1. PURPOSE
1.1 This engineering standard defines the shielding requirements for LOX pump systems.
2. SCOPE
2.1 The standard applies to LOX installations designed by Company Europe.
3. RELATED DOCUMENTS
3.1 Company Engineering Documents
None
4. Liquid Oxygen Pump Shielding Systems
4.1 Shielding has two functions: (1) to protect personnel from flame impingement, fragments of the pump system, or the spray of molten metal which could result from a fire, and (2) to minimise the possibility of damage to the pump isolation equipment, thus ensuring that the size of the fire and any consequential LOX spillage is reduced to a minimum. A LOX spill is potentially hazardous.
4.2 The extent of shielding that is required can be influenced by the following factors.
- There is a varying degree of risk depending upon the type of pump used and the duty that it has to perform.
- The risk to personnel is proportional to the amount of time that they have to spend near the pump.
- Personnel protection is provided by equipment if it is sited between the pump and the operator.
- The physical limitation imposed by the pump application (e.g., trailer-mounted pumps).
4.3 It is recognised that the best way to have a safe LOX pump installation is to have:
- A well-designed pump made of materials which provide the least hazard.
- A well-designed system which allows the pump to be cooled down quickly and reliably, and allow the pump to be run with minimal cavitation. The pump system layout, which is required to provide the proper hydraulics, must never be compromised by the requirements to fit in a safety shield.
- Well-trained operators adhering to approved operation procedures.
- An effective, planned preventive maintenance system.
4.4 The type of pump and the duty that it has to perform determine the hazard and, hence, the degree of shielding. Pumps are categorised as follows:
4.4.1 Horizontal Centrifugal Pumps: Shielding is required unless it is classified as a “low duty” pump. Low-duty pumps are those that are both direct-driven at less than 3600 r/min and have a discharge pressure of less than 10 bar (g).
4.4.2 Vertical Multistage Centrifugal Pumps: This type of pump is direct-driven and the pump body is mounted in its own insulated structure. No further shielding is required.
4.4.3 Reciprocating Pumps: Shielding is required unless it is classified as a “low-duty” pump. Low-duty pumps are those with a discharge pressure less than 20 bar (g).
5. Liquid Oxygen Pump Shielding Requirements
5.1 Area of Risk
5.5.1 Burn-through will tend to occur at areas of small thermal mass such as seals and suction pipework. It will probably not occur through the vacuum jackets or bronze pump casings.
5.2 Shielding Requirements
5.2.1 The operator must be able to start, stop, and modulate the pump system without being in “line of sight” of the pump. This can be achieved by a suitable equipment layout and/or the provision of a shield.
5.2.2 The possibility of a pump fire damaging the suction and discharge isolation valves must be minimised. This can be achieved by:
- Locating valves as far away from the pump as practicable,
- Positioning the valves so that they are out of the line of sight of the pump,
- Provision of a shield, or
- Any combination of these.
5.2.3 In the event of an emergency, the operator must be able to stop the pump and isolate it quickly at minimum risk to himself. This can be achieved by:
- Using a discharge non-return valve,
- Using a power-operated suction valve with a remote control position,
- Using a hand-operated valve with an extended spindle,
- Shielding the valve,
- Using ball valves instead of gate or plug valves,
- Providing a remote stop device, or
- Any combination of these.
5.2.4 Persons not involved with the operation of the pump must be protected from the effect of a pump fire. This can be achieved by:
- The use of exclusion zones,
- Providing a shield, or
- Siting equipment away from walkways.
5.2.5 The operator should be able to inspect the pump for leaking seals and joints with minimum risk to himself. This can be achieved by:
- Using armoured glass viewing ports, or
- Arranging the equipment so that the critical areas can be viewed through a narrow gap, in order to reduce the exposure of the operator.
5.2.6 The pump enclosure must be well ventilated and drained to prevent the build-up of vapour or liquid. It is important that the shielding requirements make provision for this.
6. RESPONSIBILITIES AND APPROVALS
6.1 Responsibilities
6.1.1 Implementation of this safety standard is mandatory: it is the responsibility of the relevant design group to engineer a system that complies with the requirements of this standard.
6.2 Approvals
6.2.1 If the option of a full shield is adopted, no special approval is required. However, if the required shielding is to be achieved by the arrangement of equipment and the addition of a partial shield, the proposal must be approved by the relevant committee. For Process Systems Design – Europe (PSD-E), this is the Oxygen Systems Working Group of the PSD-E Engineering Safety Subcommittee; for Gases Group Europe (GGE), it is the GGE Engineering and Standards Committee.
7. DESIGN CRITERIA FOR FULL SAFETY SHIELDS
7.1 Location of Equipment
7.1.1 Note: This section is intended to provide guidance to the piping and structural engineers who have to lay out the system and design a full shield. It can also be used as a guide for those who are engineering a system which incorporates a partial shield.
7.1.2 The following items should be inside the shield:
- Pump
- Suction strainer
- Flexible bellows at suction and discharge
- Elbows on inlet and discharge piping that are adjacent to pump or bellows
- Motor: it is desirable, though not mandatory, that the fan end of the motor should protrude through the shield so that outside air will be blown into the shield and, thus, the increased ventilation will reduce the chance of oxygen build-up within the shield.
7.1.3 The following items should be outside the shield:
- The remotely-operated suction shut-off valve that isolates the pump from the source LOX.
- The check valve in the discharge line.
7.1.4 Other equipment (e.g., pressure gauges, valves) that requires use during pump operation may be located within the shield, provided that they can be operated or read without anyone entering or removing the shield, and provided that they are located in accordance with the relevant system design standard. For example, valves with extended spindles projecting through the shield are acceptable.
7.2 Configuration
7.2.1 The shield should have sides at least 2 m high. It shall enclose a floor area of at least 1 m2.
7.2.2 It is preferred that the shield should have an open top, except in areas where heavy snow is expected, in which case, a roof should be provided. A gap of approximately 300 mm should be left between the top of the sides of the shield and the roof, for ventilation purposes. The roof may either be peaked with an overhang or flat with a skirt. The overhang or skirt should extend to the tops of the shield sides. The minimum horizontal distance between the sides of the shield and the edge of the overhang or the face of the skirt should be 300 mm.
7.2.3 There should be a clearance of at least 300 mm between the sides of the shield and the motor, the pump body, and the pump suction and discharge flanges.
7.2.4 It is important that the flame and debris are directed to a safe area. If necessary, a deflector plate should be installed or adjacent equipment fitted with protection plates.
7.2.5 One wall parallel to the pump shaft should be removable for maintenance purposes. Alternatively, the entire shield may be made removable, provided that suitable lifting equipment is available at the site.
7.2.6 A clearance of between 50 mm and 75 mm should be provided at the bottom of the shield to allow natural circulation of air, and prevent high oxygen concentration in the event of a leak.
7.2.7 Penetrations should have a radial clearance not exceeding 12 mm.
7.2.8 An inspection port should be provided to enable the pump seal to be viewed from outside the shield.
7.2.9 Provision should be made to enable the gearbox oil level to be checked from outside the shield. This can be achieved either by extending the sight glass outside the shield or by providing an inspection port.
7.3 Materials and Strength Requirements
7.3.1 The shield should consist of a steel frame securely anchored to the ground, and clad with steel plate securely fixed to the steel frame. It must be strong enough and thick enough to withstand the emergency release that would result from a fire in the LOX pump. It is recognised that the shield might be severely damaged.
7.3.2 The frame of the shield should be made of mild steel angle at least 40 mm x 40 mm and 6 mm thick. The distance between members of the frame should not be more than 1500 mm. The framework should be of welded construction, except where a removable side is provided. This should be attached with 6 mm bolts and nuts or equal, not more than 300 mm between centres. The preferred method is to have clearance holes and nuts tack welded on the side of the frame.
7.3.3 The cladding should be made of mild steel at least 3 mm thick. This should be attached to the inside of the angle frame, either by bolting or welding. Bolts shall have maximum spacing of 300 mm.
7.3.4 The roof should be made in a similar manner to the rest of the shield.
7.3.5 The shield should be securely anchored to the ground with proprietary drill-in anchors or equal. Resin anchors are not permitted.
7.3.6 Inspection ports should be kept as small as practicable commensurate with the ability to view the equipment specified. Individual ports should not have an area greater than 0.03 m2. The port should be made of Plexiglas or polished wired glass 6 mm thick. The aperture should be strengthened to ensure that the inspection port is not a weak area.