Hello,

The total number of sigma bonds in  pyrophosphoric acid are 12 and Pi bonds in pyrophosphoric acid are 2. The two double bonds contributes 2 sigma and 2 d Pi−p Pi.
There are 4 O-H groups = 4 sigma bonds
There are 6 P-O type of bonds.

Total no. of sigma bonds = 2+ 4+ 6 =12
Total no. of d Pi−p Pi bonds= 2

So There are 12 sigma bonds and 2 Pi bonds