Steam Solved - Steam Trap Operation
Steam Solved - Steam Trap Operation
Steam Solved - Steam Trap Operation
Steam Solved.
4 Steps to Improve
Steam Trap Operation
Steam Solved: Four Steps to Improve Steam Trap Operation White Paper
Figure 1. Steam Traps Remove Condensate, Air, and Other Gases from Steam System
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Steam Solved: Four Steps to Improve Steam Trap Operation White Paper
A. Blade erosion
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Steam Solved: Four Steps to Improve Steam Trap Operation White Paper
Condensate can also cause rust and corrosion, especially in carbon steel steam pipes,
condensate recovery systems, and tracing lines. With a properly functioning steam
trap, condensate is removed so the steam stays dry. Little air and water is present in the
system and rust is less likely to form.
If the trap fails shut, it cannot remove the condensate and rust and corrosion can
quickly follow. When rust and corrosion occur, scale and other deposits can clog
downstream components in the steam system.
Because of the safety and process issues caused by failed-closed steam traps, many
operators elect to open the bypass of failed cold steam traps creating a failed-open
trap. While this reduces the safety and process impact of the failure, it increases the
fuel consumed by the boiler and reduces the overall steam system capacity.
Subsequently, this increases the overall energy bill, and the impact to the environment.
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Steam Solved: Four Steps to Improve Steam Trap Operation White Paper
Increased boiler load—As plants age, the number of failed-open steam traps and steam
leaks often increases, and plant efficiency consequently decreases. This steam leak
increase is often known as the “phantom” load. One executive estimated that 20
percent of boiler steam production went to this phantom load, with a majority of the
leakage through failed steam traps.
Over time, without a plan to improve the health of degrading steam trap systems,
many plants would have to increase boiler output or potentially even add another
boiler. Reducing losses through steam traps can reduce this phantom load and
eliminate the need for steam system capacity additions.
Any steam trap failure stresses the rest of the steam system, and can accelerate the
failures of other traps in a downward spiral effect. Condensate back pressure increases
as traps fail open, resulting in higher temperatures that stress condensate return
pumps. High temperatures can cause pumps to cavitate, motors to burn out, and seals
to leak.
Winter conditions can exacerbate steam trap failures (see Figure 4) because of
increased stress on mechanical systems, and more repairs when issues occur. A good
steam trap maintenance program with proper attention to critical and large-capacity
steam traps will go a long way toward minimizing these and other issues.
Freezing problems
Properly-functioning steam traps are essential for good performance of a steam
system. Trap failures compound one another and lead to a range of potentially-serious
operational issues. One such issue, common in processing facilities, is freezing of
equipment during periods of cold weather. The following are some examples:
Frozen steam coils— In one plant, failure to identify steam traps that had failed closed on
steam heating coils resulted in frozen coils that had to be replaced. This occurred on
four different occasions and cost $18,000 per incident. Any steam-based heat
exchanger equipment is subject to potential similar failures.
Frozen steam-jacketed pipe— A chemical plant was offloading rail cars of viscous raw
material through steam-jacketed pipe, which heated the inner pipe and allowed the
material to flow. Key steam traps failed to drain condensate from the pipe jacket, which
eventually froze, collapsing the inner product delivery pipe and dramatically slowing
raw material offloading times. Plant personnel detected the issue when offloading took
four times longer than usual, but there was no externally-visible sign of damage. This
incident cost $120,000 in piping system damage, but was much more costly in terms of
lost production. Vessels and any other steam-jacketed equipment would be susceptible
to similar types of failure.
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Steam Solved: Four Steps to Improve Steam Trap Operation White Paper
Tracer traps—These traps drain condensate from steam tracing lines that enable
pumping fluids that would otherwise be too thick to move through a pipe (similar to
how the jacketed pipe in the above example was used). Tracer traps are generally small
in size and may be considered insignificant or unimportant. In actuality, they can be
among the most critical traps in a facility, since their failure can bring production to a
standstill. Note that actual freezing is not necessary to cause issues; mere failure of the
traps to drain condensate causes inadequate heating of the main process line, which
can slow or stop production. Thawing a process that has frozen is extremely costly and
may require manual heating of pipe sections with torches to re-flow the process fluid.
This is dangerous for flammable process fluids, and in any process plant areas classified
as hazardous.
Risk of leaks and safety issues— In cold weather, steam leaks or vapor clouds from
receiver tank vents condense and then freeze, creating slipping hazards for personnel.
One refinery assembled a “steam team” that identified these system issues so they
could be repaired.
1. Risko, J., Understanding Steam Traps, Chemical Engineering Progress, Feb 2011
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Steam Solved: Four Steps to Improve Steam Trap Operation White Paper
For decades, the best known method to identify trap failures was conducting manual
steam trap audits using acoustic and temperature sensing methods. Many plants have
adopted this practice on an annual basis, which leaves the plant vulnerable to long
periods of failures between audits—along with negative consequences to safety,
reliability, and plant operations in general.
The best manual steam trap audit programs measure temperature and the ultrasonic
acoustics generated by the flow of steam and condensate through the orifice. Trained
field technicians go from trap to trap performing each analysis individually. In the best
case—where trap type, size, and operating pressure are recorded or entered into the
measuring instrument—actual parameters are compared to ideal parameters. Some
measurement instruments make this comparison in as little as 15 seconds.
A 15-second interval only allows for, at most, one or two cycles of condensate
discharge. More often, intervals are much longer and can take many minutes between
discharges. Therefore, it is important to allow adequate time to test a trap’s operation
to reduce the likelihood of a false reading. Unfortunately, a 2-, 5-, or even 15-minute
test can miss irregular patterns and failures. Early stage failures in particular are
extremely difficult to identify within such a small time period.
Another issue that can arise is some parts of the steam system may not be in service
when the audit is performed. Only those traps that are in service can be tested. This can
leave as many as 30 percent of the traps on a site untested until the next annual audit,
when they might be offline again.
Finally, steam trap audit performance is dependent on the technician’s experience and
judgment. Technicians must decipher dynamic readings that differ according to the
type, pressure, and capacity of the trap. Each type of trap has a different operational
acoustic signature. Consistently getting steam trap audits to reflect the actual health of
the system is a problem as the training and judgment of the technician will differ. Not
only will the audit be inaccurate, but it will be inconsistently inaccurate.
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Steam Solved: Four Steps to Improve Steam Trap Operation White Paper
3. Apply real-time wireless monitoring and data analysis to these critical traps.
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Steam Solved: Four Steps to Improve Steam Trap Operation White Paper
Figure 6. Analytics Software Can Provide Data Visualization in a Simple, Easily Navigable Interface
Essentially, operations people must identify which traps are most critical to the process
and identify how much it will cost if the traps fail, and how the failed traps will affect the
process. Assigning a risk priority number(1) is a technique for assessing the risk of
potential problems identified during an FMEA evaluation. An FMEA evaluation helps to
determine which traps are critical.
With an FMEA, each failure mode is given a score that attempts to quantify:
Occurrence: likelihood the failure will occur
Detection: likelihood the failure will not be detected
Severity: amount of harm or damage the failure mode may cause
This data is used for comparison within a single process only and should not be used to
compare across multiple processes or organizations.
The following section shows how to analyze the impact of steam trap failures.
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Steam Solved: Four Steps to Improve Steam Trap Operation White Paper
If we take the example of a steam trap operating on a 100 psi steam system with an
internal orifice of 3/8 inches, we can calculate the steam loss through a blow-through or
failed-open trap.
W = 24.24 ⫻ Pabs ⫻ D2
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Steam Solved: Four Steps to Improve Steam Trap Operation White Paper
Figure 8 shows about 80 percent of steam traps in a typical plant do not have nearly the
combined financial impact of the other 20 percent of relatively higher value traps.
There are a relatively small number of traps with a very large combined financial
impact, and these are referred to as high value steam traps. High value traps are not
only those which cause significant steam loss, but also those which can severely and
negatively impact plant operation because they:
Protect important plant equipment
Have a large negative effect on plant processes in the event of failure
Are located on larger, higher pressure steam lines
Have a known high failure rate
Are out of reach or are in hazardous locations, making maintenance difficult
Number of traps 50 50
Cost of failure $40,148 $6,424
The plant was experiencing a 15 percent annual steam trap failure rate, so the financial
impact of the high value traps versus the general population of steam traps was
calculated as shown in Figure 9. In this case, the top 12.5 percent of the plant’s steam
traps were responsible for 38 percent of the steam loss.
Correcting this issue through the installation of wireless steam trap instruments
resulted in an annual savings of over $300,000.
Figure 9. Financial Impact of Steam Trap Failures for a Corn Milling Plant
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Steam Solved: Four Steps to Improve Steam Trap Operation White Paper
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Steam Solved: Four Steps to Improve Steam Trap Operation White Paper
Conclusion
Steam systems are designed with steam traps to remove condensate and air,
protecting plant equipment and allowing for efficient operation of plant processes.
When steam traps fail, there are significant negative impacts to plant operations in
terms of energy use, throughput, safety, and equipment life.
The traditional method of checking steam traps is contracting with a third party to
perform manual audits. These audits measure the ultrasonic acoustic behavior and
temperature of the steam traps to determine the condition of the traps. This method
has drawbacks in that it only considers a short snapshot of the operation, and therefore
cannot always be a good predictor of trap condition. This method is also highly
dependent on the skill and judgment of the test technician. In addition, annual audits
leave the plant operator susceptible to long periods of failed steam traps between
audits.
With the advent of wireless transmitter technology as well as analytical software—
accurate and reliable monitoring of the steam traps is now cost-effective. To
implement a continuous steam trap monitoring program, it is important to know
where the largest negative impact is on plant processes from steam trap failure, which
identifies the high value steam traps. Continuous 24/7 monitoring of these high value
steam traps will typically result in a quick payback from energy savings alone, in
addition to delivering many other ancillary benefits.
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Steam Solved: Four Steps to Improve Steam Trap Operation White Paper
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