Failure mechanisms and material degradation processes at high temperatures in ammonia synthesis

Abstract

Ammonia has been manufactured on an industrial scale for almost 100 years. Nevertheless, this process still presents a challenge to the materials involved and to the material engineers who are responsible for the selection of materials. This is due to the temperatures and the media handled. Failure mechanisms that have been known in ammonia plants since the industrial production of ammonia started are hydrogen attack, creep and embrittlement. Since the new generation of plants characterised by optimised heat recovery have been in service, metal dusting has emerged as a relatively common problem in ammonia plants following the secondary reformer. In the present study, the wide range of failure mechanisms and material degradation processes observed in ammonia plants is illustrated by a number of examples, some of which relate to the historical development of the process.

Development of Al oxide PVD coatings against metal dusting

“…Magnetron sputtering was selected to produce such films because in addition to its versatility, it has the potential to be adapted for the coating of tubes, 13 components commonly involved in metal dusting failures. [1][2][3][4] Based on the areas for improvement detected in, 12 the present investigation further explores the d.c. RMS process parameters that can lead to such improvements for Al oxide coatings on 304L stainless steel, a material often used in environments where metal dusting occurs. 14,15 Experimental procedure…”

“…A number of processes in the chemical, petrochemical, materials transformation, energy, nuclear, and other industries are affected by metal dusting. Examples include hydrogen production, 1 ammonia synthesis, 2 ethylene cracking, 3 processing of mineral oil, 4 among several more.…”

The influence of alloying elements on metal dusting behavior of nickel chromium alloys and their statistical correlation

“…Metal dusting is a high temperature corrosion mechanism relevant to iron, nickel, or cobalt alloys which are exposed to carbon producing atmospheres (i.e., mixtures of carbon monoxide, hydrogen, water vapor, and carbon dioxide) typically between 500 and 750 °C. It is observed for equipment used in hydrogen, ammonia, methanol, and gas‐to‐liquids production plants . Carbon monoxide from the gas atmosphere reacts at the metallic surface to form atomic carbon, which diffuses into the substrate.…”

“…The metallic substrate supersaturates in carbon and therefore decomposes into a mixture of graphite, oxidic, carbidic, and metallic particles (“metal dust”) . This leads to the formation of pits and possibly loss of containment …”

The influence of surface condition on the metal dusting behavior of cast and wrought chromia forming alloys

“…Several reviews of industrial failures due to metal dusting have been reported in literature 13–16. These have mainly covered wrought alloys.…”