Steam Trap Testing / Airborne UT
STEAM TRAP TESTINGSteam energy, whether produced on-site or purchased from a power utility, typically accounts for one of the main operating expenditures of any commercial facility. The incorrect functioning of even a small percentage of steam traps can therefore result in significantly higher energy costs. Malfunctioning steam traps can also cause operational problems, as well as allow severe corrosion damage to occur to nearby piping and related vales, strainers and fittings, etc.
Although a relatively simple device designed to separate and remove water that has condensed from still vaporous steam, steam traps operate under an extremely harsh environment and, like most mechanical devices, are subject to regular wear and occasional damage. A study of steam traps featured in Power Magazine identified overall failure rates as high as 50% at some facilities, and suggested that a goal for a total failure rate of between 5 and 10% was attainable in most facilities. Their estimate for trap life was only 4-5 years before the need for repair or replacement.
It is due to the critical importance of proper steam trap operation in providing safe, economic and reliable steam service that many authorities recommend periodic steam trap maintenance and/or testing. New York’s Con Edison recommends steam trap inspections every month. Others have stressed testing frequencies anywhere from once per week to once every year.
Steam traps that fail produce a host of operating problems. While increased energy costs are usually focused upon, it is the operational problems which can potentially cause the greatest economic loss. Increased corrosion rates due to accumulated condensate can take decades off the life of a steam system. Pitting and oxygen enhanced corrosion can destroy a steam line or condensate system in a matter of a few years. High temperature steam heated condensate can cause maintenance problems with pumps and require additional cooling before discharge. A faulty steam trap on a heat tracing line may not only fail to protect the equipment, but burst itself due to freezing.
Depending upon whether steam traps fail in an open or closed position creates entirely different operating problems within the steam system. Any steam trap failing in the closed or restricted position allows condensate to collect within the steam line. Although it does not contribute to a loss of steam energy, the accumulation of condensate will ultimately prevent distribution steam from passing through the line. When that occurs, the stronger steam pressure pushes “waves” or “slugs” of condensate along the pipe like a battering ram --- producing the characteristic “water hammer” effect. Left to continue, “water hammer” can loosen pipe joints, and in the worst cases, even crack pipe and pipe fittings.
Where condensate is not promptly removed, but allowed to “puddle” in areas, high velocity steam can entrain small droplets of condensate to produce an erosion or “sand blasting” effect upon downstream valves, valve seats, elbows and tees, etc. Unlike water hammer, which is rare to go unnoticed, erosion due to high velocity condensate droplets in a steam system silently destroys piping and related components until it is first noticed in the form of a leak. At that point, however, most of the damage to the system has already taken place.
Condensate left to accumulate in either a steam distribution or condensate system naturally absorbs trace amounts of carbon dioxide and oxygen, becoming highly acidic as a result. With a pH often between 5 and 6, the acidic condensate then aggressively corrodes steel pipe and components; producing localized failure of the steam system. Steam traps failing in the closed position do not fulfill the important requirement of venting air and other non-condensable gases from the live steam - further contributing to pipe corrosion.
Because steam naturally increases in acidity as it condenses into liquid form, it is a natural enemy to any steam system and one which must be constantly monitored. In fact, were it not for the problems primarily associated with condensate, steam piping systems would require very little maintenance.
Fortunately, problems associated with steam trap blockages or restrictions generally reveal themselves in the form of operating problems and complaints, thereby prompting their repair. But for problems associated with steam traps which have failed in an open or partially open position, recognition rarely occurs. Except for unusual heating patterns or noticeable sound, there are generally no external signs to indicate a defective steam trap which has failed in the open position. Under most conditions, a steam trap “blowing” or freely flowing steam will be noticeable due to the high velocity noise of the rushing steam. Smaller leaks, however, will not. A single, small, low pressure (10 PSI) leak of just 1/8th inch across a steam trap seat, for example, will waste 9.35 pounds of steam per hour. Below is a table showing steam loss per hour at various pressures and orifice sizes.
Multiply such loss against the number of steam traps installed in a typical facility and it becomes obvious as to the potential savings gained by establishing a strict steam trap maintenance program. Malfunctioning steam traps, in fact, generally account for the bulk of steam waste in any building operation. Given a normal failure rate of between 15% and 25%, it is not unusual to accumulate a loss of tens of thousands of dollars per year in even the most well maintained building operation.
Except for the most obvious mechanical failures, monitoring for such losses is extremely difficult. The large variety, type and mode of operation of steam traps make it difficult to identify a failure condition based upon any one physical criteria. Reduced operating budgets have made it almost impossible to disassemble all steam traps for periodic maintenance; large investments in highly specialized diagnostic equipment is not cost effective. Infrared measurement is applicable only under strict conditions, and ultrasound testing requires detailed acoustical knowledge of every steam trap. Add to this difficulty in diagnostics, the generally high number of traps used throughout a typical building steam system and the necessary record keeping, and it becomes easy to understand why this relatively ignored mechanical component accounts for such significant economic loss.
ADVANTAGES OF ULTRASONIC TESTING
Infrared Thermography (IR) and Ultrasonic Detection (UT) have been long recognized as the only nondestructive diagnostic methods suitable for identifying defective steam traps. IR, which measures the higher level of radiant heat energy produced by the flowing steam through the condensate line, has been shown useful as a general diagnosis tool under certain conditions of steam trap failure, though not practical for most facilities.
Piping insulation, for example, will partially shield any possible excess heat loss and therefore present a physical problem by requiring its temporary removal and replacement. With the many types and models of steam traps in service, the infrared signature of one type of failure may not be applicable to all others; thereby requiring detailed thermographic knowledge of each and every steam trap under all possible failure conditions. Minor steam leakages are rarely identified. Moreover, even when a steam leakage condition is confirmed, there is no way to quantify the degree of failure and the pounds of steam lost.
A far more definitive parameter of steam movement is its sound frequency. Since the steam path through steam traps generates a distinct sound profile, it is possible to use this information to quickly and effectively recognize steam trap failures. In addition to simply locating a failure, ultrasonic testing is also capable of measuring the magnitude of the failure and therefore the volume of steam loss over time.
For operating engineers and property managers, ultrasonic testing not only provides a far more accurate steam trap evaluation, but provides hard data as to the degree of severity for each located steam trap failure. Following high priority repairs of critical equipment, maintenance can be next directed toward those steam traps which will return the greatest in cost savings.
ULTRASONIC TESTING EQUIPMENT
Steam traps can either be defined as continuous (or modulating continuous) flow and on-off types. UE Systems’’ Ultraprobe 9000 helps an inspector readily identify the trap operation in all types of environments. UE Systems unique frequency tuning feature enables users to literally tune into the trap sound and clearly identify leaking or blowing traps. Ultrasonic steam trap inspection is considered a "positive" test in that an operator can instantly identify sound quality and intensity differentials and thereby determine operating condition accurately. As part of our testing procedure, a walk through survey is first conducted of all areas to be tested. All steam traps are identified by manufacturer, type, model and size. Operating conditions such as steam pressure, condensate rate, hours of use, equipment priority, physical location, and service, etc. are recorded. A brass tag assigning a number is attached to each steam trap for identification as part of this and any future testing survey. Irregularities in operation are noted and recommendations made.
Once data is collected, it is then entered into Conservit Steam Trap software which is designed to easily manage and analyze your steam traps. We can analyze steam loss, maintenance cost, failure trends and more. Good steam trap management software permits you to make important judgment calls based on proper information. As you gather data, you must have the ability to sort the data and convert it into useful information. As you review the results of current and past steam trap surveys, the information shows which of the steam traps have low maintenance costs associated with it.
AIRBORNE ULTRASONIC DETECTION
Ultrasonic detectors are capable of detecting sound waves having a frequency greater than 20,000 cycles per second which are totally undetectable by the human ear. These detectors are excellent at detecting developing electrical and mechanical faults. By trending these faults over time, maintenance operations can diagnose the problem and plan for a scheduled shutdown versus an unscheduled shutdown to complete the repairs needed.
East Coast Industries offers the following Ultrasonic Detection programs:
Testing Valves Assessment of Electrical Discharges such as Corona, Tracking and Arcing Leak Detection of Heat Exchangers, Boilers and Condensers Mechanical Operations Inspection Monitoring of Motors and Pumps To learn more, click here or call 732-548-4311 for more information.