In our plant there has been excessive hammer and vibration experienced in a 16" common condensate return header which discharges into the top of an open atmospheric condensate tank. Various condensate streams from process units are returned into the common 16" header. The streams are flashed at anywhere from 400 psig or 150 psig down to 25 psig (at the process units) and the liquid is pumped into the above mentioned header. There are also some streams that come from atmospheric flash tanks and are also cooled. Although I'm not 100% sure, it appears that there is a steam bubble that is getting into the system since the hammer occurs about every 30 seconds and is preceeded by noises and vibration which sound like a train arriving. When this happens the pipe skin temperatures near the tank rise from 190 to about 230-240 deg F and the steam plume at the top of the tank is increased greatly until the event is over (about 5-10 seconds) and then pipe skin temps return to 190 F. My question is how could live steam be getting into the system. I have noticed that there are some high pressure steam traps which discharge into this system. Could this be a source or would that be a continuous flow rather than the 30 sec interval?? Could the flash tanks at the units be passing steam throough the level control valves? Any other thoughts or questions for clarification?? Thanks in advance for your help!
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Hammer in Condensate System 1
- Thread starter hndler
- Start date
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1
- #2
You have definitely life steam coming into the common condensate header, 95% chance it is comming from faulty traps.
I do not think that the streams from flash tanks are contributing.
The steam will quickly cool down in the condensate creating low pressure zones. The condensate (liquid) tries to fill up the "empty" spaces creating shock waves.
To correct it you need to isolate the incoming branches and check for life steam passing through the traps. With portable airborne ultrasound detection equipment, you can check the condition of your steamtraps in an early stage.
Steven van Els
SAvanEls@cq-link.sr
I do not think that the streams from flash tanks are contributing.
The steam will quickly cool down in the condensate creating low pressure zones. The condensate (liquid) tries to fill up the "empty" spaces creating shock waves.
To correct it you need to isolate the incoming branches and check for life steam passing through the traps. With portable airborne ultrasound detection equipment, you can check the condition of your steamtraps in an early stage.
Steven van Els
SAvanEls@cq-link.sr
Although I agree with Steven that it is quite likely that you have live steam causing the problem, it is not necessarily so.
A useful question to ask yourself with problems like this is "Was it like this from day 1?" If there was a time when you did not have the problem, and then it gradually came about and got worse, then it would point you in the direction of failing traps.
However, with the conditions you have described it would be quite possible to have flash steam being generated in the line. You say the condensate tanks at the process units operate at 25 PSIG. This corresponds to about 266 F. When this hot condensate hits your atmospheric system it will flash. Similarly the high pressure traps connected to this header could be leaking, but their condensate will flash anyway.
It sounds to me like you have a piping arrangement where flash steam can accumulate (eg a high point) and then once the bubble of steam has grown sufficiently it forces its way out the pipe to give the cyclic behavior you are seeing.
If this is the casue you would have to re-route the piping, or install a vent at the high point.
regards
Katmar
A useful question to ask yourself with problems like this is "Was it like this from day 1?" If there was a time when you did not have the problem, and then it gradually came about and got worse, then it would point you in the direction of failing traps.
However, with the conditions you have described it would be quite possible to have flash steam being generated in the line. You say the condensate tanks at the process units operate at 25 PSIG. This corresponds to about 266 F. When this hot condensate hits your atmospheric system it will flash. Similarly the high pressure traps connected to this header could be leaking, but their condensate will flash anyway.
It sounds to me like you have a piping arrangement where flash steam can accumulate (eg a high point) and then once the bubble of steam has grown sufficiently it forces its way out the pipe to give the cyclic behavior you are seeing.
If this is the casue you would have to re-route the piping, or install a vent at the high point.
regards
Katmar
Tremolo
Nuclear
- Feb 26, 2003
- 77
Katmar,
Unfortunately, during the last outage, the tests we had planned could not be performed. We were going to take temperature measurements along the pipe to see if there were any hot areas which could correspond to saturated fluid conditions. However, this would have required the removal of small sections of pipe insulation and there were some asbestos concerns. So, the test was scrapped. As it turned out, during the 3 week outage, there was only 1 waterhammer event and it occurred near the end of the outage.
The big question is: how does steam get into the line? The normal condensate temperatures from various steam traps and other sources are too low to lead to any flashing in the system. So, something unexpected is occurring. I am leaning toward the theory that water is draining from the piping high point (34’ pipe length) down through the sparger in the aux boiler deaerator. My co-worker and boss doesn’t think this is happening. He believes the waterhammer event is originating in the trap header.
Another possible source of steam is through leaking steam traps. I have heard some talk of leaky steam traps, but I thought the leaking trap would just allow condensate to flow back up into the steam pipe creating a waterhammer event in that pipe. Can you explain the behavior of the leaking steam trap and how it could allow steam to enter the trap header? Also, is the method of checking for leaking traps recommended by svanels the preferred diasgnostic approach?
I will also post this update on the other thread.
hndlr,
Is your condensate return header used continuously during normal operations and is this when the waterhammer events occur? Or, as in our case during outages, does the condensate header remain fairly stagnant and do the waterhammer events occur only when the cold condensate streams from the atmospheric flash tanks are pumped into the header?
Tremolo
Unfortunately, during the last outage, the tests we had planned could not be performed. We were going to take temperature measurements along the pipe to see if there were any hot areas which could correspond to saturated fluid conditions. However, this would have required the removal of small sections of pipe insulation and there were some asbestos concerns. So, the test was scrapped. As it turned out, during the 3 week outage, there was only 1 waterhammer event and it occurred near the end of the outage.
The big question is: how does steam get into the line? The normal condensate temperatures from various steam traps and other sources are too low to lead to any flashing in the system. So, something unexpected is occurring. I am leaning toward the theory that water is draining from the piping high point (34’ pipe length) down through the sparger in the aux boiler deaerator. My co-worker and boss doesn’t think this is happening. He believes the waterhammer event is originating in the trap header.
Another possible source of steam is through leaking steam traps. I have heard some talk of leaky steam traps, but I thought the leaking trap would just allow condensate to flow back up into the steam pipe creating a waterhammer event in that pipe. Can you explain the behavior of the leaking steam trap and how it could allow steam to enter the trap header? Also, is the method of checking for leaking traps recommended by svanels the preferred diasgnostic approach?
I will also post this update on the other thread.
hndlr,
Is your condensate return header used continuously during normal operations and is this when the waterhammer events occur? Or, as in our case during outages, does the condensate header remain fairly stagnant and do the waterhammer events occur only when the cold condensate streams from the atmospheric flash tanks are pumped into the header?
Tremolo
When steam traps leak they blow of steam, remember that the pressure in your steam header is greater then the pressure in your condensate header. The termostatic steamtrap (disc type) has a metalic ringing sound when opening to discharge condensate. If it rings all the time, then the seats are starting to worn and the trap will release more steam then condensate. If you hear a scouring sound, it means that the trap is totally worn out, and repairs are not possible, only replacing the trap.
With ultrasonic detection (we use the ultraprobe 2000 from uesystems) we evaluate the trap condition in an early stage. In an early stage you can replace only the internal valve, not acting will result in trap replacement.
Steam traps will always blow some steam (driving force) in the header, if the seats are worn the steam will erode the internals of the trap very fast, and after some time you will have a direct connection between your steam and condensate header.
Steven van Els
SAvanEls@cq-link.sr
With ultrasonic detection (we use the ultraprobe 2000 from uesystems) we evaluate the trap condition in an early stage. In an early stage you can replace only the internal valve, not acting will result in trap replacement.
Steam traps will always blow some steam (driving force) in the header, if the seats are worn the steam will erode the internals of the trap very fast, and after some time you will have a direct connection between your steam and condensate header.
Steven van Els
SAvanEls@cq-link.sr
- Thread starter
- #9
Thanks to everyone for their replies.
Tremolo -- To answer your question, the system is in service all the time. There are times when some process units are down for maintenance and thus there is less flow in the system due to reduced steam load. This does change the dynamics of the hammering somewhat.
I have investigated the steam traps and that seems to be a dead end because they are all blocked away from the condensate header. Our recent investigations with temperature gun have showed temperatures in excess of 260 degrees in one 8" condensate line (another hammering line) which then combines 2 with colder streams in the 16" header near the return tank. Like Katmar said, could it be possible that the steam is condensing as the pressure is dropping and then when it gets into the 16" header and mixes with the colder streams it condenses so fast to cause the severe hammer?
Tremolo -- To answer your question, the system is in service all the time. There are times when some process units are down for maintenance and thus there is less flow in the system due to reduced steam load. This does change the dynamics of the hammering somewhat.
I have investigated the steam traps and that seems to be a dead end because they are all blocked away from the condensate header. Our recent investigations with temperature gun have showed temperatures in excess of 260 degrees in one 8" condensate line (another hammering line) which then combines 2 with colder streams in the 16" header near the return tank. Like Katmar said, could it be possible that the steam is condensing as the pressure is dropping and then when it gets into the 16" header and mixes with the colder streams it condenses so fast to cause the severe hammer?
Tremolo
Nuclear
- Feb 26, 2003
- 77
hndler,
Yes it is possible that condensation of steam on the colder water will cause a significant waterhammer event. There is a long and well documented history of condensation-induced waterhammer events. Although there are several classifications of condensation-induced waterhamemr events, they all follow a common sequence:
1. steam void formation – this has been discussed at length in your thread
2. water slug formation – your condensate header is mostly liquid, so there is plenty of water and your “slug” is actually a long water column
3. water slug acceleration – your water is initially set in motion from operation of condensate pumps
4. Steam void collapse – as the steam and water come in contact, the steam rapidly condenses leading to additional acceleration of the water slug
5. Impact – the water slug impacts a solid surface, such as a closed valve or a water column on the other side of a trapped steam void, undergoes a change in direction such as at an elbow, or passes through a sudden area reduction such as a throttled valve. The impact causes very rapid change in water slug velocity resulting in possibly high pressures and loads.
Often times the pumped flow is throttled in an attempt to reduce the liquid velocity and hence reduce the waterhammer magnitude. But, because the water slug is accelerated by rapid steam condensation, it is possible to get large waterhammer events even when the initial pumped liquid velocity is low. So, throttling the pumped flow may not have any effect.
Because the header discharge to a low pressure tank, it is inevitable that the hot condensate will flash even under normal operating conditions when all equipment is functioning properly. One solution we are considering for our system is the addition of a surge suppressor to arrest the water hammer pressure wave. We have had success in other applications. The surge tank dampens the peak water hammer pressure, slows the rate of pressure rise, and mitigates any pressure ringing in the system. Any thoughts on this approach would be welcome.
Tremolo
Yes it is possible that condensation of steam on the colder water will cause a significant waterhammer event. There is a long and well documented history of condensation-induced waterhammer events. Although there are several classifications of condensation-induced waterhamemr events, they all follow a common sequence:
1. steam void formation – this has been discussed at length in your thread
2. water slug formation – your condensate header is mostly liquid, so there is plenty of water and your “slug” is actually a long water column
3. water slug acceleration – your water is initially set in motion from operation of condensate pumps
4. Steam void collapse – as the steam and water come in contact, the steam rapidly condenses leading to additional acceleration of the water slug
5. Impact – the water slug impacts a solid surface, such as a closed valve or a water column on the other side of a trapped steam void, undergoes a change in direction such as at an elbow, or passes through a sudden area reduction such as a throttled valve. The impact causes very rapid change in water slug velocity resulting in possibly high pressures and loads.
Often times the pumped flow is throttled in an attempt to reduce the liquid velocity and hence reduce the waterhammer magnitude. But, because the water slug is accelerated by rapid steam condensation, it is possible to get large waterhammer events even when the initial pumped liquid velocity is low. So, throttling the pumped flow may not have any effect.
Because the header discharge to a low pressure tank, it is inevitable that the hot condensate will flash even under normal operating conditions when all equipment is functioning properly. One solution we are considering for our system is the addition of a surge suppressor to arrest the water hammer pressure wave. We have had success in other applications. The surge tank dampens the peak water hammer pressure, slows the rate of pressure rise, and mitigates any pressure ringing in the system. Any thoughts on this approach would be welcome.
Tremolo
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