Flame Detector Site Tube Cautions

Applies to any system using ultraviolet flame detectors.

Site Tube and Scanner

Site Tube and Scanner

Honeywell Combustion Safety’s engineering teams have found a number of cases where site tubes, which are small pipe nipples attached to burners and flame detectors, are contributing to false flame detector signals.

While scanner manufacturers recommend using only black iron pipe for site tubes, several cases have been discovered of site tubes in use that are made from galvanized or stainless steel. These materials have a low ultraviolet light absorption rate. Hence, they have been found to reflect and transmit considerable ultraviolet light generated from spark igniters.

These cases have come to light while conducting pilot spark pick up tests. The pilot spark pick up test is done to determine if flame detectors are sighted and installed correctly. In these cases, the burner management systems received flame signals, from spark only, far in excess of that required for them to think that a suitable pilot flame has been established. This situation makes for the possibility of the main fuel valves opening when there really is no pilot. If this occurs, the gas could accumulate and ignite after a delay, which could result in a fuel-fired incident.

Actions to Take:

  1. Ensure that the pilot spark pick up test is being done properly on all equipment at least
  2. Verify that galvanized and or stainless steel nipples are not used for flame detector applications. If found, remove them and install black iron pipe instead.
  3. If a pilot spark pick up test fails and galvanized and/or stainless steel nipples are not in use, involve an experienced professional to look for other issues such as the length of the tube, the possible need for orifices or issues such as electrical noise.

If you have questions on this or any other fuel system or combustion equipment safety issue, ask the experts. There is no value one can place on safety, as it also has a direct effect on production if an incident should occur due to a blatant hazard being ignored.


Honeywell Combustion Safety, formerly CEC Combustion Safety, LLC, has been in business since 1984. With engineers and staff members that sit on Code committees such as ASME CSD-1, NFPA 56, NFPA 85, NFPA 86, and NFPA 87, our inside expertise is integrated within all of our practices and our global reach ensures that customers around the world are kept safe. Contact us at +1 216.749.2992 or visit www.combustionsafety.com for additional information.

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