Stainless steel insulation issues

First, apply a layer of paint (primer or topcoat), and then apply insulation.

Stainless steel does not need to be painted before insulation.

It’s not necessary; just add a polyurethane insulation cover, and then add aluminum sheeting – that will do. The pipes in our facility are currently under insulation work

Polyurethane technical data: Rigid polyurethane foam is a low-density, micro-porous foam material with a closed-cell structure. It has a low thermal conductivity and excellent insulating properties, which makes it one of the best energy-saving materials recognized worldwide for use in insulation and heat retention applications. Compared to other insulating materials, it features a low density, low thermal conductivity, low water absorption, as well as resistance to oils, alkalis, acids, chemicals, and atmospheric degradation. Additionally, its ease of processing makes it increasingly widely used in various fields, and it is gradually replacing conventional insulating materials such as glass fiber, rock wool, cork, and polystyrene foam, which have poor insulating performance. In the field of sound-absorbing and sound-insulating materials, polyurethane foam is an effective porous sound-absorbing material with excellent sound-absorption and sound-insulation properties, making it an ideal choice for such applications. In rigid polyurethane foam—spraying is a widely used processing method. One of its features is the use of agile and convenient equipment for working at construction, renovation, or decoration sites. Using sprayed rigid polyurethane foam enables high thermal insulation performance and seals the substrate; this versatile method is suitable for both interior and exterior applications in buildings. A protective layer must be applied over the sprayed polyurethane foam to ensure reliable performance over the long term and provide fire protection. The sprayed foam bonds directly to the substrate to form a continuous, seamless coating; an additional advantage of this is that it can seal all cracks and small gaps, ensuring a tight seal around vertical structures such as chimneys, skylights, and ventilation ducts. Foam can actually adhere to any shaped clean, dry surface. When used, rigid foam does not sink or settle, allowing it to maintain its insulation properties intact. Before spraying the foam, the substrate must be properly cleaned, which involves removing loose particles, oil, or solvents that could affect adhesion, sealing large cracks in some cases, and roughening the surface. Due to the strong adhesion between the foam and the substrate, strength and stiffness are imparted to the veneer materials such as metals of different shapes, thereby **improving the structural integrity. At the same time, foam is lightweight, having the least impact on the overall load. Substrate: The compatibility between the spray foam and its substrate is very important. To achieve long-term insulation performance, it is important for there to be good adhesion between the two. The surface of the substrate should be dry, free of frost, ice, grease, oil, and loose debris or dust. There must also be no solvents on the surface. If a base coat has already been applied, sufficient time must be allowed for it to dry before starting to spray the foam. Since the adhesion strength between the sprayed foam and any particular type of substrate is very important, all substrates must be primed before spraying begins. However, if an adhesive test has already been conducted, the priming step can be omitted. The appropriate testing method is to check the adhesion strength after spraying on a surface of approximately 0.5 m2 for at least 24 hours. Common substrates The same principles apply to the surfaces of buildings, pipes, and tanks as well. Concrete: Generally, the concrete surface is first cleaned with an acid, and then a primer/sealant is applied, which should yield good adhesion. Before spraying the foam directly on the surface that has been treated, it is necessary to check the moisture content using a moisture meter, as adhesion is poor when the moisture content exceeds 10%. For metal, it should be cleaned first before applying the primer. Galvanized steel often retains oils from the production process, which need to be removed with solvents, followed by the application of a primer. As for the very smooth surface of stainless steel, it needs to be roughened in order to bond well with the primer. The aluminum surface should be cleaned with a non-alkaline solvent, and then coated with a two-component etching primer. Glass: If the surface of the glass is clean, foam can also be sprayed on it. If foam is sprayed on the inside of windows or skylights, an ultraviolet-resistant coating needs to be applied. Plastic – plastic reinforced with glass fiber usually only requires cleaning, but since its adhesion to smooth surfaces can be poor, it is best to apply a primer first. — For polyvinyl chloride, washing with mild solvents such as mineral spirits is usually sufficient. If polyvinyl chloride contains a large amount of plasticizer, attention must be paid to the risk of plasticizer migration. — Acrylonitrile butadiene styrene copolymer (ABS) is cleaned with a solvent and coated with a primer. — For existing rigid polyurethane foam, it is necessary to clean the existing foam before spraying new foam; if metal brushes are used for roughening the surface, special attention should be paid to any areas where the surface may have degraded due to exposure to ultraviolet rays. — Polystyrene board: Check that all mechanical fasteners are secure, and roughen the glossy surface of the polystyrene. Asphalt and tar: Roofs treated with asphalt and tar should be cleaned first, before applying a primer. It should be checked whether the newly laid asphalt or tar contains solvents. Old roof: When repairing an old roof, before starting to apply foam, all exposed materials should be thoroughly dried and secured. Any part that has absorbed water should be cut off and replaced. Before spraying, all uneven areas must be filled in. And remove the dust and other debris from the roof. Other existing insulating materials: Foam must not be sprayed on the cold side of other types of existing insulating materials, such as fibrous or loose filling materials. Because moisture may get trapped on this surface, leading to early degradation of the foam. Foam thickness: The ideal foam thickness is between 25 and 38 millimeters, but this is to reduce the number of air bubbles within the foam. It is best to apply the maximum allowable thickness with each use of the spray gun. It ensures effective thermal curing on the surface and proper reaction of the foam, with a minimum thickness of 13 millimeters. For example, a thinner layer applied quickly in the initial stage generally has much weaker adhesion. At the other extreme, a single spray exceeding 50 millimeters is also not suitable, as overheating of the core layer can cause charring and cracks to form within the foam. Foam quality: A fan-shaped atomization effect should be formed when the mixture exits the nozzle of the spray gun. The humidity and temperature of the air, as well as the temperature of the substrate itself, have a significant impact on the final quality of the foam. If the milky phase is too short, a coarse, orange-peel-like foam surface will form; this can also occur when a system designed for cold climates is used in warm environments. If the milky phase lasts too long, a glossy, smooth surface is formed; the foam density increases, and chemicals are wasted. Tree trunk texture – resulting from settlement – is caused by the increase in density when foam is sprayed onto vertical surfaces, a condition that makes the foam more susceptible to wind-induced ripples. At low temperatures, when foam is sprayed onto the frozen substrate (i.e., below about 10°C), the cold surface can act as a heat sink, absorbing part of the heat required to completely evaporate the foaming agent and thereby reducing the rate of the polymerization reaction. As a result, a thick, crumbly foam layer forms on the surface, leading to poor adhesion; moreover, foam bubbles are also formed later on. If the foam is sprayed on a hot substrate, the density of the foam increases due to the loss of the foaming agent, which also results in the formation of so-called pinholes. Therefore, for substrates with temperatures as high as 50°C, a special system with a longer milking period must be chosen, and the amount of foaming agent should be increased if necessary. Moisture/Humidity: It is crucial to apply the polyurethane foam to a dry surface; moisture will react with the isocyanate components, resulting in weak adhesion between the foam and the substrate, as well as the formation of a brittle surface layer. Morning moisture can also be a problem, as the substrate has been cooled over the entire night. If the risk of condensation is anticipated, special attention should be paid in the following situations: heavy roofs (such as concrete) cool down more slowly than the ambient air. Refrigerated warehouses or buildings that were once refrigerated warehouses warm up more slowly than the ambient temperature. When spraying foam near concealed lighting fixtures, special care must be taken to prevent overheating due to restricted air circulation. Fire safety regulations must be strictly followed. The electrical outlets, sockets, and junction boxes should be properly protected to prevent foam from penetrating inside. The operator’s skill is necessary to produce a foam with a satisfactory surface texture, that is, a smooth surface and uniform thickness. Operators must receive thorough training. These two characteristics have a significant impact on costs, and thus on profits as well. The operator must possess sufficient skills and experience to: select the most appropriate chemical system ； Make appropriate adjustments to the device ； Control the supportability of the selected system (mainly during the milky stage), thereby controlling the density of the foam. Understand the effects of the following environmental conditions: condensation, temperature, humidity, and wind speed. Be aware of any faults in the equipment. Note the changes in the spray pattern or foam texture. Spraying conditions: Outdoor spraying should not be carried out under the following conditions: rain, heavy fog, windy weather, visible water droplets, humidity above 80%, and surface moisture content above 10% (measured with a moisture meter). Wind: It is difficult to apply a uniform foam layer when the wind speed exceeds 25 kilometers per hour. The cooling effect of the wind reduces the surface quality of the foam, as the surface layer cannot mature properly. Construing in cold climates might be a problem. The operator must ensure that nearby property is not contaminated by foam carried by the wind. Experience shows that cars parked nearby are particularly prone to being covered with a layer of foam droplets. Due to the excellent adhesion of foam, such damage is very difficult to remove. Therefore, all vehicles should be driven to a safe location, several hundred meters away from the scene. Spraying technology: Essentially, spraying foam is a manual method, and its effectiveness depends on the movements of the operator’s hands, which in turn affects both the physical and economic outcomes. The purpose of the operation is to obtain a uniform foam layer with a specified thickness across the entire substrate, a certain height on any vertical structures, as well as an appropriate surface texture. During operation, avoid forming ridges; a properly flat and smooth surface should be achieved. The latter is particularly important from the perspective of maintaining a uniform protective coating and the associated maintenance costs. The surface texture of the sprayed foam is primarily determined by the following factor: the spray gun must be held at a perpendicular angle to the substrate, as any other angle will elongate the bubbles within the foam, thereby reducing its physical and insulating properties. At the end of each injection stroke, the wrist should be pulled back quickly and gently to mix it with the second stroke, thereby achieving a uniform thickness. However, such twitching should be minimized as much as possible to avoid a deterioration in the surface texture. It is recommended that the two spraying strokes overlap to ensure a uniform surface without ridges. It is best to minimize the number of injection strokes (in order to reduce the number of layers inside the foam), spraying the maximum allowable thickness of foam with each stroke. For example, when spraying 38 mm, it is better to complete the spraying in a single stroke rather than in three thin layers. When spraying the roof, apply the spray as quickly as possible; the directions of the successive applications should intersect in a grid pattern, with a 15-minute interval between them. This can help reduce the force exerted by the roof panel on the foam. It also prevents the formation of pinholes and reduces the \"stickiness\" of the foam. To avoid problems caused by water accumulation on the roof, it is recommended to apply the foam at a slope of at least 15 percent. Device adjustment: If the temperature is slightly below the recommended value, the pressure of each component can be adjusted. If the chemical is too hot, the spray mixture reacts too quickly and cannot be sprayed evenly. Throughout the spraying process, it is necessary to adjust the ratio of isocyanate to polyol properly; an improper ratio can affect foam formation and result in foam with abnormal physical properties. If there is an excess of isocyanate, a crisp or brittle foam is formed, which is characterized by a dark color and a smooth, hard structure. If there is an excess of polyol, a soft or spongy foam is formed, which is light in color and features a \"coarse orange peel\" texture as well as pinholes. Protective coating: To ensure the foam can function reliably and safely over the long term, a protective coating must be applied to rigid foam. Depending on the application, this coating can be: — mortar or plaster — bricks, blocks, or decorative stones — liquid coatings (applied by spraying or brushing) — materials containing inorganic fillers, which are typically specified for use in situations with fire hazards. Such protective coatings can safeguard the foam from: — impact damage, including pest infestation. —In the event of a fire, foam sprayed indoors must be protected by a barrier that meets relevant fire safety standards, such as gypsum board. —Degradation by sunlight and ultraviolet rays. The most important thing is to ensure that the protective coating is continuously bonded to the foam. The surface of the foam must be dry. To ensure proper adhesion of the coating, it must be applied within two days after foam spraying, but not later than two hours. The surface texture of the foam should be smooth, as a rough or uneven surface makes it almost impossible to achieve a satisfactory covering effect; the goal for those who handle it is to create a smooth, \"orange peel\"-like surface. Safety and health (see attachment for details): When applying the coating, operators should wear flat shoes without heels, with elastomeric soles. The foam should be applied by personnel who are familiar with the materials and have received appropriate training. Barrels containing liquid chemicals must not be stored in direct sunlight; they should be placed in well-ventilated areas. When opening the lid of a chemical container, if it is warm to the touch, it should be opened slowly and carefully to allow the pressure built up inside the container to release gradually. In case of a fire, rigid foam is an organic material; even when flame retardants are added, it will burn when exposed to fire. In areas at risk of fire, such as inside buildings, it is crucial to cover them with inorganic materials such as gypsum board, metal sheets, sprayed mud, or plaster applied with a trowel, to a thickness of at least 10 millimeters. Qualified organic coatings are applied to the foam on outdoor roofs, as the risk of roof fires is considered low. However, flame retardants are usually required to be added to foam formulations. The use of open flames, cutting and welding torches, electric heaters, and smoking is prohibited in areas where foam is stored and installed. If thermal operations must be carried out near the foam, insulation panels such as asbestos sheets should be used to isolate the foam from heat and sparks. Fire extinguishing equipment should be prepared. Spraying rigid polyurethane foam for roof systems offers the following advantages: 1. Light weight. 2. Good strength and excellent thermal insulation properties. 3. It adheres very well to all roof panels. 4. Fill and seal thoroughly. 5. Forms a smooth surface on its own. 6. For irregular roofs. 7. Easy to repair. Achieve a seamless overall design. Polyurethanes – versatile materials. Polyurethanes are among the most widely used plastics; by selecting compounds with different functional groups and molecular weights and employing various synthesis methods, it is possible to produce polyurethane products with diverse properties and various forms. Foam plastics ranging from very soft to extremely hard form a new series of synthetic materials with diverse varieties and excellent properties. As the applications of these products continue to expand, such polymers have become essential materials in a wide range of fields, from aerospace vehicles to industrial and agricultural production, from sports and entertainment equipment to people’s daily needs in clothing, food, housing, and transportation. Therefore, polyurethane synthetic materials have become one of the fastest-growing materials in recent decades. Applications of polyurethane: Automotive industry: seat cushions, interior components, body panels, bumpers, etc. Furniture: seat cushions, mattresses, chair armrests, etc. Construction: sandwich panels, spraying, high-density solid structural components, etc. Thermal insulation: refrigerators, freezers, frozen transport, etc. Shoes and boots: soles, synthetic leather for uppers, etc. Toys: items for entertainment. Packaging Others: coatings, elastomers, sealing materials, adhesives, etc. Production process: The properties of polyurethanes are determined by the production process used for mixing polyisocyanates and polyols. Currently, there are mainly two commercial polyisocyanates – MDI (diphenylmethane diisocyanate) and TDI (toluene diisocyanate). The chemical reactions of polyurethanes are controlled by selecting the manufacturing process as well as the additives and catalysts used; the addition of blowing agents allows the polymer to expand, thereby producing various types of polyurethane foams. Unlike many other plastics, polyurethane is supplied to users as a liquid chemical compound. Customers can carry out chemical reactions on their own to produce suitable polyurethane products. Polyurethane market: The main users of polyurethane are concentrated in four sectors, namely furniture, automobiles, the construction industry, and industrial insulation. Their consumption accounts for 2/3 of total polyurethane consumption. The main products of polyurethane are soft polyurethane foam plastics, rigid polyurethane foam plastics, semi-rigid polyurethane foam plastics, and non-foam polyurethane materials. In sharp contrast to the slowdown in the overall development of polyurethane worldwide, China’s polyurethane industry has shown rapid growth over the past two years. In developed countries, the application of polyurethane resins has nearly reached saturation, and the current growth rate is low; however, in developing countries, especially in China, the polyurethane industry is experiencing rapid development. Since 1990, and especially in recent years, the development pace of China’s polyurethane industry has exceeded that of developed countries, with an average annual growth rate of over 10%. With the rapid development of China’s economy, the domestic production of polyurethane products exceeds 1 million tons per year. Especially in the field of rigid polyurethane foam plastics, as the refrigerator manufacturing industry developed, it found wider applications in building insulation as well. Furthermore, with the development of industries related to housing, the demand for coatings, adhesives, and similar products is also on the rise. It can be predicted that the demand for polyurethane products will maintain a high growth rate of around 10% in the future. As the quantity increases, customers' demands also tend to become more diverse. Rigid polyurethane foam: Rigid polyurethane is an excellent insulating material and structural material. Among various polyurethane products, its production volume is second only to soft foam plastics. Isocyanate: The polyisocyanate used in the production of rigid polyurethane foam is MDI (diphenylmethane diisocyanate). Polyols: Polyols used in the production of rigid polyurethane foam include polyether polyols, polyester polyols, and other hydroxyl-containing compounds. The structure of the polyol has a significant impact on the properties of the resulting rigid polyurethane foam. In the market, for cold storage facilities, large-scale cold stores are more easily and quickly constructed using composite sandwich panels. Its face material is metal such as steel plate, which offers high strength and does not deform easily upon impact; the core material is rigid polyurethane foam plastic. Composite sandwich panels are produced by continuous or discontinuous methods. Customer: Manufacturer of composite sandwich panels. Technical requirements: environmental friendliness, flame resistance, and good stability. On-site spraying construction is more suitable for building ultra-large cold storage facilities. Customer requirements: a producer of composite materials with an oxygen index of ≥26 and excellent dimensional stability; the industry is sensitive to the price of such composite materials. Customers desire high-performance materials, and if the price is appropriate, demand is very high – around 100 tons of composite materials are needed for one ultra-large cold storage facility. In our country, rigid foam is used for insulation and waterproofing on the roofs of residential buildings and office buildings, as well as as an insulating material in cold storage facilities and grain depots. However, its use in the construction industry is not yet as widespread as in developed countries, leaving considerable room for growth. The roofs of buildings can be constructed using sandwich composite panels. Metal-faced rigid polyurethane sandwich panels are made by using flame-retardant rigid polyurethane foam plastic (available in two different formulations: PU and PIR) as the core material, and colored coated steel sheets as the face material; they are formed through continuous or discontinuous foaming of PU or PIR. Currently, metal-faced rigid polyurethane sandwich panels are widely used in China in buildings such as industrial factories, warehouses, sports venues, residential houses, villas, prefabricated shelters, and modular cold storage, serving as roof and wall panels. Customer: Composite sandwich panel manufacturer, central air conditioning ducts. With the development of modern architecture, central air conditioning has become an essential part of interior facilities. Traditional central air conditioning supply ducts are typically constructed with an inner layer of iron sheet or fiberglass, surrounded by insulation material, with aluminum foil wrapped around the surface. Such ducts are heavy, require time and effort to install, have an unsightly appearance, poor airtightness, and high energy consumption. Of particular concern is the use of highly carcinogenic insulation materials such as rock wool in some projects, which poses potential dangers to what were otherwise elegant environments. Modern architecture abroad has brought about a complete revolution in air supply ducts, using high-quality embossed aluminum foil as the inner and outer layers, with flame-retardant polyurethane rigid foam serving as the core material; these materials are used to produce core panels on production lines. Compared to traditional duct manufacturing, production efficiency has increased by 4 to 5 times, **saving on labor costs. Market demand: Flame-retardant B1 grade rigid polyurethane composite materials. This is an emerging market; currently, several manufacturers are already operating in cities such as Beijing, Shanghai, Guangzhou, Shandong, and Hunan. The entry barrier for this market is high, requiring the mixtures supplied by suppliers to have high stability. It’s somewhat similar to the refrigerator market, but the performance requirements for the materials used are much higher than those for refrigerators. For industrial equipment and pipelines, insulation is essential; many companies in the brewing, chemical, and storage industries have various requirements related to heat retention and insulation. Polyurethane rigid foam is easy to apply, hygienic, and provides excellent insulation, making it an ideal insulating material. Storage tanks and pipelines are commonly used equipment in industrial production, and they are widely employed in industries such as petroleum, natural gas, refining, chemicals, and light industry. To prevent the loss of heat or cold during storage in the tanks or during transportation, insulation measures must be applied outside the cold/heat storage tanks and pipelines. The pipes for centralized heating in towns use rigid polyurethane foam as the insulation material. Market demand: High-temperature resistant polyisocyanurate (the PIR system takes advantage of polyester polyols). Low-temperature storage tanks – The temperature of the fluid inside such tanks is below -30°C; they are primarily used for storing and transporting liquefied petroleum gas and liquefied natural gas. Stored under atmospheric pressure, liquefied petroleum gas has a temperature of about -60°C, while liquefied natural gas has a temperature of -160°C. LPG storage tanks are widely used. Market demand: High-temperature resistant polyisocyanurate (the PIR system takes advantage of polyester polyols). In the field of transportation, special transport vehicles such as refrigerated trains and trucks are advanced means of transportation that play an important role in today’s economic activities. In railway transportation, the grades of passenger trains are continuously improving. Air-conditioned trains in our country are gradually replacing older types of carriages. Air-conditioned trains are comfortable to ride in, with pleasant temperatures inside regardless of whether it is winter or summer. The inner walls of domestic large and medium-sized buses are also commonly coated with rigid polyurethane foam. The performance of the aforementioned vehicles is inseparable from the excellent insulation properties of rigid polyurethane foam. Refrigerated tank trucks are essentially mobile refrigerated tanks. Tank trucks used for transporting high-viscosity industrial oils, in which the temperature of the oil inside remains below 130°C, can all be insulated with rigid foam. The materials and structure used for the insulation of ships transporting liquefied petroleum gas and liquefied natural gas are similar to those used in tanks for liquefied petroleum gas and natural gas; the insulating material is rigid polyurethane foam plastic or its reinforced versions. Refrigerated trucks and frozen containers. Customers: various specialized vehicle manufacturers. On inland and ocean-going ships, onboard cold storage facilities are installed, and these small cold stores all use rigid foam as insulation material. Market demand: Polyurethane composites with high fire resistance ratings

Stainless steel can sometimes be painted, but usually with organic coatings; it is definitely not possible to use coatings containing lead or zinc, as this will accelerate corrosion.

The stainless steel in our facility isn’t coated with paint. Direct insulation. Only carbon steel pipes need to be coated with anti-corrosion paint for insulation

Rock wool must not be used for insulating stainless steel pipes, as it has a high chloride content. The chlorosulfonated polyethylene topcoat serves as a barrier.

Strongly oppose answers that are off-topic; it is recommended to delete them. Last edited by whb002002 on 2009-4-17 13:42 ]

Strongly oppose off-topic responses; it is recommended that they be removed. The alkaline nature of rock wool can cause corrosion to carbon steel; it poses little problem to stainless steel. However, during construction, slag contaminates the environment and is harmful to human health, so its use is not recommended nowadays. Last edited by whb002002 on 2009-4-17 13:46.]

Stainless steel generally does not need to be painted before insulation； Unless the corrosion of stainless steel by insulation materials is taken into account, the design will specify painting requirements, primarily as an isolation layer between the stainless steel and the insulation materials.

There is no need for painting; depending on whether insulation or heat retention is required, different materials are used for the insulation layer.

Rock wool is widely used for insulating stainless steel pipes. Can the chloride ions in rock wool actually corrode stainless steel? It must be under some certain operating condition, right?

Carbon steel needs to be coated with an anti-rust paint, while stainless steel does not require it

There is no need for painting; there are many examples of stainless steel covered with rock wool. If you’re still not confident, you can consider switching to aluminum silicate

There is no need for painting at all; it’s only the insulation materials used for stainless steel pipes that have specific requirements regarding chloride content.

It seems the design team has thought very carefully about everything. Generally, rock wool insulation materials contain varying amounts of chloride ions, especially those of poor quality, which have a high chloride ion content. After insulation installation, if the insulation material gets wet, chloride ions are released; austenitic stainless steel suffers from stress corrosion under the combined effect of stress and chloride ions, resulting in cracks in the pipes.

8# Zhang Jiahong: The chloride content in rock wool is indeed relatively high, but the level of soluble chloride is generally low; it does not cause corrosion to austenitic stainless steel. In practice, rock wool is used for insulation in many stainless steel pipes and equipment, yet there have been no reports of austenitic stainless steel being damaged as a result of the chloride present in rock wool.

Adding polyurethane does not require painting, but adding rock wool may require painting.

Do you use pipeline transportation for liquid nitrogen? Can polyurethane foaming be used to meet the requirements for insulation against liquid nitrogen?