Burners 101

[Mikey98118]

So, why not drive to Tacoma? Well, by  Autumn I will have undergone surgery in both eyes, and will be able to safely drive again. In the meantime, I just don't need an accident on the freeway, to make life more interesting. As you know, old age is plenty 'interesting' already, without pushing one's luck

[ThomasPowers]

I sometimes run across stainless pipe/tubing at my scrapyard; of course the town it's sort of in has a population of  626 people.  I think it comes from the small University down the road in Socorro, (Socorro pop about 10000 when the University is in session.)  I seem to recall Seattle being a tad larger when I was there last August...

[Mikey98118]

It isn't about population size; its about property values. The land became way more valuable then any scrapyard business. My favorite scrapyard sold out and moved to another part of town; they saved the name, but now sell new metal stock to local machinist firms, which sell finished parts to Boeing.

[Frosty]

Before I met Deb and I vacationed by taking a month to cruise around the lower 48 I discovered the scrap and reject disposal yard in the Boeing plants. The next time I was down I'd planned who I could ship how much with, had a budget and target list. Only to discover the plants themselves had closed and an offramp under construction. I had my eye on high temp alloy jet engine tubing and Ti forge drops but . . . <sigh> 

Property values and single buyer scrap contracts wounded my scrounger soul bitterly. I think about it every time I take that offramp or maybe it's an exchange. it's still sad.

You might know the one Mike, it was the Boeing plant that had it's own 4 lane freeway exchange to the parking lot. 

Frosty The Lucky.

 

[Mikey98118]

The only one I knew about, another favored playground, was one half a block north of the exit ramp, but yes it is looooong gone. Good thing for me, too. I was filling up my garage with "precious treasures" I dragged home from there; didn't make Kathy very happy

[Mikey98118]

More about using S.S. pipe couplings and nipples for flame retention  nozzles

When ordering stainless-steel couplings for flame retention nozzles; make sure that, after the length of threaded portion on the smaller pipe nipple is screwed into it the coupling still has a left-over portion beyond the nipple’s thread, which is at least equal to its inside diameter, plus 1/8”. A nipple that ends up too short to work perfectly as a slide-over step nozzle is just a waste of your funds and time.

You will probably have to power sand or grind the inside of the threaded section pf pipe nipple as much as 0.025” larger, to make a sliding fit with the mixing tube. After enlarging the inside of the nipple as deep as your rotary tool or die grinder can comfortably reach, cut the threaded portion off, and enlarge the area that you can now reach. Measure the length of this threaded section and ink a mark the same distance from the coupling’s edge. Then, screw the thread into the coupling, just up to snug. Lay out three equally spaced holes for set screws near the coupling’s thread. Drill and thread three holes. Clean up all burrs, and screw sets screws into you new flame retention nozzle; slide it in place on the mixing tube, to decide if three screws are adequate, or if you want place three more screw forward of them; if you do, remember to keep them 1/4” away from the ink mark, to ensure that the screws find purchase in both couple wall and nipple wall.

If you make the two threaded parts snug with each other, and do a careful job of enlarging the threaded section of pipe nipple, you may make a good enough fit to slide the nozzle where you want it, and then twist it on the mixing tube just enough to trap it in position; this allows you to use a single set screw to hold it in place, during burner tuning, and then to drill and thread a hole through all three parts, to prevent the nozzle from moving during heating cycles. Two screws are a lot less work than six.

[Mikey98118]

Passive Vortex Burners

    Let’s clarify just what is meant by the term “vortex burner”; it’s been miss-applied to any burner that swirls the fuel/air mixture at some point; that would describe most gas burners—even some Bunsen burners. Often, the term is granted to burners that swirl the flames they make. But, causing a flame to swirl happens far too late in the mixing process to provide much benefit; used this way, the description is pure hype.

    Vortex is a fluid dynamics term, describing a region in which the fluid flow (gas, liquid, or plasma) revolves around an axis line.  The vortices generated on the tailing edge of a plane’s wing only generate drag. At the other extreme, a tornado’s funnel has terrible destructive power. The gentle current of a bathtub drain effectively employs vortex flow to good purpose, and so should a burner’s air entrance.

    There are numerous ways to swirl incoming air and fuel gas, but only when the air passes through a restriction (ex. pipe reducer or funnel) can vortex movement become a practical air/fuel mixing aid. Most successful home-built burners, whether linear or jet-ejector, create a vortex. High speed tube burners are an exception, but they combine swirl from side air entrances with Bernoulli's principle to get the job done. Nevertheless, if you place a pipe reducer between it mixing chamber, and a smaller mixing tube, they will produce a nicer flame shape for hand torches.  

    Any device that creates spin at the air entrance will increase vortex flow; this includes directly opposite air openings on “T” plumbing fixtures, disc shaped choke plates near funnel entrances, or even motionless blade structures in front of a funnel opening. If you strip the impeller blades from an axial computer fan, and mount them on a burner’s gas pipe, at the funnel opening, they will significantly increase vortex movement in the funnel, even though they are still. Likewise, rib structures in mounting plates can be ground into fan like shapes, to increase vortex flow in the funnel, but to a lesser extent. Installing computer fans on linear burners will supercharge vortex flow, but this requires a complicated gas assembly, and an electrical power source. So, you are wise to move from passive to powered vortex burners in stages. Some of the parts that can be used for air openings are good for use with a moving fan, and others are not. However, the limits on shape and sizes imposed for use with moving impeller blades, do not apply to motionless blades. Thus, the blades from an axial computer fan can be safely and effectively mounted at the entrance of any funnel or pipe reducer, to improve performance, without worry.  

[Mikey98118]

HULISEN 4Pcs Cream Icing Piping Nozzle Tip Stainless Steel; these cake decorating tips come with tube already attached; 3” long; 3/4” opening diameter on long cone; 0.236” (6mm) diameter tube  for $7 through Amazon,com

Also, four larger tips 3-1/2” long; 1” cone opening on long cone; 0.312” through Amazon.com for all the mad scientist types.

The small tips can be used for 1/8"; the larger tips can be used for !/4" burners, for two-brick or coffee-can forges.

[Mikey98118]

Retraction: The larger set makes 1/8" burners, and just forget the smaller set.

[Mikey98118]

 

 

Tapered openings with mixing tubes attached

SSTs are your best construction choice, if you can find them in the size you need, at the time you need, and the price you want; due to the vagaries of the marketplace, that can be a hit-or- miss proposition. So, here are some alternate choices; they are cake icing tips with stainless steel tubing firmly attached by compression.

Because some tips are too short, they will need to have stainless-steel tubing slid over the tip’s existing tube, you may end up with a perfect sliding fit, or you may need to shorten the existing tube, and power sand or grind the end of the tube being slid over it, to create an interference fit; in this case, look to see how deeply your chainsaw grinding stone, etc. will reach into the tube, and cut the tip’s tube a little shorter than that. Keep checking the enlarging opening in the new mixing tube’s end, so as to stop enlarging it, when the tips shorten section of tubing will slip into it about 1/2” deep. Because tubing can be slightly out of round, twist the tip’s tube within the mixing tube, to establish where they fit together best; this will help establish the best interference fit. Finish pushing the tubes together by lightly tapping them. It is a good idea not to cut the mixing tube to length, until after it is tapped into place; this keeps the tubes cut end from being deformed by hammering on it.

Dxhycc 8Pcs icing tip set; stainless-steel, for $10 through Amazon.com; the funnel opening diameter on the two largest tips is 0.893”. The inside diameter of these two tips is 0.357” I.D.; they will have 3-1/2” of usable length after cutting off their slanted ends; this is just fine for using the existing tube as your burner’s mixing tube for naturally aspirated mode, or 5” length of 12x10mm stainless-steel tubing can be slid over it for use as a mixing tube, if they’re fan induced. Such a burner will have a 2.5:1 opening to mixing tube ratio, which is sufficient for naturally aspirated 1/4” burners, and invites use with a 25mm computer fan, which fits perfectly on it.

There are also two tips with funnel opening diameters of 0.935”; the inside diameter of their tubes are 0.291”, which calls for a minimum mixing tube length of 2-3/4” for naturally aspirated mode, or 4” long if they’re fan induced. You will need to slide a 10x8mm stainless-steel tube over their existing 8mm O.D. tubes to make 1/8” burners from it.  Such a burner will have a 3.2:1 opening to mixing tube ratio, which is excellent for a naturally aspirated burner, and okay for use with a 25mm computer fan. All the remaining icing tips are useless for turning into burners.

 

SUODAO 4Pcs icing tip set; 5mm, 6mm, 8mm, and 10mm diameter stainless-steel tubes, for $8.49 through Amazon.com. You have tips to build a 1/16” 1/8” and 1/4” burners among them.

HULISEN 4Pcs icing tip set; these stainless-steel cake decorating tips  for $10 through Amazon.com; they come with a tube firmly attached; they have a 1” diameter opening on a long cone; the tube’s outside diameter is 0.314” (8mm)  x 0.285” inside diameter; this provides a sliding fit inside a 10 x 8 millimeter stainless-steel spacer tube, which fits inside a 12x 10 millimeter flame retention tube, with minor   grinding with a rotary stone for chainsaws run in a rotary tool; this can be used to make a 1/8” burner.

The perfect SST for use as a 1/4" burner is a Smokehouse Chef #606 SST; it is $26 through Amazon.com. Since most people using miiature burners in heating equipment will want two or three burners, the price difference is serious. If price is no problem, than I recommend it as your best path to burner construction.

[Mikey98118]

EZ lock mandrel and cutoff disks are one of safest ways for a beginner to surface cut with a rotary tool; they are more expensive than generic cutoff discs, which run in standard mandrels, but considerably easier for a newbie to deal with, for the work needed to build a couple of burners. By the time you use up the disks in one their mandrel and disk kits, you should be well enough acquainted with surface cutting to take advantage of the more economic offers for regular discs and mandrels. You will still find yourself reverting to the EZ lock system for tricky cutting jobs. The special discs that come with this system are 1-1/2” diameters. It is wise to save the last 1” of each disc, rather than wearing them down completely. The small used discs are very handy for making interior cuts in small parts. You can buy the discs and mandrel in kit form online, and from most large hardware stores.

    Begin by inserting the EZ lock mandrel all the way into the collet nut on your ritary tool’s spindle, and then tighten the nut. To mount a disk, push the plastic part of the head down against its spring, dropping a disk past the mandrel’s bow tie shaped end piece, and then turn it ninety degrees, to lock it in place.

Note: If the disc will not clear the steel bow-tie shaped head, place it on an angle to the head, and pass one end of the opening past it, and then the rest will pass through; reverse this procedure to free a stuck disc.

The spring and locking mechanism are what makes this system unique. It eliminates the usual locking screw, so that grinding and sanding wheels can be used nearly parallel to part surfaces, without interference from a protruding screw head. The disc is positively locked, because there is no screw to loosen from vibration, allowing the disc to spin on the mandrel. But most important of all, the spring allows the disc to move out of alignment with the kerf, without creating kickbacks, by nearly eliminating torsional forces.

[Mikey98118]

Dremel #420 Cutoff discs are 15/16 " diameter, by 0.040" (1mm) thickness, and are rated to 35,000 RPM; they are sold in twenty discs kits for $4.97 through Amazon.com; they are not fiberglass reinforced, but are much more durable for steel cutting than standard 0.025" (0.635mm) thick jewelers’ discs; they have added safety over fiberglass reinforced discs during kickback, and enhanced control when cutting next to inside corners, and through forward and rear cut lines in air openings. These discs are only meant for cutting metals; do not use their sides for grinding. The smaller the air opening the handier these discs become; they are as safe as you can get, and one kit should easily provide enough discs for even a novice to build two or three small burners.

    Don’t confuse these #420 discs with #409 (jewelers) discs, which are only 0.025" thick (0.635mm).

“Just buy a Dremel” can be sound advice when it comes to their rotary tool accessories, and attachments. If you're too busy to pay close attention before every purchase; if you’d rather “just get on with the job,” then paying top prices for consistent (not necessarily best) quality is a practical choice. As you get comfortable using rotary tools, you will inevitably modify that choice a lot. With sixty-four years “on the tools,” I still choose to pay Dremel prices at times; but never out of brand loyalty.

    I think that the Dremel 575 Right Angle Attachment, 4486 Key-less Chuck, and A550 Shield are all nearly worth their prices, and will greatly aid you to do this work. The EZ Lock mandrel and abrasive cutoff discs are worth every last penny; so are Dremel’s 420 cutoff discs; their model #100 and #200 rotary tools are worth their cost. But, paying Dremel prices for their other stuff? No thanks.

[Mikey98118]

Surface cutting parts: If you stop the disc during a plunge cut (with a circular or a chop saw) before the cut is finished, it will usually cause kickback as the parts pinch together against the blade or cutoff disc. The opposite is true when surface cutting on sheet metal products, like pipe and tubing, or equipment shells. Attempting to remove a moving rotary tool or die grinder from the kerf will usually cause kickback—unless you are cutting parts in two; then, keep the disk moving at the end of the final cut, to keep a loose part from pinching against the disc.

    Any OEM (like Dremel Tools) that bothers with a thorough list of safety tips in its instruction manuals,  advises the operator to run a cutoff disc back and forth on the part surface, gradually deepening a groove at the cut line, until the disc begins to break through the groove, which is then called a “kerf.” Unlike chop sawing, or plunge cutting through wood parts, the operator is supposed to bring the disc to a halt before exiting the kerf. Surface cutting is different to other cutting processes, because your disc isn’t deeply buried in the part. There is very little material for the disc to “walk up,” creating an opportunity for kickback, as the disc stops. Also, the numerous tiny grit edges don’t have anything like the tendency to grab unto stock that the teeth of circular blades do, will they are slowing down. Most kickback from resin bonded cutting discs come from the sides of the discs binding against the kerf.    

    So, surface cutting creates a unique situation, where stopping the disc before removing it from a groove or kerf is safer than removing the disc while it is still in motion (except at the very end of a cut that will separate parts).

Die grinders are treated the same as rotary tools for surface cutting (my own description of this technique).

    You will notice that friction makes the disc want to move in one direction; take note of it, and make sure that the disc is traveling in the opposite direction, when breaking through the kerf. Otherwise, the disc will tend to bump against the end of the kerf, the second most common cause of kickback.

    Maximum safe RPMs of cutoff discs vary by manufacturer and thickness; if a marketer doesn’t list the maximum recommended RPM for a cutoff disc, the rule of thumb is not to use larger than 1-1/4” diameter generic disks at 32,000 RPM, or larger than 1-1/2” generic disks at  20,000 RPM.

 

[Mikey98118]

Burner sizes

The first thing you must decide about your burner is what size it’s going to be. Home-built burner sizes are given in accordance to schedule #40 water pipe sizes (or equivalent sizes in round tubing) used as the burner’s mixing tube, because pipes were what these burners were built from for many years (and lots of them still are). So, it’s handy to know what actual inside diameters these nominal pipe sizes have, since it’s the inside diameter you’re trying to match in an equivalent tubing size, and with whatever you use for a tapered air opening. Note that actual diameters are larger than nominal pipe sizes. The tubing you employ will seldom be an exact match with water pipe, so choose a little larger inside diameter, when possible, rather than a little smaller, for your mixing tubes. Metric stainless-steel tube can be a handy alternative to fractional tube in the smaller sizes, which are more likely to match up well with small stainless-steel funnel shapes.

Schedule #40 pipe dimensions:                       Nearest metric tube equivalents:

(A) 1/8” pipe is 0.405” O.D. x 0.270” I.D.            (1) 10mm (0.390”) x 8mm (0.312”).

(B)  1/4” pipe is 0.540” O.D. x 0.364” I.D.              (2)  12mm (0.468”) x 10mm (0.390”).

(C) 3/8” pipe is 0.675” O.D. x 0.493” I.D.            (3)  14mm (0.546”) x 12mm (0.468”).

(D) 1/2” pipe is 0.840” O.D. x 0.622” I.D.             (4)  16mm (0.624”) x 14mm (0.546”).

(E)  3/4” pipe is 1.050” O.D. x 0.824” I.D.             (5)  18mm (0.702”) x 16mm (0.624”).

(F)  1” pipe is 1.315” O.D. x 1.049” I.D.                   (6)  20mm (0.780”) x 18mm (0.702”).

[Mikey98118]

The list above doesn't include fractional tubing, which are based on fractions of and inch outside measurement; their inside measurements depend on wall thickness.

It also doesn't address sellers who list metric tubing with outside measurements that are accurate, but who are lying through their teeth about their tubing's inside measurements. You are advised to read the customer evaluations of their products, on Amazon.com, before purchase.

[Mikey98118]

Beyond the power of swirl

If there is one thing that the last seventy years of very gradual propane burner improvements has repeatedly proven, it's that adequate mixing of the air/fuel mixture in burners are over rated and underfed. What matters about this, is that how hot an air/propane flame gets is directly dependant on how well the fuel and air mixes. 

    Why choose to swirl incoming air? A naturally aspirated burner has a very limited energy budget (gained from its gas jet), to provide movement. It takes energy to move ambient air into the burner, and it takes energy to swirl that air; thus mixing it with the gaseous fuel. So, it is convenient to create forward and lateral air movement at the same time.

There are numerous ways to swirl incoming air and fuel gas.  When incoming air passes through a restricting tubular shape (ex. pipe reducer or funnel), vortex movement becomes an excellent air/fuel mixing aid. Most successful home-built burners, whether linear or jet-ejector styles, create at least some vortex flow. My high-speed tube burners are an exception, but they gain swirl from (fore and aft beveled) rectangular side air entrances, which provide spin and induction at the same time. Nevertheless, if you place a pipe reducer between their air entrances, and a smaller mixing tube, their performance will improve. Why? Because the introduction of that reducer fitting provides vortex flow.

Vortex flow in a burner provides a second engine to add to the fuel gas stream; powering your burner. But unlike any other engine you can name, it will not add to the pressure of that incoming air. Mixture rotation speed, forward flow speed, and flow pressure are all good--within the mixing tube. When the air gas mixture is dumped into a burner's flame retention nozzle, all those good things need to be modified; or they go from good to bad. Internal vanes and/or a longer mixing tube can handle excess spin and forward velocity. However all there is to handle flow pressure is the low pressure area created  in the flame retention nozzle; it is a fairly weak break.

    While a certain amount of increased pressure is needed to keep the flame from burning back into the mixing tube, that is already provided by the fuel gas stream. Added pressure in the inducted air will quickly overcome the flame nozzle's limited ability to keep the flame from being blown off the burner's end. Vortex action provides the secondary engine you want, without adding ANY additional air pressure in the mixture flow.

[Mikey98118]

57 minutes ago, Mikey98118 said:

rectangular side air entrances, which provide spin and induction at the same time.

Eek! Not so; they provide spin. The gas jet provides air induction.

[DennisCA]

Man it's beyond frustrating how impossible it is to find black iron fittings or pipes here. At least online.

[Mikey98118]

Why not use something else then? I prefer stainless steel pipe and tubing. If you had to, you could make a mold, and cast the entire burner from refractory. The only limits or in your mind.

[Mikey98118]

Years ago, a guy somewhere in Central America asked me if I thought my burners could be made like pottery, I answered "no" because the very end of the burner would probably shatter from the stress of thermal cycling in a forge. But on reflection, most of the burner could be made and fired as pottery, and the flame retention nozzle could be cast from refractory. So, you see that what I told him was wrong.

All of us on IFI have had to overcome limits of one kind or another, to produce a forge; mostly, mental limits

[Mikey98118]

Beware pipe fittings with misaligned thread, which often end up badly out of axial alignment with the mixing tube. Whether you are using a pipe reducer to build a linear burner, or a "T" fitting to build a Frosty burner, take a few minutes to lightly screw the parts together and have a close look at them, before purchase; it can save you a lot of frustration later on.

[Mikey98118]

Soldering and brazing of gas assemblies and mounting plates on burners

When affixing a nut on the underside of a mounting plate, so that a threaded gas tube can be moved back and forth in it (to adjust the “sweet spot”), when fine tuning the burner, you may come up against the need for multiple grades of silver braze fillers. The concern is that, when brazing or soldering more than one part in a small area, you can undo all your work on the first join, when making the second one; such as when brazing a mounting plate onto a funnel flange, after first brazing a nut on the plate’s underside. This is just one example of why silver braze filler wires, rods, and plates come in five main alloys, by melting temperature, which are typically: “IT” (1490 °F) “hard” (1450 °F), “medium” (1360 °F) “easy” (1325 °F); and “extra easy” (1207 °F). Melting temperatures of brazing alloys change quite a bit depending on manufacturer (extra easy can have melting temperatures between 1270 °F and 1207 °F). The melting point of pure silver is 1763 °F. Sterling silver wire melts around 1640 °F; both can be used as brazing filler. You can also use solder to extend your temperature ranges, and beyond that, parts can be glued together, to avoid melting the solder. Let me make this clear. Smart builders cheat whenever they can. Got it?

The melting point of zinc is 782 °F. Commercial silver braze filler alloys are combinations of silver, copper (to increase alloy strength), and zinc (lowers melting temperatures). Silver solder can be melted with a torch, in a bowl crucible, with borax powder added, and then small zinc sheets included into the pool, to make an even lower melting temperature filler. Dump the pool into a pure carbon container, and pull it out after it freezes into a solid, but while still hot; then, dunk it in water. Hammer your ingot into filler rod or sheet, to suit.

Why so may choices? Mounting plates aren’t the only case where multiple small parts may be joined together. You will want to hook the gas assembly up to a fuel hose via some kind of connector. Fan powered burners have gas assemblies that may need brazing and soldering in close proximity to each other.

Pickling: Fluxes can cause oxidative damage to your parts if they aren’t removed after brazing. Some fluxes can be removed with water and brushing; others are removed, and deactivated by “pickling.” Since stainless-steel fluxes are combinations of mineral salts and powerful bases, pickling solutions are made up of various different acids and water. What kind of cleaning and/or pickling solution is to be used should be mentioned on the flux container.

[Mikey98118]

Yellow Ochre is a mineral used as a paint color and pottery pigment; it is also mixed with water, and coated on metals to work as an anti-flux, to create a physical barrier to filler flow, into unwanted areas, and to help prevent filler from being lost in adjacent areas to an additional join; it is available from Rio Grande jewelers supply for $11. 50, and from several other sources.

[Mikey98118]

 

Flame Retention Nozzles

You can’t go very far along the path of flame intensification without providing an increased opening diameter at the mixing tube’s end, as a form of flame retainer; thus, their name. As the mixture exits the mixing tube, and enters the nozzle, it expands, creating a low-pressure area, which slows the exiting gas/air mixture, and helps ambient air pressure to keep the flame on the burner’s end. Furthermore, this low-pressure area also helps to keep the flame from burning back into the burner’s mixing tube; parallel nozzles with spacer rings create stronger eddy currents than tapered nozzles that have a much smaller step area (created by the mixing tube’s wall thickness only) Parallel nozzles, with their greater step width, also have greater resistance to burn-back than tapered nozzles.

    The first hobby venturi burner nozzles used a taper to increase the area of their cross-sections, providing a low-pressure point, designed to help glue the flame unto the burner’s end; otherwise, it blew off the burner, and thus blew itself out rather frequently. Such nozzles did a fine job of stabilizing venturi burners, but that is all that they did. The typical diameter increase on a tapered (“flared”) nozzle for a 3/4” pipe burner is 1/8”, and runs for about 1-1/2” of a typical stainless steel nozzle’s 2-1/2” length, but far greater increases can be seen on commercial burners in recent years. By varying the amount of the nozzle’s overhang, beyond the mixing tube’s end, you can fine tune the nozzle’s effective shape (its length to width ratio) to the mixing tube’s flow speed.

    If you put a 1/16” thick spacer ring inside the back inch of an oversized SS pipe, you would create a similar ratio in a simple shape that is easier to build, but without any performance jump. Some older burner designs are now using this very scheme.

Supposing you use a one-eighth inch thick spacer instead of one-sixteenth? The nozzle has now increased another eighth-inch overall, and no longer works properly. You have created too strong a breaking effect for the old burner’s flow velocity to balance. On the other hand, the greater breaking effect is needed on a burner with a higher mixing tube speed. Nozzle diameters change to suit burner design. Exact amount of increase between mixing tube ID and nozzle ID is also determined by overall size. The burner’s performance will increase along with the nozzle’s internal diameter up to the point that it gets too large; even an extra 1/16” can completely ruin a 3/4” burner’s performance, on some burners—not on all. Use this information to suit the nozzle to the burner.

[Mikey98118]

The red streaks that shoot forward in hot gas flames from super-heated stainless-steel flame retention nozzles are from nickel ions, as the nozzle is slowly being oxidized away. There are spikes from green light, on through the blue range, and well into the ultra violet range; but they are lost in the blue background of the flame’s color. But there is also a spike at 650 manometers (red light), which stands out from that blue background. You get a lot more streaks from #304 S.S., than from #316 S.S., because the #316 alloy contains molybdenum, which slows down its oxidation; this is also the reason why #316 flame retention nozzles outlast those made of #304.

RETRACTION

But what I previously thought and taught about the red shift in highly oxidized flames being due to super-heated oxygen molecules is wrong, because its red spike is in the infrared range (not visible). So, what causes this red shift? I’ve no clue.