Flash steam is typically generated from the condensate discharged by a steam trap, but this should not be confused with a leak.

Leaks, on the other hand, generally occur when a steam trap malfunctions. The result is the discharge of live steam.

In both cases, steam discharge can be observed at the trap outlet. The difficulty for site personnel or operators lies in how to determine whether a steam trap is leaking purely based on observation of the steam discharge from the trap. There are no easy answers, as the steam in both patterns looks very similar.

The first consideration might be whether the amount of steam discharge tells us anything. Unfortunately, the amount alone is not enough to paint the whole picture.

The appearance of flash steam can vary considerably based on the type of steam trap, the condensate load, and the operating steam pressure. See the videos below showcasing steam traps in operation to see the difference.

To start, let's observe flash steam discharged from a functioning steam trap.

Notice that the appearance of the flash steam changes significantly, even from the same type of steam trap, depending on the steam pressure.

Similarly, the flash steam generated by different types of steam traps looks different even when operating at the same steam pressure.

Based on these observations, we can see that a properly functioning steam trap may produce varying amounts of flash steam depending on the operating conditions.

Next, let's compare the differences in steam discharge of a functioning steam trap and a leaking steam trap.

In both cases, we observe a continuous discharge of steam. However, it is difficult to determine whether a trap is functioning or leaking based only on the appearance of the steam discharge. The key point lies in the difference in the quantity of condensate being discharged.

During normal operation, typically a moderate amount of condensate is released. However, when a trap leaks steam, an almost negligible amount of condensate is discharged. A cautious inspection of the pipe outlet will reveal transparent flow of live steam leaking from the trap. Traps like these are described as “blowing”.

Another indication of a steam leak is that the typical "whooshing" sound produced during condensate discharge is replaced by the high-frequency "hissing" sound of live steam and a sharp, piercing metallic sound.

It is often assumed that a continuous discharge of steam means steam is leaking, however this blanket assumption is incorrect.

Unfortunately, it is not possible to determine if a steam trap is leaking based only on a constant discharge of steam. Steam traps designed for continuous operation also emit steam during normal operation, in the form of flash steam.

Steam traps are designed primarily for either continuous or intermittent operation. This is due to the mechanical construction and operating principles of the steam traps. For a more detailed understanding of continuous and intermittent operation, the types of steam traps and their operating mechanisms, please refer to our article on Applications of Different Types of Steam Traps.

As we have observed, making a judgment on whether a steam trap is leaking or not based solely on the amount and appearance of the steam discharged is a challenge, especially when on site. However, it is possible to make an informed assessment by considering additional information about the trap, for example, the behaviour of the steam trap during condensate discharge, or the state and amount of the discharged condensate.

If you notice steam rising from a trap outlet, we recommend taking a closer look (while observing all site safety regulations of course).