New Tube Evaluations
Standard Heater Tube, Inc. has developed and patented a unique method for producing heater tubes. In the natural course of development, the Company has also developed an entirely new and quite suitable technology for evaluating fresh, new heater tubes. This technology is science-based and unique to our company.
Others have preferred making a visual assessment of a new tube and then visually “guessing” whether it has a surface that is suitable for service in D3241. This “visual guesswork” results in a lot of confusion about what is required from a fresh tube.
We employ a more objective means of evaluating tube surface quality.
Experiment: To prove out the equivalence of surfaces of various tube manufacturers, use the National Institute of Standards and Technology (NIST)-certified Surface Roughness Comparator available to top-notch machinists and metallurgists. This device, calibrated to NIST requirements, is based on an association between surface roughness and visual acuity, plus physical feel. It recognizes the reality that surface evaluation is fundamentally subjective. In short, you can “see” and you can “feel” different surface qualities (roughness) by comparing visually and tactually among surfaces. Using a set of such standards, it is easy to conclude that all tubes of viable manufacturers are at or below a “2 microinch” finish (The tube surface finish required of a new tube by D-3241). The fact that modern suppliers easily meet this requirement should surprise nobody.
Attempts to evaluate tube features by using surface profilometers have been made. British researchers compared tubes of the two equivalent manufacturers using surface profilometry, and found them equivalent. However, a critical limitation of surface profilometry (applied to heater tube surfaces) is to only assess a surface in and along two-dimensions (length and height). This technique altogether misses evaluating the surface across the dominant and critical curved tube portion. And, some researchers confuse actual surface quality with abstract surface-generated statistics. We need to use the correct tool to evaluate surface roughness. The Surface Comparitor is a tool for subjective roughness comparisons; it is one that is also standardized and calibrated for the purpose of making direct comparisons. Neither surface profilometers or the VTR are calibrated at all, and neither device is certified by NIST or any other certification agency.
Also, fuel-associated deposits generated during fuel testing are rated using an arbitrary color scale. A VTR rating of 0 or 1 represents a clean tube surface with essentially no deposits. At the other end of the scale, a VTR rating of >4 represents the darkest, heaviest fuel deposits possible. If you are lucky, your fuel will fall cleanly at one of these extremes and make for an easy rating job. This is the purposeful nature of a pass-fail test. However, some fuels are more difficult to categorize. For these more difficult fuels, optical considerations and a Standard brand heater tube become even more important.
In this situation a 3X magnification, as employed in the Visual Tuberater (VTR) commonly used to evaluate fuel deposits, is actually just a crude, low, or poor magnification. Consequently lathe marks, (disguised by millions of supplemental abrasion marks which you also can't see at the poor 3X magnification), plus reflected images, dust, dirt, glare, and a variety of streaks and smudges can make viewing and rating the tube deposit --- if one is present at all --- more difficult.
Other tube suppliers also, deliberately add millions of inherent scratch marks, gouges, harsh abrasions, and microabrasions to the tube. Some say this is tube “polishing.” But, the consequence of these scratches is to diffuse light away from the eye of the observer into countless wild, randomly chosen, directions. The result? It is harder to see, and to rate, nearby fuel-related deposits. Therefore, choose a tube source wisely.
A person rating a borderline used tube in this situation is like a city-dweller trying to evaluate bright stars on a cloudless night through the haze, dirt, and dust which accompany city living, by pointing a spotlight into the heavens. That person may think the stars are not really very bright, and may not realize the problem isn’t with the stars; it’s a built-in characteristic of the environment.
Diffusion is a random scattering of available light such as occurs, for example, with a "frosted" light bulb. Diffraction, or the bending of light around a corner, is due to the wave property of light. In refraction, the bending of light is at a distinct angle due to a change in medium density. Smart observers realize these phenomena as what they are: optical phenomena. They illustrate nothing at all about the surface of chemically inert aluminum coupons. Nor do such optical phenomena have anything at all to do with fuel chemistry or the mechanism of fuel deterioration.
Only a Standard Heater Tube allows you to avoid the confusion associated with optical effects. Where other heater tubes obscure the viewing of available deposits, Standard Heater Tubes provide a clean and honest image of real deposits. The appearance of a heater tube under light is no mystery, and there is nothing to be feared from a clean and inert tube surface.
We apply the correct new tube surface methodology to every tube we make, and we proudly employ and supply our technology to exclusively benefit our customers.