Abstract

This paper presents a state-of-the art review of the design options for subsea flowlines and production equipment for high-pressure service considering the High Integrity Pressure Protection System (HIPPS). Industry is finding prospects requiring High Pressure High Temperature (HPHT) equipment as oil and gas development extend into deeper offshore reservoirs. To develop these fields as subsea tiebacks, the design of flowlines and risers for HPHT conditions often becomes technically challenging or cost prohibitive.

One of the options is to use a HIPPS system to allow the use of a lower-pressure rated flowline compared to the wellhead and tree equipment. However, it may not be obvious whether HIPPS is cost-effective, practical or operationally acceptable. Design issues for evaluating HIPPS include: field architecture, offset distance, line size, materials, pressure rating of the system components, length and pressure rating of "fortified zones", type of control system, system reliability, dynamic pressure rise resulting from a blockage and installed cost. Another fundamental issue is "Why are land-based HIPPS systems widespread and generally accepted in the industry, but not used as yet subsea?"

For selected field architectures, the impact of using HIPPS will be illustrated with respect to these design issues. These design case studies will provide guidelines as to which combination of architectures and design parameters will be most suitable for taking advantage of the HIPPS system capabilities. The paper will also summarize current industrydesign guidelines that apply to the design of HIPPS.

Introduction

High integrity pressure protection systems (HIPPS) are the evolution of mechanical and electronic safety devices used in the process industry to handle production or transportation upsets. Simply put, HIPPS is designed to protect low-rated equipment against overpressure or abject flow accompanying the upset condition by either isolating or diverting the upset away from the low-rated equipment. However, HIPPS is more commonly referred to as a "high integrity pipeline protection system", because many HIPPS design/cost studies are associated with field layout pipeline designs.

There are two fundamental methods for maintaining a "design break" between the pressure requirement associated with conventional rated equipment and the pressure requirement for low-rated equipment:

  • Maintain an effective barrier at the boundary between the two sections (high and low pressure rating) with a safety shut-off device, and/or

  • Provide a relief safety system in the low-rated system to reduce or maintain the excess fluid flow and thereby limit the build up of pressure in that system 1

Deciding whether to use any safety system (or what type) depends on its overall cost and its reliability compared to a more conventional design. The key is "fool proof" reliability taken into account during risk analysis exercises. The barrier or relief system must be both highly effective and reliable and have a low enough failure frequency to represent an acceptable level of risk. Without these features, HIPPS will most assuredly not be recommended, regardless of cost, because of possible adverse consequences to HSE or damage repair.

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