Steam locking can lead to system damage and equipment failure if not mitigated. In this brief article, we will introduce you to three best practices that can help mitigate the risk of steam locking in your system. We will be referencing material from this Steam Theory article, which links to other resources where you can find information on steam locking and other steam system problems.
What is steam locking and why is it a problem?
Steam locking is a condition in which steam enters a steam trap ahead of condensate, "locking" the trap and preventing it from discharging condensate.
This can happen when:
Despite the risks of unmitigated steam locking, it can be difficult to pinpoint steam locking as the cause of steam system trouble.
Often the steam trap is mistakenly identified as being faulty, because condensate discharge becomes irregular. "Steam locked" traps do not stop discharging condensate, but discharge can only take place once the steam inside the trap has condensed and the trap opens again.
Actually, in such cases the steam trap is working correctly! Steam traps are designed to prevent steam leakage and allow condensate discharge.
If the steam trap is not the culprit, we much look elsewhere to find the problem, and most often the equipment or piping configuration preceding the trap are responsible.
Let's take a look at the two main causes of steam locking.
Steam Locking Caused by Equipment Configuration
Steam-using equipment such as Yankee/cylinder dryers remove condensate through stationary or rotating siphon pipes. Ideally only condensate is removed through the siphon pipes, but in practice this may be a steam-condensate mixture.
Once this reaches the steam trap inlet, the presence of steam inside the trap can cause steam locking, preventing condensate discharge.
When condensate cannot enter the trap, it will start to back up from the inlet piping back to the equipment. In the case of Yankee dryers, this means less steam can enter the equipment, lowering equipment performance.
Steam Locking Caused by Piping Configuration
A vertical rise before the trap inlet can cause steam to be locked within the trap and impede condensate discharge.
Steam, which has a lower density than condensate, will logically rise above the condensate when there is a vertical rise and enter the trap before the condensate, causing the valve to shut. Providing extra pressure to forcibly discharge condensate will not resolve the problem because the valve remains shut by steam.
Eventually the "locked" steam will condense and the trap will be able to operate normally. However, unless the cause of the steam locking is rectified, this phenomenon will continue to occur.
This reoccurring steam locking and failure to discharge condensate will result in condensate backup and the associated issues with lowered equipment performance, but in severe cases the presence of idle condensate in piping can increase the risk of water hammer and serious damage to the steam system.
3 best practices to mitigate the risk of steam locking
Since steam locking can cause serious damage to the system and lead to equipment failure, it is important to learn best practices to mitigate the risk of steam locking occurring.
1. Install steam traps with lock release valves or needle valves
Lock release valves and needle valves are similar in principle: by allowing a small quantity of steam to leak from the trap through the air venting section of the trap, steam locking is prevented.
Both are optional extras available on some TLV Free Float® steam traps.
The lock release valve uses the automatic venting feature of a steam trap (such as an X-element) to forcibly open the valve and release steam to the outlet side of the trap.
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A needle valve releases steam to the outlet side of the trap either internally, if the trap has a built-in venting feature (see above), or externally by using a bypass line.
Although we normally want to avoid steam leakage, both of these countermeasures are practical solutions to steam locking, which can present more serious problems if not rectified.
Steam traps fitted with lock release valves or needle valves are available from TLV or your local TLV representative.
2. Design and size the piping configuration to prevent steam locking
The three main piping configuration issues that lead to steam locking are:
Vertical rises in inlet piping sections will allow steam, which has a lower density than condensate, to rise above the condensate and enter the trap first.
TLV recommends to design trap inlet piping to avoid vertical rises if possible.
Rises on the outlet side of the trap tend to present fewer problems. Provided the pressure differential at the outlet allows for unrestricted flow of steam and condensate, and if no other traps follow, nothing remains to stop the steam from flowing out of the piping.
Bends in piping can cause condensate to pool in the lowest point of the piping. Steam will enter the trap ahead of the condensate.
Even if piping is installed parallel to the ground, long stretches of narrow, inadequately sized inlet piping will prevent condensate from moving ahead of the steam.
To rectify these issues, design the layout and size piping so that condensate can drain into the trap. Generally a downward sloping inlet piping configuration is recommended where possible.
3. Perform regular steam system inspections that cover the wider condensate discharge locations (CDL)
As mentioned earlier, often the finger is pointed at steam traps when condensate is not discharged normally.
Steam trap surveys first identify the low-hanging fruit, the leaking traps. Next are the "cold" traps, but it may be difficult to pinpoint steam leaking as the cause of irregular trap operation.
TLV can help by not only inspecting the steam trap itself but also the surrounding valves and piping, as well as the steam-using equipment it serves.
We can also make recommendations for how to rectify equipment or piping problems causing steam locking, and help identify further performance improvement and energy-saving opportunities in your facility.
Conclusion
Steam locking is frequently overlooked, and steam traps often receive the blame for poor equipment performance.
It is important to take into account the role of the steam-using equipment or piping configuration between equipment and the steam trap to accurately diagnose the problems.
If you are concerned about any of the issues mentioned in this article, get in touch with TLV and schedule a steam system survey.
Contact TLV to schedule a plant assessment today.
Customers in Europe can use our dedicated Steam System Analysis form to send a survey request.
Thank you for reading!
