What are the types of seal failures of DOT brass fittings

DOT Brass Fittings are key connection components used in motor vehicle pneumatic systems and are widely used in air brake systems, suspension systems, and body air distribution systems. As a pneumatic fitting product certified by the U.S. Department of Transportation (DOT), this type of brass fitting must maintain reliable sealing performance under high pressure, high temperature, high vibration and other working conditions to ensure the stability and safety of the vehicle's air system. Sealing performance is directly related to the energy efficiency, safety and compliance of the air system. However, in the long-term use process, due to factors such as material aging, process deviation, and environmental corrosion, sealing failure is more common.

Thread seal leakage
Threaded connection is one of the most common connection methods in DOT Brass Fittings. Its sealing usually relies on metal-to-metal tapered thread matching, sealant or PTFE raw tape. Thread seal failure is mainly manifested in interface air permeation, pressure drop, and thread loosening. Common causes include poor thread processing, improper use of sealant, or insufficient installation torque. Metal threads may produce micro-motion wear under conditions of thermal expansion and contraction, resulting in the gradual formation of micro-leakage paths. Thread slippage, misaligned threads, or impurities attached to the thread surface may also damage the sealing effect.

O-ring failure
As a common auxiliary sealing element in DOT brass fittings, O-rings are used to fill the micro-gap between metal contacts and enhance the sealing performance. O-ring sealing failure is a typical cause of rapid leakage and pressure loss. Failure types include material aging and hardening, permanent compression deformation, tearing, expansion and swelling, and surface cracking. The causes of failure usually include operating temperatures exceeding the tolerance range of the O-ring material, long-term continuous compression under high pressure, contact with incompatible media (such as lubricants, additives, etc.), and impurities or particles scratching the O-ring surface.

Leakage caused by structural misalignment
During transportation, assembly or operation, the structure of DOT Brass Fittings may be misaligned or loosened due to vibration, impact, excessive installation or system stress, resulting in a no longer tight sealing interface. Especially in the case of a plug-in connection structure, if the pipe is not fully inserted or the clamping mechanism is not fully locked, the internal gap will not be closed, resulting in continuous micro-leakage. When the vehicle is driving at high speed or in potholes, this kind of micro-displacement effect is particularly significant, which can easily cause intermittent air pressure loss.

Material Corrosion Failure
Brass materials are prone to dezincification corrosion in long-term high humidity and high salt environments, which manifests as powdering of the joint surface, loose structure, and hollowing of the internal structure, resulting in decreased air tightness at the joint. Even if the joint affected by corrosion has no obvious damage in appearance, it may form capillary channels inside, causing compressed air to leak. Electrochemical corrosion is also a common hidden damage, especially in the combination of joints and pipes of different metal types, which will cause local corrosion and damage the sealing structure due to the potential difference.

Thermal stress leakage caused by thermal expansion and contraction
The ambient temperature difference during vehicle operation is large, especially for vehicles operating in cold and high temperature areas, and their pneumatic joints need to withstand frequent thermal expansion and contraction cycles. The thermal expansion coefficients between brass and nylon tubes are quite different, and it is easy to form gaps at the interface under the repeated action of thermal expansion and contraction, resulting in seal failure. In addition, temperature changes may also accelerate the aging of the sealing ring, causing it to harden or lose elasticity, and eventually lose its effective sealing function.

Machining tolerance errors lead to seal failure
DOT Brass Fittings need to have extremely high dimensional accuracy and surface quality, especially in the sealing surface, thread joints and pipe mouth claws. Once the tolerance control is not strict during the manufacturing process, such as uneven sealing surface, angle deviation, and thread taper that does not meet the standard, it will directly affect the fit and clamping force of the sealing surface, causing gas to escape from the micro gap. Such problems are more common in low-cost manufacturers or non-certified products, and often leak at the beginning of use.

Improper installation operation
If the on-site installation process is not carried out in accordance with the specifications, it may also cause seal failure. For example: not tightening according to the recommended torque, not cleaning the connection surface, excessive or insufficient use of sealant, O-ring not properly in place, etc. In addition, after repeated assembly and disassembly, the joint thread or sealing surface may be fatigued, scratched or deformed. At this time, if the seal is not replaced, continuous leakage is very likely to occur.