Catalytic converters are usually flange-connected to exhaust systems, integrated with the front exhaust pipe or bolted directly to the manifold. Nuts and bolts still have to be removed, no matter what it is that separates the converter from the exhaust system. Because they are exposed to the high temperatures of the exhaust system as well as the open elements underneath the vehicle, it doesn't take long for the nuts and bolts to corrode and rust, fusing together. Removing catalytic converter nuts involves raising your vehicle and applying some heat before you even put a wrench to the nuts.
Drive the vehicle up onto ramps or hoist it upward with the jack and support it onto jack stands. Apply the parking brake.
Put on the goggles and gloves and grab the tools before crawling under the vehicle.
Light the torch and avoid laying directly beneath the catalytic converter hardware. Place the tip of the flame from the torch to the nut only, avoiding applying heat to the bolt as much as possible. Move the flame tip around the circumference of the nut every 30 seconds and wait for the nut to become a bright, cherry red; then turn off the torch.
Place a wrench on the bolt head of the connection and the ratchet and a socket on the nut. Turn the nut counterclockwise. If the nut begins to bind up, reheat the nut with the torch.
Repeat this procedure for all the nuts (and bolts) being removed and replaced.
