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 attempt a visual assessment of new tube appearance and then visually “guess” whether it has a surface suitable for D3241. This “visual guesswork” only results in confusion about what is required from a fresh tube.
We employ a more objective means of evaluating tube surface quality. We can do so because our product has a far finer, more consistent surface quality. This does more than produce a superior appearance. A finer, more consistent finish results in a finer, more consistent test result. That's why we focus our attention on real 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. Through use of official 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. However, we go farther.
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, critically important, curved tube portion. Surface profilometers also result in a misinterpretation and even misrepresentation of abstract surface-generated statistics for actual surface quality (the real, critically important, heater tube feature) We need to use the correct tool to evaluate surface quality, including surface roughness. The Surface Comparitor is not just a tool for subjective roughness comparisons; it is one that is also standardized and calibrated to permit direct comparisons. Neither surface profilometers nor the early Visual Tube Rater (VTR) are calibrated at all, and neither device is certified by NIST or by any other certification agency.
Also, fuel-associated deposits generated during fuel testing are often still 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 visual 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 commonly employed to evaluate fuel deposits in the Visual Tube Rater (VTR), is actually 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 carefully and wisely.
Newer technologies provide for measuring deposit thickness down to the nearest nanometer. For this application, our tubes are also superior. Since our tube finish is finer and more consistent, it delivers finer and more consistent results. Whereas other suppliers choose to hide the amplitude and periodicity of a rougher and much coarser underbelly by abrading their product, we actually eliminate the amplitude of machining marks and reduce their periodicity to zero. When a nonamoeter-level deposit is graded, only the deposit is detected, unaltered by irregular ups and downs of random machine tool marks and wildly applied and misdirected scratches.
Only a Standard Heater Tube allows you to avoid the confusion associated with the vagaries of machining and resulting optical effects. Where other heater tubes obscure the viewing of available deposits and obstruct accurate nanometer-level measurement, Standard Heater Tubes provide a flawless measurement surface as well as an honest and real deposit image. The appearance of a heater tube under light is no longer important, is no mystery, and there is nothing to be feared from a clean and inert tube surface.
We apply correct new tube surface methodology to every tube we make, and we proudly employ and supply our technology exclusively to benefit our customers. This policy results in our acceptance and neutrality toward ASTM, as presented in the following Section: Our ASTM Policy.