Sulfide Stress Cracking Assessment of Carbon Steel Welding with High Content of H<SUB>2</SUB>S and CO<SUB>2</SUB>at High Temperature: A Case Study

In the oil and gas industry, it has been established that for pipelines fabricated with carbon steels, their limitation is related to H2S and CO2 environments, which is 7 to 10 psia of partial pressure of CO2. Therefore, in carbon steel cracking is shown, after 7 or 10 psia of partial pressure of CO2. The experimental work was performed under static conditions in autoclaves within a pH of 3 to 3.8;partial pressures of 16 - 96 psi for H2S and 15 - 53 psi for CO2, in the temperature range of 25°C - 150°C. It was observed that the average yielding stress used in Sulfide Stress Cracking (SSC) tests decreases with temperature increment. Hydrogen Induced Cracking (HIC) evaluations showed that X52 steel, under conditions, was not susceptible to HIC. Results of SSC did not show indications of cracking after exposure to sour solutions, except for the specimen exposed to high H2S and CO2 content (96 psi of H2S and 53 psi of CO2 of the partial pressure) and high temperature (150°C). Microcracks located between the upper and lower weld beads were also observed. However, the highest average corrosion rate was 0.27 mm/year (10.6 mpy), which occurred in samples exposed to 96 psi of H2S and 53 psi of CO2 at 150°C. Likewise, the highest localized corrosion (severe pitting attack) was obtained at the same environment with a corrosion rate of 4.2 mm/year (167 mpy). The oil and gas industry could use carbon steels pipelines in partial pressure higher than 10 psia.

Relationship between microstructure and hydrogen induced cracking behavior in a low alloy pipeline steel

Hydrogen induced cracking（HIC） behaviors of a high strength pipeline steel with three different microstructures, granular bainite ＆ lath bainite（GB ＋ LB）, granular bainite ＆ acicular ferrite（GB ＋ AF）, and quasi-polygonal ferrite（QF）, were studied by using corrosion experiment based on standard NACE TM0284. The HIC experiment was conducted in hydrogen sulfide（H_2S）-saturated solution. The experimental results show that the steel with GB ＋ AF and QF microstructure present excellent corrosion resistance to HIC, whereas the phases of bainite lath and martensite/austenite in LB ＋ GB microstructure are responsible for poor corrosion resistance. Compared with ferrite phase, the bainite microstructure exhibits higher strength and crack susceptibility of HIC. The AF ＋ GB microstructure is believed to have the best combination of mechanical properties and resistance to HIC among the designed steels.

Inclusion Characterization in High Strength Low Alloy Steel for Pipeline Application

In this work several methods including sulphur printing,modified spark spectrum analysis and SPEED-SEM-EDX methods were used to study the morphology,composition and distribution of inclusions in pipeline steel.The procedure for the last-mentioned method includes:metal sample preparation using Selective Potentiostatic Etching by Electrolytic Dissolution (SPEED) together with inclusion observation and detection using SEM-EDX equipment.The results of sulphur printing and spark spectrum analysis showed that there was a well-defined centerline containing relatively high concentrations of sulphur in the steel slab studied in this work.The results of SEM study showed that most inclusions found in the steel samples were globular in morphology,and roughly 2-5 micrometers in size.The inclusions were rich in sulphur and manganese.Some inclusions with a bright globular shape contained Al,Ca,Mn and S,and were likely composed of MnS,CaS and calcium aluminate.It was concluded that sulphur printing is a convenient and inexpensive method for inclusion analysis,Spark Spectrum Analysis provides a complete and self-contained technique for inclusion detection,and the SPEED-SEM-EDX procedure is best suited for in-situ and three-dimensional observation of inclusions.