Currently, the traditional insulation materials used in shipbuilding for steam pipes are mainly mineral wool, rock wool, etc. These traditional insulation materials are used in different parts of the ship body due to their different characteristics and differences. With the continuous improvement of industrial requirements, the limitations of traditional insulation materials have become increasingly prominent, and they are no longer able to meet the increasing quality requirements of industrial production. Therefore, it is urgent to develop new materials with more stable performance, better insulation effect, and more harmless and environmentally friendly properties to replace traditional insulation materials. This has led to increasing attention being paid to the research of new aerogel insulation materials.

1. Traditional insulation materials
Traditional insulation materials for ships mainly include inorganic fibers, such as rock wool, ceramic wool, and glass wool. Some special parts of the ship body also use organic and inorganic mineral insulation materials.
1.1 Inorganic fibers
1.1.1 Rock wool
Rock wool is mainly made from pure natural minerals such as dolomite and basalt, and after being heated and melted, it is spun into non-continuous fibers using a high-speed centrifugal method. It also requires the addition of certain amounts of dust-proof oil, hydrophobic agents, and binders to form different specifications and uses of rock wool products. The rock wool products obtained through this process have low density, stable chemical properties, excellent insulation, fire resistance, and sound absorption properties, and are also inexpensive. However, due to the brittle and coarse nature of rock wool fibers, poor heat resistance, and especially when absorbing moisture or aging, their operating temperature is limited to 650 ℃ to 850 ℃. Most existing rock wool materials do not meet the standard of A-level fire separation materials. In addition, rock wool materials also have poor water repellency, are prone to falling off after rain, have poor vibration resistance, are prone to generating dust during construction, and are irritating to the skin of construction workers.
1.1.2 Ceramic wool
Ceramic wool for ships is made from natural obsidian or aluminum oxide and silicon oxide powders and other ceramic materials through high-temperature melting, compressed air blowing, and then prepared by a collecting device. It has a high-temperature limit of 1000 ℃ to 1200 ℃. It has the advantages of fine fibers, light weight, high strength, good elasticity, insulation, fire resistance, sound insulation, corrosion resistance, mechanical vibration resistance, etc., and can meet the ship protection grade standards in the thermal protection level of ships. Ceramic wool has replaced asbestos boards, perlite boards, and frogstone boards, which are easily broken traditional insulation materials, and is used as A and B-level partitions, fire insulation materials for bulkheads and decks, and A and B-level fire insulation materials. Compared with rock wool, ceramic wool can effectively reduce the spatial position of the structure and help save material costs. Its low skin irritation to humans, ease of construction and maintenance, and other characteristics make it widely used in ships and have a wide range of applications.
1.1.3 Glass wool
Glass wool is mainly made from quartz sand, limestone, and dolomite as the main raw materials, along with some chemical raw materials such as soda ash and borax, mixed and melted. It is then blown by high-temperature gas to obtain an artificial non-alkaline ultra-fine glass fiber.
It has the following many advantages: its fiber diameter is fine (about 1 μm), and its density is low (as low as 20 kg/m3); secondly, it has good insulation and heat insulation performance at both high and low temperatures, low thermal conductivity (0.034 W/mK); finally, it has good processing performance, sound absorption performance, corrosion resistance, aging resistance, low slag particle content.
Therefore, as an insulation material, glass wool was widely used in naval ships' cabins and submarine enclosures in the United States since the 1970s.
However, the operating temperature of glass wool is low, usually between 500 ℃ and 600 ℃, so non-alkaline ultra-fine glass wool cannot be directly used as A-level fire separation materials.
1.2 Organic
Common insulation materials also include porous materials formed by foaming organic polymer materials, such as polyurethane foam (PU), polyimide (PI) foam, and phenolic (PF) foam. 1.2.1 PU foam insulation materials
PU is formed by reacting polyurethane with catalysts and foaming agents. The commonly used PU foam on ships is mainly rigid hard PU with closed pores. PU has excellent insulation and cold preservation properties (thermal conductivity is 0.0233 - 0.0256 W/mK), especially in low and ultra-low temperature environments. Therefore, it is quite common in the construction of cold storage in long-distance ships.
Advantages: In addition, it has high strength and pressure resistance (0.196 MPa) and a narrow temperature range (-110 ℃ - 130 ℃), which is suitable for insulation and refrigeration equipment, cold storage, insulation boards, wall insulation, pipe insulation, and insulation filling materials for storage tanks, etc.
Disadvantages: The fire resistance of PU, compared with other insulation materials, is relatively poor, which limits its application.
1.2.2 PI foam insulation materials
PI foam insulation materials are foam materials formed by the foaming reaction of polyimide with foaming agents and stabilizers. Since its development, it has been applied in aerospace insulation and has been one of the most expensive and best-performing foam materials among organic foam insulation materials.
Its characteristics are low density (5 - 8 kg/m3), which can significantly reduce the weight of ships.
The temperature range of PI foam insulation materials is -260 ℃ - 350 ℃. At extremely high temperatures, polyimide will decompose.
1.2.3 PF foam insulation materials
PF is a foam insulation material formed by cross-linking and foaming after reacting甲醛 and phenol to form a pre-polymer. Expanded perlite
Pure natural perlite sand， after preheating and instantaneous high-temperature roasting expansion， will obtain a white granular material with a honeycomb-like structure inside - expanded perlite， which is also a widely used insulation porous material (thermal conductivity is approximately 0.076 W/mK).
Advantages： Expanded perlite has good insulation efficiency， fire resistance， environmental protection performance， and chemical stability. It has a wide range of applications and shows excellent performance in many fields.
Disadvantages： However， this material has poor water resistance and high water absorption rate， which will cause it to crack easily and reduce insulation performance over time， affecting the technical performance after hardening. Therefore， in the application of insulation and heat preservation in the ship field， polymers such as polysiloxane are added for chemical modification to improve its mechanical properties.
Inorganic mineral insulation materials， in addition to the above inorganic fiber materials， also include porous insulation materials. For example， siliceous earth， lime， etc. are used as main raw materials， and fibers are added after various processes to make silicate calcium products， which can be used for fireproof partitions and high-energy pipelines in ships.
Expanded perlite
Pure natural perlite sand， after preheating and instantaneous high-temperature roasting expansion， will obtain a white granular material with a honeycomb-like structure inside - expanded perlite， which is also a widely used insulation porous material (thermal conductivity is approximately 0.076 W/mK).
Advantages： Expanded perlite has good insulation efficiency， fire resistance， environmental protection performance， and chemical stability. It has a wide range of applications and shows excellent performance in many fields.
Disadvantages： However， this material has poor water resistance and high water absorption rate， which will cause it to crack easily and reduce insulation performance over time， affecting the technical performance after hardening. Therefore， in the production process， inorganic solvents and additives are often used to effectively increase its resistance to moisture and corrosion.
Inorganic mineral insulation materials， as a new type of inorganic insulation material， have their special advantages：
First， compared with traditional inorganic fiber materials， there is a significant improvement in insulation efficiency；
Second， inorganic mineral materials usually have high temperature resistance， good chemical stability and fire resistance；
Third， most inorganic mineral materials have abundant raw materials and have a small impact on the environment during production， which is in line with the concept of sustainable development；
Fourth， the density is low， and the weight is light， usually ranging from 10 to 20 kg/m3.
However, the advantages and disadvantages vary, and the drawbacks of this type of material can also be seen:
First, the thermal conductivity of inorganic mineral materials is generally around 0.03-0.05 W/(m K), which is higher than that of organic materials, potentially affecting the insulation effect;
Second, inorganic mineral materials usually do not have good plasticity, which may make it difficult to adapt to the complex shapes and structures of ship pipelines;
Third, inorganic mineral materials are usually hard, and construction requires professional techniques and equipment, making the construction process more difficult;
Fourth, the residual high corrosive chemical substances during the material synthesis process not only pose certain safety risks in use but also increase the maintenance and maintenance costs in the later stage.

2 Advantages of Aerogel Materials
2.1 Low Thermal Conductivity
Currently, the lightest solid material is aerogel, which has an extremely low thermal conductivity (less than 0.015 W/mK at room temperature, and is an excellent insulation material. Aerogel includes oxide aerogels (such as SiO2, Al2O3, etc.) and carbon-based aerogels. Currently, the most mature process is SiO2 oxide aerogel. On one hand, the low-pore nanostructure formed during the synthesis of aerogel can effectively prolong the heat conduction, which is the reason why aerogel has an extremely low thermal conductivity. However, the high porosity and low density characteristics of aerogel result in significant brittleness, and infrared rays are prone to radiate through at high temperatures, increasing heat conduction, making it difficult to directly use.
To achieve better usage effects, it is usually compounded with fibers, pigments, etc., such as aerogel and glass fibers, and the thermal conductivity of the compounded material is 0.018-0.021 W/mK, which is much lower than the thermal conductivity values of traditional insulation materials (0.018-0.48 W/mK) (see Table 1). Compared with traditional insulation materials, the energy-saving effect of the composite material can be improved by 30%-50%, which is conducive to its application in pipelines, building insulation, and other fields.
2.2 Fire Resistance Performance
The usage environment of marine fire-resistant insulation materials is mainly to maintain a suitable working and living environment in the cabin and to provide insulation and heat protection for fireproof and thermal pipelines. The performance of this material will directly affect the comfort, safety, and service life of the ship, and even the combat effectiveness of the troops. Therefore, when using this material, a comprehensive performance evaluation of multiple aspects needs to be carried out. The fire resistance classification of ships includes A, B, and C levels. Aerogel, as an inorganic material, has strong fire resistance, a wide temperature usage range, and resistance to temperature shock. It has A-level fire resistance and is very suitable for ship scenarios with high fire resistance requirements. In the event of a fire or accident, it can effectively protect the equipment. Aerogel can meet the non-combustibility requirements, and silicon-based aerogel, as a green material, has low flame spread, no toxicity, and meets the requirements of ship use.
2.3 Reduction of Insulation Layer Thickness
Aerogel composite materials not only have low thermal conductivity but also, at the same insulation effect, their usage thickness is only 1/4 to 1/2 of traditional materials. The difference becomes more obvious as the temperature increases. Therefore, aerogel composite materials can significantly reduce the insulation layer thickness in dense pipelines and narrow spaces, improving space utilization, reducing transportation load, and effectively increasing the ship's space.
2.4 Anti-Aging Ability
The hydrophobicity of aerogel is not less than 98%, and the volume water absorption rate is no more than 1%. It has extremely strong hydrophobicity. However, the unique porous structure of aerogel has permeability, which effectively avoids corrosion of equipment and pipelines, improving equipment safety. In addition, compared with traditional insulation materials, aerogel has stronger anti-aging ability. Data shows that its lifespan is 8-10 times that of conventional materials, and only requires less maintenance cost to achieve reliable insulation effect. In terms of construction, aerogel is absolutely hydrophobic and does not require special waterproofing during transportation and construction. Even when soaked by rain, it will not cause disintegration or settlement. It can also be stored in a humid environment. Finally, its extremely strong mechanical properties are due to the excellent flexibility, toughness and compressive strength provided by the base material. It can be used in some pipes, supports and pipe supports, meeting various design and construction installation requirements.

3 Case Analysis
An example of using aerogel material for insulation renovation of the smoke ducts in a shipyard was analyzed and compared with the insulation effect of traditional mineral wool. This provides certain references for the application of insulation engineering in ships.
3.1 Summary of Working Conditions
Ship pipe temperature: 600 ℃; Pipe outer diameter: 1,240 mm; Pipe length: 1.5 m; Wind speed: 0 m/s; Average ambient temperature: 25 ℃.
3.2 Insulation Scheme
The renovation plan was to replace the 200 mm mineral wool with 150 mm aerogel felt (60 mm ceramic fiber inside and 90 mm glass fiber outside).
3.3 Insulation Effect
According to GB 50 264-2013 "Industrial Equipment and Pipeline Insulation Engineering Design Code", the thickness of the insulation layer, surface temperature, heat loss and annual heat dissipation were calculated before and after the renovation. The calculation results are shown in Table 2. The advantages of the aerogel scheme are as follows:
First, the thickness of the insulation layer is reduced. The 150 mm aerogel thickness can meet the insulation requirements, and the diameter after insulation is reduced by 100 mm, reducing the occupied space of the pipeline and improving the utilization of the pipe gallery;
Second, the surface temperature of the aerogel insulation scheme is 45.03 ℃, much lower than that of the mineral wool (56.61 ℃). As the operating time increases, the surface temperature of the mineral wool gradually increases, and the measured data on site exceeds 60 ℃.
Third, the heat loss and annual heat dissipation of the aerogel scheme are 30% less than those of the mineral wool, which is conducive to energy conservation;
Fourth, the construction difficulty of the aerogel scheme is low, the installation is simple, and the maintenance cost is low. Combined with the high strength and good stability of aerogel, it can maintain good insulation and heat preservation effects for a long time without collapse or uneven thickness. The service life is longer.

4 Conclusion
At present, conventional aerogel products in China are relatively mature. In the future, they will develop towards lightweight, high-temperature resistance and low cost. As a new type of fireproof and heat insulation material, aerogel applied in the insulation system of ship pipelines can effectively improve insulation performance and reduce energy loss; under the same insulation effect, using aerogel can greatly save material costs, reduce the thickness of pipeline coating and the occupied space of the pipeline layout; lightweight aerogel products can further reduce the overall weight of the ship system; at the same time, with the reduction of cost, aerogel products have more advantages in economic performance compared with traditional materials. It is believed that in the near future, aerogel products will have wider application and extension in the ship field.