A catalytic converter is designed to reduce normal exhaust emissions. It can mask problems that are related to the fuel or ignition systems, or mechanical problems. This will overwork the converter and it probably will not last as long. An overworked converter will lose efficiency. Converters do not usually just stop working. They just work less and less efficiently. Before replacing a converter, determine whether there is another problem that has contributed to its failure. Installing a new converter might fix the problem for a while, but it is sure to come back when the converter fails once again.
A replacement converter is often bolted on with new gaskets. Some of them require welding for installation. Be sure to get an EPA approved equivalent replacement.