of the sort of savings which can be made is illustrated for integrally bonded clad plates in Figure 1. Clad steel plates have been utilised with great success in processing vessels, heat exchangers, tanks and a variety of material handling and storage facilities as well as for making longitudinally welded clad pipe. Clad steel has been available in various forms for more than 40 years and has been widely used in the chemical, oil refining and chemical transport industries and more recently in oil and gas production. Yet despite this there are still concerns regarding the use of clad steel..