Components operating in hh temperature hydrogen service are susceptible to hydrogen attack. The API 941 Nelson Curves are an empirical formulation designed to identify safe operationl limits with respect to temperature and hydrogen partial pressure. Inthis paper, mechanism based modelling techniques are applied to characterise hydrogen attack, manifest as ither surface decarburisation or internal methane bubble formation.

Process of hydrogen attack
Rate constant for hydrogen permeability

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Figure 1: Process of hydrogen attack

Figure 2: Diffusion and permeability data for hydrogen and carbon in iron and

low-alloy steels

Figure 3: Hydrogen solubility in low-alloy steels

Figure 4: Manifestation of hydrogen attack

Figure 5: Preliminary model of the Nelson Curves

Points: API 941, 4th Edition 1990 Lines: Model

Figure 6: Rate constant for carbon diffusion

Figure 7: Rate constant for hydrogen permeability

... It is worthy of comment that there are initiatives in progress, within API, EFC and elsewhere to address these shortcomings in what is otherwise the best assessment approach currently available. Brear and Church (1996) have demonstrated that the Nelson Curves can be modelled in simple terms of carbon and hydrogen solubilities and diffusivities and this work is currently being extended to address the kinetics of hydrogen attack. Work in Japan, particularly on C½Mo steel (Kawano, 2004), has led to the development of kinetic formulae for hydrogen attack, which are now sufficiently well accepted to have found a place within the API RP580/581 procedure for risk-based inspection. ...

This chapter outlines the technical approaches that can be made to address the integrity, failure risk and remaining safe serviceable life of plant used for the catalytic reforming of naphtha feedstock. In dealing with Catalytic Reformer Units (CRUs) the chapter will consider the major components, comprising fired heaters, reactors, transfer pipework and combined feed heat exchangers, in the overall context of an integrated, risk-based framework for integrity assessment.

  • Kioumars Poorhaydari Kioumars Poorhaydari

In this review article, many aspects of high-temperature hydrogen attack of steel are examined in a practical, topic-based format similar to that of API RP 571. This article is a result of reviewing over 220 articles on the subject, published mostly between 1938 and 2020, while some of them were already review articles citing research going back to the late nineteenth and the early twentieth centuries. The paper not only examines the historical evolution of our understanding of the damage mechanism, but it also discusses the current state of knowledge and the fields that are still under development or improvement. Questions are raised on a few important interpretations/classifications, namely the inclusion of decarburization as a form of HTHA, the division of incubation period to detectable and non-detectable stages of attack by API RP 941 and the recent distinction of non-conventional or non-classical HTHA in the literature, which may need re-evaluation. At the end, the interactions between HTHA and some other (related) damage mechanisms are discussed briefly and a failure case study is presented and discussed with respect to the use of incubation curves for the effect of an upset condition. View the full text at: https://rdcu.be/ctKLe

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