Why consult the dead on behalf of the living?
Luke 11:1-2 (KJV)
1 And it came to pass, that, as he was praying in a certain place, when he ceased, one of his disciples said unto him, Lord, teach us to pray, as John also taught his disciples. 2 And he said unto them, When ye pray, say, Our Father which art in heaven, . . .
In Jesus' example, His prayer is addressed to the Father not a saint.
By the way, Catholics don't pray to the saints expecting that the saint will grant their request, they pray that the saint will intercede with God on their behalf.
Now is this praying to dead saints scriptural?
Consider Isaiah:
19 When men tell you to consult mediums and spiritists, who whisper and mutter, should not a people inquire of their God? Why consult the dead on behalf of the living? 
The Holy Bible : New International Version (Grand Rapids: Zondervan, 1996, c1984). Is 8:19-20.