Papers by Keyword: Sulphidation

Abstract: High temperature sulphide corrosion and equipment failures have been reported in several crude and condensate processing facilities of petroleum refineries. Affected materials were carbon and low alloy steels operated in temperatures ranging from 200 to 300°C.These failures were attributed to specific sulphur species and were not anticipated by corrosion prediction tools used for their material selection. The corrosion mechanisms of these species are not fully understood. This paper presents Takreer Research Centre (TRC) research work for isolating the active sulphur species responsible for the corrosion. Two condensate samples were first analysed for total sulphur, hydrogen sulphide (H₂S), Mercaptans (RSH) and other impurities. Using Gas Chromatograph with Sulphur Chemilumenesence Detector (SCD), it was possible to identify Mercaptans and sulphides from the process samples. Laboratory corrosivity testing of condensate sample using carbon steel and low alloy steel coupons at 275°C indicated that the corrosion rate was mainly related to the Mercaptans species within the Total Sulphur. The results concluded that specific dissociation temperature of respective Mercaptans is a useful tool in predicting the possibility and extent of corrosion and its vulnerable process loop.

Abstract: Because of considerable experimental difficulties, the defect structure of NiS₂ has not been elucidated so far. The first step in these investigations was to explain which sublattice of this compound is predominantly disordered. In order to solve this problem, the mechanism of sulphidation of NiS to NiS₂ has been studied using marker technique. These experiments have been carried out at temperatures 823-923 K in sulphur vapors under pressure 10³ 10⁵ Pa. It has been found that the predominant defects in NiS₂ occur in cation sublattice. The problem then arised whether these defects are cation vacancies or interstitial cations. This phenomenon could have been explained in studying the kinetics of NiS sulphidation as a function of sulphur activity. It has been found that the parabolic rate constant of this reaction increases with sulphur activity, strongly suggesting that cation vacancies, and not cation interstitials, are the prevailing defects. If, namely, interstitial cations would prevail, the sulphidation rate would be virtually pressure independent.

Abstract: The high temperature corrosion behavior of Fe20Cr6Al-Y,Hf steel was studied in the range of temperature 800-1000oC in H2/H2S atmospheres at pS2=10-2 ,10-3 and 10-4 Pa sulphur vapor pressures. Kinetics depend on the temperature and sulphur vapor pressure. After 24 hours the whole specimen was practically consumed because the samples were 0,06 cm thick. Morphology of the scales have been performed by SEM techniques. Phase and chemical composition have been studied by EDX and XRD techniques. It was found that scale formed on Fe20Cr6Al-Y,Hf alloy was built with porosity sulphides layer. EDX analysis of the scale surface show that the any aluminum, hafnium and yttrium sulfides were found in the formed scale layer, however small amounts of Al2S3 was detected in scale/steel interface. Also internal sulphidation was observed. A phase analysis of the formed scale revealed that it is composed mainly of an FeS, Fe7S8 phases and CrS, Cr5S6. Result were compared with data obtained on the pure Fe and Cr samples.

Abstract: This paper discusses the design and development of sulphidation resistant coatings. The first section discusses the rationale for designing and developing such coatings. The rationale for selecting the coating systems has been derived from our work on the HT sulphidation behaviour of MCrAlYX (M=Co, or Co-Fe and X=V, Nb, Mo and W) type of coating alloys. This work has allowed the establishment of the mechanisms of sulphidation and led to the choice of the coating systems discussed here. The second section describes the sulphidation performance of several selected coatings, single and multilayer, deposited on Ti, TiAl and Ni-based alloys at 750-850oC in environments of low oxygen and high sulphur potentials.

Abstract: This paper discusses the design and development of sulphidation resistant coatings. The first section discusses the rationale for designing and developing such coatings. The rationale for selecting the coating systems has been derived from our work on the HT sulphidation behaviour of MCrAlYX (M=Co, or Co-Fe and X=V, Nb, Mo and W) type of coating alloys. This work has allowed the establishment of the mechanisms of sulphidation and led to the choice of the coating systems discussed here. The second section describes the sulphidation performance of several selected coatings, single and multilayer, deposited on Ti, TiAl and Ni-based alloys at 750-850oC in environments of low oxygen and high sulphur potentials.