Hostile Environment Brief Summary
Discussion -Carbon Steel Cables
H2S affects carbon steel cables by causing hydrogen "embrittlement"; surface pitting and blackening of the steel will be noticed, along with the smell of "rotten eggs", and the armor wires can snap easily when flexed back and forth. The molecule causing the "embrittlement", H2 is small and mobile and often quickly leaves the steel as soon as the cable leaves the well. A cable can have brittle wires immediately after being removed from a well containing H2S and several days later the same cable will appear to have ductile wires. Although some operators have reported use of plough steel cables in wells with 200 ppm to 300 ppm (parts per million), H2S in conjunction with a good inhibitor such as 'S 1000'. Please note that temperature and other materials in the well can strongly influence the steel corrosion rate. Also, it is known that even though an operator is able to enter and leave a well containing corrosive elements, the damage done to the cable may not show up until several jobs later. Chemical contents of boreholes vary over a broad range. The cable user should consult a metallurgist about the reaction of high carbon steel (270,000 psi tensile minimum, 0.65% minimum carbon, 0.65% minimum Mn) with the specific materials in the bore-hole under consideration. Please note that new cables offer better resistance to H2S than used cables, as the galvanizing coating on the armor wires is attacked preferentially by the H2S , forming zinc sulfide, ZnS, rather than FeS, and the structural integrity of the steel is therefore less affected. CO2 in oil wells forms carbonic acid, which eats carbon steel fairly easily. It has been shown that 27% concentration of CO2 will destroy a cable in less than one hour at ambient temperatures. CO2 attack is reduced by the use of Baroid 'Cote1-11', although the actual protection provided is not definitely known.