Sulfidic Corrosion with Hydrogen Present

For the corrosion process to proceed, the corrosion cell must contain an anode, a cathode, an electrolyte and an electronic conductor. When a properly prepared and conditioned mud is used, it causes preferential oil wetting on the metal. As the metal is completely enveloped and wet by an oil environment that is electrically nonconductive, corrosion does not occur. This is because the electric circuit of the corrosion cell is interrupted by the absence of an electrolyte. Excess calcium hydroxide [Ca(OH)j] is added as it reacts with hydrogen sulfide and carbon dioxide if they are present. The protective layer of oil film on the metal is not readily removed by the oil-wet solids as the fluid circulates through the hole. 

It is rare in actual applications that only one corrosion inhibitor is used. Synergistic blends of two or more inhibitors can take advantage of the strengths of each. Table 10-1 compares the performances of several of these blends to that of a chromate-zinc blend under different operating conditions. Note that while the chromate-zinc blend offers the best corrosion inhibition with no contaminants present and at high temperatures, other blends are close, and do not present the environmental problems that chromates do. With petroleum ether, hydrogen sulfide, or hexane contaminants present in the cooling water, the Polyphosphate-HEDP-Carboxylate blend performs the best, followed by Zinc-HEDP. 

Inhibitor Blend Concentration (ppm) Corrosion Rate (mpy) Corrosion Rate (mpy) with Petroleum Ether Contaminant (40 ppm) present Corrosion Rate (mpy) with Hydrogen Sulfide (10 ppm) present Corrosion Rate (mpy) with Hexane (30 ppm) present Corrosion Rate (mpy) at High Temperature (170-180° F)... 

Geochemistry and Environmental Considerations. The geochemistry of steam-dominated geothermal resources is concerned primarily with condensable and noncondensable gases in the steam. The amounts and composition of noncondensable gases in Geysers steam vary rather widely within the steamfield as shown in Table 1. The predominant gas is carbon dioxide (qv) in all cases. The most important noncondensable gas, however, is hydrogen sulfide, because H2S can present both corrosion and environmental problems. 

Sulfate-reducing bacteria (SRB) are some of the most common and problematic microorganisms of environmental and economic importance in petroleum industry. The effects caused by SRB activity are mainly the souring of oil and gas deposits and in problems related with microbially influenced corrosion (MIC). The toxic hydrogen sulfide produced may also present a health hazard to workers and may decrease oil quality by the souring of oil and gas [1],... 

If the operation is clean, as it usually is when hydrogen is present, the iron sulfide corrosion product is not protective. Under these conditions, the corrosion rate is linear and does not decrease with time, and chromium additions are not beneficial. Carbon steel and 9% chromium steel corrode at substantially the same rate and a 5% chromium steel may corrode even faster than the other two. So don t waste your money by picking a chromium content higher than you need to resist hydrogen attack. 

SSC SSC is an important cracking phenomenon in hydrogen sulfide medium and a special case of HIC. Natural aqueous environments contaminated with hydrogen sulfide are very corrosive. The hydrogen sulfide present in salt water in sour oil wells places an upper limit of 620 MPa on the yield strength of steel that can be tolerated. 

Alkali Treatment. Caustic washing is the treatment of materials, usually products from petroleum refining, with solutions of caustic soda. The process consists of mixing a water solution of lye (sodium hydroxide or caustic soda) with a petroleum fraction. The treatment is carried out as soon as possible after the petroleum fraction is distilled, since contact with air forms free sulfur, which is corrosive and difficult to remove. The lye reacts either with any hydrogen sulfide present to form sodium sulfide, which is soluble in water, or with mercaptans, foUowed by oxidation, to form the less nocuous disulfides. 

Some of the most obvious examples of problems with gas and materials are frequently found in refining or petrochemical applications. One is the presence of hydrogen sulfide. Austenitic stainless steel, normally a premium material, cannot be used if chlorides are present due to intergranular corrosion and subsequent cracking problems. The material choice is influenced by hardness limitations as well as operating stresses that may limit certain perfonnance parameters. 

Water and sulfur compounds are the principal non-hydrocarbon impurities present in light ends which frequently require removal. The sulfur compounds of concern are concerned with here are hydrogen sulfide and mercaptans, both of which have to be removed almost quantitatively from any light ends cut which is going to be marketed. There are two reasons for this First, they have an objectionable odor, even in minute concentrations. Second, they may cause corrosion either by themselves or through their combustion products. 

Some of the factors that contribute to the internal corrosion of tin plate cans are (i) the ratio and concentrations of citric to malic acids which in turn depend upon the strain of fruit, the extent of ripeness (ii) nitrate present in the fertilizers may find its way into fruits and vegetables and the nitrate may be reduced to hydroxylamine and support the detinning process (iii) pesticides containing dithiocarbomates may find their way in and attack iron (iv) phosphates, citrates and the low pH of cola-type beverage may dissolve iron (iv) meats, fish and peas contain sulfur-bonded protein molecules, which can decompose to H2S and attack the tin and iron, forming the respective sulfides. Hydrogen sulfide can react with Sn and Fe, yielding FeS and SnS, which are not poisonous, but impart some color to the canned product. 

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