Flowmeter Type for Firewater Lines 2

[sshep]

Friends,

My company proposes to meter and charge operating units for firewater at our complex. Presummably this is for billing units that use excessive amounts for washdown, detecting leaks, etc.

A design was proposed that used orifice plates. This does not seem appropriate for firewater. I am sure NFPA has standards for appropriate metering technology, but I cannot find anything useful in NFPA 24. Does anyone know of a standard on this?

best wishes,
sshep

 

[DRWeig]

You might consider red-flagging this post and moving to the NFPA forum:

http://eng-tips.com/threadminder.cfm?pid=184

I would be worried about any sort of additinal restriction in a fire line...

Good on ya,

Goober Dave

Haven't see the forum policies? Do so now: Forum Policies

 

[bimr]

Try the FM guide:

http://www.fmglobal.com/assets/pdf/fmapprovals/1046.pdf

http://www.preso.com/resources/products/PFB_Annular_Form4-25-10_7-07.pdf

 

[Pumpsonly]

What you need is a totalising type flow meter and most of this type are positive displacement type which has high pressure loss and are. not be suitable for fire service.

You will have to use magnectic flow meter which could be costly.

http://www.flowmetersource.com/Totalizing_Flow_Meters/No-moving-parts/Water-Corrosive-Fluids.html

 

[ports394]

pumpsonly, what about a large Turbine? It's not as accurate, but the pressure drop will be relatively low.

 

[sshep]

Thank you my friends,

The FM literature bimr gave on this subject is related to firewater pump testing which allows for almost any type of flow meter and focuses on flow rate, accuracy, etc.

I made a trip to an old unit I worked in which I know already has a firewater supply meter installed. The type was magnetic which has minimal intrusion into the line. I gave a star to pumpsonly since he called it right. The fear is line restrictions like orifice plates and annubars which could be points for debris to get caught- possibly I am paranoid, but I can see I am not the only one with this concern. I think a turbine meter is far too intrusive for this application, but thanks for the input.

Best wishes always,
sshep

 

[pennpiper]

I have another concern with what is being proposed here by the original poster (OP).

Based on what is suggested here by the OP each of these in-plant Units only have one Fire Water (FW) feed line. And they want to put a meter on this line.

Now, based on my experience In-Plant processing Units always had a FW loop that went around the four sides of the complete Unit. The FW Main on each side of this Loop is also the side of an adjacent Loop for another Unit or Area. At the main junction points (corners) there would be Segment isolation valves. Branches into the Units from the FW Main would also have isolation valves. These branches fed Deluge systems, Fire Hydrants and Monitors.
Your options seem be very costly:
a). Add a flow meter to every FW Branch (from the Main)into each Unit.
b). Have a FW distribution manifold at the FW Pumps and then dedicated mains (with Flow Meters) to the individual Unit & Area FW Loops. These individual Unit Loops could not have any common lines.

This brings up a serious question. With the traditional design of a FW Loop system, if there is a rupture in one of the segments, that segment can be isolated and the remaining segments can be fed via alternate routes. If you choose option b). above and you have a rupture in the loop protecting a Unit and that Unit has a Fire, what do you do?

I think the MBA's at your company need to reconsider their ridicules idea of charging Units for water use to wash down and clean up after maintenance.

The bottom line in all this is safety. Safety in the proper design of the Fire Water system and Safety in the Operating walkways of the Units.

 

[Thealanator]

Does each unit/section have its own flow switch? Could you base usage on the amount of time a switch is in a tripped state?

 

[bimr]

I agree with pennpiper that this proposal doesn't make much sense.

In the plants that I have worked in, one did not mess with the fire water system. The fire water system was reserved for fires. If someone turned the fire water service on, the pressure dropped, an alarm sounded and the fire pumps were then activated. Fire pumps typically have a much larger flow rate and can not be operated continuously except during a fire when the hydrants are open.

In addition, if other users are currently using the fire water service simultaneously when the fire occurs, will there be adequate water flow for the fire?

Another point is the billing. Most meters do not have an acceptable accuracy for custody billing. The magmeter probably has the best accuracy with an error somewhere around 1-2% depending on the flow and size of meter.

If you just want a general idea of the water volume, you probably can get by with a pitot tube type water meter at much less expense. However, the price of magmeters has dropped over the years and may be attractive.

 

[sshep]

My Friends,

This site is one of the largest petrochemical manufacturing sites in the world. The firewater systems are all looped, and well laid out. It is recognized that firewater is the most critical safety system. In fact, the movie "Catch a Fire" with Tim Robbins describes a real historical attempt to blow up this site, the first step of which was to disable the fire water system. My company takes this stuff seriously.

It isn't really an accounting issue, but rather to monitor leaks and other uses. You can well imagine that as over time the need arises to run additional fire water jockey pumps to maintain the system pressure, people will want to know where the water is going and why.

best wishes,
sshep

 

[pennpiper]

Sshep,
You seem to be changing your story. Your original post said this: "My company proposes to meter and charge operating units for firewater at our complex. Presummably this is for billing units that use excessive amounts for washdown, detecting leaks, etc."

Your latest post says this:
"It isn't really an accounting issue, but rather to monitor leaks and other uses. You can well imagine that as over time the need arises to run additional fire water jockey pumps to maintain the system pressure, people will want to know where the water is going and why."

I wonder what the real story is?

If you really want to do something positive that consider finding and fixing the leaks.

How do you find them?
- You divide the total system in half
- run one half with your existing pumps
- Rent pumps for the second half (short term rental)
- Pressure up both halves and see if you have a leak.
- If only one side has a pressure drop than you know it is in that half.
- now divide the leak half in half again (now a quarter)
- pressure up and check for leaks.
- divide again and check for leaks.
- keep doing this until you narrow down and isolate the leak to one segment or line.
- Now dig up the line and fix the leak.

Do this for both side of the total fire water system.

 

[sshep]

My goal was simply to find if there was any standard for metering.

How and why this is being done is a management decision for which I have only speculated on, but I don't really care for purposes of identifying technology. This is a massive site. I believe this effort is driven by concern over excessive use (leaks or other purposes). The meters are to monitor the system. The first step of improvement is usually to measure. I believe that making units pay is probably just to raise awareness.

Thanks for the suggestions on finding leaks. I will suggest your idea if I have an opportunity to do so.

best wishes,
sshep