Finding out failed steam traps and fixing them up can avoid the wastage of steam and improve the productivity and performance of the steam system. It would be worthwhile to understand the implications of steam trap failures on the performance of the steam system.
Simply put, steam traps fail in two ways: open and closed. When a steam trap fails open, it acts like an open valve, completely leaking the steam and condensate. When a steam trap fails closed, it acts like a closed valve not allowing the steam and condensate to pass through it. Whether a steam trap fails open or closed, it does equal damage to the steam system and hence, should be repaired or replaced.
Failure detection is easy if a steam trap fails open and it discharges into the open. If a stem trap fails closed or if a steam trap from which condensate is being recovered fails open, the detection becomes difficult. Hence, it is always advisable to use correct equipment to monitor the steam trap performance on a regular basis.
If a steam trap fails closed, following are the different problems associated with the failure.
Presence of water i.e. condensate in the steam system results in a phenomenon called as water hammer. Condensate, if not removed by a steam trap accumulates at the bottom of the steam lines. In such situations, a bi-phase flow exists in the piping. During such bi-phase flows, condensate is dragged by the steam to travel along with the steam at speeds much higher than the maximum allowable speed for condensate. This results in slogs of condensate travelling at very high velocity in the steam lines. When this slug hits some bend or some equipment, a pressure wave is generated which is called as water hammer. Fail closed steam traps are the major reason for water hammer.
When a steam trap installed on a process equipment fails closed, it stops removing condensate from the process. As a result, condensate accumulation takes place inside the process vessel. Water logging has multiple disadvantages with respect to the performance of the process. First of all, the product which is surrounded by water won’t get heated. This results in non-uniform heating of the product. Water logging will also increase the time required to heat the product to the desired temperature.
Condensate is pressurized fluid. If condensate remains in the steam system and there is a sudden drop of pressure, it will flash and will expand in its volume. Such sudden expansion can damage the piping. Water hammer as well as moisture entrained in the piping can damage various equipment fitted on the line.
When a steam trap fails open, it simply acts like an open valve and hence, a lot of steam would leak through it. As a result, the overall steam consumption of the plant will go up, reducing the efficiency of the operation.
If a leaking trap is discharging to the drain, the entire steam and hence the heat energy that is being leaked, will be wasted. This also increases the boiler load. Many times, it has been observed that a same size of boiler can be used to heat more processes if all the pipe leaks and leaking steam traps are repaired or replaced.
(Source: Forbes Marshall)Read More
Why Steam Traps Fail?
Authors: Bruce Gorelick, Enercheck Systems and Alan Bandes, UE Systems, Inc.
Properly functioning steam traps open to release condensate and automatically close when steam is present. Failed traps waste fuel, reduce efficiency, increase production costs and compromise the overall integrity of the steam and condensate systems. Traps should be tested on a regular basis — or the neglect may be quite costly.
There are three general conditions, which adversely affect traps:
- Dirt – by far the leading cause of failure resulting in either a leaking or plugged trap.
- Pressure surges (due to sudden steam valve openings, improper piping, or trap misapplications) resulting in water-hammer and subsequent damage to the internal steam trap components.
- Over-sizing IB traps can lose their prime; TD traps can experience rapid cycling.
How do we keep problems to a minimum and keep energy costs in check? One simple way is to look for warning signs. Let’s review the most evident signs that should signal a distress call from your steam system.
- The once lazy plume from your condensate stacks is now an out of control freight train. The steam that is standing at attention from your stack, like a soldier standing at attention, is costing you dearly.
- Condensate back pressures that have slowly been rising have been causing your electric condensate pump to self destruct. High temperature condensate cannot be handled by conventional electric pumps. Temperatures over 212 degrees Fahrenheit cause conventional electric condensate return pumps to cavitate. Motors burn out and mechanical seals begin to leak when steam is present.
- Pressure reducing valves (PRVs) or control valves fail to maintain set pressures. Fully or partially plugged traps prevent condensate from being eliminated from the steam space. Un-drained condensate at PRV stations will back up into the steam line and will wiredraw the heads and seats of the reducing valves. Wiredrawing is when high velocity water in the steam system cuts (scores) the surfaces of heads and seats. Even small microscopic cuts will prevent the proper operation of these valves.
- A production capability has been reduced. Open or closed traps that have failed will negatively impact production. Plugged traps will back condensate up into the process and dramatically reduce system efficiency. Blowing and leaking traps are costly to production due the added and unnecessary energy consumption.
- Pipe wall thickness of the condensate system has become an issue. Fully open or partially opened steam traps that are not repaired in a timely manner will deteriorate the condensate return piping. Some of the early warning signs begin with steam leaks.
- The cost to maintain heat exchanger bundles, humidifiers, HVAC coils and other equipment has dramatically increased. Failed traps will prevent proper operation of sensitive equipment. When steam traps fail in a closed position, over time, the stagnant condensate will turn to carbonic acid (co3). Carbonic acid will deteriorate all the metal it comes in contact with. Beyond increased energy consumption, failed open traps will also cause control and efficiency issues.
- Water hammer can develop in neglected or mismanaged steam and condensate systems. Water hammer literally sounds like someone is hitting a pipe with a hammer. In some cases water hammer can occur when a portion of the steam condenses into water within steam piping. Left un-drained, condensate will spill into the steam system and begin to accumulate. Eventually a wave of water will be created. This slug of water can be carried at high velocity until it reaches an obstruction like a closed valve, a lower elevation, or a sudden change of direction. A trap that is blowing steam can also cause water hammer. Blowing traps create back pressure in the condensate system piping. If condensate piping is already undersized, the problem will be compounded by the additional pressures found by the faulty traps. Un-drained condensate can back up into the steam distribution piping. From the standpoint of plant safety, it is essential to test and maintain the steam trap population. Type “steam water hammer accidents and fatalities” into a search engine; the results should be convincing enough to create an immediate action plan.
The Action Plan
- Perform a regularly scheduled steam trap survey.
- Identify system design issues.
- Perform an insulation audit. Areas where insulation has been removed and never replaced will significantly add to your overall steam production costs.
- Using ultrasound detection equipment, test bypass valves if they exist in your steam system. They may be leaking through when they ought to be shut.
- Turn off seasonally operated equipment such as unit heaters.
- Periodically test control valves or shut off valves in the HVAC system with a hand-held IR temperature instrument and an ultrasonic leak detector. If they are even partially leaking through, they are adding to overall energy costs.
- Audit the system and unused inventory equipment. Remove defunct systems.
- Whenever possible and practical, use a computerized system to control and monitor processes.
Purchase Proper Test Equipment
Even if outside technical professionals are contracted to test the steam system, from time to time, a problem will occur. Time is money. Having the proper equipment and just one trained employee can avoid costly downtime. The two basic pieces of equipment to own are an infrared thermometer and an airborne ultrasonic instrument. Such equipment is readily available in all price ranges. A thermometer with simple features is fine; however, an ultrasonic listening device should be selected more carefully and must have clear signal quality.
This is similar to purchasing an audio system for your home and comparing one set of speakers with another set. When listening to a quality speaker system the nuances of what was actually recorded opens your ears to new level of listening. The same is true of listening to a steam trap. With a fine instrument you can even hear the snap crackle- pop of steam passing across the head and seat of a wiredrawn inverted bucket trap. After all, “hearing is believing.”Read More