3.1 Introduction

Design of pipeline involves selection of pipeline diameter, thickness, and material to be used. Pipeline diameter should be selected on the basis of flow capacity required to transport production fluids at an expected rate provided by the oil or gas wells. This task demands a comprehensive flow assurance analysis assuming the worst operating condition during the whole life of the pipeline. Due to the complex nature of multiphase flow as described in Appendix A, a calibrated computer model in flow assurance analysis is required. In the last decade, multiphase flow simulators have gained significant popularity. Both steady-state and transient simulators have been used for pipeline design and for pipeline operation simulations. Flow assurance analysis is described in Chapter 15.

This chapter covers wall thickness design for subsea steel pipelines and risers as governed by US Codes ASME/ANSI B32.8. Other codes such as Z187 (Canada), DnV (Norway), and IP6 (UK) have essentially the same requirements, but should be checked by the readers.

Except for large diameter pipes (over 30 in.), material grade is usually taken as X-60 or X-65 (414 or 448 MPa) for high-pressure pipelines or on deepwater. Higher grades can be selected in special cases. Lower grades such as X-42, X-52, or X-56 can be selected in shallow water or for low-pressure, large diameter pipelines to reduce material cost, or in cases where high ductility is required for improved impact resistance. Pipe types are:

• Seamless

• Submerged arc welded (SAW or DSAW)

• Electric resistance welded...