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.
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
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.
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.
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.
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.