Application Background of 4 inch diesel exhaust flex pipe and 5 inch exhaust flex pipe

If you already read our previous article about 2 inch and 2 1/2 inch exhaust flex pipes, then you may already notice, that kind of size is more used to solve the problems of regular family car repair and standard replacement. Their demand is stable, and turnover is fast. But when the exhaust system goes into diesel engine and higher flow situations, the selection logic of flexible connection parts will obviously change. This is the background why 4 inch diesel exhaust flex pipe and 5 exhaust flex pipe appear.

4 inch flex pipe exhaust in diesel engine

4 inch flex pipe exhaust is most commonly used in medium-displacement diesel engines, light trucks, and some construction equipment. Compared to gasoline vehicles, this kind of system normally has longer exhaust pipes, heavier total weight, and more obvious axial movement caused by thermal expansion and contraction. If full rigid connections are used in the middle or front section, the weld and flange position are easy to get fatigue in advance.

When we supply to customers, we often see 4 in flex exhaust pipe is placed in the middle of the exhaust system, to absorb thermal expansion and relative movement of the frame. This kind of position does not require the flex pipe to be very "strong", but it needs to be reliable for long time. If the structure of the exhaust flex pipe is not stable, then it will become the weak point of the whole system.

Special 5 exhaust flex pipe

5 exhaust flex pipe is not our most regular production size, but after confirming the application condition, we can also provide according to demand. Because it mostly appears in large-displacement diesel, modified exhaust, or special fleet projects, the purchasing is usually project-driven, not long-term stock-driven. Actually, 5 inch bellows has higher technical requirement than regular size. This is mainly due to the physical characteristic changes from big diameter.

Because 5 inch exhaust systems are mostly used for large displacement engine, the exhaust flow is big and low-frequency vibration is strong. This brings very high requirement to the spring rate and fatigue life of bellows. And more truck spare parts buyers will choose the integrated pipe with flexible part, this kind of "plug and use" integrated trend is a big test for engineering flexible custom ability. As a factory with more than 30 years manufacturing experience of flexible exhaust connection parts, YDCT already made many suitable parts for related customers.

Why 4 inch and 5 inch exhaust flex pipe must use Interlock Liner

In big diameter exhaust flex pipe, whether use Interlock Liner or not is not an optional thing, but a basic condition. No matter it is 4 inch diesel exhaust flex pipe or 5 inch diesel exhaust flex pipe, if there is no inner liner structure, the bellows layer will directly face high speed, high temperature exhaust gas flushing, and the life will be clearly shorter. You may hear someone focus on the importance of the outer braided mesh, but in big diameter usage, the function of Interlock Liner is often more important.

FAQ

Q: How long can 4 inch diesel exhaust flex pipe work in actual use?

A: This is one of the most common questions during inquiry and aftersales. We also seldom give an "exact years" answer.

From real applications, even if the 4 inch diesel exhaust flex pipe is made of 304 stainless steel, under high temperature, high vibration, and frequent thermal cycle condition, the working life still will be affected by many outside factors. For example, if the engine vibration is not shared by other structures, or if the exhaust system does not have enough support points, or if the flex part is in long time stretching or twisting state.

In heavy-duty diesel vehicles or long time running machines, the normal accepted life in the industry is about 1–2 years stable use. If installation condition is not good, or the whole exhaust pipe put stress on the flex pipe, early leakage or fatigue cracks are not rare. So in projects, we more prefer to confirm the real working condition with customer, not just simply promise "how many years it can use". The flex pipe is not used for bearing the whole system, it is only a buffer part.

Q: Do 4 inch or 5 inch exhaust flex pipe need extra support and fixing?

A: The answer is yes, and the bigger the size, the easier to ignore this problem.

Compared with 2–2.5 inch exhaust flex pipe, 4 inch and 5 inch exhaust flex pipe have heavier weight, and more obvious movement from thermal expansion and contraction. If the whole exhaust system only relies on the flex pipe to "hang", then it will quickly become the stress concentration point.

In our past cases, many early damage problems are not from material quality, but from the exhaust system does not reasonably share the weight and vibration. The correct way is: the flex pipe only absorbs the movement and vibration, the weight and structure stability still should be held by the fixed pipes and hangers. So when we give technical suggestions to customers, we usually remind, big size flex pipe must be used with proper support design, not only depend on the flex part itself.

Q: Is it necessary to use higher grade stainless steel for 4 inch / 5 inch exhaust flex pipe?

A: This problem happens very often among diesel vehicle and commercial vehicle customers, especially in high humidity, high salt, or long-time running environment.

From our real feedback, if big size exhaust flex pipe uses low grade material, it is easy to appear corrosion problem at weld seam or bellows forming part, and then reduce the structure strength. Especially for diameter bigger than 4 inch, once the local corrosion happens, the crack will grow faster.

Because of this, for this kind of size, we only suggest 304 stainless steel or better anti-corrosion material, and default recommend to use with Interlock Liner. This is not for “showing good spec”, but because big diameter exhaust system has higher requirement for structure stability