Protecting Integrity of Fired Heaters
-Richard D Roberts, Quest Integrity Group, Ashish Khera, Allied Engineers

In order to eliminate the chance of any human fatalities or injury in a plant, it is of utmost importance to maintain integrity of assets. This article highlights significance of Asset Integrity Management (AIM) programmes for fired heaters by leveraging Advanced Intelligent Pigging Inspection and Fitness-for-Service Software Technologies

Refineries and chemical plants are complex operating facilities which are typically designed to operate continuously between scheduled maintenance turnarounds. Among a variety of operating assets within these facilities, fired heaters play a critical role in the day-to-day plant operation. Maintaining and protecting the operational integrity of these assets must remain a high priority for plant operators. Unexpected failures can quickly become costly, which drives the demand for an effective Asset Integrity Management (AIM) programme. Lack of an effective AIM programme onsite can elevate the risk of human fatalities or injury.

For well over a decade plant engineers and inspectors have gradually integrated the use of ultrasonic-based intelligent pigging technologies into their AIM and inspection programmes. Intelligent pigging enables nearly 100 percent inspection coverage of complex configured serpentine coils in convection and radiant sections of fired heaters. This proven technology provides accurate inspection data allowing engineers to make critical decisions regarding the safe operation and necessary maintenance regimes for fired heaters. Continuous advancements in the technology have also increased the capabilities of these tools and extended these benefits to even more complex heater coils, including those which are joined via common header.

The Plant Inspectors Challenge
Accurately assessing the condition of fired heater coils has proven challenging due to several factors. Conventional Non-Destructive Testing (NDT) methods, such as manual ultrasonic (UT) or radiography (RT), are ineffective in accurately assessing 100 per cent of the internal condition of fired heater coils. The process is further complicated by serpentine coil lengths in excess of 1,524m (5,000’), raised surfaces such as studs and fins, multiple short radius 1D x 1800 return bends, and inaccessibility.

Specially configured remotely operated autonomous internal inspection tools, commonly referred to as intelligent pigs, were developed in the 1990’s resolving these challenges. This innovative technology enables complete coil inspection within the convection and radiant sections without the need to access confinement of the furnace box. The use of UT-based intelligent pigs has significantly improved inspection data quality and coverage area and has also significantly reduced safety risks attributable to refinery fired heaters.

Intelligent Pigging Technology
During a typical operation, the intelligent pig is transported through the interior of the serpentine piping coil via a column of liquid (eg, water, diesel, glycol, etc.), which provides both propulsion and coupling for the ultrasonic transducers. The inspection data is stored electronically in onboard memory as the un-tethered intelligent pig rapidly travels through the piping coil. At the conclusion of an inspection run, the data is immediately downloaded onto a laptop computer. This provides immediate access to high resolution graphical images and quantitative test results. Anomalies such as internal or external corrosion, erosion, pitting, bulging, swelling, and other deformations are easily located and quantified while custom software provides the ability to view the entire coil in both two -dimensional (2D) and three-dimensional (3D) graphics.

Asset Integrity Management Programme
Conventional inspection practices previously used by refiners to determine condition assessment of furnace coil piping have proven time-consuming and costly, while providing only minimal inspection coverage, ultimately compromising the plants Fired Heater Asset Integrity Management (AIM) programme. The combined cost of lost production, scaffold erection, inaccessibility, piping surface preparation, and inspection labor quality varies widely. Furnace down times of several days or even weeks can be expected when conducting a typical coil inspection with manual inspection practices. Additionally, these practices provide limited inspection coverage and/or non-quantitative test results.

Conventional NDT inspection methods for furnace piping coils typically consist of manually collecting UT spot readings at given increments along the piping coils axial length, typically at four 900 intervals around the circumference (ie, top, fire side, bottom, and refractory side), if access permits. In most cases, the convection section of fired heater coils is not inspected due to complete inaccessibility. On the rare occasion when the convection section of the heater coil is accessible, raised surfaces such as fins and studs prohibit the application of any external surface NDT inspection technique. The typical strategy for bare surfaced accessible piping requires the Non-Destructive Evaluation (NDE) technician to return to these exact locations year after year to gather comparison data. Repeatedly identifying these exact locations is difficult, inaccurate, and inefficient. The sparse amount of thickness data collected is then applied to insufficiently calculate corrosion rates, which the plant reliability engineers rely upon to make critical decisions involving current piping condition and remaining life.

Remaining Life Assessment (RLA)
Historically only limited inspection data was applied when performing complex calculations associated with determining Fitness-for-Service (FFS) and Remaining Life Assessment (RLA). With today’s computer horsepower and sophisticated software there’s no reason why 100 per cent of the inspection data collected is not applied when performing FFS and RLA calculations in accordance with the most widely used national standard, API-579 / ASME FFS1.

At the conclusion of evaluating a fired heater coil while applying all accessible inspection data in combination with API-579 / ASME FFS1, the output provides refinery engineers with the necessary confidence of making sound operating decisions regarding asset repairs or extending run times . Reliability engineers also have the option of integrating FFS/RLA software with their day-to-day engineering software packages to further enhance decision-making capabilities. Available software packages ensure no inspection data is unused, thereby providing further confidence to the end user.

Conclusion
Combining intelligent pigging and FFS/RLA software technology is key to a complete and comprehensive Fired Heater AIM programme. Technological advancements provide greater capability to refinery and chemical plant engineers, particularly those operating complex fired heaters. Inspections are completed quickly, minimising furnace down time and preliminary results are available within minutes after the data is downloaded from the intelligent pig. The results enable engineers to make real-time decisions concerning the return of the furnace to service.

Utilisation of this system enables plant engineers to determine corrosion rates more accurately than ever before. The data is easily archived for direct comparison with future inspection data. Accurate corrosion rate information can improve run times, which results in increased plant throughput, efficiency, and reliability, as well as decreased risk of unplanned shutdowns and safety risks.

References:
  1. API-573, Inspection of Fired Heaters and Boilers, Washington DC USA
  2. API-579 / ASME FFS1, Fitness for Service, Washington DC USA
  3. Paul, Ron (2008) NEXT Energy New Horizons – Out of Pipe Thinking, Chevron, San Ramon California USA.
  4. Firth D., Hill T., Simmonds S., Keen D., Thomas C., (2007) Risk-Based Management of Refinery Fired Heaters, Bahrain
  5. Roberts R., (2008) MENDT - Combining Both Ultrasonic Intelligent Pigging Inspection and Customized Remaining Life Assessment Software Minimizes Chance of Failure, while Maximizing Reliability in Fired Heater Serpentine Process Coils, Bahrain
  6. Braun M., Roberts R., (2007), Refineries at Risk: Aging Infrastructures, PSM Concerns, and Capacity Requirements Drive Global Acceptance of New Inspection Technology for Fired Heaters, San Antonio Texas USA