We would like to share experience about washout drill pipe. We observed pressure gradually dropped from 4,100 psi to 3,600 psi (500 psi pressure loss) with same pumping rate 800 GPM. There was no mud weight or mud properties change at that time. Then, we tried to switch to another pump but the same problem still occurred so there must be something wrong down hole or surface.
When we observed pressure loss, we stopped rotating and drilling, just only circulating, and figured out where the washout was.