Furnaces, or fired heaters, are fundamental components of oil refining and chemical processing. Fired heaters in oil refineries are employed as a means to raise hydrocarbon products to the elevated temperatures and pressures necessary for separation, distillation and reforming processes. Generally, fired heaters contain serpentine coils of horizontal and/or vertical tubing, usually in the region of 3-inch to 12-inch nominal bore. The total axial length of a single serpentine “pass” can be in the region of 100-1,500 meters. Fired heater tubes can be interconnected by various systems, including short-radius return bends, long-radius return bends and plug headers (mule ears). The process conditions in which the process tubes are exposed to mean metallurgic anomalies and discontinuities are commonplace. It is therefore imperative the tubes are maintained and the condition is inspected and assessed at defined periods in order to maximize performance and efficiency and minimize safety risks.
It is well documented the inspection of fired heater coils using intelligent pigging techniques has been well established in recent years. As a direct descendent of in-line inspection technology used for the inspection of pipelines, ultrasonic intelligent pigs — or “smartpigs” — accurately assess the integrity and physical condition of process tubes, allowing any detected anomalies to be immediately reported to refinery engineers. Smartpigs are free-swimming, untethered devices that are propelled through tubing/piping systems using a free-flowing liquid within a looped system. The liquid also acts as an ultrasonic couplant between the ultrasonic transducer faces and the internal tube wall. Recent advances in electronic circuit design have resulted in miniaturized components and circuitry. This, combined with the evolution of lithium-ion battery technology, has resulted in a much smaller and more compact intelligent pig, which employs many of the same technical capabilities as traditional pipeline in-line inspection tools.
Historically, conventional hand-held ultrasonic techniques (UT) have been employed to assess the geometric dimensions of tube walls within fired heaters. Limitations inherent in conventional UT inspection techniques include poor data coverage (typically three measurements per tube), a time-consuming process, and a plethora of human and systematic errors. Automated ultrasonic smartpigs overcome all of these associated limitations. Furthermore, smartpigs eliminate the need to access the combustion chamber of a fired heater during an inspection operation, making the use of internal scaffolding redundant. A smart-pig inspection of a process coil will typically obtain in excess of 8,000 circumferential wall thickness and internal radii measurements per foot. It follows that the smartpig is capable of detecting and accurately locating areas of localized wall loss (internal or external) as well as diametric damage caused by creep, such as swelling, bulging, ovality, etc. By fully utilizing the large quantity of measurements obtained from a smartpigging inspection, highly accurate fitness for service and remaining life assessments can be performed. The smartpigging operation typically takes approximately one hour per pass and is usually carried out in conjunction with mechanical decoking (pigging) using the same pumping arrangement for both operations. By employing this combined maintenance service during a turnaround period, the smartpig completely verifies the cleanliness of the process tubing.
In recent years, the rapid evolution of technology has resulted in this method of inspection becoming increasingly popular among refiners as well as steam generation plants, with smartpigging becoming the obvious choice for increased performance, efficiency and safety.
For more information, contact Dr. David Thewsey at dthewsey@cokebusters.com.