TLC for Stainless
Computer users envy the guy with a faster processor, car lovers envy anything with more horsepower, woodworkers want a larger table saw. And homebrewers aspire to owning as many shining stainless-steel vessels as possible. Stainless-steel kettles with stainless immersion coolers, stainless hot liquor tanks, stainless mash tuns and stainless fermenters. Is this madness, envy or a sensible aspiration?
Stainless is the homebrewer’s metal of choice — not because it is the perfect material; it isn’t. Silver, aluminum and copper all conduct heat better. But stainless steel shines because of its invisible barrier to rust. Iron and steel corrode in the atmosphere; they rust, forming big flakes of red-orange oxide. But when chromium is added to steel, an invisible “passive” film, only a few molecules thick, covers the surface and prevents rust. This makes it as corrosion-free as gold.
So what, exactly, is stainless steel? Stainless, unlike mild steel, contains only a bit of carbon and 10 percent or more chromium by weight. It’s the surface film of chromium that resists oxidation and makes the material “passive” or corrosion-resistant. If this oxide film is damaged — mechanically or chemically — it is self-healing in the presence of oxygen. So stainless steel resists rust and will continue to do so, if treated correctly. There are other reasons why stainless is the metal of choice in the food and beverage industry, but the most important is that it can be easily cleaned by almost any method.
There are more than 60 grades of stainless steel, each with a special purpose. The divisions are centered around the alloying elements that affect the group’s micro-structure. The 400 series of metals — 405, 409, 430 and so on — are magnetic and don’t weld well. They’re used in knifes, surgical instruments, bank vaults and automobile exhausts.
Homebrewers are concerned with stainless steels that have had more chromium and some nickel added. These metals are used for kitchen sinks, food-processing equipment, restaurant food-preparation areas, ovens and chemical vessels. The 300 family (304, 310, 316, 317) are also the stainless steels used for brewery equipment. The 304 is the most commonly used, 310 is designed for high temperature, 316 offers improved corrosion resistance and 317 has the best corrosion resistance. Most high-quality brew kettles are made of 304 and 316 is the best steel for fittings and tubing. Often you’ll find stainless-steel cooking pots, even big ones, marked with 18/8 or 18/10 on the bottom. This is the alloy content — 18 percent chromium and 8 percent or 10 percent nickel. Both are good quality.
According to the Specialty Steel Industry of North America (SSINA), a trade association, stainless steels have some limitations: The maximum temperature under oxidizing conditions is 925° C (1695° F), and they are suitable only for low concentrations of certain very powerful reducing acids. Neither of those drawbacks affects homebrewers. What is important to us is that in crevices and shielded areas, there might not be enough oxygen to maintain the passive film. Then corrosion might occur. That means when adding a nipple or coupling, or at any joint in the metal, you could actually experience rust! Another significant problem is that very high levels of halide ions, especially the chloride ion, can break down the passive surface film. That means bleach is a potent enemy of stainless steel.
Caring for your stainless:
Even an inexpensive stainless-steel brew pot costs nearly $100. If you have larger pots, like those manufactured especially for homebrewers by Polar Ware, you’ve invested more than $100. And a fifteen-gallon, three-vessel system? Even if made from three legally obtained kegs, you still have at least $300 invested by the time they are cut and equipped for brewing. Proper cleaning and care protects your investment and ensures successful brewing.
Another reason for keeping your stainless steel stain- and corrosion-free is iron. Rust is iron and stainless steel contains more than 70 percent iron. Iron is not good for either your beer’s flavor or your yeast’s health.
Caring for your stainless steel is not difficult. Ordinary household soaps and detergents can do most of the necessary cleaning. For heavy-duty grime, common cleaners like Bar Keeper’s Friend, Zud or even Comet can remove most soils. One of those woven nylon scrubbers will loosen almost any soil.
Problems can occur when homebrewers use chloride-based cleaners, like chlorine bleach. Bleach is incorporated into many cleaners — and used by many homebrewers for sanitizing. Chloride ions will attack your stainless steel and remove the invisible chromium oxide shield. The first solution is the easiest: Don’t use bleach on or in your stainless-steel utensils. If you must, rinse repeatedly and air dry.
Also, don’t allow any cleaners to dry on the surface of stainless-steel utensils or pots. Rinse thoroughly after use. Don’t let chlorinated sanitizing solution sit in your kettle; it will attack the surface right at the liquid-air boundary. Don’t clean with steel wool pads; they leave steel particles embedded in the surface that will become rust. Once surface rust has breached the protective chromium layer, the iron in your stainless steel vessel will itself rust. Use Scotch Brite scrub pads.
For more serious cleaning, rely on products like Five Star Chemical’s PBW (Powder Brewery Wash), which does not contain chlorides. After welding or brazing be sure to clean the surface and repassivate by drying in the air.
Keeping stainless passive:
We keep mentioning “passivating” or “passive.” All that means is that stainless steels are naturally resistant to rust, similar to the so-called “noble” metals: gold, silver and platinum.
Your new stainless vessel arrives with its invisible chromium surface layer — the passive surface — intact and gleaming. If you create a deep scratch, do some welding or let beerstone build up (beerstone is a combination of organic compounds bound to oxalates of calcium and magnesium, all found in your wort), the passive layer could lose its integrity. Corrosion gets a great starting place under the beerstone because there is no free oxygen to maintain the passive chromium oxide. If those brownish or whitish deposits on the bottom of your brew kettle aren’t removed, you could develop severe pitting underneath them.
Commercial manufacturers quickly clean stainless steel by dipping it in nitric acid to remove all traces of free iron. This absolutely not a do-it-yourself project. To keep your vessel passive, or to repassivate it, all you need to do is clean it! Scrub your kettle till it shines, rinse it thoroughly and let it air dry for a couple of weeks. The passive layer will form naturally, spontaneously, as long as there is oxygen.
If you have severe cleaning problems, Five Star makes Acid #5, a mix of nitric and phosphoric acid. Use it according to directions, by circulating a dilute solution and then air drying. That’s as close as most homebrewers should get to professional passivation.
Working with stainless steel:
Now that you know a bit about stainless steel, perhaps you’d like to add a ball valve or thermometer or sight glass to your brew kettle. None are impossible projects for any competent do-it-yourselfer.
Working with stainless steel is no different from working with any other metal. You can cut it, grind it, drill it, solder it or weld it. However, most tools used on stainless should never be used on any other material — not aluminum and particularly not on mild steel. Steel will contaminate your grinder(s) and metal brushes and in turn contaminate your stainless. It’s not that bits of mild steel will immediately cause a failure in the stainless, more that molecules or particles will imbed themselves into your work and rust will form.
This means that you must have separate tools — wire brushes and grinding wheels in particular. What about separate drills, shears or files? That’s not practical, and those edges that have been drilled, cut or filed can be ground or brushed to remove stray particles of mild steel, according to the experts at the SSINA. Once mechanically cut, stainless steel should naturally form its protective oxide coating.
The entire 300 family of stainless steel is very tough metal. It is highly alloyed and the process used to form it into shapes also hardens it. If you won’t take my word for it, try to drill a hole into 1/8-inch stainless sheet stock.
Stainless steel has a high level of chromium and can’t be cut with simple oxygen-acetylene cutting torches, due to the very high melting point of the chromium oxide that’s formed when heated. High-speed abrasive wheels (die cutters and die grinders) can be used for any necessary cutting of sheet, thin plate and bar material. With good technique and practice, even large-radius curves can be cut.
Abrasive cutting generates heat. So take care not to overheat the cut edge. Always use fresh or dedicated abrasive discs or wheels. And always observe safety precautions like wearing gloves and goggles and removing watches, rings, and necklaces.
The best way to cut stainless or any steel is with a plasma arc cutter; it cuts steel using ionized gas, usually ordinary air. An electrical field creates a plasma — a mixture of free electrons, positively charged ions, and neutral atoms — which exists at sun-like temperatures up to 55,000° F. This incredible heat melts metal and the gas jet removes the molten metal.
Plasma arc cutters are expensive and generally not home equipment unless you’re a sculptor or metal crafter. There is some controversy about cutting stainless with plasma arc cutters. Some say the spray of molten metal adheres to nearby metal, like the sides of your freshly cut kettle or keg. Others insist this is not true. In any case, protect any exposed surface with a noncombustible covering.
Assuming you consider yourself handy with tools, there are some special or different tools you will need for working with stainless steel.
Your stainless tool box: …things that drill, cut, grind…
Drills and a drill motor: The motor should have a low range of under 1800 rpm. While wood cuts best at high rpm, steel cuts best at 500 to 1,000 rpm. Because stainless is harder than mild steel, your drill bits should be titanium-coated or carbide. Unfortunately, they are more expensive than common high-speed steel (HSS) bits — which will work in a pinch on thin stock. But forget trying to drill through a converted keg with HSS bits. Buy individual titanium drills; we suggest 1/8-inch for pilot holes ($3 for two) and larger bits like 7/8-inch ($18) as needed.
Hacksaw: An ordinary hacksaw can cut stainless steel. Use a 32 tooth-per-inch (tpi) blade for thin stock up to 16 gauge (0.062 inch) and 24 tpi when the stock is thicker — between 1/16-inch and 1/4-inch — as with a coupling. Cut on the “push” stroke and do not drag or slip the blade on the reverse stroke. Instead lift it clear of the work.
Jig saws and “Sawzall” reciprocating saws also can cut stainless and require less effort. Again, use 32 tpi blades for thin stock and 24 tpi blades for thicker. Jig saws cost $30 to $150. Genuine Milwaukee Sawzalls are around $170; other reciprocating saws are $40 and up. Blades like RemGrit (carbide coated, 6- and 8-inch) cost $5 to $7. Ordinary 24 tpi metal-cutting blades are $10 for ten.
Files: A single-cut or double-cut mill file costs $5 to $7. Longer is better and you’ll need to have several diameters of round files and half-round files.
Grinders: Dremel tools, pneumatic and electric die grinders, bench grinders and angle grinders can all perform the grinding chore. A bench grinder will cost $35 to $100; die grinders are $30 to $100 with pneumatic (air) grinders lowest in cost; angle grinders are $10 to $79; Dremel tools cost $30 to $50. Remember to purchase cutoff and grinding wheels reserved just for stainless.
Plasma arc cutters: Though you can use it for welding or brazing, you cannot cut stainless steel with a regular oxy-acetylene torch. For serious cutting, you’ll want a plasma-arc cutter that generates up to 55,000° F heat. SSINA says that these “thermally cut” edges may be changed chemically and metallurgically. They add that “dressing is necessary so that impaired areas of mechanical and corrosion-resistant properties are minimized.” In other words, grind it clean and let nature repassivate the surface. You’re looking at $720 for an HTP MicroAir 125 with a built-in air compressor. Other manufacturers charge more.
Your stainless tool box: …things that solder, braze, weld…
Acetylene-air torches: These are familiar tools to plumbers. Hotter than propane or MAAP (methlacetylene gas; it burns hotter than propane), they use acetylene gas and air. Acetylene-air torches would provide plenty of heat for soldering (400° to 500° F) and perhaps enough for brazing (1000° to 1400° F.) They’ll cost $100 to $190 and require purchase of an acetylene tank for another $60 to $200.
Oxy-acetylene torches: These cost anywhere from $90 to $400 new. This a great way to start joining metal. I recommend a kit from Henrob (Henrob 2000) because of its versatility. You can weld copper, aluminum and steel, and braze (but not weld) stainless steel and aluminum. The set comes with cutting and acetylene-air soldering attachments. Its special design operates similar to the shielding gases of MIG and TIG (for more on these acronyms, see below). A #1 tip will braze stainless like a dream. If you purchase oxy-acetylene welding equipment you’ll have to buy tanks of gas for $60 to $200 each.
GMAW or MIG: Gas Metal Arc Welding or Metal Inert Gas welding (also called “squirt” or wire welding) is a good bet for stainless. MIG gets the “inert gas” tacked onto the “metal arc welding” name because a continuous flow of inert gas — argon, carbon dioxide, helium, hydrogen or a mixture — surrounds the weld. A good small unit requires 220V/30 amps and will cost upwards of $700. Some good 110V MIG welders, intended for sheet metal only, will work on 110V/25 amps and cost as little as $409 (the HTP America MIG 120) and will weld metal to 1/4 inch.
GTAW or TIG: This stands for Gas Tungsten Arc Welding or Tungsten Inert Gas. If you want to play in the brewhouse and make pretty toys, TIG is the holy grail. Learning TIG welding means school and practice. And until I researched this article, I thought it meant spending $1,200 minimum. Surprise! HTP America makes a tiny TIG welder that costs $400 (plus $60 to $160 for gas).
A beginners’ guide: …how to join stainless steel…
Stainless steel can be mechanically fastened with fasteners, such as nuts, bolts, washers and screws. Be sure these fasteners are also made of stainless, to prevent corrosion. Stainless can also be soldered, brazed or welded. Each method has its own requirements, strengths and weaknesses.
Soldering:
Soldering is a low-temperature joining process using an alloy — usually a mixture of tin, lead, antimony and sometimes silver — with a melting point around 500° F. Metal surfaces are usually dirty, so a cleaning mixture called “flux” is applied before heating. Flux melts before the solder and aids in its flow.
Stainless steel can be easily soldered with familiar tools and techniques. All you need is a heat source, flux and the correct solder. All surfaces in the joining area must be cleaned thoroughly with a rag and any good solvent. If the surface is smooth, roughen it with sandpaper. Never use steel wool. For a heat source, a powerful soldering iron will do for joining small plates together, and perhaps even adding a fitting.
Stainless conducts heat more slowly than copper or steel and the iron should be held in contact with the joint longer. This ensures solder penetration into the joint. Heat is concentrated at the soldering point and stays there longer. So use a somewhat cooler iron; it will be more effective.
Silver-soldered joints are very strong in terms of sheer (think right-angle forces like cutting) but do not have the same structural strength offered by welding. The metal flows into and between surfaces, so if you are joining a 3/4-inch nipple to a thin 16-gauge pot, the only mechanical contact is that hair-thin 16-gauge circle. Harris Welco, a welding-supply company, recommends two of its products for silver-soldering stainless steel, StayBright (430 °F melting point) and StayBright 8 (535 °F). Both are rated by the NSF (National Sanitation Foundation) for food-service use and require Stay-Clean liquid flux. Our limited experience says silver solder is effective, but may crack after a year or two of homebrewing service.
When soldering stainless you need adequate heat; MAAP gas might work, acetylene-air or oxy-acetylene is preferred. The surfaces must be absolutely clean and fluxed. If the flux flows and the solder doesn’t, don’t add more heat. Stop, cool the surfaces, reclean and flux again. It is surprisingly easy to overheat the metal; then it gets brittle and cracks or breaks.
Be sure the flux is a phosphoric acid, not a chloride-containing flux. Phosphoric acid fluxes clean up with water and are active only at soldering temperatures, 350° F to 550°F.
Brazing:
Brazing is a higher-temperature metal-joining process. A brazing flux is applied to a filler rod of brazing metals (usually brass with other alloys, like silver) to aid in cleaning the surface chemically (oxide removal). The metals to be joined are heated to a glowing-red temperature and the brazing rod fills the gaps between the pieces. The melting point of the filler metal is typically above 840° F but less than the melting point of the metals being joined. Brazing is our choice for homebrewers as it is simple, more people have the equipment and skills, and the cost is low if you own the equipment.
Harris Welco recommends a brazing rod containing 45 to 56 percent pure silver, plus copper and nickel. It produces a connection (a fillet) comparable to professional welding.
Harris Welco’s SafetySilv 56 is NSF approved, and with stainless steel you want to use the Stay-Silv Black Flux. Regular white flux is for lower-temperature applications; stainless takes more heat to braze than copper or steel and the flux has a tendency to burn up because its active range is lower. Black Flux has a greater range and the alloy will “wet out” easily; it melts, cleaning and protecting the metals to be joined and promoting a good bond. SafetySilv 56 is a low-temperature brazing alloy — 1205 °F melting point — making it easy to work with.
Welding:
Welding actually melts both metals to be joined, creating a uniform union. (The melting for point for various metals ranges from 600 to 3300 °F; 304 stainless melts at about 2600° F). Welding is the skill that separates normal homebrewers from really crazy ones. Why crazy? An hour of welding time at a good welder’s shop is less than $50 and could encompass 5 to 10 projects if you’re organized. Or the cost might only be a couple of cases of stout.
Learning to weld will cost you a term’s worth of evenings, $40 to $200 in course fees, plus another $40 to $300 in lab fees, tools and specialized clothing. Then there’s another cost for equipment. But if you can learn to weld, do. You’ll never regret it.
Most trade schools and community colleges spend lots of time teaching gas and stick welding. But you cannot weld stainless with oxy-acetylene equipment and you can’t weld thin stainless with stick and a buzz box. You must have either GMAW or GTAW, also known as MIG or TIG to most of us. If you have no welding skills, MIG is the easiest to learn. TIG more closely resembles the skills of traditional welding and is by far the most difficult skill to acquire.
Stainless School: Welding 101
Whichever welding method you choose to learn, remember that stainless steel conducts heat slowly and concentrates it in the weld zone. Chill bars (large chunks of similar-shaped copper plate) will help minimize heat-produced distortion.
To prevent internal damage (the flow of shielding gasses is only on the outside) you need to flood the opposite side of your weld with a neutral gas like argon. If you’re welding a coupling into a kettle, run an argon gas hose into it, tape the cover on, tape all the cracks and then weld. This will minimize or eliminate oxidization on the opposite side of the weld.
If you’re just beginning to weld, invest in a self-darkening helmet like those made by Speedglas. These wonders transform from the modest filtration of cheap sunglasses to a shade dark enough to allow you to look into a welding arc in thousandths of a second. Why would you spend $100 to $360 on a welding helmet when they’re available for $50? Because it’s safer and simpler. No more nodding your head violently to flip down a heavy helmet. No more striking your arc half an inch off target. The Speedglas 9000V (Variable) we tried could be adjusted from an “off” shade that was just dark enough for gas welding to a shade appropriate for stick, MIG or TIG.
MIG Basics:
As the operator pulls a trigger to start feeding a wire electrode onto a metal surface, a valve opens and flows an inert gas around the soon-to-be-established electric arc. This cools the weld and prevents the creation of oxides — corrosion — in the weld puddle. This permits welding exotic materials like aluminum or stainless steel, where oxides created by breathable air will ruin or prevent a good weld.
Some companies, like HTP America, manufacture small rigs that work on 110V/25 amp current and some can be adjusted to weld even razor blades together. Don’t be fooled by MIG welders that use flux-cored wire exclusively. You can’t weld thin — under 1/2-inch — stainless steel with flux cored wires. Buy one that accepts or requires inert gas shielding.
MIG is the easiest welding to learn and novices can be making clean welds with good penetration (melting the metals together) in a matter of hours. A decent MIG, like the HTP MIG 120, will cost $410.
TIG Basics:
Why is TIG the choice of professional stainless welders? Control. Like MIG, TIG welds are surrounded by a flow of shielding inert gas. Like oxy-acetylene welding, there is a “torch,” an electric one that creates a high-temperature electric arc between torch tip and work surface. Expensive rigs have a foot pedal that controls the heat of the molten welding puddle by varying the amperage of the arc. They also have the ability to jump the air gap between torch tip and work surface for easier arc starting. So the operator has three things to control: foot control, welding rod and torch head.
The inexpensive HTP Invertig 100 ($399) uses a simpler method called “scratch start.” The operator touches the metal to be welded with the tungsten electrode (torch tip). If he’s lucky the arc will strike and the electrode won’t weld itself to the surface. With a constant current, heat is controlled by moving the torch. The electrode is tungsten and is the point current flows from. Tungsten is the chosen metal because it doesn’t melt. To add filler metal an operator feeds bare welding rod into the puddle. This requires skill.
The reason TIG is preferred is that you can weld aluminum, stainless steel or even titanium if you have the skill, the correct gases and the correct filler rod. Smaller, thinner welds put less heat into the welded metal and cause less problems with warping or changes in molecular structure that might lead to corrosion or cracking.
