Summary
In petroleum production, the problem of corrosive media attacking metallic
structures is almost ubiquitous. Particularly severe environments are
encountered in the production and transport of wet natural gas containing
corrosive components, such as hydrogen sulphide and carbon dioxide. When
exploring new gas fields, it is therefore a prerequisite to take into account
the corrosivity of the respective fluids in all stages of the field
development, material selection, field layout, and facilities design. In
preparation of the subsequent production phase, reliable corrosion monitoring
programs have to be selected, established, and implemented as necessary.
Furthermore, the financial aspects always play an important role, thus posing a
real challenge for the engineer forced to seek a compromise between economics
and design.
This paper gives a comprehensive overview of these considerations regarding
four different OMV gas fields, two in Austria and two in Pakistan, which were
successfully developed and brought onstream between 1967 and 2003. These fields
not only vary in their geographical position, but also in their gas
compositions, production start, and the location of gas dehydration units.
One major aspect dealt with in each of these cases was material selection,
including metallic as well as nonmetallic and composite materials. Where the
initial decision was made in favor of carbon steel, different methods of
corrosion protection, the application of corrosion inhibitors, corrosion
monitoring, and intelligent pigging are discussed in the paper.
A comparison of the various methods of resolution worked out for all four
case histories, as well as the experience gained in more than three decades of
production and transportation of wet, corrosive natural gas is presented.
Furthermore, results of the ongoing corrosion monitoring measurements in
operation in the mature gas fields are discussed under the aspect of the
remaining facility lifetimes.
Introduction
To achieve long lifetimes of the production facilities, the production and
transportation of wet, corrosive natural gas requires selection of suitable
material and measures for combating corrosion. In addition to the liquid phase,
which may show a low pH value and some amount of chlorides, the existence of
the corrosives CO2 and H2S in the gaseous phase can pose
serious corrosion problems. The presence of H2S, leads to the
problem of general corrosion; additionally, it can lead to stress corrosion
cracking (SCC) if the materials are not properly selected. Furthermore, some
operational parameters, such as chlorides in the produced water and high
temperatures, can intensify the corrosivity of the fluids. Stress corrosion
cracking is taken to be one of the most dangerous forms of corrosion because it
can result in an unexpected failure of a component, causing shutdown times and
high financial losses caused by the need for extensive repair or reinstallation
(e.g., of a pipeline), but above all, it canalsocause a potential environmental
and safety risk.
Carbon dioxide sweet corrosion is also a well-known problem in gas
production. CO2 dissolves in brine to form carbonic acid that
ionizes to yield a low-pH value. The resulting acidic solution strongly
enhances the corrosion in the carbon steel pipes and facilities. The presence
of CO2 can lead to corrosion rates of several mm/year if no proper
corrosion protection measures are applied.
© 2007. Society of Petroleum Engineers
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History
- Original manuscript received:
19 February 2006
- Meeting paper published:
12 June 2006
- Revised manuscript received:
19 September 2006
- Manuscript approved:
21 September 2006
- Version of record:
20 August 2007
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