Dear Aspirant 

IOCL is indian oil corporation limited is a public sector industry or the one that run under government finance and fund. And getting an engineering post there is a dream come true for some student. One can become engineers there either after clearing GATE (graduate aptitude test for engineering) or by directly appearing in IOCL conducted exam. 

Good luck for your future :) 

Feel free to ask if you have any further queries. 

It depends on the division you get while joining the organization. These are the following options

1. If you are allotted Refinery Division, then you will be put in mechanical maintenance department ( a service department) which role is to maintain the equipment be it rotary and static and pipe networks within a plant.
2. If you are allotted Pipeline Division (there is a high probability of getting pipeline division for a mechanical engineer) here also your role will be same but you don’t have to deal with some static equipment i.e. columns, reactors etc.
3. If you are allotted Marketing Division then you will rarely be able to use your learnings as a mechanical engineer.

I hope it helps you.