Suspension Preparation - TM-1-1500-335-23

T.O. 33B-1-1 3-67 3.5.6.5.3 The advantages of water instead of oil for magnetic particle wet method baths are lower initial costs, lower viscosity (about 1 centistoke), non-flammability and ready availability. The disadvantages of water include potential corrosion, electrical conductivity, freezing and the requirement for more conditioners to assure adequate particle function. 3.5.6.5.4 Water baths without auxiliary heating can be used only in shop areas where the temperature is above freezing. Use of anti-freeze liquids is not feasible because the viscosity of the bath then exceeds the maximum allowable. Because the detergents that assure wetting of surfaces can cause foaming of the bath, circulation systems must be designed to avoid air entrapment or other conditions that produce foam. Anti-foaming agents help minimize this tendency, but are not 100% effective. 3.5.6.5.5 Since water is a conductor of electricity, units in which it is to be used are designed to isolate all high voltage circuits in such a way as to avoid all possibility of an inspector receiving a shock. The equipment SHALL be thoroughly and positively grounded. Corrosion of parts of the units can occur if proper provision is not made to avoid this. However, units designed to be used with water as a suspension liquid are safe for the inspector and minimize the corrosion problem. There is no restriction as to the water that is used for the bath, as there is in the case of oil. Ordinary tap water is suitable, and hardness is not a problem, since the mineral content of the water does not interfere with the conditioning chemicals necessary to prepare the bath. 3.5.6.5.6 NOTE The use of water bath suspension is not recommended for field NDI laboratories unless adequate base laboratory facilities exist to test the serviceability of the wetting agents, dispersing agents, corrosion inhibitors, anti-foam agents, and other additives that are required in the water suspension. Where water is used baths SHALL be carefully controlled to prevent corrosion and assure adequate wetting of parts to be inspected. This requires weekly monitoring of corrosion inhibitor and wetting agent concentration. Wetting agents and rust inhibitors must be used with water-type wet baths. Usually the magnetic particle concentrates provided include the correct amounts of wetting agent and corrosion inhibitor for initial use. However, these materials are available separately so concentrations can be maintained or adjusted to suit the particular conditions. Reference SHALL be made to the manufacturer's recommendations for the correct quantity of wetting agent to be added. 3.5.6.6 Suspension Preparation. 3.5.6.6.1 Tank Inspection and Cleaning. When a new unit is being installed or after dumping a dirty bath from a unit in use, the agitation/circulation system must be inspected and cleaned as necessary to insure that it is not contaminated with dried particles or dirt. 3.5.6.6.2 Vehicle. Fill the tank with oil or water as required, and operate the agitation system to make sure it is functioning properly. If petroleum based bulk vehicle is used, the following check SHALL be performed on bulk vehicles prior to formulating the inspection bath to prevent unsatisfactory bulk magnetic particle vehicle from being introduced into the magnetic particle inspection system. a. Loosen cap, cover, seal, or plug on the bulk vehicle container. b. Leave the container undisturbed for at least one (1) hour.