Monel: Characteristics, Uses and Problems
- CSI Division:
- Division 5 - Metals
- Metal Materials
- Last Modified:
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Margot Gayle, David Look, John Waite. Metals in America's Historic Buildings. Washington, DC: National Park Service, 1995.
L. William Zahner. Architectural Metals. New York: John Wiley & Sons, 1995.
This document includes general information on the characteristics and common uses of Monel and identifies typical problems associated with this material along with common causes of its deterioration.
Monel is a group of nickel alloys, primarily composed of nickel (up to 67%) and copper, with small amounts of iron, manganese, carbon, and silicon.
Characteristics of Monel:
- discovered due to the efforts of Robert Crooks Stanley, who worked for the International Nickel Company (INCO) in 1905
- named in honor of the president of the company, Ambrose Monell; the last "L" was dropped for trademark purposes
- stronger than steel
- resistant to corrosion
- low coefficient of thermal expansion
- highly resistant to alkalis
- improved sanitation
- fairly inexpensive
- can be welded, brazed and soldered
- in the 1920s and 30s, Monel was available in both hot-rolled and cold-rolled sheets; today it is available in plates, rod, bar, tubing, and more rarely in castings
- typical finishes included brightly polished, "hand-forged" black, and two-toned
- in outdoor applications, Monel develops a patina ranging from light gray-green to medium brown
- popular between 1909 and World War II when nickel was diverted to war use and lower priced stainless steel superseded Monel
- available in sheet form for architectural applications
- installed as a sheet roofing membrane in 1908
- in the late 1920s, Monel was began to be used for grocery coolers, countertops, sinks, laundry and food preparation appliances, roofing and flashing
- other uses for sheet and plate Monel were ductwork, flashing, gutters and downspouts, mail chutes, laundry chutes, elevator fittings, lighting fixtures, and skylights
- Monel castings were also popular and included grilles, rosettes, plaques, handrail fittings, molding, pilasters, mullions, and door jambs
- Monel forgings were used for hardware
- Monel bar and rod stock were used for window screens, gates, public directory boards, railings, and divider strips in terrazzo floors
- other common applications for Monel included tie wire for securing lath in plaster walls and suspended ceilings, fasteners for tile roofs and anchors for stone cladding
- Monel began to be displaced by stainless steel in the mid-20th century as stainless steel could produce the same forms at a lower cost (due to use of less nickel)
- a modified, less expensive use of Monel included laminating a thin sheet of Monel to an inexpensive backing material; two examples include Monel-clad steel and Monel-laminated plywood
NATURAL OR INHERENT PROBLEMS
- Surface discoloration: Can occur from exposure to atmospheric conditions
- Pitting: Can occur if exposed to stagnant salt water
- nitric oxides and sulfur dioxides, combined with water, are very corrosive to Monel.
- nitric and nitrous acids can be very corrosive to Monel at room temperature
- hypochlorites are severely corrosive to Monel if not diluted
- Acid and alkaline oxidizing salts, ferric chloride, ferric sulfate, cupric chloride, stannic chloride, mercuric chloride and silver nitrate are all corrosive to Monel.
- resistance to sulfurous acid varies depending on climatic conditions
- organic acids (acetic and fatty acids) have little to no effect on Monel
- Stress corrosion cracking: Exposure to aerated hydrofluoric acid in moist conditions can cause this to occur
- Galvanic corrosion: Metals, such as aluminum, zinc and iron will corrode when in contact with Monel AND exposed to severe weather conditions; therefore, use of these metals as fasteners for Monel should be avoided