Subsea HIPPS Design Procedure
Authors: Aruo R. , Lund B.F. , Onshus T. 
Published: October 2008

ABSTRACT
The paper is based on a feasibility study investigating the possibilities of using a HIPPS (High Integrity Pressure Protection System) to protect a subsea pipeline that is not rated for full wellhead shut-in pressure. The study was called the "Subsea OPPS Feasibility Study", and was performed by SINTEF, Norway. Here, OPPS is an acronym for Overpressure Pipeline Protection System.
A design procedure for a subsea HIPPS is described, based on the experience and knowledge gained through the "Subsea OPPS Feasibility Study".
Before a subsea HIPPS can be applied, its technical feasibility, reliability and profitability must be demonstrated. The subsea HIPPS design procedure will help to organize and plan the design activities both with respect to development and verification of a subsea HIPPS.
The paper also gives examples of how some of thediscussed design steps were performed in the "Subsea OPPS Feasibility Study". Finally, further work required to apply a subsea HIPPS is discussed.

1. INTRODUCTION
The paper is based on a feasibility study performed by SINTEF, Norway, in 1993-94. The study was called the "Subsea OPPS Feasibility Study". The objective of the study was to describe the state-of-the-art, evaluate possible limitations, and provide a decision basis for application of subsea HLPPS systems.
In this paper OPPS and HIPPS are used as synonyms, where OPPS is an acronym for Overpressure Pipeline Protection System, whereas HIPPS is an acronym for High Integrity Pressure Protection System.
The background for the increasing interest in the application of a subsea HIPPS is that several potential subsea field developments, both in the North Sea and in other areas of the world, are marginal fields with high well pressures (above 5000 psi), and long distance (more than 20 km) to existing infrastructure. If pipelines from such fields to their host platforms (i.e. the platform where the oil/gas is processed) are designed for full pressure, the development may often be unprofitable.
If the pipeline could be designed for lower pressure than the wellhead shut-in pressure, the development of the field could become profitable.
In the following, a pipeline rated for lower pressure than the wellhead shut-in pressure is denoted a low pressure pipeline.
There are lots of examples of other applications of HIPPS systems, see Onshus, et.al. (1995) for an overview.
With respect to application of a HIPPS in subsea production systems, there are several activities going on. Currently, there are feasibility studies for at least two subsea field developments where the application of HIPPS is being evaluated. One study has also been performed in UK, which complements the Subsea OPPS Feasibility Study, see Bayly and Loth (1994).
The overall conclusions from the Subsea OPPS Feasibility were:A subsea HIPPS can be designed to give acceptable performance with respect to safety for personnel and environment.For a field development, the total risk level (including the subsea HIPPS) will have to be assessed and compared with the risk acceptance criteria defined for the current field development.