Abstract

Offshore processing platform involves large volumes of hydrocarbons at high pressure and therefore these systems represent high risk to personnel, environment and asset.

The main objectives of this article are:

  • Understand well the new methodology of safety integrity analysis for piping and vessels under fire scenario

  • Provide information on what is acceptable and unacceptable rupture

  • Understand the methodology for fire depressurization calculations, rupture calculations and mitigation methods to achieve safe design based on actual project experience

  • Comprehend inputs required by technical safety

In earlier method, the pressurized segment exposed to fire is depressurized to 6.9 barg or 50% of design pressure (whichever is lower) within 15 minutes. 15 minutes depressurization time had been a generalized time with set of parameters and might be too long and could lead to unacceptable rupture in the piping and vessel in some cases due to excessive stress generated due to fire.

The new method is an iterative process of designing a depressurization system with major focus on evaluating actual stress in the piping and vessels installed on topside. The new method actually checks the rupture time for a segment under fire and assesses if rupture is acceptable or not based on acceptance criteria from technical safety.

This paper discusses the actual calculation methodology for piping and vessel integrity analysis based on actual project experience and importance of safety input for the analysis.

This method actually determines if rupture is acceptable or not. Unacceptable rupture shall demand for some mitigation actions/design improvements suggested below in order to ensure overall topside safety in case of fire.

  • Increase or utilize flare system capacity

  • Increase pipe wall thickness

  • Selection of material with higher UTS values at elevated temperatures.

  • Provide Passive fire protection (PFP) that will allow pipe or vessel to sustain for longer fire duration. (Focus shall be on fast depressurization and other options)

It is very important to check the integrity of entire piping and process equipment's on the process platform which results in reducing the risk of missile effect due to rupture that can cause fatalities or serious injuries and consequently reduces the risk of damage to neighboring pressurized hydrocarbon system further reducing the risk that may lead to major economic losses and environmental disasters.

The new methodology described in this paper is used in international projects and when applied ensures a step forward towards achieving safe and cost effective design which in turn shall care for human life, asset and environment which is top priority.

This method is published in new edition of international codes and standards.

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