3.6 Steam traps

Common Steam traps types

Thermodynamic
Application

• Steam tracer lines or small steam headers
• Low flow rates
• Good for startup air venting, 
• Compact in size

Common problems

• Clogging
• Disc stuck or worn
• Seat worn
• Unreliable, requires frequent PM

Troubleshooting

• Check for cycling noise to verify functionality. No cycle indicates Failed in open, fast cycle indicates flow too high or faulty. 
• Open blowdown to remove particles, if any.
• Remove cover to lap seat and replace disc if blow down does not works, 

Problem faced during maintenance

• Steam cuts on seat, as it may not be made from harder material like the disc.
• Some welded to pipe models where lapping needs to be done, has to be performed in the field.
• Old isolation valves to these welded traps could be passing steam, as such it is either difficult or in some cases dangerous to perform maintenance.
• Old isolation valves could be leaking steam at packing and could only be repaired during shut down. 
• Mix up of steam trap models, ie. Spirax Sarco thermodynamic traps TD42 comes in various models for high pressure rating, high condensate flow, low condensate flow rate and they may use different disc types and these could be mismatched by maintenance operators.

Thermostatic bimetallic

Application

• For low to mid flow rates such as large or HP steam distribution headers
• Long life span

Common problems

• Clogging at strainer, ball/seat area or bimetallic plates
• Valve setting runs out.

Troubleshooting

• Particles trapped on bimetallic plates n valve assembly will impede on operation, blowdown if possible, clean assembly and adjust valve setting. 
• Servicing will usually fix this steam trap, internal assemblies can be rather costly to replace. Costs usually about 40-50% of a new bimetallic steam trap, especially for high pressure versions.

Problems faced with maintenance

• Open blowdown to remove particles, if any.
• Expensive spare parts, difficult to justify for PM budget until major system breaks down eg. pipeline puncture.
• Steam cuts at the valve assembly, if none blow to remove dirt with compress air. 
• Need training for maintenance operator to adjust bimetallic valve properly

Balanced pressure

Application

• Venting air during start up
• LP Steam headers and small steam equipment
• Long life span

Common problems

• Stuck capsule
• Punctured capsule

Troubleshooting

• Open blowdown to remove particles, if any.
• Clean or replace capsule

Problems faced with maintenance

• None so far.

Ball Float
Application

• For High condensate flow rates, such as condensate discharge of steam heaters.

Common problems

• Does not vents trapped air in system, will requires a air vent mechanism.
• Air vent mechanism stuck
• Float mechanism stuck 

Troubleshooting

• Open blowdown to remove particles, if any.
• Particles trapped on valve assembly will impede on operation. Remove and clean assembly if stuck.
• Steam cuts at the valve, if none blow to remove dirt with compress air. 

Problems faced with maintenance 

• Thin and small width graphite gaskets used, prone to damage followed by leakage during start up. Ensure installation is monitored by competent supervisor.
• Provide IOM to maintenance operator, assembly can be confusingly installed in wrong direction and etc at times.
• Bolts may be stuck if it was never serviced throughout, prepare additional bolts.

Inverted bucket
Application

• Vents trapped air very well
• Moderate condensate loads,

Common problems

• Bucket assembly stuck
• Loss of prime

Troubleshooting

• Open blowdown to remove particles, if any.
• Check for cycling noise to verify functionality. Close downstream valve to prime the trap with condensate to restore functionality.
•  Remove for service or repair if priming does not work.

Problems faced with maintenance

• Provide IOM to maintenance operator, assembly can be confusingly installed in wrong direction and etc at times.
• Bolts may be stuck if it was never serviced throughout, prepare additional bolts.

Tutorials
Visit Spirax Sarco tutorials for more information regarding sizing, application, maintenance of steam traps. Its a brilliant webpage.
http://www2.spiraxsarco.com/resources/steam-engineering-tutorials/steam-traps-and-steam-trapping/why-steam-traps.asp


General Maintenance Guidelines
Steam traps are automatic valves meant to eliminate condensate out of steam systems to improve system efficiency, as presence of condensate reduces heat transfer. It is one of the most neglected item in a process plant, as such it poses a risk to steam system blow outs.

But this device appears to be harmless and runs on its own. Why bother? The amount of discharge is insignificant to cause any damage. No!

When steam trap maintenance is absent, wear and tear tend to cause it to pass steam. Over time, as it gets excessive, significant two phase flow within the system will take over and cause erosion and pitting internally (Imagine sand flowing at high velocity thru the pipes which peens and grinds down on the surface), these effects enhanced with CUI in corrosive and humid environment, which eventually leads to pipe puncture.  (Some photo of the leaks to be attached.)

This is a well known problem in the industry, as steam operate at much higher velocity about 30 -60m/s, when it enters condensate stream heavily, it increases velocity of the condensate, therefore:

• The flowrates increases beyond the design for condensate flow,
• Condensate droplet impingment prevails which can be detrimental to tees and elbows over time.

Good design practices

1.  keep traps as close to condensate lines as possible and keep the return lines as insulated.
2. Size the condensate line for flash steam flow, assuming 15 to 20% traps are passing
3. Make use of flash drums closer to point of condensate generation to minimize effect of flashing steam in long condensate pipes.
4. Assign separate condensate lines for the various steam pressures ie. LP, MP, IP, HP.
5. Minimize sharp bends and injection points by using swept tees, 45EL or diffusers respectively.

Schedule & Recording keeping
A schedule should usually be available to determine steam trap survey on regular intervals and these can vary depending on willingness to invest or past operating experience basis, for example. If otherwise please develop such a schedule to ensure steam traps maintain in good condition.

Regular schedule

• A Check on all steam traps in the plant every 1 year
• Blow down on all steam trap line blowdown valve every 3 months

Risk based schedule

• A Check on all thermodynamic traps every 6 months
• A Check on all mechanical traps every 2 years
• Blow down on all high particulate lines every 1 month
• Blow down on others every 6 months

Survey and Repair Records

• These records will allow future generations to make decisions whether to replace a steam trap or not, as some could be costly.
• Survey records shall be kept as there could be thousands of steam traps in a plant and it will not be easy to manage the repair and maintenance effectively without one.
• Repair records shall be kept so recurring problems could be identified for redesign, decisions could be made whether to invest in new steam traps or spare part replacement.
• Repair records could also help to develop spare pares strategy as we now know the usage pattern. This strategy will also be effective to help cost saving intiative in spare parts purchase during construction of new plants

Troubleshooting & Survey
Simple methods to identify faulty steam traps
1) Temperature method
Run a temperature gun on the pipe before and after the steam trap. As pressure difference exist due to resistance and separation, there will be a temperature difference across the trap. This is the most suitable test on higher pressure steam lines where dT across the trap is relatively higher. If there are no temperature difference across the trap, it is likely passing steam.

Run the temperature gun on the trap. Cold could mean its failed close/clogged. Hot could means its working or passing steam.

2) Visual method
Open vent/drain valves before the steam trap (live steam will release), after the steam trap (flash steam will release).  If nothing is released after a long wait the steam trap has failed in close position, if all you see is steam blowing out in a jet then it has failed in the open position.

3) Listening - audible noises
This method involves holding a long metal rod, one end touching the trap and one end touching your ears. The effect of condensate passing can be confirmed when cyclic action of the steam trap is heard.

4) Listening - Ultrasonic testing
This is the most reliable method and will probably require engaging and external vendor/operator to perform the task. Steamtrap vendors such as Spirax Sarco & armstrong intl would normally offer complete steam trap survey services for an entire plant at a nominal fee.

Watch this video for a detailed guide with illustration to troubleshooting the traps by Armstrong intl.
Guidelines for Steam Trap Troubleshooting: http://youtu.be/smjuAEZOrlk