Process and metallurgical evaluation of outlet pigtails damage in the primary steam reformer of an industrial ammonia plant

•Causes of damaging 12 outlet pigtails of primary reformer have been investigated.•A detailed process and metallurgical evaluation has been performed.•The failure of pigtails was due to subjecting over-design operating temperatures.•The failures of pigtails were independent of quality defects tube manufacturing.

In spite of improvements in reformer tube metallurgy and manufacture, outlet pigtail tubes are now seen as a critical and weak link component of primary steam reformer in ammonia plants and often require replacement before the reformer tubes. The present work has been focused to find out causes of damaging 12 outlet pigtails of primary steam reformer in the ammonia plant of Shiraz Petrochemical Complex (SPC) after 7–8.5 years of operation from metallurgical and process point of view. A process evaluation based on operating variables and a detailed metallurgical investigation based on microstructural assessment, chemical and reduced thickness analysis, micro hardness measurements, metallography and tensile properties of pigtail samples has been performed. The obtained findings demonstrated that the failure of outlet pigtails was attributed to over-design operating temperatures. Under operation at high temperature, the pigtails undergo the advance stage of irreversible creep and failed before their designing life span.