Dead legs in CIP distribution pipework

[johno1234]

It is widely accepted that when there are dead legs in CIP distribution pipework, rinsing time or volume has to be increased to purge cleaning materials from the dead legs....Does anybody have a way of calculating/quantifying the impact on rinsing volume and therefore cost. I am thinking about a formula that considers flow velocity, pipe diameter, length of dead leg etc etc.

 

[BigInch]

Never seen one.

**********************
"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/

 

[HEC]

I'm sure there is not one. Dead legs will add to rinse volumes and all the added headaches there. Best approach is to avoid dead legs. There are many valves around depending upon your industry taht will achieve your aim. The price may be aditional pipework to loop past usage points or additional isolation valves to reduce deadlegs. Many ways to thrash the skin off the cat!

Mark Hutton

 

[johno1234]

Hi Mark,

Thanks for the response, issue is that I have existing plant and am trying to put together a business case to remove the deadlegs based on utilities cost improvement.

 

[skearse]

Can't help with the utilities cost, but depending on what's in the line you may be able to include the safety aspects:

http://www.chemsafety.gov/index.cfm?folder=news_releases&page=news&NEWS_ID=426

 

[rconner]

What is the specific piping material and (all) services involved?

 

[ash9144]

This is going to depend on pipe material, configuration, various components, type of material being cleared, material used to clear, level of "cleanliness" desired. Way too many variables to give a rule of thumb to.

I would recommend some time in the field with the people actually doing the clearing and base your case study on that.

 

[pennpiper]

The business case may boil down to what the process is and what is the gross revenue for this facility?

If the process is Medical Grade or Food Grade and there is contamination caused by dead legs which results in the loss of your license to produce then you could be out of business.

Simple math.

 

[HEC]

Empirical may be your only option then, i.e. set up a test. Take a sample system and sketch the isometric so you can get pipe volumes from it. To estimate the affect of deadlegs you will want to find the difference in pipe volumes to rinse a change through. For example for a given pipe length it will require a minimum of 1 volume to rinse or change the contents. This is naïve in the extreme, generally 1.5 to 2 depending upon mixing/dilution and other affects. This calculated volume will be the ideal. At the delivery end of the CIP distribution branch install a method for interface detection. Using this you can record the actual volumes required to flush the distribution system through. This is a simplified methodology, there are many more steps to ensure safety etc.
On thinking further is the CIP distribution system continuously full. If this is the case there will generally only be small volumes that diffuse down the open stagnant branches. The amount that diffuses down will be dependant upon the period of wash step. The minimum amount that will mix down the pipe will be the volume occupied by about 1.5-3d.


Mark Hutton

 

[johno1234]

Hi All,

Thanks for all the useful comments, it looks like I am going to have to either model the issue mathematically, with some assumptions....or run a variety of tests on a pilot rig and then validate on a full scale plant. I was hoping to find that work already done, and you can bet that when I have done it, I will find some simillar work done years ago.

Cheers Johno

 

[BigInch]

Don't worry. Such things are so dependent on configuration of the pipe sytem, unless you're talking about something like a straight run past a full size horizontal branching tee of a length less than 10 diameters, if you did find any previous work, I doubt you'd be able to use it for another system of particular interest anyway.

**********************
"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/

 

[hacksaw]

gee. if you have to model it mathematically it wont fly anyway...

dead legs are prohibited in most CIP systems. it is that simple. That said, you can estimate the volume of the dead legs, estimate the mean fluid velocity (it is half the normal flow velocity), and use that to estimate the amount of reduction in cleaning time and resources were the dead legs were removed.

 

[BigInch]

Would that by chance be independent of length?

**********************
"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/

 

[CMA010]

You could determine it iterative with validation (PQ)/commissioning? You don't say what industry you're in, but in pharmaceuticals CIP recipes, sequences, rinse tmes etc are determined like that.

 

[rconner]

While I know it is not the answer to your specific question, I think there are many references at least in municipal, fire protection and civil engineering fields involving water delivery etc. that encourage figuring out some means of “looping” as opposed to dead end delivery in those piping systems, with varied explanations/reasons that I believe may include the following:

1. Better reliability (With looping a specific service location can in effect be “fed” from more than one direction; also, assuming sufficient number and spacing of shut-off etc. valves, if a line is broken or shut-down for maintenance etc. at any location service is not necessarily interrupted in most of the system.)
2. Minimizing stagnation for most or all of the system, in that in theory withdrawal from any point on a loop makes at least some water flow in the entire loop (At least in the field of water delivery the word “stagnant” of course can have unattractive connotation or results for any piping system, perhaps most notably from the standpoint of water quality).
3. More/Better flow [Assuming a particular service location can be “fed” from both directions (as per “1” above), a given flow volume (e.g. gpm etc.) can often be achieved or with less head loss/velocity and perhaps without going to very large pipes with a loop – this may be particularly helpful in fire protection or combined service pipelines.]
4. Less freezing risk in extreme or unanticipated exposure conditions at any location, at least when there is any flow in a loop.
5. Less magnitude of “water hammer” or that might occur more selectively in some situations at least at the end of some lengthy “dead ends.

Also, while structures such as (flush) hydrants are sometimes also provided at the ends of dead ends to facilitate rinsing or flushing, I guess it might be possible with a loop (and valving etc.) to flush or rinse the system in whatever direction and to whatever location one wants to and has means to handle the water etc., if this were desirable.

Finally, I guess any “cost” associated with looping and valves etc. could be debated by an Owner and/or regulators, in light of any value they might place on such benefits.