Slurry Pump Suction Liner Wear

Anyone experience excessive erosion wear (pumping a heavy sand slurry)
on slurry pump suction liners.  We had been testing a urethane product
with great success, then changed the discharge piping from 20" to 24"
diameter and reduced our suction liner wear from 52 weeks to 4 weeks. 
Process conditions have not varied that much.  Any comments would be
appreciated.  Pumping a slurry density of 1.4 gms/ml, 16000 usgpm,
discharge pressure of 300 psig.