What is a steam trap failure?
When a steam trap fails, it does not discharge condensate efficiently. You may observe steam leaking from the steam trap even when condensate is not being discharged. As steam leakage is unsightly and dangerous, a plant would normally be motivated to correct this immediately.
However, there are cases where the leakage is so minor that the amount of steam leaking is not visible. Nonetheless, such leaks can contribute to hundreds, if not thousands of dollars in steam losses per year. Moreover, the user may experience other issues such as process temperature not being reached, or water hammering. Such issues are difficult to diagnose and you may not realise that it is due to a faulty steam trap.
Economic loss due to leaking steam trap
This is obvious. But exactly how much of your profit margin is being eaten away by steam losses?
This table shows an approximate steam loss calculation for a thermodynamic steam trap at 3 barg. Of course, there are many variables and assumptions made. It depends on the number of hours in operation per year, the type of steam trap, cost of steam etc. Nevertheless, if a single steam trap can cost hundreds per year, imagine a refinery with thousands of steam traps, with a steam trap failure rate of 3% to 5%. The financial loss could number in the millions every year!
Process temperature is lower than expected
Process equipment such as heat exchangers, pumps, vessels, steam tracing which rely on steam to heat the process medium inside. A common complaint is that the temperature cannot be achieved. The causes are endless, but one cause could be due to blockage of the steam trap.
When a steam trap is blocked due to dirt, pipe scale, rust, packing and joint material or debris, condensate cannot be discharged. Condensate will build up all the way through the steam tracer / heat exchanger. Steam is unable to pass through and provide adequate heating to the vessel / heat exchanger.
What are the signs and how to rectify?
- • Check the temperature of the steam trap. If the temperature is way below 100°C, it could mean that the steam trap is choked with condensate.
- • Try to clear the choke by opening the bypass. You may notice that there may be a lot of condensate being released. Once all the condensate is cleared, the steam should start flowing again.
- • At this point, the steam trap may or may not work again. If the steam trap is still not discharging condensate properly, we suggest to remove the steam trap for servicing to check the internal parts.
Excessive amounts of steam flashing
It is common to see steam flashing during condensate discharge. The type of steam trap, whether it is ball float, thermodynamic or thermostatic makes a difference. First of all, we must differentiate between steam flashing and steam leaking.
What is steam flashing?
When hot condensate at high temperature is discharged at lower pressure, flash steam will be produced. This is because the hot condensate contains excess energy which prevents it from staying in liquid form. The excess energy is released in the form of steam.
One difference flash steam and live steam is the pressure and speed at which the steam moves. Live steam tends to have a high velocity, and shoots out in a ‘straight’ trajectory.
Many people see excessive flashing, and believe that their steam trap is leaking. However, this may not be the case, especially for temperature control traps. A temperature control trap has a bimetal disc that opens and closes at set temperatures.
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- Temperature Control Trap Thermostatic TB1N
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- TB51 Thermostatic Temperature Control Trap
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- Miyawaki TB7 Temperature Control Steam Trap
In this case, excessive flashing could simply be because the set temperature of the temperature temperature control trap has been set too high. The condensate is discharged prematurely, and some live steam is lost in the process. Furthermore, the hot condensate being discharged produces flash steam by itself.
Improper sizing of steam traps
Other reasons for excessive flashing could be wrong sizing of steam traps. Some types of steam traps are designed to keep small amounts of condensate within the trap as a water seal. When this water seal is not present, steam would leak when the valve opens to discharge condensate. Because of the wrong sizing, the steam trap is unable to maintain a proper water seal, and therefore leading to excessive live steam being lost during condensate discharge. Wrong sizing can also lead to early steam trap failure.
What can I do about excessive flashing?
A deep understanding of the various types of steam trap and the on site conditions are needed to diagnose if the steam trap is indeed leaking. There are tools available, such as ultrasonic vibration detector, thermal imaging and stethoscope methods to check the condition of a steam trap. Techmatic is a provider of such services.
Conclusion
There are many types of steam trap failures which cannot be seen easily. If left unchecked, these will lead to profit loss, environmental hazards, downtime, out of spec product etc.
The most challenging aspect in a steam trap management is the benefits are not easily visible. Many top management do not devote enough resources to a proper steam trap maintenance plan. That is why many companies prefer to engage professionals like Techmatic to manage and maintain their steam traps. It takes a combination of specialised tools, technical knowledge and field experience to successfully carry out a steam trap inspection.