Numerical simulation for erosion effects of three-phase flow containing sulfur particles on elbows in high sour gas fields

Sulfur particles carried by high-speed flow impact pipelines,which may cause equipment malfunctions and even failure.This paper investigates the scouring effect of mist gas containing sulfur particles on elbows in highly sour gas fields.The multiphase-flow hydrodynamic model of the 90
elbow was established by using the computational fluid dynamics(CFD)method.The scouring effects of the gasliquid mist fluid with the water-liquid fraction of 20%and particles with the diameter of 0.01 e0.05mm on elbows were explored within the flow velocity range of 0e20 m/s.In addition,the influences of secondary collision,mean curvature radius to diameter(R/D)ratio,inertial force,drag force,and Stokes number on trajectories of sulfur particles were studied.Moreover,the influences of hydrodynamic parameters of multiphase flow on corrosion inhibitor film were analyzed with the wall shear stress as the reference value.Serious erosion mainly occurred in the extrados of elbow as well as the junction between downstream pipeline and the intrados of elbow,the maximum erosion area occurs at 61.9
.When the incident position of the particle was far away from the top of the inlet plane,the probability of secondary collision became smaller.Furthermore,the erosion rate decreased with the rise in the R/D radio.The maximum erosion rate of elbow increased with the increase in the Stoke number.The maximum erosion rate reached 0.428 mm/a at 0.05mm particle diameter and 20 m/s fluid velocity.The wall shear stress increased with the increase in fluid velocity and mass flow rate of particle,the fitting function of the wall shear stress curve was the Fourier type.The results indicated that highvelocity particles had a serious erosion effect on elbows and affected the stability of the corrosion inhibitor film.The erosion effect could be retarded by controlling the velocity and diameter of particles.The results provided technical supports for the safe production in highly sour gas fields.

Effect of Plastic Deformation and H_2S on Dynamic Fracture Toughness of High Strength Casing Steel

The effects of plastic deformation and H2 S on fracture toughness of high strength casing steel（C110 steel） were investigated. The studied casing specimens are as follows： original casing, plastic deformation（PD） casing and PD casing after being immersed in NACE A solution saturated with H2S（PD＋H2S）. Instrumented impact method was employed to evaluate the impact behaviors of the specimens, meanwhile, dynamic fracture toughness（JId） was calculated by using Rice model and Schindler model. The experimental results show that dynamic fracture toughness of the casing decreases after plastic deformation. Compared with that of the original casing and PD casing, the dynamic fracture toughness decreases further when the PD casing immersed in H2 S, moreover, there are ridge-shaped feature and many secondary cracks present on the fracture surface of the specimens. Impact fracture mechanism of the casing is proposed as follows： the plastic deformation results in the increase of defect density of materials where the atomic hydrogen can accumulate in reversible or irreversible traps and even recombine to form molecular hydrogen, subsequently, the casing material toughness decreases greatly.

Stress corrosion cracking of L360NS pipeline steel in sulfur environment

Slow strain rate test(SSRT)and tensile fracture observation are applied to study the stress corrosion cracking(SCC)of L360NS pipeline steel.5.0 wt.%sodium chloride solution containing elemental sulfur and 0.5 wt.%glacial acetic acid solution containing elemental sulfur are used.The results show that brittle fracture mainly occurs on the samples in high sulfur environment.In the sulfur suspension solution,the SCC sensitivity of L360NS pipeline steel increases along elemental sulfur content.In sulfur melting cladding condition,obvious corrosion can be observed with a large amount of corrosion pits appearing on the gauge section of the sample.The corrosion products are Fe1txS,black easily detached,and H2.In sulfur suspension and sulfur melting cladding conditions,stress oriented hydrogen induced cracking(SOHIC)is the main cracking,which is caused by the joint effect of SCC and hydrogen induced cracking(HIC).