steel coil

Oftentimes, using stainless steel components seems like a simple solution to corrosion on coils. You may see fins or tubes or other parts of the system show signs of corrosion, and it seems that the best option is to change the coil to stainless steel, solving the corrosion problem permanently. While this seems like a simple solution to a significant problem in the HVAC, industrial, and commercial systems where coils are found, the answer to the question “should I make an all-stainless coil?” is far moare complex.

While it’s true that stainless steel has excellent corrosion resistance properties, when used in a heat exchanger it can have poor heat transfer characteristics. So, it’s possible that by solving the corrosion problem using stainless, other system issues could result. Performance reduction, exceeding fan or motor capacities, and exceeding space or structural limitations of the existing unit are all possibilities when changing a system’s materials to stainless. Finally, there are the economics – is the stainless steel solution a viable commercial option for the installation?

As the system engineer, you are faced with a dilemma: meet the overall system constraints, solve the corrosion problem, and maintain a budget so the project moves forward. These priorities often conflict with each other, but the evaluation and balancing of these objectives are where Super Radiator can lend a hand.

To better understand the potential impact of using an all stainless steel heat exchanger, let’s evaluate an example 400,000 BTU/HR (33 tons or 119 kW) cooling coil. For the example, we’ll use 45° F water and a 36” x 45” coil with standard copper tubes and aluminum fins. The coil for this installation will be 12” deep, weigh 320 pounds and have a cost factor of 1.0. This is our base unit and is the component currently installed in the system.

The question is what is the impact of changing the heat exchanger to all stainless steel? There are two ways to evaluate the case: keep the same unit capacity or fit the space of the current unit.

Here are the results of using all stainless steel:

  • Maintaining capacity: Air pressure drop = increased 2.3x; Weight increase= 6x; Depth increase= 2.2x ; Cost Factor = 6.8x.
  • Air pressure drop= no change; weight increase 1.5x; Capacity Decrease = 40%; Cost Factor = 4.

To summarize, changing the coil from the copper and aluminum to all stainless steel will be a cost increase between 4 and 7 times the original coil. Moreover, it will either not fit in the existing unit, or short the system capacity by 40%.

If the system being designed is new, the larger size or different capacity could be reconciled with adjustments to other system components, such as changing the fan to accommodate the higher levels of air friction or altering the unit design to create more space for the larger coil. However, for an existing system, this may not be possible.

Stainless steel or other high corrosion-resistant material may be the only option in some systems: high temperatures, abrasive environments, extreme caustic chemical solution. For many cases, a basic coil with a high-quality coil coating can solve most coil corrosion issues. Let’s evaluate the impact of this option.

Based on Super Radiator research, using a coil coating has little impact to the thermal performance of the coil. However, coating does incur additional cost compared to an uncoated coil. Electro-deposition (E-coat) and baked phenolic (such as Heresite P413) are the most common, quality coil coatings. The example coil, with the coating will have cost factor of 1.3. The price is higher than the bare coil, but coating is a great option to solve the corrosion issue, meet the performance needs of the system, and fit the space.

Copper fin and tube are often considered for corrosive, abrasive, or harsh environments. For select installations, an all-copper construction is a good option. Adding to our example from earlier in the document, a copper coil will have a cost factor of 1.5. However, the copper construction does have the benefit of 3.5% increased capacity. Using copper fins keeps the air friction the same as with aluminum fins. The coil weight does increase by 1.8x.

Is all stainless steel construction the best option to solve the corrosion issue on your finned tube coil? It may be. But there may be better options.

Stainless steel: The ideal material for heat exchanger construction

Stainless steel has proven to be a particularly reliable and durable material here. Heat exchangers made of stainless steel are particularly resistance to corrosion and deposits of limestone and other residues are minimized.

Common tube bundle heat exchangers and special heat exchangers can be realized using stainless steel without problem. If single parts are welded to each other, each welded seam always marks a possible weak spot. Always rely on an experienced manufacturer due to reasons of reliability during operation. We have the necessary expertise and experience to perform welded seams cleanly and reliably according to the WIG and/or MIG procedure. Naturally we are certified according to DIN EN ISO 3834-3:2005.

Austenitic stainless steels such as Type 304 (UNS $30400) and Type 316 (UNS 31600) are frequently selected for heat exchangers placed in cooling water service. These alloys generally perform well in clean water and are expected to give a long service life with minimal problems. Unfortunately the assumption that cooling waters will be clean is often misleading, and unexpected failures can result from localized corrosion mechanisms such as pitting, crevice corrosion, microbiologically influenced corrosion (MIC), and stress-corrosion cracking (SCC). Localized corrosion may be associated with water chemistry parameters such as temperature and chlorides, deposits that accumulate in the system, microbiological activity, operational factors such as low water velocity and stagnant water after hydrotesting, and variations in steel chemistry at inclusions and welds. An overview of localized corrosion mechanisms for stainless steel is presented along with corrosion tendencies for modem versions of Types 304/316 stainless steels.

300-series stainless steel (SS) alloys are often used in exchangers at power plants, refineries, chemical plants, and paper mills. Types 304 (UNS $30400) and 316 (UNS 31600) are popular and cost-effective choices for general purpose stainless steels in cooling water service (Table 1). Austenitic SS alloys are ductile, tough and most importantly, easy to form and weld. Type 304, also known as “18/8,” is the most widely used SS alloy in the world. Typical applications would include shell and tube heat exchangers, plate and flame exchangers, piping, and water jackets for process reactors. With shell and tube heat exchangers, cooling water can be on the shell side or tube side, and the exchanger orientation can be horizontal or vertical. When the environmental conditions are conducive for localized corrosion, Type 316 is recommended because the addition of molybdenum increases resistance to pitting and crevice corrosion.

A wide variety of higher alloyed specialty stainless steels are available environments or critical stand-by water systems, but at a premium price. For example, 6% Mo superaustenitic SS alloys such as AL6XN will not suffer pitting or crevice corrosion when immersed in ambient temperature seawater. AL6XN heat exchanger tubing costs nearly four times as much as Type 304, based on 2002 prices 1.

Today’s 300-series Stainless Steels

Modem versions of products are usually thought to be equal or better than the old ones they replace. This, however, does not hold true for 300-series stainless steels. Types 304/316 alloys being produced today are not as corrosion resistant as those produced 20 to 30 years ago ~. Because of advances in SS melting practices, ladle refining, and economic competition between manufacturers, typical 300-series SS alloys now have chemistries very near the absolute minimum of the ASTM requirement. This is largely due to the widespread use of argon-oxygen decarburization (AOD), which has facilitated pinpoint control over both major and minor alloying elements (Ni, Cr, Mo, C, N, S) 2. For example, 20 years ago typical Type 304 had a chromium level of approximately 19% and Type 316 had a molybdenum content close to 2.6% 1. Modem Type 304 has chromium levels just above 18%, and the molybdenum content of Type 316 now runs below 2.1%. The nickel content of Type 304 has also dropped nearly 1% over the years, while Type 316L is leaner by more than 2% nickel and 1-1/2% chromium 2.

The Introduction of Stainless steel coil

Stainless steel capillary
First, the definition of stainless steel coil
Stainless steel coil, generally diameter of 0.5 to 20mm, thickness of 0.1 to 2.0mm plate mounted or mosquito coils installed; widely used in chemical, mechanical, electronic, electrical, textile, rubber, food, medical Equipment, aviation, aerospace, communications, petroleum and other industrial fields.
Stainless Steel Coil Picture Picture provided by Jiangsu Yeqing Stainless Steel Co., Ltd
Second, the type of stainless steel coil
Stainless steel industrial pipe, ultra-long coil, U-tube, pressure pipe, heat transfer tube, fluid pipe, spiral coil Features: high temperature steam, impact corrosion, ammonia corrosion; anti-fouling, Safe and reliable; pipe wall is uniform, wall thickness of only 50-70% of the copper, the overall thermal conductivity is better than the total thermal conductivity is better than, Brass; the old unit is the transformation and manufacture of new equipment ideal heat exchanger products. In the petrochemical industry, electric power, nuclear industry, medicine, food and other industries can be widely used.
Third, the use of stainless steel coil
Industrial stainless steel coil: heat exchangers, boilers, petroleum, chemical, fertilizer, chemical fiber, pharmaceutical, nuclear power and so on.
Stainless steel coils for fluids: Beverages, beer, milk, water systems, medical equipment, etc.
Stainless steel coil for mechanical structure: printing and dyeing, printing, textile machinery, medical equipment, kitchen equipment, automotive and marine accessories, construction and decoration.
Bright stainless steel coil: welded by a good stainless steel strip and then reduce the wall, from thick to thin wall, this process can make the wall thickness uniform, smooth, and reduce the wall of the wall to form a seamless tensile effect. Seamless in accordance with the naked eye, but the process is the pipe. Reduce the wall with the process of bright annealing, so that the inner and outer walls will not form oxide, inside and outside the bright, beautiful, this is really medical products needed. The next process needs sizing, that is, a small pull process to determine the diameter, diameter tolerance can generally be positive and negative 0.01m
3/8 “* 0.049 * (1 ~ 2000m)
1/8 “* 0.035 * (1 to 3500 m)
1/4 “* (0.035” to 0.049) * (1 to 1800 m)
1/2 “* 0.049 * (1 to 1000 m)
Φ3 * 0.9 * (1 ~ 3500m)
Φ4 * 0.9 * (1 ~ 2500m)
Φ6 * 0.9 * (1 ~ 1700m)
Φ8 * 1 * (1 ~ 1000m)
Φ10 * 1 * (1 ~ 8000m)
Φ (10-26) ★ (1-2) length (1-800m) diameter according to customer requirements
Material: 201,202,304,304 L, 316L, 317L, 321 (also according to user requirements)
Pressure: 60-100MPa
Implementation of the standards: in line with ASTM A269-2002.JIS G4305
Technical requirements

What Kind of Savings Come from a Stainless Steel Heat Exchanger?

Waste-oil combustion is an environmentally friendly and efficient way to power your boiler, space heater, or furnace. Waste-oil combustion helps you save money, energy, and the planet, all while staying more comfortable in your home or office. At the heart of waste-oil combustion technology is the heat exchanger – the component that transfers energy from the oil into heat. The heat exchanger is crucial for cooling and heating purposes. The heat exchanger most affects the safety and performance of your unit, making it an important piece to optimize. A stainless steel heat exchanger offers a range of benefits compared to other materials.

Higher Product Quality 

Stainless steel is one of the toughest and most durable materials in the world. It is better equipped for handling high temperatures and resisting corrosion than aluminum, iron alloys, or steel alloys are. Stainless steel heat exchangers have 10.5% more chromium than alloys, making it incredibly resistant to corrosion and rust – two common problems with boilers, heaters, and furnaces.

Stainless steel also offers quality in terms of thermal conductivity. Thermal conductivity is the measure of how well a unit can transfer heat. The higher the thermal conductivity, the better the unit performs. While aluminum’s thermal conductivity is greater than any kind of steel, aluminum will corrode and warp over time. Stainless steel, on the other hand, will never lose its shape or ability to conduct heat.

Manufacturers of stainless steel heat conductors overcome the problem of lower thermal conductivity by making the walls of the component thinner. Thinning the walls maximizes heat exchange while retaining the lasting strength of the original material. Thinner, more durable stainless steel heat exchangers offer better performance than even galvanized steel. The high tensile strength of stainless steel means it can withstand high pressures despite thin walls – something other metals cannot manage.

Better Reliability

The properties and capabilities of stainless steel give it a lasting reliability that one cannot enjoy with heat exchangers made from other materials. Temperature tolerance and corrosion resistance are two major factors for waste-oil combustion, where traces of sulfur cannot mix with water condensation anywhere within the chimneystack for optimal performance. Stainless steel heat exchangers are best in class for both these factors, beating out the competition by a long shot.

Stainless steel heat exchangers carry a lifetime warranty. By comparison, copper alloy heat exchangers have warranties of just five to 10 years, and aluminum ones may have warranties of up to 15 years. Manufacturers offer lifetime warranties on stainless steel heat exchangers, because they’re confident the units will last for life. Stainless steel won’t crack under pressure as other materials do – important for performance and long life, but also for personal safety. A cracked heat exchanger can release deadly carbon monoxide gas into your home. Stainless steel protects your investment and your family.

Lifetime Returns on Investment

Claims of the higher cost of stainless steel compared with carbon steel are off base. While the initial price of a stainless steel heat exchanger will be more than other materials, the long-term return on investment is much higher with stainless steel. Buyers get much more for their money – higher performance, better durability, and a part that lasts a lifetime. The buyer saves hundreds of dollars on replacement heat exchangers every five to 15 years, and maintenance and repair costs of an inefficient appliance. A heater that stays cleaner and rust-free longer is low maintenance.

Stainless steel heat exchangers in waste-oil combustion systems also maximize energy efficiency. They enable a sustainable heating device that produces a clean, high-quality product with minimum energy expenditure. Thin stainless steel exchangers conduct heat faster than carbon steel materials, saving energy and requiring less oil to burn. Overall, the higher temperature tolerance and better corrosion resistance of stainless steel guarantees better product quality, reliability, and lifetime performance – reducing costs over time.

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