Analyzer Probe Insertion Device

[NewMechanicalEngr]

I am new to this website as well as engineering. I have a specific question regarding inserting a sample probe in a relatively high pressure line.

We have a 400 psig line that was hot tapped and valved. We now have a retractable probe that will mount to the 1-1/2" full port valve. After connecting the probe assembly, the valve will be opened. Then, the packing nut will be loosened so that the probe can be forced down into the pipeline. THe probe is 3/4" S160 316SS.

1) Any recommendations as to how to calculate the force needed to insert the probe? I am thinking the force needed to overcome the packing on the probe will be greater than the axial force needed to push the pipe into the pipeline. Any advice?

2) Are any of you familiar with a device that would be mounted on the probe that would be used as a safety/inertion device? We are looking to make this a safe device. We do not want the probe shooting out after the packing nut is loosened. We do have an "end stop" on the probe, but don't really want to find out if it works!!!

Any help, advice, info, etc would be greatly appreciated.

 

[m777182]

I would prefer to fix the probe into a bypass line with a valve upstream and another one downstream and I would direct the flow with the valve on the main line.No loosening of packing nuts.
m777182

 

[jmw]

Depends on your probe manufacturer.
Jiskoot, for example, provide a hydraulic jack for inserting and removing probes. Some others provide a hand wheel device and screw system.
Many of these devices are optional bolt on systems so are not required on a one per probe basis.
What does your probe manufacturer say?

There have been serious accidents, and even fatalities, with mis-operation when inserting or extracting devices into pressurised lines (though some are undoubtedly due to trying to hot tap non-hot tap devices) and whereas logic suggests to me that slackening packing nuts is not a good idea i would suggest you consult with the device manufacturer and ensure that ther is a proper safety and instruction manual available and understood.

JMW

http://www.ViscoAnalyser.com

 

[djs]

Force to insert: A * P = 0.375*0.375*3.14159*400=177 lbf

I do not think that you will be manually inserting the probe by hand!

 

[rhodie]

What happens when the probe breaks off during insertion?

Try the bypass idea!

 

[hydrae]

In the water works industry we hot tap lines all the time, but your pressure is more that 4 times what we would call high pressure.
For the 1.5" and 2" devices, the units we would use incorporate a jacking screw mechanism to assist in inserting the flow meter or probe into the stream.
What is the diameter of the packing? Since you are using a 1.5" valve, if the packing is 1.5" diameter the forces would be
0.75*0.75*3.14*400= 706#
The packing forces are small compared to the internal pressure on the probe, you can also test the packing forces before the valve is opened.

As jmw suggested, contact the manufacture for procedure and safety instructions.

Also prepare backup plans such as pipeline shutdown and projectile exclusion areas in case the worst happens.

Hydrae

 

[CharlieH]

Thanks for all the great suggestions and assistance. To ensure safety and reliability, we found a company that sells an Automatic Insertion Device that uses the line pressure to actually insert the probe. The unit has an oil tank taht is used as the presuurizing medium between the line and the piston that is attached to the probe shaft. There is a collar lock that you lock on the probe shaft and once inserted to the depth you set, you then secure the locking collar to the probe unit that houses the shaft. I don't know if it is proper to share the name of the company on this forum, but I can say that it appears to be a nice unit.

We are in the midst of specifying two units and the company has been a pleasure to work with. I will update the forum as to how we like the units once installed and working. The units are in the $2000 price range which is not a bad price considering what you get.

Thanks again for all your advice!!!

 

[jsummerfield]

Essentially the same thing that would happen when the probe breaks off during insertion applies to main line and the bypass line. A different issue pertains to probe failure due to vibration, etc. We have information that permits calculating the natural frequency and wake or Strouhal frequency for thermowells based upon ASME PTC 19.3 construction. Similar data would not be available for the analyzer probe. The bypass stream could limit the velocity. In any case, keep the probe short. Also, lowering the probe diameter would reduce the insertion force.

John

 

[jmw]

A good point by Jsummerfield: from my experience with Jiskoot, they have their own program for calculating vortex shedding effects and I would expect (hope) similar data to be available from any of the manufacturers.

JMW

http://www.ViscoAnalyser.com