For routes where the weight concept applies there is no limit on the number of pieces that can be checked in as long as the weight allowance for the total number of pieces is not exceeded.
However, limitations may apply based on aircraft carrying capacity.
To purchase excess baggage login to Manage Booking (you will require PNR/ticket number/Privilege Club number and passenger's last name).
Once you retrieve your booking, then click on "Purchase Excess baggage" on the right panel to purchase excess baggage online.
For other enquiries contact your local offices, contact details can be found in the following link https://www.qatarairways.com/en-qa/worldwide-offices.html