Clarity against IGST

You Need to collect IGST. As you are doing inter-state supply IGST will be applicable.

Office of the recipient is not important. The place of supply is Important. Your supply is to another state.

Sush*t jee
The place of supply means Tax invoice addressed people (BHEL Tiruchy).

Here it involves two transactions

First leg of transaction is between A and CSecond leg of transaction is between C and B

In this type of transactions, initially C places order to A and directs him to deliver the goods to B. On such direction, A delivers the goods to B by acting as an agent to C. The departure from normal transaction here is that purchase order for supply will be made by one person and actual delivery will be made to different person and in that chain 3 parties are involved to complete the transaction. 

According to sec 10 b
Supply is on direction of third person so
SGST AND CGST applicable

Thank u Mr. Sandèep Upahyay Brother.

Yes! you have to charge CGST n SGST only, because you have recd instructions as well as payment from BHEl-Thiruchy only (INTRA STATE). Delivery is irrelevant. 

further I also agree @ AZGHAR, @ SANDEEP openions.

Thank u to all