Material pricing and availability can fluctuate based on market supply and demand, the quantity required for your exchanger, and the components needed. Copper was a low-cost option a few years ago, but now due to supply, it is more expensive than stainless steel. Conversely, Titanium used to be one of the most expensive alloys but is now more reasonably priced. Typically, the more nickel content in a metal, the higher the price.
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Here is the relative ranking for some of the common metal material options by price from highest to lowest:
1. MOST EXPENSIVE: Nickel 200, also known as UNS N, is a commercially pure nickel alloy. It is one of the most widely used nickel alloys due to its excellent mechanical properties and high corrosion resistance. Nickel 200 consists of 99.6% pure nickel, with small amounts of impurities such as iron, copper, and manganese.
2. Alloy 625, also known as Inconel 625, is a nickel-based superalloy known for its excellent strength, corrosion resistance, and high temperature performance. It is composed mainly of nickel, with significant amounts of chromium and molybdenum, along with smaller additions of niobium, iron, and other elements. Alloy 625 is widely used in various industries, including aerospace, chemical processing, oil and gas, and marine applications.
3. Monel 400 is a nickel-copper alloy known for its excellent corrosion resistance in various environments. It is composed of approximately 67% nickel and 30% copper, with small amounts of iron, manganese, carbon, and silicon. Monel 400 is highly resistant to corrosive substances such as acids, alkaline solutions, and saltwater. It is often used in applications where resistance to corrosion, erosion, and high temperatures are essential.
4. Hastelloy C22 is a nickel-chromium-molybdenum alloy known for its exceptional corrosion resistance in a wide range of aggressive environments. Hastelloy C22 is particularly resistant to pitting, crevice corrosion, and stress corrosion cracking. Hastelloy C22 is often chosen for chemical processing and waste treatment.
5. Hastelloy C-276 is a nickel-molybdenum-chromium alloy that is renowned for its corrosion resistance and high-performance properties. While similar to Hastelloy C22, Hastelloy C-276 has lower chromium content, easier weldability, and slightly higher upper temperature limits. Hastelloy C-276 is used in various industries, including chemical processing, pollution control, pulp and paper production, and petrochemical applications.
6. Duplex is a super duplex stainless steel alloy that offers excellent strength, corrosion resistance, and durability. It is part of the duplex stainless steel family, which combines the desirable properties of both austenitic and ferritic stainless steels. Duplex is characterized by its high levels of chromium, molybdenum, and nitrogen, providing superior resistance to corrosion and high mechanical strength.
7. AL6XN is a high-performance austenitic stainless steel alloy that offers exceptional corrosion resistance and mechanical properties. It is specifically designed to withstand highly corrosive environments, including chloride-rich environments, acids, and seawater. AL6XN is known for its versatility, making it suitable for various applications in industries such as chemical processing, pulp and paper, oil and gas, and desalination.
8. Titanium is a lightweight metal known for its high strength, low density, and excellent corrosion resistance. Titanium is widely used in various industries due to its unique combination of properties.
9. Duplex is a stainless steel alloy with a combination of austenitic and ferritic microstructures, known as a duplex structure. It offers excellent strength, corrosion resistance, and durability, making it suitable for a wide range of applications. Duplex is highly popular in industries such as oil and gas, chemical processing, marine, and pulp and paper.
10. 316L stainless steel is a commonly used grade of stainless steel known for its corrosion resistance, high strength, and versatility. It is an austenitic stainless steel alloy with low carbon content, making it suitable for various applications where resistance to corrosive environments is essential. It is widely used in marine applications, chemical processing, dairy, and pharmaceuticals.
10. 304L stainless steel is a commonly used grade of stainless steel known for its corrosion resistance, versatility, and ease of fabrication. It is an austenitic stainless steel alloy with low carbon content, which enhances its weldability and reduces the risk of sensitization to intergranular corrosion. In comparison to 316L SS, 304L SS has no molybdenum content and it&#;s less resistant to chloride-induce corrosion. It is suitable for general-purpose uses that don&#;t require the enhanced corrosion resistance of 316L SS.
12. LEAST EXPENSIVE: Carbon steel is a type of steel that primarily consists of iron and carbon, with other elements present in smaller amounts. It is one of the most commonly used materials in the manufacturing and construction industries due to its affordability, strength, and versatility.
Typically, the higher priced alloys are also in shorter supply, due to lower demand and the higher cost of carrying inventory. This directly affects the lead-time of these materials, often by 2-4 times that of more common alloys like carbon steel and stainless steel. Quantity of these higher alloys can also greatly affect price. Steel mills typically don&#;t run small batches of tubes or plate or they will charge for the entire mill run if they do.
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Heat Exchanger tube switching material from CS to SS
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MVPs
(Mechanical)
(OP)
3 Dec 12 18:31Got a request to evaluate the mechanical integrity assessment for changing the tubes of two exchangers ( AXM and NEN type) from carbon steel to stainless steel. Because of difference in heat transfer coefficients of CS and SS, our process group wants to reduce the SS tube wall thickness from that for the CS. Currently, the carbon steel tube that we need to replace is size at 3/4" with 0.083" thickness. The process engineer propose to offset heat transfer change by decreasing the wall thicknesses from 0.083" to 0.065" of SS material ?. But this need to be confirm by mechanical engineer if there is any issue on mechanical strength. I did verify the minimum required tube wall thickness due to internal and external pressure. It turns out that the thickness of 0.065" 316 SS tube material is acceptable . But for fixed end tube design, I am not sure how to justify tube to tube sheet joint load because SS tube obviously will experience higher thermal expansion stress than CS. In addition to tube to tube sheet joint load, Do I need to verify tube sheet design as well because of tube material change ?
It will be appreciated if you can give me quick response.
Replies continue below
(Mechanical)
3 Dec 12 23:34It's worth looking into in light of the additional consideration that you will also have more mechanical strength lost in the tube-to-tubesheet joint (assuming expanded tubes) after you achieve the 8% to 10% (I think that's about where it will end up) wall reduction after rolling.
(Mechanical)
5 Dec 12 11:04abehong as these are both fixed tubesheet exchangers you absolutely need to evaluate the proposed designs with Part UHX calculations or something similar. Due to the change in metallurgy differential expansion may present problems that did not exist before the change. There is more involved that the tube wall and tube-tubesheet joint. Tubesheet thickness, stresses in integral cylinders, tube and joint strength all come into play. As for categorizing the joint strength Appendix A contains factors to account for different coefficients on thermal expansion. For stainless tubes in CS tubesheets, I would not normally consider the joint strength to decrease due to thermal effects.
Regards,
Mike
(Mechanical)
5 Dec 12 14:28issues are:
worse thermal expansion, worse thermal stress+ lower yiled stress= more fatigue damage
better corrosion resistance
lower youngs modulus may imply vibration worsens- may need closer spaced supports, ditto thinner wall + lower section modulus
may need to anneal tube bends
dissimilar metal weld at tube sheet
(Materials)
7 Dec 12 16:49What material are the current tubesheets? and what is their condition?I am a bit concerned about galvanic corrosion of the tubesheets.This is actually a very common change.The only risk of vibration is from the thinner walls, the modulus is about the same.The biggest issue is that you are lowering the back pressure on the system.If there are centrifugal pumps used the pressure/flow will change.
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Plymouth Tube
(Chemical)
8 Dec 12 18:52I would doubt that going to CS from SS will have much effect on the overall heat transfer coefficient when you look at film and fouling coefficients effects in addition to the effect of the tube material. Reducing the wall thickness in terms of maintaining overall heat transfer doesn't make sense to me.
I have typically seen wall thicknesses for SS tubes less than that of CS tubes because of the higher corrosion resistance for SS. That depends however on the fluids in question and expected corrosion rates.
(Materials)
11 Dec 12 15:30Austenitic SS is implied by the CTE concern, but is ferritic SS possible?
Beware of SCC lurking in the bushes whenever 300 SS is proposed as a magic bullet.
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