How big is the difference between nickel-copper pipes and copper pipes?
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These days, my company is bidding for lithium bromide units; one bidder uses nickel-copper tubes, while the other two use copper tubes. According to those who use nickel-copper pipes, at high temperatures above 100 degrees Celsius, the corrosion resistance of pipes containing 5% nickel is 30 times that of copper pipes, while the corrosion resistance of pipes containing 10% nickel is 60 times that of copper pipes. This one-person opinion is also untrustworthy; is it really that extreme? Also, the quote from this company is much higher than that of other companies. They say that nickel-copper pipes are much more expensive than copper pipes, but by how much exactly?
The corrosion resistance of nickel-copper alloys is much greater than that of copper pipes, and the price difference is significant; currently, the price of nickel materials is around 600,000 to 700,000 yuan per ton. I’m not entirely sure about the corrosion resistance of nickel-copper alloys compared to copper pipes, but the former does indeed have excellent corrosion resistance.
Thank you to the friend on floor 2. I would like to ask further: The company that uses nickel-copper pipes said that at temperatures above 100 degrees, copper pipes will develop pitting after 5 years of use, whereas nickel-copper pipes do not. I want to know what the electrochemical corrosion reactions involved are, and also where this pitting usually occurs in copper pipes For example, is it the raised or recessed line of the thread, or is it general pitting?
Under reducing conditions, the AL400 alloy exhibits better corrosion resistance than industrial pure nickel (UNS N02200), and under oxidizing conditions it has better corrosion resistance than refined copper alloys. AL400 alloy cannot be used in highly oxidizing acids such as nitric and nitrous acids; in such environments, chromium stainless steels should be used, such as the Allegheny Ludlum E-Brite alloy (UNS S44627) or 310 alloy (UNS S31000). In moderately reducing acids, or in neutral or alkaline solutions, the AL400 alloy can be considered. This alloy exhibits good corrosion resistance in most alkalis, salts, organic substances, and atmospheric environments. This alloy can be used as a cooler for caustic alkalis, but it suffers from stress corrosion cracking in environments with high temperatures, high stresses, and high concentrations of alkaline solutions. The AL400 alloy can be used in reducing acids, such as sulfuric acid and hydrochloric acid, especially when there is no air or oxidizing substances present in the acid. This alloy exhibits excellent resistance to chloride stress corrosion cracking. Its main application area is in seawater and brackish water. The AL400 alloy undergoes corrosion in sulfur-containing gases at temperatures above 371°C, as well as in molten sulfur at temperatures above 260°C. Mechanical properties: Table 4 shows the typical mechanical properties of AL400 in the annealed state; Table 5 shows those of AL400 in the hot-rolled state. Mechanical properties of sheets, thin plates, and strips: For sheets, the values are yield strength in MPa, tensile strength in MPa, elongation in %, and elastic modulus in GPa. Yield strength: 240 MPa; Tensile strength: 520 MPa; Elongation: 45%; Elastic modulus: 180 GPa. Yield strength: 310 MPa; Tensile strength: 550 MPa; Elongation: 30%; Elastic modulus: 180 GPa. Table 6 presents the typical mechanical properties of AL400 in the cold-rolled state for thin plates and strips. Yield strength: 650 MPa; Tensile strength: 760 MPa; Elongation: 5%; Elastic modulus: 180 GPa. Under all conditions, the V-notch impact toughness value at room temperature is between 135 and 325 joules. High-temperature tensile properties: Table 7 shows the high-temperature tensile properties of the AL400 alloy in its annealed state; above 343°C, the material’s creep resistance must be taken into consideration.