Safety Shutdown Philosophy

 

1. Abstract

The Safety Shutdown concept is focused on the prevention of hydrocarbon release, stopping the flow of hydrocarbon to a leak, and minimizing the effects of hydrocarbon that are released. Additionally, fire and toxic gas protection is also provided.

The primary goal is to maximize available production and at the same time to shore in a safety manner to equipment and personnel. This goal will be accomplished by employing a Keep It Simple and Safe philosophy and a Four-Level Shutdown concept.

2. Implementation

The basis for implementing the Safety Shutdown concept is the American Petroleum Institute Recommended Practice RP 14C. This Recommended Practice was used as a guide in developing the shutdown logic. API RP 14C provides two levels of protection to prevent or minimize the effects of an equipment failure. The two levels of protections are

• The highest order (primary)
• The next highest order (secondary)

Listed below are examples of undesirable events that cause alarm and/or shutdown action. This is not an all inclusive list, it is however illustrative of the protection philosophy.

• Overpressure
• Underpressure
• Leak
• Liquid Overflow
• Gas Blow-by
• Fired Equipment Protection
• High Hydrogen Sulfide Concentration
• Fire

Risk severity is divided into Four (4) Levels of Shutdown. These different risk levels will be utilized to protect equipment and personnel, while maintaining production as high as practical.

The shutdown levels are defined as follows:

Level 1: Local System Shutdown. It involves only services not imperative to the main process.

Level 2: Main Process Train Shutdown. It will allows continued operation of the remainder of the facilities and will permit the process train to be corrected and put back on stream.

Level 3: Critical Process Shutdown. The facility is shutdown by an essential single train process or by fire, high toxic gas, or combustible gas alarm. All ESD valves should be closed. All high pressure gas inventories should be relieved to flare only in the event of fire or high toxic gas alarm. Power generation should remain in operation until low fuel gas pressure causes shutdown. Utilities and equipment auxiliaries should remain in service as long as possible.

Level 4: Abandonment. It should be actuated only by senior personnel from the central control room. All ESD valves should be closed and all gas inventories should be vented to flare. The facility should be de-energized except for emergency and other essential power source.

3. Examples

Followings are specific examples that illustrate the Four Level Shutdown philosophy.

Level 1 (Local System Shutdown)

• High or Low Pressure in an incoming flow line to a production header, would shut-in only the affected well.
• The Water Injection System can be automatically shut down, but would not affect oil production.
• The Hot Oil System can be automatically shut down, but would not affect oil production.

Level 2 (Main Process Train Shutdown)

• A gas compression train can be automatically shut down, but would not affect the oil production.
• An oil production train can be automatically shut down, and oil production affected only by volume loss from the affected train.
• A gas turbine generator set can be automatically shut down. If the oil train pump can still maintain full production, no reduction in oil production is required. Otherwise curtailment of oil production or standby power augmentation should be required to prevent a level 3 shutdown.
• The Glycol Regeneration Unit can be automatically shut down, but not affect Fuel Gas, Gas Lift Gas Flow or Oil Production. A facility shut down would occur only if the problem is not corrected before the residue gas moisture analyzer reaches the shutdown value.

Level 3 (Critical Process Shutdown)

• Instrument air failure (automatic)
• Leak detection in any main oil production header
• Combustible gas sensors (automatic)
• Fire sensors (automatic)
• Hydrogen Sulfide sensors (automatic)
• Critical Process Shutdown, i.e. Fuel gas (automatic)
• Manual

Level 4 (Abandonment)

• Manual initiation required by senior personnel only and would be confirmed over the public address system.

Review design philosophy for the flare, vent, relief, and blowdown systems for additional information.