How to choose the material of car exhaust pipe

Blieve that friends who have changed the exhaust pipe know that the exhaust pipes that they buy and change are generally made of stainless steel. Even some high-end exhaust pipes are made of titanium alloy. Have you ever considered why these materials are used for exhaust pipes? What material is most suitable for making exhaust pipes? Today, I will use this article to explain the exhaust pipe material in detail. For friends who have changed or want to change the exhaust, conduct popular science and solve their doubts.

First of all, We need to understand the working conditions of the exhaust pipe, that is, the working scene of the exhaust pipe. The function of the exhaust pipe is to discharge exhaust gas from the engine, purify the exhaust gas and play a certain muffler effect. The temperature of the exhaust gas is generally 300-400 degrees Celsius, and some are even close to 1000 degrees Celsius. The closer it is to the engine, the higher the temperature. The continuous output of gas from the engine involves the concept of exhaust back pressure. Exhaust back pressure is the resistance of gas output, which can also be understood as the pressure of gas on the pipe wall. Generally speaking, 1.0 liter displacement is about Around 25kpa, if it reaches 1.6 liters, it will be around 40kpa. Engines with different displacements and powers have different back pressures. At low temperatures or after parking, the temperature of the exhaust pipe decreases, and a large amount of water will accumulate in the muffler; the pH of the condensate is 8-9, which is weakly alkaline, and this condensate has a corrosive effect on the exhaust pipe. Therefore, the material of the exhaust pipe needs to have good stability at high temperature, high temperature oxidation resistance, corrosion resistance, cold and heat fatigue and good processing performance.

Usually the exhaust pipes of our family cars are made of ordinary steel and stainless steel. Among them, ordinary steel is the most common. Generally, the exhaust pipes that we buy and modify are made of stainless steel.

Ordinary iron

Ordinary iron has good processing properties and low cost, so it was used in large quantities in automobiles in the early days, but because of its poor corrosion resistance. After using it for about half a year, at most 1 year, the inside will gradually delaminate, forming exhaust blockage, which will seriously affect the power and cause the exhaust to be unsmooth and increase the fuel consumption, and the muffler skin is prone to leak points. Later, some manufacturers applied a high-temperature corrosion-resistant coating on the surface of the exhaust pipe to extend the service life of the exhaust pipe. But it will cause corrosion in the subsequent solder joints without coating protection. At present, ordinary iron exhaust pipes will gradually be replaced by stainless steel exhaust pipes.

Ferritic stainless steel

Here is a quote from the description of ferritic stainless steel in the encyclopedia:

Containing 15% to 30% chromium. Its corrosion resistance, toughness and weldability increase with the increase of chromium content, and its resistance to chloride stress corrosion is better than other types of stainless steels. In this category, there are Crl7, Cr17Mo2Ti, Cr25, Cr25Mo3Ti, Cr28, etc. Because of its high chromium content, ferritic stainless steel has better corrosion resistance and oxidation resistance.

Ferritic stainless steel has a small thermal expansion coefficient, high thermal conductivity, good high temperature oxidation resistance under repeated heating and cooling conditions, and good pitting corrosion resistance. Later, it became the material of choice for automobile exhaust pipes. It is believed that ferritic stainless steel exhaust pipes will be widely used in household car exhaust in the future.

Titanium alloy material

Titanium alloy is an alloy composed of other elements based on titanium. It has a stable structure. Its main advantages are better oxidation resistance, low temperature toughness, corrosion resistance, and its wear resistance is also superior. At the same time, the density is smaller than that of stainless steel (the weight of titanium alloy is smaller than that of stainless steel under the same volume), but the strength is more than 40% higher than that of ferritic stainless steel. Therefore, for some extreme conditions, the exhaust pipe can be made of titanium alloy.

How to choose materials when changing the exhaust?

The modified exhaust pipes currently available on the market are all stainless steel, and the specific model is SUS304 stainless steel. Yes, it is what we call ‘food grade’ stainless steel, which is often used in kitchenware and kettles. It is also a widely used material model for exhaust pipes. Generally speaking, the corrosiveness and stability of SUS304 stainless steel have met the normal working conditions of exhaust pipes, and the service life is very long. The use of stainless steel with higher specifications will only increase the cost and process complexity, and it is not very meaningful. This material can be used to modify the tail end or the middle tail end. So why is there such a thing as a titanium alloy exhaust pipe? This is for those professional racing or extreme enthusiasts to fully explore the power of the car. For example, in order to reduce the weight of the car (the density of titanium alloy mentioned above is lower than that of stainless steel), the power of the car is greatly increased by changing the engine, brushing the ecu, and changing the air intake, resulting in exhaust back pressure and gas temperature much higher than the original car's rated range Case.

The muffler under the GRWA brand, including SS201, SS304, SS409, truck aluminum plating and flowmaster aluminum plating and other materials, can meet the various needs of customers. If you have any questions about the material of the muffler, you can consult us, and we will reply to you as soon as possible.

In the next issue, let's talk about the material, cost performance and purchase guide of the muffler in the mainstream market!

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