Pigging Program 1. The Field Engineer evaluates all information supplied to him by the customer, to determine approximately the amount of build up and deposit hardness. 2. Once the system is full and any product or debris has been flushed out, the operator will perform a FLOW-TEST. This involves the operator setting the flow at a particular flow rate and recording the acquired pressure. This will be done at several different flow rates so as to make a comparison on completion of cleaning. This also aids in determining coke build up if heater requires cleaning in the future. Example: Pre cleaning Post cleaning 500 GPM = 65 PSI 500 GPM = 56 PSI
3. A full diameter foam pig will be inserted into the launcher and displaced through the system at low speed. This is to determine that the pass is clear of obstruction such as TIs (Thermal Instrumentation). The foam pig will indicate whereabouts and quantity of build up by pressure profile on chart recorder. This step also allows the Field Engineer to make a determination of the size and type of stud to be used on the first decoke Pigg® run. 4. The first decoke Pigg® to be displaced is under sized and, in some instances, will be assisted by a foam pig to prevent excess by-pass. As it moves through the coil, pressure increases are closely monitored and a profile is established to determine deposit thickness. This size of decoke Pigg® will be used until the pressure readings indicate the first layer of the deposit is removed. 5. A pressure profile has now been established allowing the technician to concentrate on sections with excessive build up. NOTE: An important aspect of the DDT pigging procedure is the method of “Cleaning in Contaminated Areas only,” which is a patent protected procedure. Contaminated areas are defined as locations of excessive coke build up or abnormal restriction within the tubes. Cleaning in these sections is accomplished by displacing the cleaning Pigg® repeatedly back and forth through these contaminated sections until the thickness of the coke layer (or abnormal restriction) is comparable to coke layers in the remaining tubes. At this point, the cleaning runs are expanded until further sections of excessive coke build up are encountered and the same procedure is then repeated. When all the abnormal restriction has been levelled, cleaning runs are then conducted from launcher to launcher. This procedure greatly reduces unnecessary contact with less contaminated or clean pipe sections and will reduce the time required to clean the heater.
6. Continuation of progressive pigging increases the size of Pigg® in increments concentrating on sections with excessive build up. As the decoke Pigg® nears the clean I.D. of the tube, stud selection becomes critical to avoid tube erosion. Only when conditions dictate, more aggressive studs are used to fracture the deposit. Iron sulphides and scale are particularly difficult to remove and do require a more aggressive approach. If this is the case, then all information will be discussed with the customer representative. 7. Less aggressive studs are used as the deposits become depleted and more uniform. The water returns from heater are closely observed for a diminished or non-existent slurry return. In conjunction with a smooth pressure profile on the chart recorder and the condition of the previously run Pigg®, the Field Engineer can determine that the pigging program has been completed. 8. A large diameter foam pig will then be displaced through the system to remove any debris and confirm that the pass is free from any contaminants. 9. A final FLOW TEST will then be performed in order to compare the pressure drop and flow-rate with the initial data obtained at the beginning of the pigging process. 10. Demineralised water can now be used to flush system if required. 11. Excess water can now be removed if contracted to do so. The customer should supply an air or nitrogen supply and hoses to connect to a launcher of an adequate pressure and flow to displace large low density foam pig through the system. 12. Inspection by visual or intelligent pigging inspection can be performed. This is an optional extra that clients must request in advance. Designated customer personnel should be present to confirm that pigging procedure is satisfactory and does meet with approval. 13. Craneage and mechanical assistance may be required to assist in moving launchers and valves and other equipment to other connections. 14. Any other passes will be cleaned in the same manner. Other passes may be cleaned in less time due to information gained on previous passes. |