The erection is the first work schedule for a factory. It does not matter with the age of the factory because inside of an industry boundary an extinction project can be start or a new unit of the production line can be made. In this time all machinery and electrical equipment will install in the factory.
Erection basically is Installation of the Instruments like Tubing, Cable, Instruments and then During Commissioning of them to be sure as per the standard and recommended drawings and specification. whereas Testing Commissioning is the process for starting up of the plant which include the Loop-Checking to Pre-Commissioning and to final start up.