I’d like to ask gently: is heat transfer oil flammable?

Reply to 1# geddddd: It is mainly determined by the inherent properties of the heat transfer oil: (Refer to the following information.) Types of heat transfer oil: Based on their composition and the manufacturing processes used, heat transfer oils can be divided into synthetic heat transfer oils and mineral heat transfer oils. 1 Synthetic heat transfer oils mainly include the following types: 1) Alkylbenzene-type (benzene ring-type) heat transfer oils. These are compounds in which a benzene ring is attached to alkane side chains; they are products resulting from the combination of short-chain alkyl groups (including methyl, ethyl, and isopropyl groups) with the benzene ring. Its boiling point is between 170–180°C, and its freezing point is below -80°C; therefore, it can be used as an antifreeze. The advantage of such products is that they do not tend to form precipitates within their suitable operating range, with compounds containing isopropyl side chains being particularly good for this purpose. 　　2) Alkylnaphthalene-type heat transfer oils This type of heat transfer oil consists of compounds in which alkyl branches are attached to benzene rings. The side chains attached to it are generally methyl, dimethyl, isopropyl, etc.; the type and number of these attached side chains determine the properties of the compound. Alkylnaphthalene with a methyl group attached to the side chain, used in gas-phase heating systems operating in the range of 240–280°C. 　　3) Alkyl biphenyl-type heat transfer oils This type of heat transfer oil consists of compounds in which alkyl side chains are attached to the biphenyl ring. It is composed of short-chain alkyl groups (ethyl, isopropyl) combined with biphenyl rings, and the type and quantity of alkyl groups determine its properties. The greater the number of alkyl groups, the poorer its thermal stability. Among such products, heat transfer oils synthesized from the meta and para isomers of isopropyl along with biphenyl offer the best quality; they have a boiling point of >330°C and good thermal stability, making them ideal for use in the 300–340°C range. 　　4) Diphenyl and biphenyl ether low-melting mixture type heat transfer oil: This type of heat transfer oil is a low-melting mixture of diphenyl and biphenyl ether, composed of 26.5% diphenyl and 73.5% biphenyl ether. Its melting point is 12°C. The first synthetic aromatic heat transfer oil used in the world was Dowtherm, which is characterized by good thermal stability and a high operating temperature of 400°C. Such products have the best heat resistance among organic heat carriers because there are no alkyl side chains attached to the benzene ring. This low-freezing mixture with a freezing point of 12.3°C is economical to use at room temperature, as its boiling temperature lies in the range of 256–258°C. This is because the melting points of both substances are high (biphenyl is

It is flammable; in the past, a leak in the mechanical seal of the heat transfer oil transfer pump in a hydrogen production facility caused a fire. Fortunately, the damage was not severe and the fire was extinguished promptly.

Since it is a hydrocarbon, it is naturally flammable; based on its flash point, it seems to belong to Category C (flash point > 60°C)

Oils are of course flammable. It is not only flammable; if heat accumulates, it can catch fire on its own. In our factory, spontaneous combustion has occurred due to leaks from flanges onto the insulation material.

This post was last edited by flootherm on 2011-9-2 at 18:59. I have written similar replies before; I’m posting them again for reference: 1) Generally, heat transfer oils are hydrocarbons and are flammable. You can ask the heat transfer oil supplier for the relevant safety parameters of that oil, such as flash point, ignition point, auto-ignition point, etc., so as to obtain this information. 2) Heat transfer oil for heating (heat transfer oil used for cooling and in the gas phase – standards for which have not yet been established). According to item 5 of the new standard «Organic Heat Transfer Oils GB 23971-2009», its closed-cup flash point must be at least 100 degrees ； 3) However, heat transfer oil is usually used at temperatures above its flash point in a sealed environment; it is safe as long as there is no leakage, but it becomes dangerous in the event of a leak. (After all, leakage accidents don’t occur very often.) 4) Whether heat transfer oil will catch fire depends on the three elements of combustion – fuel, oxidizer, and ignition point (temperature), which are necessary conditions for combustion. The presence of the necessary conditions for combustion does not mean that combustion will necessarily occur; four further sufficient conditions are also required: a certain concentration of combustible material, a certain oxygen level, a certain amount of ignition energy, and an uncontrolled chain reaction. The above are the necessary and sufficient conditions for combustion; the fire-extinguishing mechanism of fire extinguishants works by removing one or several of these conditions, thereby stopping combustion. 5) It should also be noted that the flash point of heat transfer oil changes during use at high temperatures – it decreases due to the pyrolysis of the heat transfer oil at high temperatures, which results in the formation of smaller molecular substances (for example, mineral-based heat transfer oils generally have a relatively high flash point when new, but their flash point drops rapidly once they are in use). Therefore, the better the thermal stability, the less likely it is to undergo cracking, resulting in better safety. Is someone trying to block me? I don’t understand. The posted message cannot be retrieved.

Heat transfer oil is flammable. I used to think that since it could be used at such high temperatures, it shouldn’t be easy to ignite, but during the last welding operation, a little welding slag fell on the insulation material, and some heat transfer oil spilled onto it as well; the insulation material caught fire.

Heat transfer oil is difficult to ignite on its own, but fires can occur naturally at very high temperatures； Furthermore, various applications of heat transfer oil involve flammable and explosive substances. As described in the scenario on the 7th floor, it was fortunate that the leakage occurred on the insulation layer; if it had happened on exposed pipelines carrying such flammable and explosive materials, the consequences would have been severe. Therefore, it is essential to pay close attention to the safety aspects related to the use of heat transfer oil, by taking measures to prevent leaks, protect against burns, and ensure a safe distance from pipelines carrying flammable and explosive substances.

Our workshop uses heat transfer oil from Xiefei Company, and we conduct regular analyses of parameters such as residual carbon. As the level of residual carbon increases, its flash point decreases gradually, making it more prone to spontaneous ignition. During the operation of the heat transfer oil system, measures such as nitrogen sealing should be employed to ensure that the heat transfer oil does not oxidize. Several accidents occurred in my workshop where large amounts of heat transfer oil spilled and caught fire. At the beginning of a leak, there is usually no open flame, only smoke; however, when the leaked oil comes into contact with flammable materials, it can catch fire on its own over time. There is also oil that seeps into the insulation material; when the aluminum covering outside the insulation is removed, it comes into contact with air immediately, which can also lead to fires.

Reply to 9# tomorrow8: What kind of pads do you use?

We use steel pads – it’s a one-time solution. It’s recommended to avoid asbestos; it may seem fine at first, but dealing with leaks later becomes troublesome.