الفهرس 
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Abstract
Thesis Summary
The oil and gas industry mainly depends on carbon steels as a primary material of
construction. Steels are used in every aspect of the industry from drilling to production and
processing facilities hence carbon steel is the most important material used in the oil and gas
industry. At least 80% of all components in the oil and gas industry are made from carbon
steel because it is inexpensive, readily available, and easily fabricated. Although carbon steel
is the first choice for most applications due to its low cost, availability of most products
forms, high strength grades and excellent weld-ability, it corrodes. Corrosion is a severe
problem in oil and gas processing it causes a major economic loss due to plant shutdowns.
In this thesis a real corrosion failure case study was investigated: On a routine
inspection of an unmanned offshore crude oil producing platform, a failure was observed in
one carbon steel ball valve in a 12” crude oil pipeline. The failure occurred in the valve body,
where the 1.5 inch bleed plug (fitting) was found sheared off the body. This could have led to
oil leak resulting probably in fire and environmental hazard.
Failure analysis procedures were designed to investigate the root cause. The
procedures included visual inspection, analysis of the operating conditions including oil
pressure, and metallurgical investigation, dimensions measurements, ultrasonic testing,
chemical analysis, microscopical investigation (optical and SEM), testing mechanical
properties. This was made on the whole valve including valve body, seat, bleed plug and ball.
It was proved that the failure was not related to any obvious personal factor and
neither were any abnormal operating condition recorded; thus mechanical reasons were
excluded. The internal visual inspection showed that there was a gap formed between the ball
and the seat, due to the decrease in seat thickness; this was confirmed by ultrasonic test. This
indicated that the service fluid may have flowed between the ball and seat, resulting in
corrosion occurring in the seat. This reason was validated by the chemical analysis where the
seat was found to be carbon steel with martensitic structure. Chemical analysis of the
corrosion products indicated that the main corrosion mechanisms is CO2 corrosion.. It is also
probable that over-stressing the bleed fitting due to uncontrolled manual tightening might
have led to thread damage.
Another part of the thesis covers the study of the corrosion behaviour of different
carbon steel with different microstructure and chromium content. Fluid and environmental
conditions in one of the biggest petroleum fields in the red sea were simultaed. Weight loss
experiments were used to give a comprehensive understanding of the corrosion behaviour. It
was found that that 1%Cr steel decrease the corrosion rate the occurrence of a compact and
self-repairable Cr-rich scale. All the martensitic microstructure have exihibited higher
corrosion rates than the ferrite and pearlite microstructures.
Secondly a review corrosion types and select the most credible ones to study the
effect of the most important parameters: effect of Chlorides, sulphates, and bicarbonates, and
of produced water pH, and then relate the pH to water resistivity. Study effect of geometry on
corrosion rates. Propose a practical system to minimize corrosion rate in petroleum facilities:
corrosion management. Give new ideas and guidance to future researchers who are interested
in corrosion prevention
Key words: Corrosion, corrosion in oil and gas, carbon steel corrosion behaviour, failure
investigation, metallurgical failure analysis, weight loss, low alloy steel,
pitting corrosion, CO2 corrosion