What is slope reversal?

[indimech]

Hi Everybody!

In many pipe specs it is mentioned that be sure that the slope is not reversed at any point.

What does it mean? Does it mean that through out the complete piping the slope should be in same direction ? or does it mean that the slope should not be against the flow direction?

thanks in advance

 

[zdas04]

I have to say that I've never heard that term. Is it used in any of the ASME or ISO specs? I've spent most of my career in the Rocky Mountains and I've never seen a line that didn't have high and low points all over the place. It would be nice if that weren't true, but it is.

David

 

[BigInch]

Are you working with gravity flow lines, if so slope each line only in the direction of flow.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[SNORGY]

If it is facility piping, it might be another way of saying "SLOPE ---> ; DO NOT POCKET".

I have not heard of the term, so that is my best intuitive guess.

Regards,

SNORGY.

 

[indimech]

The complete line which appears in the spec is:
"All pipes must be sloped to a low point drain. Be sure that the slope is not reversed at any point."

The specs belong to sanitary compressed air which comes in contact with product as well as some intermediate products for body care creams.

The plant is for FMCG products making detergents and fabric enhancers. Process piping is mostly sanitary design.

Biginch:
Piping is not gravity flow.

Snorgy:
What is the meaning of "Do not pocket"? Does it mean a U loop should not be in piping with out drain?

Thanks

 

[NozzleTwister]

A few years ago I worked on a 1400 deg. F stainless steel piping system that we were required to maintain a minimum slope cold and during all operating scenarios.

Due to thermal expansion, we had to specify different installed slopes for each leg of the system so it always had at least the minimum specified slope when the system was hot.

Deflection of the system from dead weight could reverse the slope from the theoretical slope as well.

I think this is what they are talking about.


NozzleTwister
Houston, Texas

 

[BigInch]

It means slope the pipe in one direction only (to a drain). A pocket is a low point where liquid will collect.

It is ambiguous for a pipe that has a drain located somewhere in the middle, in which case you would have to slope both ends toward the drain and therefore would have to reverse the slope.

The conventional way to say this in an English contract document or on a piping drawing is exactly as Snorgy says above, "DO NOT POCKET" while showing the minimum slope value with directional arrow to the nearest appropriate drain for various points on the pipe.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[Pawel27]

The problem is that for Assembly load case slope may be correct, but for other load case piping may work quite different and slope could reverse. Then liquid is collected in some areas and "water hammer phenomena " may appears. This is not undesirable dynamic phenomena. The purpose of the designer who select piping supports is to guarantee correct slopes in all load cases.

 

[indimech]

Thanks everybody for contribution.

 

[Pawel27]

I am sorry - the second last sentence should be: This is undesirable dynamic...

Some more comments:
Slope not always should be in flow direction. It depends on piping kind. The purpose is that water does no collect - that is all.

 

[Compositepro]

"All pipes must be sloped to a low point drain. Be sure that the slope is not reversed at any point."


The specification seems pretty clear to me. I does help to understand that moisture condensation in compressed air lines is a very common problem. If this is sanitary air that contacts food and cosmetics, you do not want it to contain water that may have been collecting in pipes for days.

 

[SNORGY]

Also note that if the requirement is that there is to be no "pooling" of liquid in the pipe spans, this will have some impact on your pipe support spacing, TOS elevations at each support, and pipe minimum wall thickness even before you start thinking about dynamics.

Regards,

SNORGY.

 

[TBP]

Steam lines can be run with either forward or reverse slope. Forward - the condensate gravity draining (running with the steam flow) to the drip-legs is preferred. This is not always feasible, so then a reverse-slope is used. In this case, condensate gravity drains along the bottom of the line, against the steam flow. If a reverse slope is used, there should be reduced distances between drip legs and/or go to the next pipe-size up, to reduce the steam velocity.

Spirax Sarco's literature explains all.

 

[25362]

I read in a dictionary of scientific and technical terms that geologists define reverse slope as

A hill descending away from a ridge.

 

[BigInch]

Then what's a hill decending towards a ridge, or a hill ascending away from a ridge?

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[25362]

The same dictionary tells us that Geologists call slope as the inclined surface of any part of the Earth's surface. In addition, the book says same experts define slope failure as

The downward and outward movement of a mass of soil beneath a natural slope or other inclined surface; four types of slope failure are rockfall, rock flow, plane shear, and rotational shear.

Did you know that in Mining Engineering there is a function named slope engineer?

 

[NozzleTwister]

LOL, I guess if a hill descends towards a ridge, then it wouldn't be a ridge any more.

NozzleTwister
Houston, Texas