Quest Integrity Group Integrated Lifecycle Management Solutions
As seen in the July/August 2012 edition of the Nitrogen+Syngas Magazine
Reformer Tube Inspection Technology
Globally, hundreds of plants have relied upon the inspection data produced by the Laser Optic Tube Inspection System (LOTIS®) technology. Further complimenting LOTIS is MANTIS™, the external tube crawler technology. A combined internal and external inspection approach has provided clients with the ability to inspect steam reformer tubes, with or without the presence of catalyst.
The time-proven, laser-based LOTIS technology provides advance warning of problems prior to tube failure by identifying failure mechanisms such as creep strain (most prevalent), bulging, swelling, manufacturing flaws and metal dusting damage. The inspection technology also provides baseline measurements for new tubes to determine condition at the manufacturer prior to shipment to the plant.
The external tube crawler technology, MANTIS, is ideal for use between catalyst changes because catalyst removal is not required to perform an inspection. Both LOTIS and MANTIS can be rapidly deployed and provide inspection rates of 100 or more tubes per shift. The data collected imports directly into LifeQuest™ Reformer, the software platform used to determine remaining life.
Inspection Data Analysis
The company's inspection data is presented in 2D and 3D formats covering the full length of each tube. The 3D views provide visualization of the entire tube set in the reformer and allow the client to troubleshoot problems. The results are highly accurate and repeatable. Individual tubes are assessed to Level 1 fitness-for-service.
The data is combined and displayed to allow comparison of each tube from successive inspections whether from LOTIS and/or MANTIS. Line graphs are produced to compare creep strain at inspection intervals.
Reformer Tube Life Assessment
Quest Integrity Group has invested more than 35 years in high temperature alloy research. The LifeQuest Reformer software combines fitness-for-service and a proprietary materials database to determine the remaining life of individual tubes. The finite element modelling approach assesses creep and stress to quantify damage by percentage of creep and percentage of through-wall cracking. The assessment features a proprietary advanced creep model covering the primary, secondary and tertiary regimes.
This integrated inspection and assessment methodology has significant economic benefits. It minimizes the risk of unplanned shutdowns due to tube failure, allows reformers to be operated more aggresively and provides a wealth of diagnostic information.
The reformer tube creep assessment methodology has a sound technical basis. The material database and advanced creep model capture the unique behaviour of HP alloys. The finite element module captures stress and temperature gradients as well as cyclic effects. The analysis works seamlessly with the diameter inspection data (LOTIS internal and MANTIS external crawler).
Advanced Engineering Capabilities
The company's advanced engineering capabilities include the assessment of high temperature components such as header systems, pigtails, riser and bull tees. Such capabilities include computational fluid dynamic (CFD) modeling of reformer systems including furnace combustion modeling, flue gas ductwork flow, convection sections and primary and secondary burners. Materials engineering and laboratory support for reformer components include accelerated creep rupture testing, 3D elastic-plastic Finite Element Analysis of (FEA) components, metallography and failure analysis of reformer components, risk-based inspection and temperature correction solutions for IR tube metal temperature measurement.
Areas of Concern
The primary reformer encompasses the entire front of the plant and includes the following areas:
Each area has unique failure mechanisms and can be broken down further, e.g.:
Combustion systems: The condition of the combustion system significantly affects the performance of the steam reformer. Regular burner maintenance and adherence to operating procedures are key to overall success. Uneven firing causes distress to the tubes and internal refractory linings. Excessively low air levels can also have detrimental effects. The value of visual examinations and regular measurements are often overlooked.
Inlet and Outlet Pigtails: The general condition of the inlet and outlet systems can be assessed. Inlet and outlet pigtails vary immensely, and as a result, each design needs to be modelled using a combination of pipe stress analysis and the correct material properties for the hot conditions under which it operates. Condition assessment of the pigtails should be carried out regularly; they are key components in the steam reformer design. Typical pigtail failure mechanisms include weld cracking, weld fatigue, stress corrosion cracking (SCC) and thermal stress along with creep.
Reformer casings: Thermal imaging of the exterior surfaces of casings and the cold outlet headers can be performed. The results are compared against design criteria and a report can be generated to highlight areas of concern, such as gas tracking along with actions for the next turnaround.
Outlet systems: Many different outlet systems exist for primary reformers. Designs can vary widely from plant to plant. These systems are typically complex, and careful design and construction is essential for long term operation. When failures occur, finite element analysis can be used to help solve the associated complex problems, particularly when combined with computational fluid dynamics to ensure the correct diagnosis. Many plants operate for years without incident and then suddenly fail. Some of these failures can be avoided if a plant operates within the original design criteria, however, many plants have been up rated and operate with greater flows and temperatures, giving rise to potential failures as a result.
Waste heat boilers: Waste heat boilers are one of the most talked about types of equipment in a plant; without them the plant cannot operate. Historically waste heat boilers have been the second-most troublesome piece of equipment in a plant. The reformer assessment can be extended to also cover the waste heat boiler. Waste heat boilers are complex heat exchangers; these can suffer from thermal and mechanical stresses local to the tube-to-tubesheet welds and tube sheet to shell connections.
Convection sections: Convection sections are often compromised of many tube passes and contain natural gas and mixed feed heaters, super heaters and economisers. These components are large assets in their own right and are generally the most difficult to inspect; in fact, many go uninspected for years. Quest Integrity Group's FTIS™ ultrasonic inspection technology navigates 1.0D bends down to 3" internal diameter (88.9mm) and inspects 100% of the tube length and diameter. The technology also inspects finned tubes. The ultrasonic measurement data are then put directly into LifeQuest™ Heater software to determine remaining life.
In summary, an integrated solution encompassing advanced inspection, engineering assessment and vast historical expertise and knowledge can prove invaluable in helping syngas plant operators maximize the safety, efficiency and productivity of their assets.