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Technical Discussions
krish
krish
08:37 Nov-17-2006
Corelation to measue pipe wall thickness with process temperature

Is there any direct correlation method is available to calculate the pipe wall thickness using fluid temperature and pipe skin temperature to calculate the remaining wall thickness.?We have observed process fluid temperature around 505 Deg.C and the pipe skin temperature around 469 deg.C.What is the drop in temperature per mm thick of pipe?Pipe material is low alloy steem(P11).
Regards,




    
 
 Reply 
 
S.V.Swamy
Engineering, - Material Testing Inspection & Quality Control
Retired from Nuclear Fuel Complex , India, Joined Feb 2001, 787

S.V.Swamy

Engineering, - Material Testing Inspection & Quality Control
Retired from Nuclear Fuel Complex ,
India,
Joined Feb 2001
787
04:30 Nov-20-2006
Re: Corelation to measue pipe wall thickness with process temperature
Dear Krish,

Yes, you can set up a graphical correlation by using a section of pipe with carefully ground surface so that you create known thicknesses and use a sensitive thermocouple or thermography equipment to monitor the variation of surface temperature with thickness.

There are likely errors from scale inside the pipe, oxidation/scale/paint etc. on the outside surface causing emissivity differences etc.

If you are trying to set up this technqiue for early detection of hot spots (caused by corrosion and resulting in low wall) before they lead to failure, it is better to go in for non-contact techniques.

Regards.

Swamy

----------- Start Original Message -----------
: Is there any direct correlation method is available to calculate the pipe wall thickness using fluid temperature and pipe skin temperature to calculate the remaining wall thickness.?We have observed process fluid temperature around 505 Deg.C and the pipe skin temperature around 469 deg.C.What is the drop in temperature per mm thick of pipe?Pipe material is low alloy steem(P11).
: Regards,
------------ End Original Message ------------




    
 
 Reply 
 
P V SASTRY
R & D, NDT tecniques metallurgy
TAKEN VRS FROM THE POSITION OF SR. DEPUTY GENERAL MANAGER BHEL CORPORATE R&D, India, Joined Jan 2003, 195

P V SASTRY

R & D, NDT tecniques metallurgy
TAKEN VRS FROM THE POSITION OF SR. DEPUTY GENERAL MANAGER BHEL CORPORATE R&D,
India,
Joined Jan 2003
195
01:53 Nov-20-2006
Re: Corelation to measue pipe wall thickness with process temperature
To get any meaningfull values one has to also consider other parametes like internal mass flow, pressure and the external conduction/covection environment which are not exactly constants and the measuring thermocouples do not respond fast enough. Also the points of measurement of internal fluid temperatures and the metal temperatures are normally quite apart in a practical situation. Under the circumastances the efficacy of calculating the remaining wall thichkness using two temperatures needs further exploration.

It is assumed that the tubes/pipes are not in line of sight(at the given temparatures) for using thermography which other wise is better suited for detecting the hot spots/zones than the proposed solution. But this method can be employed during acid cleaning when the temperatures raise much above the ambient but compfortable for thermography.

Though it is a bit on the extreme, I know a utility that has taken more than 30,000 thickness readings on boiler tubing, during a shut down but cirtainly they do not have to depend on any other less precise methods.

----------- Start Original Message -----------
: Dear Krish,
: Yes, you can set up a graphical correlation by using a section of pipe with carefully ground surface so that you create known thicknesses and use a sensitive thermocouple or thermography equipment to monitor the variation of surface temperature with thickness.
: There are likely errors from scale inside the pipe, oxidation/scale/paint etc. on the outside surface causing emissivity differences etc.
: If you are trying to set up this technqiue for early detection of hot spots (caused by corrosion and resulting in low wall) before they lead to failure, it is better to go in for non-contact techniques.
: Regards.
: Swamy
: : Is there any direct correlation method is available to calculate the pipe wall thickness using fluid temperature and pipe skin temperature to calculate the remaining wall thickness.?We have observed process fluid temperature around 505 Deg.C and the pipe skin temperature around 469 deg.C.What is the drop in temperature per mm thick of pipe?Pipe material is low alloy steem(P11).
: : Regards,
------------ End Original Message ------------




    
 
 Reply 
 
krish
krish
00:34 Nov-21-2006
Re: Corelation to measue pipe wall thickness with process temperature
----------- Start Original Message -----------
: To get any meaningfull values one has to also consider other parametes like internal mass flow, pressure and the external conduction/covection environment which are not exactly constants and the measuring thermocouples do not respond fast enough. Also the points of measurement of internal fluid temperatures and the metal temperatures are normally quite apart in a practical situation. Under the circumastances the efficacy of calculating the remaining wall thichkness using two temperatures needs further exploration.
: It is assumed that the tubes/pipes are not in line of sight(at the given temparatures) for using thermography which other wise is better suited for detecting the hot spots/zones than the proposed solution. But this method can be employed during acid cleaning when the temperatures raise much above the ambient but compfortable for thermography.
: Though it is a bit on the extreme, I know a utility that has taken more than 30,000 thickness readings on boiler tubing, during a shut down but cirtainly they do not have to depend on any other less precise methods.
: : Dear Krish,
: : Yes, you can set up a graphical correlation by using a section of pipe with carefully ground surface so that you create known thicknesses and use a sensitive thermocouple or thermography equipment to monitor the variation of surface temperature with thickness.
: : There are likely errors from scale inside the pipe, oxidation/scale/paint etc. on the outside surface causing emissivity differences etc.
: : If you are trying to set up this technqiue for early detection of hot spots (caused by corrosion and resulting in low wall) before they lead to failure, it is better to go in for non-contact techniques.
: : Regards.
: : Swamy
: : : Is there any direct correlation method is available to calculate the pipe wall thickness using fluid temperature and pipe skin temperature to calculate the remaining wall thickness.?We have observed process fluid temperature around 505 Deg.C and the pipe skin temperature around 469 deg.C.What is the drop in temperature per mm thick of pipe?Pipe material is low alloy steem(P11).
: : : Regards,
------------ End Original Message ------------
Thanks to Mr.Sastry & Swamy.We have measured the outside temperature using thermal imaging camera after removing the insulation and got around 463 Deg.C.The inside process fluid temperature is measured using Thermocouple inserted into the pipe using well and measured aroung 505 Deg.C both are in the same location/spot.The difference in temperature from inside to out side surface due to the following reason,
1)Loss thro wall thickness of pipe
2)Loss thro atmosphere air current
3)Loss due to internal coke build-up which will act as a insulator.In the near by suspected coke build-up
location we have got around 388 Deg.C(dead zone,TEE with end flange for man entry where severe coke build-up is expected).Is it possible to calculate drop in temperature per mm thickness.
regards,



    
 
 Reply 
 
S.V.Swamy
Engineering, - Material Testing Inspection & Quality Control
Retired from Nuclear Fuel Complex , India, Joined Feb 2001, 787

S.V.Swamy

Engineering, - Material Testing Inspection & Quality Control
Retired from Nuclear Fuel Complex ,
India,
Joined Feb 2001
787
05:14 Nov-21-2006
Re: Corelation to measue pipe wall thickness with process temperature
Dear Krish,

As I already mentioned, it is better to generate a graphical calibration curve using a number of spot thickness measurements and the corresponding temperature. Since you mentioned about coke buildup, if the wall thickness is same but the inside buildup of coke is different, the outside temperature would be different. So, first, you will need a profile of coke buildup inside.

If you can remove the outside insulation, it is better to take a number of wall thickness readings as suggested by Shri Sastry. That would eliminate the other factors. Of course, the effect of other factors on the system performance and the tube life needs to be separately evaluated.

There could be other approaches for a Non-destructive evaluation of the inside surface w.r.t. the surface condition, coke buildup etc. and then use that information to modfify the temperature profile data.

With best regards,

Swamy

----------- Start Original Message -----------
: : To get any meaningfull values one has to also consider other parametes like internal mass flow, pressure and the external conduction/covection environment which are not exactly constants and the measuring thermocouples do not respond fast enough. Also the points of measurement of internal fluid temperatures and the metal temperatures are normally quite apart in a practical situation. Under the circumastances the efficacy of calculating the remaining wall thichkness using two temperatures needs further exploration.
: : It is assumed that the tubes/pipes are not in line of sight(at the given temparatures) for using thermography which other wise is better suited for detecting the hot spots/zones than the proposed solution. But this method can be employed during acid cleaning when the temperatures raise much above the ambient but compfortable for thermography.
: : Though it is a bit on the extreme, I know a utility that has taken more than 30,000 thickness readings on boiler tubing, during a shut down but cirtainly they do not have to depend on any other less precise methods.
: : : Dear Krish,
: : : Yes, you can set up a graphical correlation by using a section of pipe with carefully ground surface so that you create known thicknesses and use a sensitive thermocouple or thermography equipment to monitor the variation of surface temperature with thickness.
: : : There are likely errors from scale inside the pipe, oxidation/scale/paint etc. on the outside surface causing emissivity differences etc.
: : : If you are trying to set up this technqiue for early detection of hot spots (caused by corrosion and resulting in low wall) before they lead to failure, it is better to go in for non-contact techniques.
: : : Regards.
: : : Swamy
: : : : Is there any direct correlation method is available to calculate the pipe wall thickness using fluid temperature and pipe skin temperature to calculate the remaining wall thickness.?We have observed process fluid temperature around 505 Deg.C and the pipe skin temperature around 469 deg.C.What is the drop in temperature per mm thick of pipe?Pipe material is low alloy steem(P11).
: : : : Regards,
: Thanks to Mr.Sastry & Swamy.We have measured the outside temperature using thermal imaging camera after removing the insulation and got around 463 Deg.C.The inside process fluid temperature is measured using Thermocouple inserted into the pipe using well and measured aroung 505 Deg.C both are in the same location/spot.The difference in temperature from inside to out side surface due to the following reason,
: 1)Loss thro wall thickness of pipe
: 2)Loss thro atmosphere air current
: 3)Loss due to internal coke build-up which will act as a insulator.In the near by suspected coke build-up
: location we have got around 388 Deg.C(dead zone,TEE with end flange for man entry where severe coke build-up is expected).Is it possible to calculate drop in temperature per mm thickness.
: regards,
------------ End Original Message ------------




    
 
 Reply 
 

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