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Ornamental  & Miscellaneous Shop Talk Fabricator Official publication of the National Ornamental & Miscellaneous Association Is your stainless rusting?

n contamination is not the only cause of rust problems. In This this article, we explore additional bank sources of as well as depository is showing sig- solutions. nificant rust stains. See the related article on page 46 to learn how the By John Campbell author helped to restore the metal to look Like the words “cruel kindness,” stainless like new. steel appears to be an oxymoron, especial- ly when NOMMA members relate some of their experiences with staining and rusting on fabrications like stainless gates and handrails. The causes are often puzzling. Why does a stainless steel tubular handrail show a pattern of rusting like a barber- What makes

an alloy stainless? For your pole? Why does a stainless steel gate information exposed to a atmosphere bleed An iron base alloy with 12 percent or  rust? What caused the rust on a stainless more is considered a stainless steel bicycle rack? To find the answers to steel. Although there are five types of About the author: Mr. these questions would take the sleuthing stainless alloys (ie. ferritic, martensitic, Campbell was skills of our finest forensic detectives. austenitic, precipitation hardening, and formerly self- duplex) the austenitic AISI 300 series employed for 26 years with Two major alloys make up over 75 percent of all cor- Castings possibilities rosion resistant applications from Consultants The experts on stainless alloys conclude handrails to commercial kitchen appli- Inc. and is now that there are two major reasons for rust- ances. a highly regarded industry like stains on stainless steel. Surface con- Two chromium-iron base alloys with author and senior writer for Fabricator. He is based in the tamination with iron or steel dust particles chromium contents of over 12 percent are suburbs of Milwaukee, WI. is the first possibility. Fabricating steel and the ferritic and martensitic. Both are mag- What is ? stainless in the same area is just one of netic; and the martensitic alloys like AISI Passivation is the oxidizing many sources of this contamination. The 410 can be heat treated, hardened, and process that causes the other cause is penetration of stainless tempered to the desired balance of ductili- chromium in the stainless to steel’s passivated surface by halogen . ty and hardness. Knives in quality stainless combine with available oxy- These complaints occur with installations tableware are commonly AISI 410. They’re gen to form a chromium film. of AISI 304 stainless near seawater or magnetic; whereas, spoons and forks around a source of halogens like winter stamped from AISI 304 are non-magnetic. Tip: A way to prevent rusting around heat-affected zones, street or chlorine treated swimming Adding nickel to chromium-iron alloys called sensitization, is to fab- pools. A candid explanation to a customer produces an austenitic grain structure. ricate with alloys of low car- who wants stainless steel, thinking they’re The combination of 18 percent chromi- bon content or alloys with buying the ultimate insurance against cor- um-8 percent nickel in the AISI 300 series carbon stabilizing elements rosion, may be easier before the purchase is typical of these stainless grades. AISI like and niobium. than after. 302 and 303, both of which have carbon

Reprinted from January/February 2005 n Fabricator 1 contents of .15 percent max., are less Although passive films form on stainless spontaneously corrosion resistant than AISI 304. in the presence of , some fabricating specifications mandate Additions of sulfur and phosphorous chemical passivation in an oxidizing medium like nitric acid. produce the free-machining grade AISI 303. The more popular alloys for sheet, tubing, and pipe are AISI 304 and 316 (.08 percent max carbon). um, forming chromium-carbides in Halogen salts undermine For fabrications where intergranular the heat affected zone (HAZ). That passivation corrosion is a concern, lower carbon prevents chromium from developing are one of the most alloys (.03 max), like AISI 304L and the surface that make the common elements in nature, and that AISI 316L, are available. With only 5 alloys stain resistant. whole family of halogen salts, identi- percent to 10 percent content The condition is called sensitiza- fied by the suffix ine, like chlorine, these alloys in the austenitic annealed tion. A solution annealing heat treat- are active , good current carrying condition will be non-magnetic. ment will restore the free chromium; and highly corrosive to One caution: do not correlate but that’s not always practical with stainless steels. These salts will even magnetic permeability with corrosion large, rangy fabrications that will destroy Teflon. Stainless steels are not resistance. Bend an elbow in AISI 304 warp at high temperature. Another going to resist staining and rusting in stainless and the bend becomes mag- way to prevent sensitization is to fab- saltwater atmospheres without peri- netic. Cold working changes the grain ricate with alloys of low carbon con- odic cleaning and passivation. structure, but not the chemistry. To tent (.03 percent max AISI 304L) or Although passive films form on retain the former austenitic structure alloys with carbon stabilizing ele- stainless steels spontaneously in the requires a solution anneal heat treat- ments like titanium (AISI 321) and presence of oxygen, some fabricating ment (1895° F for 304 and 2003°– niobium (AISI 347). Sensitization specifications mandate chemical pas- 2048° F for 316 plus a rapid quench), explains why rusting on stainless steel sivation in an oxidizing medium like not too practical for a large fabrica- fabrications is first noticed around nitric acid. Without a steady supply tions. ASTM A-511 covers seamless the welds. Those heat affected zones of oxygen stainless steels will corrode. stainless tubing for general mechani- may be depleted of chromium. In halogen salt solutions like salt cal applications. Specifications for Normal atmospheric environ- -nickel alloys such as low carbon stainless grades are cov- ments are not severe enough to Monel are more corrosion resistant ered by ASTM A-312. Any fully cause intergranular corrosion in a than stainless steels. Engineering annealed specification will be more heat affected zone; but rusting will compromises are generally a matter expensive. occur adjacent to the welds. When of cost. While on the subject of magnetic and if intergranular corrosion does permeability, be aware that stainless occur, the welds fall away from the How does finish steel casting alloys known as CF-8 corroded HAZ like wads of chewed affect staining? and CF-8M, the cast equivalents of bubblegum. Several NOMMA members men- AISI 304 and 316 respectively, may tioned that surface finishes affect the have magnetic properties. The What does resistance of stainless steels to stain- chemistries of the cast stainless alloys the nickel do? ing. David Lazarus at Polished Metals are not identical to the wrought Nickel added to the chromium in Ltd. said that 85 percent of their alloys; their chemistries are adjusted the 18-8 stainless alloys stabilizes the stainless steel sales are shipped with a to enhance fluidity. Casting grades austenitic structure and helps #8 mirror finish, which could can have a ferrite content up to 15 improve the passivity of the alloy. In increase the price 33 percent to 40 percent and be within alloy specifica- the presence of oxygen, the stainless percent over a #4 satin finish. He tion. In addition, beware of checking steels of the 300 series spontaneously believes that the smoother finish is alloy inventory with a magnet. Non- develop a chromium oxide film. The easier to maintain, which makes magnetic alloys like Monel (70 Cu-30 oxide films on metals like aluminum sense. Rust stains on a satin finish Ni) become magnetic in unheated and silver are visible. However, tend to follow the direction of the northern warehouses when the tem- chromium oxides are not visible on grinding. One tiny spot bleeds a perature drops below zero. stainless. brown streak an inch long in either For most fabrications AISI 304 is direction following the finish crevice. How welding changes the stainless alloy of economical John O’Reilly of MMF Architectural chromium content choice. To enhance the alloy’s resist- agrees, pointing out how depositions One of the problems with welding ance to pitting, molybdenum is of salt are trapped in the crevices of a stainless steel stems from the carbon’s added. Alloys with moly additions are brushed finish. In the design stages affinity for chromium. Under welding AISI 316 (2–3 percent) and AISI 317 alloy selection and finish are two temperatures carbon will absorb up (3–4 percent). Both are more resist- important considerations. Wherever to 17 times its own weight in chromi- ant to halogen salt exposure. salinity is part of the environment,

2 Reprinted from Fabricator n January/February 2005 Blasting stainless with glass beads or silica sand previously used heat into the surface that the alloy’s to blast steel will impinge surfaces with iron. Any used on grain structure changes, destroying its steel will also impart iron to stainless. natural ability to passivate. Less hazardous solutions of citric acid have successfully removed rust stains. The higher polished surfaces O’Reilly recommends AISI 316 stain- less steel surfaces. clean better than those with deeper less instead of AISI 304 along with a One time we vacationed on the grinding marks. (See article on pg. mirror finish. island of Vieques, close to Puerto Rica. 46). Although nitric acid and hydro- The villa, where we stayed, stood high fluoric may impart a more lasting Surface on the Atlantic side of the island with passivating film on stainless, it’s more contamination stainless steel handrails above the hazardous to handle. Iron or steel particles that accu- rocks. The railings were badly rusted mulate on a satin finished handrail because the maintenance crew cleaned What’s the difference between are going to rust when exposed to them with steel wool pads. passivation and ? the atmosphere. For this reason, fab- In tropical climates, under a blis- Passivation is the oxidizing process ricating stainless steel should be done tering sun, corrosion accelerates rap- that causes the chromium in stainless in an area separate from grinding idly, whether it is galvanic, crevice steel to combine with available oxy- and welding of alloys. The air corrosion or intergranular. As a gen- gen forming a chromium oxide film. in a plant carries metallic dust parti- eral rule, the rate of corrosion dou- It can occur naturally or with the cles. A finished stainless assembly bles for every 18°F increase in tem- help of an oxidizing agent like a solu- will often have a static electric charge perature. Despite the heat, stainless tion of nitric and hydrofluoric acids. that attracts and pulls plant dust steel alloys like AISI 316 with a mir- Citric and phosphoric acids also have from the air. ror finish, regularly cleaned with passivating affects. Kane Behling, supervisor of the plain water, will hold up fairly well in Pickling is used more often to polishing department at R & B a Floridian atmosphere. remove scale and surface contamina- Wagner, cited an example in his own tion like the chromium depleted backyard of how iron dust travels. How to restore a layer of stainless steel; yet, it may He lives in a suburban community rusted surface? have passivating affects as well. in close proximity to a few manufac- To restore a surface that will passi- Pickling is aggressive enough to turing plants. “I can’t walk across vate spontaneously, clean the surface remove free iron that has begun to wet grass on my lawn in my stocking using a mild detergent and warm rust; whereas, spontaneous passiva- feet without collecting rust on my water. If degreasing is necessary, use a tion will not remove rust or stains. socks.” non-chlorinated solvent. Many clean- Pickling procedures are outlined People, who should know better, ers and bleaches contain chlorides under ASTM A380. make mistakes in handling stainless which will leave a residue in the steels. A foundry producing both car- crevices of polished surfaces. Where to place bon steel and stainless once cleaned There are commercial prepara- the emphasis their stainless steel castings in a tions, both liquids and gels, for In the care and maintenance of Wheelabrator, a device that uses steel removing rust from stainless steel. A stainless steel good house keeping shot. Stored outdoors, those castings hot pickling solution of nitric and practices are the rule. To achieve bled rust like they were . hydrofluoric acid (10 percent nitric maximum corrosion resistance it’s Blasting stainless with glass beads or and 2 percent HF) at 120ºF to 140ºF important to use the alloy that best silica sand previously used to blast is the most effective way of removing suits the environment. The frequency steel will impinge surfaces with iron. surface contamination; but, it’s not and cost of cleaning stainless will be Any abrasive used on steel will also recommended unless you have the lower than for most other alloys, off- impart iron to stainless. tanks and the safety equipment to setting the higher cost of the product. Although suppliers like Polished handle it. In diluting acids of any Usually, a detergent and warm water Metals ship their stainless steel prod- kind, never pour water into the acid. will restore a passivated surface. In ucts with a vinyl , dragging Add the acid to the water. Outside the example of the all-night deposito- stainless tubing or pipe across steel jobbing sources, who do both pick- ry (see article at right) rust stained by storage racks is another source of ling and electro-polishing, often han- street-salts and automotive exhaust, a iron contamination. Most people in dle large fabrications. citric acid cleaner removed the stains the business know this, but new Light grinding with clean aluminum and restored passivation. In selling employees are often unaware of the oxide is effective for removing stainless steel fabrications the manu- problem. More important, people in rust stains. Pickling gels are marketed facturer has the obligation of explain- charge of maintaining properties are to remove weld stains. With belt ing to the customer how to maintain often unaware of how to clean stain- sanders it’s possible to put so much the product’s lasting beauty.

Reprinted from January/February 2005 n Fabricator 3 Focus on Alloys Cleaning Stainless Steel

Before and After

A test on a nearby night deposit box yields positive results.

Kane Behling, the polishing supervisor at R & B Wagner, The top section of the depository appeared to have a #4 pointed out that his bank had a stainless steel all-night finish, unidirectional, horizontal to the driveway. That sec- depository that was a good example of stainless steel rusting. tion showed the worst brown staining, stains that ran per- “It makes we sick, every time I visit the drive-through pendicular to the finish. The depository was installed flush (and see that),” Behling explained. “Go, look for yourself.” to the brick masonry of the bank, which made me wonder Sure enough, the depository Behling spoke of showed if there was some residue from the masonry that ran onto corrosion some authorities describe as tea-stains; others the top panel. Masons commonly use a refer to the discoloration as rouging. Having read a little solution to clean cement-work; and stainless steel doesn’t about products touted for cleaning, I decided to try one. take kindly to reducing acids like HCL or any Getting a sample product for testing was a lot easier than influence. That’s possibly one reason for the top section of getting the bank’s approval. the depository showing the worst staining. Bank managers are skeptic when someone volunteers to I finished spraying in less than a minute. Making an clean their bank depository. Doing it for free fueled their allowance for the cold temperature, I ate breakfast at a skepticism. To obtain permission required a few telephone local restaurant, allowing the acid solution a good half- calls out-of-state, a discussion with their contract mainte- hour to work before rinsing the surface. nance firm, and finally, notification of the local police. I I returned at 7:35 a.m. and sprayed water on the depos- didn’t want to be intercepted by an officer itching to collar a itory, then wiped it as dry as possible with a clean cloth. bank robber or interrupted while photographing and clean- The stains on the top section were less obvious, but not ing a money-drop before the bank opened. completely removed. The more highly polished side panels The Saturday I chose to test a citric acid cleaner turned and recessed surfaces cleaned beautifully, which confirmed out to be a rainy morning with a chilly temperature of 39º F David Lazarus’ belief (Polished Metals Ltd.) that mirror , not the best temperature for testing any acid cleaning com- finishes are easier to maintain. I sprayed the top section pound. Fortunately, the all-night depository was under roof, again with the acid solution and using a dry Scotch-Brite® adjacent to the drive-through window. pad applied a little elbow-grease. Satisfied that the deposi- Lee Kremer, President of Stellar Solutions in Algonquin, tory looked 100 percent better than before, I took some IL, supplied a spray bottle of their CitriSurf 77 Plus®, final photos and left the bank before it opened. which he recommended for the removal of rust stains on The Citri-Surf 77 Plus®, one of many such products mar- stainless as well as for passivating the surface. At 7 a.m., keted by Stellar Solutions, did a quick, effective cleaning job. before turning our clocks back in late October, the ambi- The product meets the requirements of ASTM A-967, which ent lighting was poor. Nevertheless, I took several photos replaces QQ-P-35C, for cleaning and passivating stainless of the depository, a product of the Hamilton Safe steels. A similar cleaning should be performed two or three Company. After donning a pair of latex gloves, I sprayed times a year to maintain the stainless steel brightness. the entire stainless surface with the citric acid product. —John Campbell

4 Reprinted from Fabricator n January/February 2005