Catalytic steam reformer tubes non-destructive inspection technology investigation and advancement : a dissertation presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Engineering at Massey University, Manawatu Campus, New Zealand
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Date
2018
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Massey University
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Abstract
Catalytic Steam reforming is a chemical synthesis process used in the production of
hydrogen by mixing hydrocarbon with steam in the presence of a metal-based catalyst. This
is achieved in a steam reformer plant where the mixture of gases is elevated to high pressure
and temperature through a continuous process for efficient mass production of syngas to meet
the global hydrogen demand. One of the challenges in operating a steam reformer plant is
monitoring and maintaining the tubular reactors (Reformer tube). Under the severe service
conditions the tubes a subjected to various degradation mechanism which ultimately
determine the service life. With the tubes accounting to over 20% of the capital cost of a
reformer plant, it is of great significance to maximise the service life of each tubes, which has
been the motivation to the advancement in metallurgy and NDT technology around reformer
tubes from the introduction of Catalytic Steam reforming in the early 20th century.
Under the influence of long-term exposure of mechanical stressing and elevated temperature,
reformer tube is subjected to a material degrading phenomenon call creep deformation. In
1952, F.R. Larson and J. Miller devised the Larson-Miller Parameter which predicts the
lifetime of a material based on service temperature and stress-rupture time and for decades
this method was used design and managed reformer tubes on a time-based strategy of 10,000
service hour. However, case studies have time and time shown premature rupture of reformer
tube causing unexpected downtime resulting in significant loss in production and asset.
Hence engineers and researchers have worked on a more direct method of assessing the
remaining service life of reformer tubes.
Inline pipe inspection is a hot area of research in robotics and automation. Eddy current, laser
profilometry, ultrasonic and infrared thermography is the four technology that is currently
dominating the Reformer industry, of which laser profilometry assessment being the only
method capable of early stage creep detection. While other fields of pipe inspection have
advanced and industrially applied over past decades, it is the author's opinion that NDT
technology for reformer tube is outdated with areas of innovation. The aim of this research is
to investigate an alternative solution to overcome the challenges and limited faced in modern
systems and contribute to the advancement of NDT of Catalytic Steam reformer tubes.
Presented in this dissertation is a new framework for an autonomous Reformer Tube
inspection system, which incorporates a number of innovative elements for improved creep damage assessment. The program for this work is comprised of three studies. In the first
study, the challenges around process profilometry dataset is demonstrated, the limitation in
the available methods is discussed, and the impacts in regards to detection creep deformation
is identified. Based on the finding, a three-stage creep detection algorithm (CDA) is derived,
offering a dynamic solution to distinguish two modes of isotropic and anisotropic creep
deformation. The system is experimentally assessed using a set of profilometry measurements
collected from retire reformer tube.
In the second study, a novel method for tracking a motion of an object moving inside a
reformer tube is devised. Literature study showed that conventional profilometry system
suffers from measurement uncertainty cause from an uncontrolled rotation of measurement
instruction during an inspection. Because location information gives valuable insight as to the
performance of the plant, the long-range optic solution is conceptualised, based on polarising
filters and Malus Law, to overcome these limitations. In this research, a proof of concept
experiment is conducted to evaluate and justify the conceptual method through the
development of a working prototype. This novel technique is named Optical Position
Tracking (OPT) system.
Presented in the final study is an autonomous reformer tube inspection system developed on
the basis of the results and finding in the first portion of the research. The contribution of this
research is demonstrated with a working prototype justifying the practicality of CDA and the
OPT system. The design incorporates wireless communication, modular design, and modern
semiconductor sensing technology. In conclusion, this research met the first milestone for an
ongoing research to progress the NTD industry.
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Keywords
Tubes, Steel, Creep, Testing, Nondestructive testing, Chemical reactors