Pipe connection bonding test
Pipe connection bonding test
(OP)
We have a powder transfer system: blowers, diverter valves, piping with large radius bends, to transfer powder from one silo to another.
Piping is aluminum (not sure exact spec), about 4" diam.
At the connection where two pipes are joined, the plant has installed a short cable, external to the pipe, from one pipe to the other, connected with a 'tab' welded to each pipe. This is to dissipate any static buildup during the transfer of material.
Every year or so, each of these 'bonds' are tested using a standard Fluke 87 for resistance. The probes of the Fluke 87 are pressed against the side of each pipe.
Is this a good test to verify the bond between the two pipes? I didn't think the 87 would produce enough voltage to give a good reading...and that a milliohmeter would be better.
I've also used a clamp-on ground tester to test grounds. Could this tool be used to test the bond cable?
Piping is aluminum (not sure exact spec), about 4" diam.
At the connection where two pipes are joined, the plant has installed a short cable, external to the pipe, from one pipe to the other, connected with a 'tab' welded to each pipe. This is to dissipate any static buildup during the transfer of material.
Every year or so, each of these 'bonds' are tested using a standard Fluke 87 for resistance. The probes of the Fluke 87 are pressed against the side of each pipe.
Is this a good test to verify the bond between the two pipes? I didn't think the 87 would produce enough voltage to give a good reading...and that a milliohmeter would be better.
I've also used a clamp-on ground tester to test grounds. Could this tool be used to test the bond cable?
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RE: Pipe connection bonding test
The instrument should be 'better' than the pass/fail limit by roughly a 10-to-1 ratio. For example, if the limit is 1 ohm, then the meter should be capable of reading to 0.1 ohms.
RE: Pipe connection bonding test
RE: Pipe connection bonding test
We work for the same company at the same plant.
My question to all is:
Is a standard DMM (Fluke 87) a good enough tool to verify bonding connection/resistance?
______________________________________________________________________________
This is normally the space where people post something insightful.
RE: Pipe connection bonding test
RE: Pipe connection bonding test
Even something as simple as a 12V battery with a 1-2 ohm resistor supplying current would be a valid test providing some stress. Just use a small lamp across the resistor to verify current is flowing and measure voltage across the bond. This will tell you if things are about to fail either mechanically or from corosion.
RE: Pipe connection bonding test
Given that the issue here is static electricity, do we really need to use a high current test? While NFPA 77 calls for a maximum of 10 ohms, there is information in the IEEE Green Book that suggests that resistances of 1,000,000 ohms or less are sufficient to prevent the build of of static charges.
RE: Pipe connection bonding test
That said, anything over an ohm on a metal to metal connection indicates there is some kind of problem with an oxidation layer forming. It doesn't take much to get rid of a static discharge and often voltage will break down an oxidation layer. My concern is the DVM test gives no indication that a connection will fail in the future. You shouldn't test with a higher current than a DVM unless there is no possibility of ignition from a spark.