Leak detection and control

Tuesday, 24 November 2015 08:50

1- Leak detection:

Ammonia leak is easily to detect by its characteristically pungent odor. The location of a small leak may often be determined by holding a moist strip of phenolphthalein or red litmus paper near the suspected leak source. The rapidity and intensive of the color change in the paper will give some indications of leak proximity or size. In the presence of ammonia, phenolphthalein paper will turn from white to pink or deep red, whereas the red limus will become blue.

When an ammonia leak occurs, personnel trained for and authorised to handle such situations shoukd take immediate steps to locate and control the situation. Respiratory equipment and protective clothing as may be necessary and suitable for ammonia should be worn. All other persons must be kept away from the affected area and keep on the windward side of the leak when possible.

Should an individual become trapped in an ammonia contaminated atmosphere, breathing should be help to a minimum and eyes opened only when necessary. Because ammonia vapor is lighter than air, a traped person should remain close to the floor while seeking an escape route. If respiratory equipment is not available, some temporary protection may be afforded by holding a wet cloth over the nose and mouth.

2- Leak control:

If a leak occurs in equipment or piping, shut of the ammonia supply and carefully vent all ammonia from the system before attemping to dismantle any part or make repairs. The apperance of frost on an external surface indicates the presence of liquid ammonia vaporizing in the system. Accordingly, the frost should be allowed to dissipate before breaking any connection. If welding is required, the system should be thoroughly purged until all ammonia and any oil residue has been removed.

A leak at valve stem can usually be stopped by tightening the packing gland nut. A leak at a valve bonnet may be stopped by tightening the bonnet threads or the bolts hodding the bonnet to the valve body. All tightening should be performed slowly and without application of excessive force. If tightening procedures failed to stop the leak, the valve should be closed.

A leak or discharge from pressure relief devices may occur if the pressure within the equipment, piping, tank or container exceeds the rates pressure setting of the device or if the device is faulty. Reducing the pressure within the system by removing ammonia as vapor to process or cooling the container with a water spray may permit the device to reseat. If reseating does not take place, replace the device by suitable one. No attemp should be made to plug, cap or otherwise tamper with a pressure relief device under any circumstances.

If liquid leak from a cylinder, position it if possible so that the vapor instead of liquid escapes because vapor escape often less than liquid. If possible, move the cylinder to an area of reduced hazard. If no risk is entailed, reduce the pressure in the cylinder by removing the ammonia to the process as a vapor. Reduce the ammonia vapor in the atmosphere with a water spray applied to the risk area.