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piping sloping 1
- Thread starter sk10009
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Normally you want to be able to drain piping from time to time and it helps when you get down to the last few drops if the pipe is sloped.
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Going the Big Inch!
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Yorkman
Mechanical
- May 10, 2006
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A lot of the reasoning for pipe slope/pitch is depended on what fluid you are running in the line. I'm sure Big Inch will agree that the pitch of a steam main is critical to the safe and smooth operation of a steam system to insure proper and timely condensate removal. On refrigerant lines it is vital for oil return in the suction and discharge of HCFC and HFC lines. Liquid lines of HCFC and HFC systems are not as critical were the oil is misable. But with ammonina liquid lines where the oil is not misable the lines require pitching and "drop/out" pots to keep oil out of the system.
Just my three cents.
I'm not a real engineer, but I play one on T.V.
A.J. Gest, York Int./JCI
Just my three cents.
I'm not a real engineer, but I play one on T.V.
A.J. Gest, York Int./JCI
In power plant steam lines the rule of thumb has always been a pitch (slope) of 1/8 inch per foot towards the "drip leg" where the condensate can be trapped out of the system.
In chemical plants we use the same slope when we can. You would like to have the piping be as "self draining" as it can be when out-of-service, especially in systems that are transporting reactive chemicals. You would like to have these lines drain back to the vessels and where that is not possible, provide a "drip leg" with a small bore block valve to drain the leg manually. The idea is to keep the lines clear when the pumps stop so that you will not have the reactions continuing in the piping (and perhaps plugging them). To some degree, we would use the same principles in refinery piping. If the line is heat traced, we would like it to be self draining to be sure the lines are clear in case the steam or electric power are temporarily lost and the piping temperature cools.
In chemical plants we use the same slope when we can. You would like to have the piping be as "self draining" as it can be when out-of-service, especially in systems that are transporting reactive chemicals. You would like to have these lines drain back to the vessels and where that is not possible, provide a "drip leg" with a small bore block valve to drain the leg manually. The idea is to keep the lines clear when the pumps stop so that you will not have the reactions continuing in the piping (and perhaps plugging them). To some degree, we would use the same principles in refinery piping. If the line is heat traced, we would like it to be self draining to be sure the lines are clear in case the steam or electric power are temporarily lost and the piping temperature cools.
NozzleTwister
Mechanical
Let me bring up something else to consider.
Some lines that I have worked on have been required to have a specified minimum slope at all times, hot or cold. When that's the case, the installed slope on some legs may need greater than the minimum slope so you still have the required slope when the line is hot.
NozzleTwister
Houston, Texas
Some lines that I have worked on have been required to have a specified minimum slope at all times, hot or cold. When that's the case, the installed slope on some legs may need greater than the minimum slope so you still have the required slope when the line is hot.
NozzleTwister
Houston, Texas
I guess the simple answer to why lines are sloping is "so that liquids will gravity drain in the direction of the slope".
For our lines going to sump (mostly drains, drip pans, etc), we use 1:100 slope. I think I have also seen 1:125.
"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
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For our lines going to sump (mostly drains, drip pans, etc), we use 1:100 slope. I think I have also seen 1:125.
"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?
Yorkman
Mechanical
- May 10, 2006
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For the most part that's true. With refrigeration lines that "gravity drainage" is assisted may maintaining minimum flow velocities to insure proper oil return. When the line is running horizontal the min. velocity is usually 500ft/min. with vertical lines that velocity rises to 1000-1500ft/min. and a max. velocity of 4000ft/min. for both horizotal and vertical lines as a general guide line. Although somewhat off topic I thought it might be worth mentioning.
I'm not a real engineer, but I play one on T.V.
A.J. Gest, York Int./JCI
I'm not a real engineer, but I play one on T.V.
A.J. Gest, York Int./JCI
If you want to know the truth, mine are sloped because they're on the side of a 2000 meter high mountain. Its damn hard to get those level. 
Going the Big Inch!
Going the Big Inch!
Air lines should be sloped away from the compressor (direction of air flow) so the condensation can move with flow and be collected in drip legs at lowest point and be manually or automatically drained.
Bud Trinkel CFPE
HYDRA-PNEU CONSULTING, INC.
fluidpower1 @ hotmail.com
Bud Trinkel CFPE
HYDRA-PNEU CONSULTING, INC.
fluidpower1 @ hotmail.com
Water and sewage lines, although buried, are sloped to high points to allow air to be evacuated through air release valves and drained through scour valves.
Geoffrey D Stone FIMechE C.Eng;FIEust CP Eng
Geoffrey D Stone FIMechE C.Eng;FIEust CP Eng
KiwiMace
Mechanical
- Feb 2, 2006
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re yorkmans comment on drop out pots: The refrigeration drop out pots, or dog legs in vertical risers, are actually to ensure that the oil is conveyed *away* from the compressor discharge and making it back around to the compressor sump, correct? (question posed as a statement)
Yorkman
Mechanical
- May 10, 2006
- 269
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Cinci,
Agreed, the major concerns with oil travel in any ammonia system is to keep it's affect's to a min. in the evaporator, condenser, discharge lines and suction lines. Some systems drain and remove collected oil using dog legs, others use seperaters with floats and hot gas to return it to the compressor. The evaporators and recievers in many of these systems incorporate dog legs to seperate and remove oil from these areas.
I'm not a real engineer, but I play one on T.V.
A.J. Gest, York Int./JCI
Agreed, the major concerns with oil travel in any ammonia system is to keep it's affect's to a min. in the evaporator, condenser, discharge lines and suction lines. Some systems drain and remove collected oil using dog legs, others use seperaters with floats and hot gas to return it to the compressor. The evaporators and recievers in many of these systems incorporate dog legs to seperate and remove oil from these areas.
I'm not a real engineer, but I play one on T.V.
A.J. Gest, York Int./JCI
The amount of slope or pitch to a pipeline as it pertains to drainage is entirely dependent on the viscosity of the fluid flowing through the pipe. Obviously oils or a slurry of some sort would have different flow characteristics than say, condensate. If there are solids present, you don't want the solids to seperate from the liquids. A perfect example of this is in sanitary sewage lines. 1/8" per foot pitch on sanitary waste lines ensures that those "little doggies" keep moving with the liquids.
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