We have numerous failures of our thermocouples over a number of frame 5 machines (about 30 in 4 years)

Questions..
1. Does this sound reasonable?

2. What is the normal changeout service cycle for frame5?

3. Is there any upgrade from the RTO 65970 model T/C?

 

There really is no change-out period or recommendation.

You need to provide information about the failure mode--are they failing open circuit?

Are they burning?

Are they failing because the tips are rubbing/chafing on the radiation shield?

Is the wiring insulation getting burned or chafed?

Are the leads breaking off?

Next you need to analyze the installation. Are they overly bent/manipulated when being installed?

Are they properly secured--or left to flap around without any support?

Are they inserted too far into the radiation tube?

Is the compression fitting used to secure the T/C in the radiation shield being tightened excessively, causing the leads in the sheath to be crushed?

There is something amiss with the way the exhaust T/Cs are being handled, installed or treated at your site--because this failure rate is very excessive. There are base-loaded machines with twenty year-old exhaust T/Cs. The period of time you are talking about would preclude worries about a bad batch of T/Cs. So it's most likely something about the way the T/Cs are being handed or installed.

Many sites have switched to much more user-friendly T/Cs with much more flexible and easy to install and secure leads. If the machine is not under warranty or some kind of long-term service agreement you are free to work with a vendor to source T/Cs suitable for the service (expected exhaust temperature; compartment temperature; etc). Many sites have found more suitable and less expensive T/Cs that are much easier to install.

But, the problem(s) you are describing are not typical and are not likely attributable to the T/Cs, but rather to something amiss with their handling and/or installation. Many people excessively over-tighten the compression fitting used to secure the T/C in the radiation shield. There is no high pressure fluid which might leak from the fitting like if it was being used for a high-pressure hydraulic system. This is one of the most common causes of premature failure, followed by improper insertion in the radiation shield (the T/C tip should be about 0.125-0.250 inches) from the inside surface of the radiation shield <b>when the compression fitting is properly tightened.</b> Failure to properly secure the leads and excessive bending during installation round out the list of common failure causes.

Hope this helps.