Answer
Scope of SEQ Survey on Fixed CO2 System
During an SEQ survey, the Surveyor and Chief Engineer inspect the entire installation across four main zones:
- CO2 Central Battery Room:
- Ventilation: Mechanical exhaust ventilation working properly (fans drawing from the bottom of the room, as CO2 is heavier than air).
- Illumination & Access: Explosion-proof light fittings, clear egress paths, and self-closing door with keys kept in a break-glass box nearby.
- Environment: Room temperature maintained below 55°C.
- Distribution Piping & Discharge Nozzles:
- Blow-Through Test: Annual blow-through of distribution lines using dry compressed air or nitrogen to ensure piping is clear of debris/rust and nozzles are unobstructed.
- Section Control Valves: Visual inspection and manual operation of manifold directional valves, ensuring clear markings identifying the protected spaces.
- Pilot Control & Alarm Cabinets:
- Remote Release Cabinets: Checking microswitches that trigger pre-discharge visual/audible alarms and shut down E/R ventilation fans, fuel pumps, and fire dampers upon opening the cabinet door.
- Pilot Cylinders: Checking N2 or CO2 pilot gas cylinder pressures, operating wires, pneumatically operated actuators, and manual trip handles.
- Safety Mechanisms:
- Pressure Relief Valves (PRVs): Verifying PRVs on the discharge manifold and pilot lines are free of corrosion and calibrated.
- Safety Interlocks: Verifying two-step release operation (Step 1: Open control cabinet / stop ventilation; Step 2: Open pilot/master valve and discharge gas).
2. CO2 Cylinder Testing & Maintenance Procedures
The maintenance and testing of high-pressure seamless steel CO2 cylinders follow strict intervals per MSC.1/Circ.1318/Rev.1:
Monthly Visual & Pressure Checks (Gauges / Leakage)
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Annual Level Check (Ultrasonic / Weighing - Max 10% Loss)
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10-Year Hydrostatic Test (100% Battery Tested / Min 10% at 10 Yrs)
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Cylinder Inspection, Valve Refurbishment & Refilling
A. Annual Contents / Level Verification
- Frequency: Every 12 months.
- Requirement: All cylinders must be checked to verify gas content. If a cylinder shows a loss of contents of more than 10% by mass, it must be recharged.
- Testing Methods:
- Ultrasonic Liquid Level Indicator: Portable ultrasonic device applied to the outer cylinder shell to identify the liquid-gas interface line.
- Mechanical Weighing: Disconnecting the discharge hose, unbolting the cylinder clamp, lifting the cylinder with a weighing frame/load cell, and comparing the gross weight against the stamped tare weight.
- Radioactive Liquid Level Gauges: Used on specialized installations.
B. Hydrostatic Pressure Testing (Hydraulic Stretch Test)
- Frequency:
- At 10 years from date of manufacture: At least 10% of the total cylinders must undergo internal inspection and hydrostatic testing.
- If one or more of the 10% tested fail, 50% of the remaining cylinders must be tested.
- If any of the 50% fail, 100% of the cylinders must be tested.
- Before 20 years from date of manufacture: 100% of all CO2 cylinders must undergo hydrostatic pressure testing.
- Test Pressure: CO2 cylinders are designed for a service pressure (Ps) of 125–150 bar and are hydrostatically tested at 250 bar (1.5 to 2 times working pressure) for a minimum duration of 30 seconds to 2 minutes.
the following parameters must be verified and documented:
- 1. Stamped Data Verification:
- Read and verify original markings stamped on the cylinder neck: Tare weight (TW), Water capacity (WC in liters), Test pressure (TP), Working pressure (WP), and Previous test dates/symbol.
- 2. Pre-Test Inspection:
- External Visual Inspection: Check for wall thinning, deep scoring, pitting, gouges, arc burns, and severe corrosion.
- Internal Inspection: Use a low-voltage internal inspection lamp/endoscope to check for internal rust, water ingress, or oil contamination after blowing off residual contents.
- 3. Volumetric Expansion Test (Water Jacket Method):
- Measure total volumetric expansion under full test pressure (250 bar).
- Calculate Permanent Volumetric Expansion (PVE) after pressure release. If PVE>10% of Total Volumetric Expansion, the cylinder fails and must be condemned/scrapped.
- 4. Cylinder Valve Inspection & Refurbishment:
- Dismantle the main operating valve; replace all soft internal rubber/PTFE seals and O-rings.
- Inspect the Bursting Disc / Pressure Relief Safety Disc fitted to the valve body. Discard and fit a original factory-calibrated burst disc (typically rated at 190–225 bar).
- Inspect siphon tube (dip tube) inside the cylinder to ensure it is firmly attached and unblocked (ensures liquid CO2 discharge).