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Water flow readings on old steel piping

Water flow readings on old steel piping

Water flow readings on old steel piping

(OP)
I recently attempted to obtain some flow readings on a 6" steel line that has been in service for 50 years.  I used a ultrasonic flow meter mounted to the exterior of the line with no sucess.  I think the internal corrosion in the line is preventing a proper reading.  I was wondering if anyone has had any experience or suggestions/methods on how to obtain a flow rate on a pipe that has been in service for many years and has internal corrosion, without breaking the line and taking an outage.    

RE: Water flow readings on old steel piping

It is not nearly as surprising that the UT meter didn't work as it is surprising that they ever work (the technology has its place, but too many operators think it is magic).  

A 50 year old water line is an amazingly difficult flow problem.  The combination of corrosion and scale is far from uniform so the ID of the conduit is far from constant.  Consequently, the velocity of the fluid at any given point is subject to be vastly different from any other point.  Any meter that is inferring a flow rate from velocity (or its surrogate) is going to give you a different mass flow rate at nearly every point (violating the Continuity Equation).

Your only option is a "bucket test", but that requires taking the line out of service.  With the constraints you provided, I think you are out of luck.
 

RE: Water flow readings on old steel piping

unless you have extremely high quality water, it is amazing this line carries any flow at all. Steel waterlines of this vintage generally have gone past their useful life and should be scheduled for replacement.

RE: Water flow readings on old steel piping

Honeywell has a dual channel average path ultrasonic flow meter I was going to purchase.(project is now on hold) It looked better than others.
You could mag the pipe get an average ID.  Take your pressure drop accross the pipe and estimate flow. I assume the pipe is full.

RE: Water flow readings on old steel piping

Is there some way that you can infer the flow rate from devices or systems connected to the pipe?  To me, trying to work with just the line itself seems to be a losing proposition.

RE: Water flow readings on old steel piping

(OP)
Thanks all for your input.  

I have attempted to infer the flow rate from the centrifugal water supply pump, however it is quite old and finding a pump curve for it has not been successful.  There are a few pressure gauges in the system, but they are d/s of a strainer and throttling valve so inferring flow rates through these components requires some guessing.

I guess without taking an outage and shutting off the flow, the best I can do is make some assumptions and calculate the flow rate.

 

RE: Water flow readings on old steel piping

Of course you can calculate flowrate from pressure drop along a pipe.  A flow element is a flow element and flow must always have some relationship to the element's pressure drop, unless its frictionless.  The better you know the relationship, the better the measurement.  Just some flow elements give you a bigger signal over a shorter length than others can.  If you had to guess the primary parameters of either a long enough piece of pipe or a meter of some kind, I would think you could guess the pipe parameters and calculate flowrate from the pipe's pressure drop far easier and even more accurately than you would be able to do if you had to start by guessing the meter's and its installation parameters.

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

RE: Water flow readings on old steel piping

Dear JTmech,

Have you considered a hot tap flow meter? You only mention that it is a "steel" pipe (I assume carbon steel). A hot tap averaging pitot tube (AP) would require welding a thread-o-let on the pipe, installing a threaded nipple and valve, then drilling into the pipe with a hot tap drilling machine (where the pressure is contained). You would retract the drill, bleed off the pressure in the drill assembly, then thread the hot tap AP assembly into the valve. This can all be done without depressurizing the line. Once the sensor is installed, you could connect a DP gage and calculate the flow rate (based on a DP vs. flow cuve supplied by the manufacturer). If you are looking for a "one time" measurement, this would get you in the ballbark. If you were looking for a permanent installation with an electronic output, you could span a DP transmitter (with a 4-20mA output)based on the gage reading.

If you are not comfortable welding onto the pipe, you could use a pipe saddle with the appropriate FNPT connection for the access valve.

3 cautions: Pipe must be full and there must be enough velocity to produce a readable DP. Wall must be of ample thickness for welding and/or drilling.

How clean is the water?

RE: Water flow readings on old steel piping

do a quick search on "tuberculation" and view the typical photographs of 50 yr old iron/steel piping, and you may see the folly in using a UT flow device in such an application.

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