Different types of leaks behave differently. The geometry of the leak, pressure, material, humidity, temperature, and flow rate are all factors that influence the behavior of a leak. Too many interfering factors bring great challenges to leak detection.
The following three hard-to-detect types are examples that I have collected and analyzed.
Type 1: Beam Leaks
When using tracer gas for leak detection, sometimes you may only be able to locate a narrow area. At the same time, you get a leak indication, but it is far away from the test object (a few feet/decimeters), so the cause is unknown.
The leak you find may be a very small, high-velocity beam of tracer gas, almost like a narrow laser beam from a laser. The farther away from the leak, the wider the beam spreads out, but even at a considerable distance from the leak, the beam may still be very narrow.
The gas beam may hit the operator or surrounding structures and “bounce back”, causing the operator to lose track of where the beam is really coming from. Noticing this hard-to-detect leak can save valuable inspection time.
Type 2: Aluminum casting leaks
Aluminum castings can contain air pockets that form as a result of gas trapped in the molten metal as it solidifies. Such pores can be very large and obvious; or they can be very small and cause little problem.
The pores may be enclosed within the part, with no openings to connect the surfaces, but they may also connect one or both surfaces. The latter case will create a leak path through the aluminum casting.
The leaks in the casting may be pinhole shaped, which in turn may act as a thin pipe through the casting. These leaks are largely predictable. However, leaks can also be porous, which usually involves a large number of very small leaks that together can create a larger leak. If the leak area becomes large, it may be difficult to detect the leak with a suction gun because the gun cannot detect the overall leak flow.
A difficult form of leakage to detect in metal castings is seepage, which connects to a larger hidden cavity that acts as a gas reservoir during leak testing.
This structure can lead to a considerable delay between the gas injection process and the gas leakage process towards the opposite side of the leakage point.
As for semi-hidden, fully closed leaks, they are also difficult to detect if the leak test is performed on a “as cast” part, and if the leak test is followed by some kind of machining that opens such closed leak holes.
Tiny air holes can also be sealed off during various liquid treatments or spraying processes. This situation should be carefully considered when deciding where in the manufacturing process to perform leak detection.
Typically, leak detection is recommended after machining and pickling processes are completed and prior to surface treatments such as painting, electrochemical coating or oxidizing.
Type 3: Unobtrusive Liquid Leakage
When a product is tested for liquid leaks, the result may be that the product is not leaking, but leaks can be detected if the product is inspected with a tracer gas leak detection method.
Leak holes can deliver the leaking liquid to the surface of the leak at such a slow rate that the liquid is vaporized as it reaches the surface outside the object. The liquid evaporates so quickly that there is no visible trace of the leak at the point of leakage.
