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Problem Solving – Using Engineering to Ensure Reformer Tube Life

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World Fertilizer,

The inspection and life assessment methodologies that support steam reformer integrity combine to deliver a powerful tool in providing important information required to ensure the reliable operation of reformer furnaces. The following case study is one example that exemplifies the flexibility and problem solving capabilities of comprehensive reformer care practices.

A reformer on a large manufacturing complex had operated reliably and conservatively for 10 years. Inspection and life assessment of the tubes was undertaken with some specific questions in mind over and above the fundamental issue of tube life. The plant was undergoing a significant debottlenecking exercise during the turnaround. This had an impact on the furnace, and was expected to result in an increase of approximately 20°C in operating temperatures during subsequent operating periods. A critical issue therefore was to understand the impact of this temperature increase on remaining life of the tubes. Quest Integrity’s LifeQuest™ Reformer software has the capability of assuming changes to operating conditions in the future. The analysis does not require plant temperature data as an input to the assessment. The software calculates an effective temperature at which the tube has operated in order to generate the level of creep strain that is measured during the inspection. In most assessments, that same creep effective temperature is used for future operation. In this case, the plant owners specifically requested that the effect of a 20°C increase be assessed. This was undertaken and no tube replacements were recommended prior to 2021. This result provided confidence that the plant debottlenecking exercise being undertaken would not impact adversely on the safe and reliable operation of the reformer.

The plant inspectors had noted hot spots near the top of a few tubes leading up to the outage. It was reported that the hotspots had been present for approximately 18 months. The inspection data did indeed show the consequences of these hotspots (Figure 1). The LifeQuest predictive facility assumes that previous damage has accumulated since the tube was commissioned. However, in this case the plant operators were of the opinion that these hot spots had only been present for approximately 18 months. The assessment was therefore undertaken by assuming all the creep damage at this location had occurred in the previous 18 months. This assessment indicated that replacement would not be recommended prior to 2024. If the hot spots were eliminated, longer lives, at least based on damage at this location could be expected.

Figure 1. Tube profile showing unusual growth at the top of the tube. 

The calculated temperature data from the assessment was then compared with plant pyrometer IR measurements. The calculated tube metal temperatures at this location show good agreement with the maximum tube temperature exceeding the average by approximately 20°C. The measured temperatures however show a tendency to suggest that the central tubes are running hotter. It is well known that infrared measurement technologies may suffer errors due to issues such as path length and reflectivity. It is suspected that the IR measurements techniques on this site would benefit from the application of correction software to improve accuracy.

By utilising a comprehensive assessment plan, the plant received an abundance of useful information that was derived and tailored to address specific issues and problems within the facility.

Author: Charles Thomas, Quest Integrity

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