A method for on-line pigging in a tube coil for a furnace in a delayed coking system (116, 117), characterised in that the method comprises: terminating a process fluid supply to the furnace; introducing high pressurized steam from a first pressurized steam source through the tube coil and a main line, and from a second pressurized steam source through a second line connected to the main line for forcing any remaining process fluid in the tube coil and the main line to a closed blowdown system header or a delayed coking drum (116, 117), whereby the tube coil, the closed blowdown system header and the delayed coking drum (116, 117) are in fluid communication with each other; isolating a vent, in fluid communication with the second line, from the main line by introducing high pressurized steam from a third pressurized steam source through the second line to maintain a constant pressure against one side of at least two closed valves (124, 146) positioned in fluid communication with the vent between the vent and the main line while introducing the high pressurized steam from the first pressurized steam source and the second pressurized steam source; terminating the introduction of the high pressurized steam from the first pressurized steam source, the second pressurized steam source and the third pressurized steam source; removing steam from the main line through the vent by opening the at least two closed valves (124, 146) between the vent and the main line; isolating a drum input line, in fluid communication with the main line, from a portion of the main line by introducing high pressurized steam from a fourth pressurized steam source through a third line connected to the main line to maintain a constant pressure against one side of at least three closed valves (110, 112, 136) in fluid communication with the drum input line, wherein two of the closed valves (110, 112) are positioned on the main line between the drum input line and the portion of the main line, and one of the closed valves is positioned on the third line between the main line and the closed blowdown system header; disconnecting the tube coil from the main line and the first pressurized steam source; connecting the tube coil to a pigging unit after the main line reaches atmospheric pressure; and introducing water from a water source to the pigging unit for driving a pig through the tube coil. terminating a process fluid supply to the furnace; introducing high pressurized steam from a first pressurized steam source through the tube coil and a main line, and from a second pressurized steam source through a second line connected to the main line for forcing any remaining process fluid in the tube coil and the main line to a closed blowdown system header or a delayed coking drum (116, 117), whereby the tube coil, the closed blowdown system header and the delayed coking drum (116, 117) are in fluid communication with each other; isolating a vent, in fluid communication with the second line, from the main line by introducing high pressurized steam from a third pressurized steam source through the second line to maintain a constant pressure against one side of at least two closed valves (124, 146) positioned in fluid communication with the vent between the vent and the main line while introducing the high pressurized steam from the first pressurized steam source and the second pressurized steam source; terminating the introduction of the high pressurized steam from the first pressurized steam source, the second pressurized steam source and the third pressurized steam source; removing steam from the main line through the vent by opening the at least two closed valves (124, 146) between the vent and the main line; isolating a drum input line, in fluid communication with the main line, from a portion of the main line by introducing high pressurized steam from a fourth pressurized steam source through a third line connected to the main line to maintain a constant pressure against one side of at least three closed valves (110, 112, 136) in fluid communication with the drum input line, wherein two of the closed valves (110, 112) are positioned on the main line between the drum input line and the portion of the main line, and one of the closed valves is positioned on the third line between the main line and the closed blowdown system header; disconnecting the tube coil from the main line and the first pressurized steam source; connecting the tube coil to a pigging unit after the main line reaches atmospheric pressure; and introducing water from a water source to the pigging unit for driving a pig through the tube coil.