This article describes an engineering methodology for understanding risk, particularly in catalyst tubes, and making decisions regarding operation. A successful case study is described in which the production of a hydrogen-constrained unit was optimised through inspection and engineering.

INTRODUCTION

Primary steam reformers represent an integral part of the process chain in

ammonia, methanol and other petrochemical plants. By nature their design is often aggressive, due to the need for harsh operating conditions and specialty materials. A failure in the primary reformer typically has large financial implications, most often into the millions of dollars, as significant downtime is incurred alongside the costs of tubes, engineering and catalyst.

The primary damage mechanism in catalyst tubes is creep, which causes diametric expansion and eventually leads to leak failure. Creep is a highly temperature-dependent mechanism, and the service tube of a catalyst tube is exponentially affected by tube metal temperature (TMT). The "rule of thumb" is that 10-15°C change (approximately 20-30°F) can halve or double the life a tube. As one tube failure most often necessitates a plant shutdown, it is therefore said that the reliability of a reformer is controlled by the maximum tube metal temperature.

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