Advances in Pipeline Materials for Demanding Subsea Service
Authors: Bell B. 
Published: October 2008

This paper is concerned with the developments in materials for submarine pipelines. Major advances have been made in recent years which have transformed the viability of many otherwise un-economic subsea developments.

Materials selection is primarily governed by consideration of the corrosivity of the fluids (ie compatibility of chemical composition and service environment). However, there are several other important factors that must be considered in order to optimise material selection. These can be grouped as follows:Fracture toughness with respect to unstable initiation and possible ductile fracture propagation.Control of chemical composition and mechanical properties in pipe production, particularly with regard to the use of seamless or seam-welded pipePipeline construction with regard to field welding, method of installation, inspection and repair. This paper attempts to outline not only the subject of material selection based on corrosion resistance requirement for various service conditions, but also explains how the factors outlined above also ultimately affect the current choices of materials.

INTRODUCTION

This paper is concerned with advances in materials for submarine pipelines. While the developments have been sufficient to transform the economics of many potential developments. they are relatively subtle and have passed unremarked.. Techno-economic materials selection is primarily governed by consideration of the corrosivity of the produced fluids (ie compatibility of chemical composition and service environment), however there are several other important factors that must be considered in order to optimise material selection. These can be grouped as follows:Fracture toughness with respect to unstable initiation and possible ductile fracture propagation.Control of chemical composition and mechanical properties in pipe production, particularly with regard to the use of seamless or seam-welded pipe.Pipeline construction with regard to field welding, method of installation, inspection and repair.

This paper attempts to outline not only the subject of material selection based on corrosion resistance requirements for various service conditions, but also explains how the factors outlined above also ultimately affect the current choices of materials.

MATERIALS SELECTION BASED ON CORROSION RESISTANCE

General

During a pipeline conceptual design phase, extensive environmental data is produced. This information is then used to develop a design premise. At this stage, decisions can be made concerning the corrosivity of the produced fluids, the final decision concerning the pipeline material selection then being a part of the detailed design. The basic information required to evaluate pipeline material selection, based on corrosion considerations is:Maximum operating pressure (including shut-in pressure).Pipeline diameter and wall thickness.Pipeline strength grade (eg XGO etc).Maximum operating temperature (normally at wellhead),Method of production (eg enhanced recovery using water injection or gas lift).Composition of produced fluids.Level ofH2S, CO2 and chlorides.Flow regime.Injection water velocity and oxygen content.

From a knowledge of the above facts, a corrosion philosophy can be established. Measures that are available