Selection process was two step - a written test ( equal question from technical and aptitude) followed by technical interview.

In technical they asked mostly from Fluid machinery (Pump and turbines). Few question from power cycles.
To have a good knowledge of your project work (BTP and MTP) will be helpful.

I personally attended 5 interviews and all were quite peaceful.

NTPC - about welding, pump manufacturing, hydraulic coupling, etc.
RIL - pump, power cycle.
Daimler - About the project work.
Market RX - some puzzles and case study.
i2 technology (R&D profile) - just an algo to be written for a problem

Core company usually don't pay much stress over HR but certainly one should have a little knowledge about the company for which he is sitting for. Also prepare well for some basic HR question like : tell me about yourself...........
Why we should hire you?

Be true to yourself unless it is very much required. Confidence is the key and be confident that you are competent. If you have some communication problem then better to prepare ahead by giving some mock interview with your friend. In fact in my case few question came directly in interview which i prepared while mock interview.

Company was opened for Mechanical, Chemical, Electrical and Metallurgy departments. Finally 25 students got placed in RIL. Other than that, around 7 students got PPO. For mechanical dept. only dual degree student were allowed to sit for this company. Total 15 students sat in written test from mechanical dept. out of which 6 students got finally placed.
I was lucky to be asked the questions which I knew well. Also be humble and don't unnecessary show off