Date of Award

11-2008

Document Type

Thesis

Degree Name

Master of Science in Material Science Engineering (MSMatSE)

Department

Materials Science

First Advisor

Dr. Saud Aldajah

Second Advisor

Dr. Ahmed AI-Awar

Third Advisor

Abdennour Seibi

Abstract

The United Arab Emirates (UAE) is one of the key players of the oil and gas industry of the world; with oil reserves estimated at 9% of the total world reserves, the petroleum industry is considered to be the backbone of the economy.

In one of the gas processing facilities in Abu Dhabi, UAE; a case of material failure occurred in the fractionating column twice in a cycle of less than 2 years. The materials used for the internals of the column was stainless steel 316L. The different types of stainless steel corrosion were studied with emphasis on the suspected stress corrosion cracking; superalloys were also studied as an alternative material, especially nickel based superalloys.

The material failure was investigated in relation to the type of failure, and all the operating conditions associated to the corroded part of the column were studied and identified. Several tests were conducted to analyze the feed and the product of the column, as well as the presence of chlorides in the zones that suffered mostly of severe corrosion.

In an effort to conduct accelerated stress corrosion cracking tests, all test were carried out according to ASTM G36 standard, which does not replicate the exact field conditions, but provides us with guidelines in which the material possesses better stress corrosion resistivity.

The experimental work included testing the stainless steel 316L in an accelerated corrosion environment, and comparing the results with a proposed higher corrosion resistant nickel alloy (Inconel). According to ASTM G36 standard; the boiling magnesium chloride provided the accelerated corrosion environment, and the test materials were shaped into U-Bend specimens as they undergo both plastic and elastic stresses. The specimen were then tested to determine the time required for cracks to initiate. The cracked specimens were prepared for scanning Electron Microscope examination.

The results of the experimental work showed that the main mode of failure was stress corrosion cracking initiated by the proven presence of chlorides, hydrogen sulfide and water as elevated temperatures. Inconel 625 samples in controlled environment showed better corrosion resistance as it took an average of 56 days to initiate cracks, whereas it took an average of 24 days to initiate cracks in stainless steel 316L samples. The SEM macrographs showed that the cracks in the stainless steel 316L samples were longer, wider, and deeper compared to the cracks of Inconel 625.

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