Tube Finishing Study
Information on tube finishing was delivered in a Presentation to ASTM Subcommittee J during a meeting of Committee D02 on Petroleum Products and Lubricants in Bellingham, Washington during December of 2016. The information ---upgraded here to include deposit ratings by Metrology in addition to the basic visual ratings --- generated a conclusion that tube finishing methods are irrelevant to the JFTOT fuel ratings obtained. Subsequent supplemental data only reinforced the conclusion.
This Study was undertaken in response to dual hypotheses presented by others to Subcommittee J on Aviation Fuel. These postulated that (1) bias exists in JFTOT results due to tubes of different suppliers, and (2) the presumed bias is correctly attributed to different tube finishing methods employed by tube suppliers. An additional goal was to produce supplemental fuel breakpoint data to reveal any existing differences in tube performance during JFTOT testing.
While D3241 Permits Either Metrology or VTR ratings to be employed, the Equivalence Protocol (RR:D02-1550) mandates use of Visual Ratings, and a prior Falex Tube Equivalence Study employed Visual Ratings. Therefore, visual ratings were initially obtained, followed later by Metrology ratings. (It is recognized that VTR and Metrology ratings are in basic agreement). Within Subcommittee J, there is growing interest in two types of Metrology ratings (ITR & ETR). Subcommittee J expressed a desire to see equivalence by Metrology.
All results fell within a five degree range of breakpoint values. The variables evaluated included Alcor and Falex methods and the method employed by Standard Heater Tube, Inc.
Additionally, two "combination" procedures were included for completeness. These involved (1) using Brasso to abrasively polish a "raw," "blank" or "unfinished" tube of Standard Heater Tube, Inc., and (2) using the patented finishing method employed at Standard Heater Tube, Inc. to overlay an Alcor tube with a second finishing process. Using VTR ratings as a testing criteria, the original data are in total agreement. All five different tube finishing methods produced equivalent breakpoint data. And, breakpoint data show all tubes are equivalent.
ITR Metrology results were also independently obtained, as shown in the following Figure. These results confirmed the conclusion from the VTR ratings. There is no "tube bias" due to tube finishing variables, and all tubes did give statistically equivalent breakpoints.