Unfortunately, when it comes to steam traps, people often ignore them. There’s a complacency about them that is costing steam users much more than they realize. The hard reality of a plant maintaining its boiler and forgetting about the rest of the steam system can be a horribly wasteful proposition. Losses can include not only wasted energy but replacement of damaged equipment and misuse of man-hours. It is not uncommon to discover system losses in the hundreds of thousands of dollars.
- When steam traps cause a back-up of condensate in a steam main, the condensate is carried along with the steam. It lowers steam quality and increases the potential for waterhammer. Not only will energy be wasted, equipment can be destroyed. Waterhammer occurs as slugs of water are picked up at high speeds in a poorly designed steam main or in pipe coils or where there is a lift after a steam trap. In some systems, the flow may be at 120 feet per second, which is about 82 m.p.h. As the slug of condensate is carried along the steam line it reaches an obstruction, such as a bend or a valve, where it is suddenly stopped. The effect of this impact can be imagined. It is important to note that the damaging effect of waterhammer is due to steam velocity, not steam pressure. It can be as damaging in low pressure systems as it can in high. This can actually produce a safety hazard, as a valve or a strainer can be blown out by the force of waterhammer.
- Condensate in a system is destructive. It can cause valves to become wiredrawn and unable to hold temperatures as required. little beads of water in a steam line can eventually cut any small orifices the steam normally passes through. Wire-drawing will eventually cut enough of the metal in a valve seat that it prevents adequate closure, producing leakage in the system.
- Most traps fail in the open mode. When this occurs, at times, a boiler may begin to work harder to produce the necessary energy to perform a task which, in turn, can create high back pressure to the condensate system. This inhibits the discharge capacities of some traps, which may be beyond their rating, and cause a system inefficiency. While most traps operate with back pressure, they’ll do so only at a percentage of their rating, affecting everything down the line of the failed trap. Steam quality and product is affected.
- A closed trap produces condensate back-up into the steam space. The equipment will not produce the intended heat. As an example, if there are four coils in a dryer and only three are operating, it will take longer for the dryer to dry a product, which will have a negative effect on production.
- Excluding design problems, two of the most common causes of trap failure are oversizing and dirt.
- Oversizing causes traps to work too hard. In some cases this can result in blowing of live steam. As an example, an inverted bucket trap can lose its prime due to an abrupt change in pressure. This will cause the bucket to sink, forcing the valve open.
- Dirt is always being created in a steam system. Excessive build-up can cause plugging or prevent a valve from closing. Dirt is generally produced from pipe scale or from over-treating of chemicals in a boiler.
Source: Literature review: Steam Source Book
