PIPE STEEL CRACKING RESISTANCE IN AQUEOUS HYDROGEN SULFIDE SOLUTION OVER THE TEMPERATURE RANGE 20 to 150 °C

摘要

Sulphide Stress Cracking (SSC) resistance of steel is determined by a number of factors of which the key ones are hydrogen sulphide pressure above solution, pH value and temperature. The most hazardous temperature range resulting in this mode of corrosion damage is 15...40 °C. At higher temperatures, pipe steel SSC resistance is to increase while at a temperature of 80°C and above, pipe steels are not susceptible to SSC. Test to evaluate SSC resistance of pipeline steel specimens were performed with the use of a special Testing Autoclave intended for making SSC tests in corrosion aggressive environment by application of Slow Strain Rate Test Method (SSRT). From the steel stress-strain graphs, obtained for aqueous hydrogen sulphide solutions it follows that increase in temperature leads to the increased true tear resistance and higher plastic deformation capability. This can be attributed to a smaller amount of iron with hydrogen sulphide compounds being formed on the steel surface as a consequence of lower hydrogen sulphide water solubility with increasing temperature, as well as to the effect of temperature on the proper hydrogen sulphide adsorption process by retarding it. Therefore, the obtained experimental results demonstrate that steel C-90 being placed into hydrogen sulphide solution (P_(HZS) - 1.5MPa) is exposed to hydrogen sulphide corrosion cracking over the temperature range 80...150°C. Peak loads being determined through the stress-strain diagrams, which have been obtained for hydrogen sulphide solutions over the temperature range under examination, are to be close. Their values are smaller than those of the same parameter obtained in the open air tests. True tear resistance is to increase as temperature rises.