Pipeline insulation issue

This post was last edited by hch506 on 2009-6-6 at 11:05. Hello, the original poster: Polyurethane foam plastic can be used for this purpose. A new type of insulating material has been developed in China – modified polyurethane foam plastic for cryogenic applications (PUH, PUB). This material is suitable for use in gas liquefaction equipment, liquefied gas carriers, and pipelines for transporting low-temperature liquids within a temperature range of -196 to 90°C. It has been successfully applied in practical production; for example, 40m3 liquefied ethylene tankers equipped with this material achieve a vaporization rate of only 0.11%/day. It can be used not only for insulating LNG pipelines but also for pipelines transporting low-temperature liquids such as liquid oxygen, liquid nitrogen, and liquid argon in air separation equipment. PUH and PUB modified polyurethane foam plastics have a low thermal conductivity, which decreases further at temperatures below -60°C. Another advantage is that their closed pore ratio exceeds 90%, so moisture absorption has little effect on their thermal conductivity. They also exhibit good dimensional stability; they can be pre-formed into the desired shapes in factories or applied via spraying on-site. They are safe and reliable to use, cost-effective, require minimal maintenance, and are easy to repair after mechanical damage. The key advantage of PUH and PUB modified polyurethane foam plastics lies in their improved ability to withstand pressure differences in the pores under cryogenic conditions, as well as their better dimensional stability. This prevents cracks from forming in the material under such conditions, ensuring long-term safe and normal operation and thus excellent insulation performance. Moreover, these materials contain no chloride ions, so they do not cause corrosion to steel or other metal pipes. Taking an LNG pipeline capable of transporting 718 MPa, 141 K, and 65,000 m³/h as an example, this analysis compares two types of insulation structures: those using PUH and PUB modified polyurethane foam plastic for insulation and those using vacuum multi-layer insulation, in terms of insulation performance, dimensions and weight, construction complexity, pipeline cost, maintenance requirements, and service life. **Insulation Performance**: When PUH and PUB modified polyurethane foam plastic is used as the insulating material, its low thermal conductivity is advantageous. At -163°C, its thermal conductivity is around 0.10121 W/(m·K). Another advantage is the high closed pore ratio, which means moisture absorption has little impact on its thermal conductivity. In vacuum multi-layer insulated pipelines, the absence of air convection results in significantly improved insulation performance. The radiation-blocking materials used effectively prevent heat radiation from penetrating. For example, in a pipe with an inner diameter of Φ32 mm, the heat loss in the straight sections is only 0.11 W/m. **Dimensions and Weight**: The thickness of the insulation layer in polyurethane foam plastic-insulated pipelines is designed based on a heat loss of 20 W/m. The pipes are made of Φ180 mm × 8 mm stainless steel, with an insulation layer thickness of 120 mm. The outer diameter of the pipeline is Φ420 mm. The weight of each 1000-meter section of pipe is approximately 42 tons. Vacuum multi-layer insulated pipelines are also designed with a heat loss of 20 W/m. The inner diameter of the vacuum tube is Φ180 mm × 8 mm, while the outer diameter is Φ325 mm × 4 mm; both are made of stainless steel. The weight of each 1000-meter section of such pipelines is about 70 tons. Although the space occupied by these two types of insulated pipelines is similar, the density of the modified polyurethane foam plastic used for insulation is only 30–40 kg/m³. Therefore, the insulated pipelines made from this material are lighter, weighing only 0.16 times that of vacuum multi-layer insulated pipelines. **Construction Process**: PUH and PUB modified polyurethane foam plastics have good dimensional stability, allowing them to be pre-formed into the desired shapes in factories or applied via spraying on-site. The modified polyurethane foam plastic insulation structure is typically created by shaping the foam plastic into the appropriate forms based on the pipeline’s outer diameter and insulation layer thickness, followed by installation on-site. The insulating material also requires moisture-proof measures and protective coatings. The insulation layer consists of two layers, with each layer having a thickness of 50–60 mm. During installation, the joints between layers are arranged offset from each other, with overlaps used at the connections. Such overlapping joints help prevent surface condensation or freezing. Elastic glass fiber or mineral wool is used at the overlapping joints to provide effective compensation. The shrinkage coefficient of modified polyurethane foam plastic depends on the manufacturing process and density; it is slightly higher than that of common 304L stainless steel. Therefore, the inner diameter of the innermost insulation layer is slightly larger than the pipeline’s outer diameter (by about 20 mm). This allows the pipeline to move freely within the insulation layer when it contracts at low temperatures. Additionally, the insulation material itself contracts at low temperatures, and without sufficient clearance, it could squeeze the pipeline, causing damage to the insulation material. Each insulation layer must have some degree of freedom to move, including the outermost protective layer. The outer surface is covered with aluminum or galvanized iron sheets with a thickness of 0.125–0.150 mm. Other insulation materials that can be used include: polyurethane foam plastic: -65 to 80°C; polystyrene foam plastic: -65 to 70°C; foam glass: -196 to 400°C. These values are for reference only; the actual choice should be determined based on your own requirements

The poster should check out the download address for GB/T11790-1996 General Rules for Insulation Technology of Equipment and Pipelines on the forum: http://bbs.hcbbs.com/thread-7702-1-1.html

The insulation material used for the liquid nitrogen pipelines I’ve come across is rigid polyurethane that is foamed on-site, and its insulating performance is quite good. The insulation thickness can be calculated by referring to GB50264

Hello, can we talk?

Reply to 1# cwtjg: For liquid nitrogen cooling, low-temperature elastic insulation materials can be used. These materials offer excellent insulation properties; they are closed-cell foams that do not require a moisture barrier, and their thermal conductivity ranges from 0.030 to 0.039, ensuring long-term stability； It can maintain its flexible state at low temperatures, without becoming brittle or cracking ； It only needs to be bonded with Armaflex adhesive, which makes installation easy and produces no dust; the installation time is half that of traditional foam materials ； It can be reused, as long as it has not suffered significant damage during disassembly for maintenance, it can be used again ； Using this material can save a significant amount of cooling energy each year.

Commonly used in the market today for insulation are foam materials such as polyurethane PUR, modified polyurethane PUB, PUH, and polyisocyanurate iPIR, in combination with foam glass; insulation is also achieved using low-temperature rubber and plastic flexible foam materials.

For insulating liquid nitrogen pipelines, materials such as polyurethane and modified polyurethane are used; they are cost-effective, but the downside is that it’s difficult to ensure waterproofing, and they may fail after around a year. Vacuum tubes offer the advantage of excellent insulation results, with a smaller outer diameter for the pipes – for example, if the inner pipe has a diameter of DN40, the outer jacket will have a diameter of DN100. The downside is higher costs, but in the long run, using vacuum tubes is still more economical. There is also another type of foam insulation material called Ales from Germany – it is used for insulating pipelines and storage tanks in the LNG industry. I haven’t seen it used in practice yet, but there’s a guy on the forum who often promotes this product; you can search for it on Baidu

The analysis upstairs makes a lot of sense; each material has its own advantages and characteristics, and the key is to consider the specific circumstances of use. Among low-temperature insulation materials, both German Ales and Italian K-FLEX have been localized in China. This material is a fake product and is not imported from abroad.