Safety shields are commonly used in chemical plants to prevent injury to personnel, damage to environment or surrounding equipment in the event of leak or spray-out of hazardous chemicals from flanged connections. Flange guards are also used in steam piping and oil and gas installations. Flange guards are often provided with snap-lock feature that enables their quick installation on flanged connections.
Image courtesy: www.crp.co.uk
Leak Detection in Flange Guards
Most often it is important to identify leaks immediately so that preventive action can be taken. Early leak detection helps reduce maintenance costs in plants by preventing downtime from failures or accidents. Leak detection is achieved using the following:
- Transparent shielding
- Leak Indicator patches
Leak Indicator patches are made of pH sensitive material. Weep holes are located behind the pH indicating patch that immediately signals a leak due to change in color of the patch in the presence of an acid or an alkali. The pH patch is replaceable which allows reuse of the shield. If early leak detection is critical, the flange shields should be inspected regularly and should be part of the routine maintenance plan.
Flange guards are available for use on various types of valves, expansion joints, hoses, pipe vents, sight glasses, instruments etc.
Image courtesy: SAFE-RING
Flange Guard Materials
Spray shields are available in Teflon, polypropylene, PVC, stainless steel and other material depending on the application.
Flange guards in non-metallic materials are suitable for lower temperatures. Flange guard in polypropylene material provides resistance to a wide range of corrosive chemicals up to 100°C in temperature. Non-metallic guards are UV stabilized to prevent UV degradation. Where a high pressure or high temperature spray-out is expected, metallic spray shields should be used. Stainless steel 316 flange guards are used for high pressure service and temperatures up to 400°C. Some manufacturers such as SAFE-RING incorporate a patented C-shaped diffuser in their design to safely dissipate the high pressure jet. Some manufacturers use a mesh type liner to diffuse the high pressure jet.
Spray guards are available with nipple at the bottom for containment or spill recovery.
Commonly used locations
- Piping near head and eye level.
- Piping near walkways and traffic areas, including areas with overhead piping.
- Unloading/loading areas, including docks and terminals.
- Piping on discharge side of pumps.
- Piping in tight, confined spaces.
- Piping conveying flammables near hot surfaces and instrument panels.
Resistance chart for common chemicals
Table below may be used as a rough guideline for temperature resistance of flange guard material.
It is important that the Manufacturers recommendation be used for correct selection of flange guard materials on a project.
| Chemical | Maximum Temperature ºF | |||
|---|---|---|---|---|
| Polyethylene | Poly Vinyl Chloride | Polypropylene | PTFE | |
| Ammonia | 170 | 170 | 200 | 450 |
| Ethylene Dichloride | Not recommended | Not recommended | 75 | 450 |
| Hydrochloric Acid (to 35% conc.) | 75 | 75 | 200 | 450 |
| Hydrofluoric Acid (to 85% conc.) | 75 | 75 | 200 | 0 |
| Nitric Acid (to 30% conc.) | 150 | 150 | 150 | 450 |
| Oleum | Not recommended | Not recommended | Not recommended | 450 |
| Sodium Hydroxide (to 50% conc.) | 170 | 170 | 200 | 450 |
| Sulfuric Acid (to 30% conc.) | 170 | 170 | 200 | 450 |