Regarding internally insulated pipes

The poster is referring to vacuum insulation pipes with good thermal insulation properties. Such pipes use pearlescent sand filled between the inner and outer tubes as a support mechanism; the inner tube is covered with metal-coated foil that prevents heat transfer through radiation, and the space inside is evacuated. The production of such pipes is carried out in short sections, and ordinary insulation is still used at the joints. The shorter the inner tubes at the joints, the less ordinary insulation is needed, resulting in a better insulating effect. (I’m not sure if this addresses the original question; it’s just for reference.)

Article 3.1.3.5 on page 14 of the \"Code for Design of Industrial Metal Piping\" GB50316-2000 mentions insulated pipes. Since I am not clear as to what exactly such insulated pipes are, I would like to ask the experts here if there are any different opinions. Thank you!

Yes, I’ve heard of vacuum being used in cryogenic liquid storage tanks, but I haven’t heard of similar technology being used in pipelines.

There are methods for internal insulation of pipes, and they are also used in flue gas pipes. It is not affected by environmental conditions and is also more aesthetically pleasing. But as for the specific approach, I am also looking for relevant information. Hehe

An article from Google; for reference, please visit http://www.jsdhl666.cn/newdis.asp?id=306 – Construction Plan for Insulation in Coal Gas Pipelines. I. Project Overview: The Huaye Special Steel 34*8.2 regenerative pusher-type heating furnace uses coal gas for heating, which helps save energy, maintain a constant temperature, and reduce environmental pollution. The coal gas pipelines are an important part of this regenerative pusher-type heating furnace. The insulation for gas pipelines is of the internal type; the insulating material used is a lightweight cast material, with a casting thickness of 70 mm. 1. The gas pipelines are available in various specifications such as φ2220, φ1520, φ1220, φ1020, φ820, φ720, and φ276, with a length of approximately 200 meters. 2. In accordance with the owner’s schedule, the internal insulation work is to be completed by March; given that temperatures in Baotou are low in March, it falls within the winter construction period. 3. Ensuring the normal operation of the heating furnace depends largely on the insulation of the gas pipelines. According to standard construction methods, insulation inside gas pipelines should be applied after the pouring of the pipeline material is completed; however, since almost all of the gas pipelines have already been assembled, this makes it very difficult to carry out the internal insulation work. 　 In the past, proper attention was not given to the corrosion protection of steel structures and grid structures; manual rust removal was the only method used, along with the application of ordinary red lead primers and standard paints. After half a year or a year, the coating would bubble, allow rust to show through, and peel off, leading to corrosion of the steel, and repair became very difficult. The damage to the anti-corrosion layer is caused by various factors, with the main reasons being the corrosion resistance of the coating material and improper application methods. Steel structures and grid structures are exposed to the air for long periods of time. When climate conditions change and the relative humidity of the air exceeds a certain critical value, a water film forms on the surface of the steel. This critical humidity level depends on the condition of the steel surface as well as whether there are any moisture-absorbing substances on it. The corrosion of steel is primarily electrochemical corrosion. Differences in material composition arise when steel structures are welded, and welding slag as well as stress can act as the cathode and anode areas of a corrosion cell. In particular, if the rust on the steel surface is not removed thoroughly, a layer of rolled iron oxide remains on the surface of the steel. Some people think that this oxide scale is not rust, but that’s not the case; it is actually a product of corrosion at high temperatures, primarily iron tetraoxide. In water containing trace amounts of salts, the electrode potential difference between it and steel can reach 0.26 volts. In the water film, the rolled scale acts as the cathode, while pure steel forms the anode. The anode is continuously corroded, while the cathode gradually expands; the rust products break through the coating, leading to corrosion of the steel structure. To carry out effective anti-corrosion work and achieve long-term corrosion protection, three basic requirements must be met: proper surface treatment, the use of high-performance materials, and achieving a sufficient coating thickness. 1. Surface treatment: Surface treatment is very important; with the same type of paint and the same corrosive environment, using different application techniques can extend the product’s lifespan by three to five times. The dirt and rust layers on the steel surface must be removed, especially the black oxide scale that forms during steel rolling; this scale acts as the cathode for electrochemical corrosion and is the source of corrosion, so it must be eliminated. The surface treatment quality should meet the Sa2.5 grade specified in the pre-treatment standards for steel surfaces prior to painting. Second, material selection: Applying specialized anti-corrosion paint to the surface remains the primary method for protecting steel structures and grid structures from corrosion at present. Based on their protective functions, anti-corrosion paints can be divided into primer, intermediate coat, and topcoat. Each layer of paint has its own characteristics and performs a specific role; when combined, these layers form a composite coating that enhances anti-corrosion performance and extends the product’s lifespan. 4. Coating thickness: Paint is an intermediate material for corrosion protection, and a coating is formed only after application. If the coating thickness is uneven, burrs on the steel surface or peaks from anchor spinning will expose the coating. If the coating is applied only a few times, pinholes may form in the coating, and oxygen, chloride ions, water molecules, and other substances in water can pass through these weak points, causing the steel to rust and corrode. The volume of the corrosion products expands, forming rust scales that gradually grow larger, until the coating bubbles and peels off. 　　To prevent water, oxygen, and electrolytes from penetrating the coating, it is best to use several high-performance anti-corrosion coatings to form a thickened composite anti-corrosion coating system, namely: a heavy-duty anti-corrosion coating system. 　　From the formula: T = L²/6D, it can be seen that the service life T is proportional to the square of the coating thickness L. Increasing the coating thickness enhances its insulating capacity, and it is an effective way to prolong the coating’s lifespan and protect steel. By using a new type of high-solid-content thick-coat paint, a heavy corrosion-resistant coating with a thickness of 250–500 microns can be achieved after just a few applications; whereas an ultra-heavy corrosion-resistant coating can reach a thickness of 1000–2000 microns (Reference: \"Practical Handbook of Coating Technology\" by Ye Yangxiang). The thickness of the corrosion-resistant coating should generally be at least 200 microns, and it must be uniform, continuous, and free of pores. Before delivery, inspections should be carried out using a thickness gauge and an electrical spark leak detector; the inspection and acceptance procedures specified in the Chinese Petroleum and Natural Gas Industry Standard SY/T0447-96 can be referred to. 5. Corrosion protection: For the corrosion protection of the steel structure in an airport hangar and of its grid structures, shot blasting is used to achieve a rust removal level of Sa2.5. An inorganic zinc-rich coating is applied as the primer, epoxy colored paint as the intermediate coat, and a fire-retardant paint as the topcoat. It has excellent quality and is expected to last for over 30 years. 　　A construction machinery factory uses imported epoxy colored paint. Rust removal is carried out using shot blasting, followed by the application of epoxy paint, ensuring excellent quality. A factory is located to the east of a chemical plant; the highly corrosive gases such as chlorine and sulfur dioxide emitted by that chemical plant cause severe damage to the equipment, steel structures, and cable trays in this factory. The bridge deck is a steel structure that is 10 meters high and 4 meters wide, with a total length of over 10 kilometers. It was originally painted with ordinary paint, which led to severe corrosion over time. Epoxy enamel paint and chlorinated rubber paint were used for the anti-corrosion overhaul, and to this day the coating remains intact with no corrosion occurring on the cable trays. 　　This composite coating structure can also be used in steel equipment and structural frameworks that come into contact with water, such as wet gas tanks, steel swimming pools, and sewage treatment plants, providing excellent corrosion protection.

I’ve learned from everyone here: at our site, the outer wall of the pipes is first insulated with silicate insulation material (commonly referred to as internal insulation), and on the outside, galvanized iron sheet is used for insulation (commonly referred to as external insulation). Looking at the question posed by LZ, I thought it was asking about that insulation material

I worked on a project for the recovery of carbon black exhaust gases, and one of the pipes used in that project had internal insulation; it was made of cast material containing refractory cement and similar substances. In order to allow the cast material to adhere to the pipe walls, many Y-shaped steel bars were welded inside the pipe, and their length was likely determined based on the thickness of the cast material I think this might fall under internal insulation, and thanks to the person on floor 2 for helping me gain some knowledge! Thank you! I also came across this by looking at GB50316!

I also came here after seeing 50316 and doing a search. I’m also not sure what internal insulation pipes are; external insulation pipes are easy to understand, as they are quite common. I would like to ask the experts: in what situations is internal insulation used? What are the differences between internal insulation and external insulation?

On Baidu Wenku, I found a PPT titled “Introduction to the Process of Undersea Pipeline Laying”; it contains several images that can help you understand the topic. It’s a PPT I came across quite recently as well