Deluge and Sprinkler Systems

How deluge and sprinkler systems work

A deluge system keeps its pipework dry downstream of a deluge valve. The valve's clapper is held shut by water or air pressure in a pilot line, or by a solenoid. When fire or gas detection, a fusible plug in the pilot line or a manual release drops that pressure, the clapper opens. Water then flows from every open nozzle in the zone at once. Deluge covers the drill floor, well bay, wellhead area, mud processing modules, fuel and oil storage and the helideck surrounds.

A wet sprinkler system keeps water in the pipes up to closed heads. Each head opens on its own when its glass bulb bursts or its fusible link melts. An alarm check valve signals the flow to the fire panel. Accommodation and some control areas use sprinklers.

Configurations

Key specifications

Standards and what they ask of used parts

• Chapter 8 of the FSS Code covers automatic sprinkler systems on SOLAS units. Heads in accommodation must operate between 68°C and 79°C (154°F and 174°F), except in hot spaces such as drying rooms.
• ISO 13702 and NORSOK S-001 are common references for offshore deluge layout and application rates.
• NFPA 15 covers water spray and deluge on units built to US codes. NFPA 13 covers sprinkler installation and NFPA 25 covers testing.
• NFPA 13 allows only new sprinklers to be installed. Never reuse a sprinkler head taken from another system.
• NFPA 25 requires standard-response sprinklers to be replaced, or samples tested, at 50 years. Fast-response and dry heads fall due sooner, and heads in harsh or corrosive environments every five years.
• GRE pipe used dry in deluge service must hold a fire-endurance approval for that condition under IMO resolution A.753(18) as amended.

Failure modes and inspection

Blocked nozzles are the commonest deluge fault offshore. Corrosion products, scale and marine growth from seawater-filled mains wash into dry pipework and lodge in nozzle bores. Flushing dry pipework after each test and using corrosion-resistant pipe such as Cu-Ni or GRE cut the risk. A full-flow test, with every nozzle checked for discharge, finds them.

Other points to check:

• Deluge valve clapper, seat and diaphragm for corrosion and wear
• Trim, pilot lines, fusible plugs and solenoids against the release logic
• Time from trip to water at the furthest nozzle
• Internal corrosion of galvanised pipe, especially at low points
• Strainers upstream of the valve and nozzle bores
• Sprinkler bulbs, frames and deflectors for paint, damage or corrosion

Documentation

• Valve listing or type approval, model and size
• Hydraulic calculation for each zone and the as-built drawings
• Trip test and full-flow test records
• Hydrostatic test certificates for skids and spools
• Material certificates for Cu-Ni or GRE pipework

Integration and compatibility

Check the valve trim voltage and signals against your fire and gas panel, and the pilot line medium against what your unit runs. Zone demand plus hydrant demand must stay within your fire pump curve. Flange ratings and pipe material must match the ring main. Mixing copper-nickel with steel needs insulating joints to stop galvanic corrosion.

Refurbishment and buying used

A used deluge valve can be overhauled with the maker's seal kit and trim parts, then pressure and trip tested. Ask for the model and size so spares are available. Unused surplus valves and skids from cancelled projects are good buys if the size, pressure rating and trim match. Nozzles are cheap enough to buy new. Sprinkler heads should only come new or as unused surplus in sealed packaging. Naventr can put your questions on test records to the Seller. Tyco and Minimax are well-known makers of deluge valves and sprinkler components. For the water supply, see fire pumps and hydrants.