During a recent turnaround, it was found that the vacuum unit heater tubes are badly coked (1/2" to 1"thick coke layer as per the inspection Engr). Due to shortage of time we could only manage steam spalling. The heater tubes are plug head tubes ( we do not have any drawing of the plug head tubes).
Can we do Pig Cleaning of the tube? Wil the plug make any hinderance to the movement of the pig?