Almost all catalytic converters manufactured by the automotive industry are placed inside a stainless steel shell. The intention is to allow the outer shell many more years of life than an aluminium metal shell. A shell made of a weaker metal could easily fail due to exposure from adverse weather conditions. Weaker metals are vulnerable to deterioration and can cause exhaust leaks that would directly effect the purpose of the catalytic converter. Because of their exterior design, the internal components of a converter are more vulnerable than the exterior. The interior and exterior design of a catalytic converter has many elements that can preserve its intended longevity. While an average lifespan of seven to 10 years--depending on the elements and condition of the vehicle--are common for most original converters, aftermarket converters usually only survive for half that amount of time due to inferior construction.
The exterior shell is only one of the variables involved in the lifespan of a converter. A vehicle that rarely sees adverse weather conditions, where sand and salt are applied to the surfaces of roads, will last much longer than one that experiences them frequently. However, the exterior shell of a converter has nothing to do with how it functions. The internal component of the catalytic converter can be compromised by a poorly performing engine or a faulty oxygen sensor. Air and fuel need to be mixed properly together for a combustible engine to emit pollutants. Oxygen sensors monitor this even mix. If the fuel gets too rich or too lean, more pollutants will be released into the atmosphere, and the catalytic converter can be compromised by being exposed to the wrong temperature or build-up of carbon. When the oxygen sensor fails, it also fails to communicate correctly with the engine's computer. The engine makes adjustments to allow the vehicle to run under any condition, and either too much fuel or too much oxygen is then exposed to the catalyst. Too much fuel creates more unsupervised heat in the exhaust, melting the internal catalyst. Too much unsupervised oxygen allows potential pollutant particles to not burn properly and then adhere to the catalyst, thereby clogging it. A smooth-running engine which has had stringent maintenance repairs for tune-ups, fuel injection cleanings and oxygen sensor replacements, will contribute to the longevity of the internal catalyst.
Catalytic converters were first introduced in the mid 1970s to prevent harmful pollutants from entering the atmosphere. At the time, they were called two-way catalysts because they minimised the emissions of carbon monoxide and dangerous hydrocarbons. Vehicles manufactured today use three-way catalysts that also help eliminate nitrogen oxides from entering the atmosphere. Platinum and palladium are coated with ceramic and formed into a honeycomb or beads, and placed in a chamber--the external shell. The combustible engine emits harmful exhaust and the converter converts the exhaust into less harmful substances. The catalysts help to convert carbon monoxide into carbon dioxide, and hydrocarbons into carbon dioxide and water. The three-way catalysts now convert the nitrogen oxides into less harmful nitrogen and oxygen.