Experimental Study on Local Erosion of 304 Stainless Steel Bends with Gas Carrying Sand

Abstract:

Experimental study on local erosion of 304 stainless steel bends with gas carrying sand induced by SiO2 sand blast was studied in terms of wall thickness loss along the band periphery and micro-morphology on the inner wall surface of the longitudinal section of a band after erosion test. The result shows that the erosion of the stainless steel bend caused by sand particles is mainly concentrated on the outer half of the band and the ratio of the mass loss of the outer half to that of the inner half of a band, namely index α, increases with the increase of the particle size of the sand. Particles with small mean diameter have a greater effect on the dimension of eroded area, but less influence on the wall thickness loss. The maximum impact angle is 55° for a band with R=1.5D, where is apt to be suffered from perforation,leading to failure of the band. The size of pits induced by erosion increases but their quantity decreases with the increase of the sand particles size. The abrasion mechanism for particle impacting on the stainless steel bend may mainly be ascribed to deformation wear,as well as to low angle microcutting wear, moreover, their comprehensive effect results in perforation and cut damage of the bend.

Key words:  stainless steel bend    local erosion wear    pipe flow state    deformation wear
Jiaqiang JING1,2,Yinuo ZHOU1,Sijia ZHENG1,Kai WANG3,Zongjun QIU4,Xuantao JIANG1
1. State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu 610500, China
2. Province Key Laboratory of Oil and Gas Fire Protection, Chengdu 611731, China
3. CNOOC Research Institute, Beijing 100027, China
4. Xinjiang Petroleum Survey and Design Research Institute Limited Company, Urumqi 830026, China

1 Introduction
Gas-carrying sand is widely distributed in the fields of onshore and offshore oil and gas, coalbed methane and shale gas, such as gas mining, transportation, and treatment. The sand flows through the fluid to the bends, valves, and tees, etc. Severe erosion or even abrasion of perforation poses a great threat to human safety, economic production, and the surrounding environment [1, 2]. For example, gas drilling averages 30 m per drilling, and a puncture leak occurs in the bend portion of the ground chip discharge pipe, which seriously affects the working efficiency of the drilling and is not conducive to safe production on site [3].
Erosion wear is a malignant material wear degradation process with complex physical processes, which depends mainly on environmental conditions, material type and incident conditions (incidence angle, incident velocity, particle size and shape, particle hardness) [4], to date Domestic and foreign scholars still have great controversy about the mechanism of erosion [5]-[10]. Only a limited theoretical analysis can be made on the basic phenomena of erosion wear, and an erosion equation with limited application range is proposed. Bend is an important part of the pipeline system. Due to its wide application and erosion, it was experimentally analyzed by many foreign researchers [11]-[16]. However, they did not study the different positions of the bend. The similarities and differences of erosion mechanisms and the specific magnitude of erosion angles are unknown. In recent years, with the continuous development of applied computational fluid dynamics (CFD) technology, CFD technology is widely used in bend erosion. Forecast [3,17]-[25], but the conclusions drawn by different people based on different erosion models are quite different.

20180629010304 39068 - Experimental Study on Local Erosion of 304 Stainless Steel Bends with Gas Carrying Sand

Fig.1 Schematic diagram of transparent erosion tester under pipe flow state

In order to visually and effectively observe the erosion of the stainless steel bend, in order to explore the erosion mechanism at different positions of the bend, this experiment uses the EDM digital linear cutting machine to cut the bend axially, using OptimScan high-precision blue light 3D scanner and XP300C polarized microscope measured the wall thickness loss and microscopic shape after bend erosion, analyzed the distribution and strength of bend wear, and provided theoretical basis for changing the structure of bend and increasing its service life.
2 Experimental methods
A rectangular 304 stainless steel bend with good corrosion resistance and good mechanical properties (Φ32 mm × 3 mm, R = 1.5D, where R is the radius of curvature and D is the diameter of the bend) is used as the target material for erosion research, and its density is 7.92 g/m3, tensile strength 522 MPa, and hardness HV200.
The bend was cut axially from the middle by an EDM CNC wire cutter (accuracy 0.01 mm) to observe the eroded shape of the SiO2 particles inside the bend, and to explore the position of the particles at the entrance of the bend (0° to 15°). The erosion mechanism of the center position of the bend (45°~60°) and the exit position of the bend (75°~90°). Erosion particles of 35 mesh, 60 mesh and 80 mesh quartz sand of the same type were used. The density and hardness were 2.65 g/cm3 and HV 700, respectively, and these particles were mostly polygonal.
The erosion wear of the bends under the three particle sizes was measured by a laboratory-made transparent tube flow erosion wear device. The experimental setup is shown in Figure 1. The outer half of the bend and the inner half of the bend are respectively marked with the inlet end. After alignment, they are fixed with a loose nylon cable tie. Because there is a gap of about 0.02 mm between the outer half ring and the inner half ring, the tape is sealed to reduce air leakage. . After being compressed by the compressor, the air enters a 0.8 MPa gas buffer tank. After the compressed gas is regulated, it is metered by the LUGB/E type gas vortex flowmeter, and then the grain feeder carries the sand into the straight pipe section of the transparent plexiglass. Outer diameter: 32 mm, inner diameter: 26 mm, length: 1.8 m), and the actual rate of the particles is measured by 3D-PIV. The straight pipe section and the bend are connected by a corrugated rib hose with an inner diameter of 32 mm, and carbon steel is used. The hose clamp is fixed to prevent the joint end from slipping off; the gas-solid two-phase flow passes through the bend and enters the horizontal pipe, and the gas-solid two phases are separated by the particle collector, and the solid particles are collected.
In order to judge whether the pipeline system is uniform and continuous sanding, the sound wave receiving probe is installed at the bend to receive the sound wave energy generated by the particles hitting the bend, and the electric signal generated by the PC processing is amplified by the preamplifier and the main amplifier respectively. . By analyzing the sand acoustic signal map and combining the stainless steel bend mounting positions of Kuan et al. [26] and Christopher et al. [27], the particles satisfy the condition of uniform and continuous distribution at the test stainless steel bend.
Adjust the opening of the valve to control the flow rate of particles with different particle sizes (25±1) m/s, and ensure that the particle feeding rate is 26.5 g/s. The analytical balance with an accuracy of 0.1 mg is measured every 2 min. The amount of erosion wear of the inner and outer half circles in the three particle sizes of 35 mesh, 60 mesh and 80 mesh, 16 groups for each particle size, and the sand yield was about 50 kg. In order to accurately measure the wall thickness loss of the bend and to characterize the intensity distribution of the bend wear, the thickness of the bend before and after the half circle erosion was measured with the OptimScan blue light 3D scanner and processed by Geomagic Qualify 11 software. Loss of wall thickness of the bend (addition of a wall loss of 120 kg for a set of 60 mesh particles). The microscopic morphology of the outer half of the bend under different particle sizes was observed and analyzed using an XP300C polarized light microscope (high-light irradiation on the surface of the sample to be measured), and the erosion mechanism of the particles at different positions of the bend was investigated.
3 Results and discussion
3.1 Mass loss characteristics of the inner half and outer half of the stainless steel bend
After the erosion of SiO2 particles with different particle sizes, the relationship between mass loss and erosion time of the outer half circle and the inner half circle of the bend are shown in Fig. 2a and b, respectively. In general, for similar particle velocities, shapes, densities, and hardnesses, the larger the particle size, the greater the kinetic energy and impact force of the particles, and the more severe the erosion [28], but it can be seen from Figure 2. The mass loss of the outer half circle and the inner half circle of the bend decreases with the increase of the particle size in the same time, because the smaller the particle size, the more the number of particles under the same mass flow rate, that is, the SiO2 particle impact The total number of bend walls increases, and small particles are susceptible to gas turbulence, resulting in larger erosion areas, resulting in greater material quality loss.
20180629010647 47720 - Experimental Study on Local Erosion of 304 Stainless Steel Bends with Gas Carrying Sand

Fig.2 Mass loss of the outer semi-bend (a) and inner semi-bend (b) vs impact time for different particle size

Comparison between Figure 2a and b shows that after 32 min erosion, the mass loss of the outer half of the stainless steel bend at different particle sizes and the mass loss ratio of the bend half circle (indicated by α) are 11.7, 13.7, and 15.3, respectively. As the particle size increases, α also increases, and the specific reason may be that the larger the particle size, the lower the collision probability of the particles with the inner half circle of the bend under the action of the gas turbulence, and the smaller the loss of the inner circle in the bend. As a result of the increase in particle size, α increases. When the α value is further analyzed, the mass loss of the outer half of the bend is greater than that of the inner half of the bend. That is, the erosion of the bend by the particles is mainly concentrated in the flow state. The outer half of the bend is consistent with the simulation results of Huang et al. [3]. According to Figure 2a, the mass loss of the outer half of the bend is specifically analyzed. After the erosion of 50 kg of SiO2 particles, the mass loss of the outer half of the bend increases as the particle size changes from 35 to 60 mesh, 60 to 80 mesh. 0.6828 and 0.3818 g.
3.2 bend wall thickness loss
Since the erosion of the particles on the bend is mainly concentrated on the outer half of the bend in the pipe flow state, the degree of erosion of the bend by the particles is only characterized by analyzing the wall thickness loss of the outer half of the bend. The wall thickness before and after the outer half-bend erosion of the bend was measured by a 3D scanner. After being processed by Geomagic Qualify 11 software, the wall thickness loss and wear intensity distribution of the outer half of the bend were obtained, as shown in Figure 3, in which the dark blue The color area is the irremovable error generated by the calibration paper, and the airflow direction is from bottom to top. Comparing the analysis of Figures 3a~c, as the particle size decreases, the erosion area of the corresponding bend gradually increases, and the maximum wall thickness loss of the erosion increases first (35 mesh to 60 mesh) and then decreases. (60 mesh to 80 mesh) trend, which can also explain that after 50 kg particle erosion, the area of bend erosion by 80 mesh particles is the largest, but the maximum wall thickness loss is relatively small. The greatest loss of mass occurs in the outer half of the bend. Comparing the analysis of Fig. 3b and Fig. 3d, the maximum erosion thickness of the same particle size increases with the increase of sand production, and the position of the maximum wall thickness loss is basically unchanged, and the size of the erosion area is basically the same.
20180629011215 86264 - Experimental Study on Local Erosion of 304 Stainless Steel Bends with Gas Carrying Sand

Fig.3 Wall thickness loss and distribution of wear strength of the outer semi-bend (r =particle size, Qs=sand production): (a) r =80 mesh, Qs=50 kg; (b) r =60 mesh, Qs=50 kg; (c) r =35 mesh, Qs=50 kg; (d) r =60 mesh, Qs=120 kg

20180629011339 58692 - Experimental Study on Local Erosion of 304 Stainless Steel Bends with Gas Carrying Sand

Fig.4 Geometrical characteristics of bend

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Fig.5 Position for taking value of the outer semi-bend

20180629011554 90083 - Experimental Study on Local Erosion of 304 Stainless Steel Bends with Gas Carrying Sand

Fig.6 Wall thickness loss of the outer semi-bend vs bending angle θ for different particle size

In order to accurately reflect the wall thickness loss of the stainless steel bends at different erosion angles, and to determine the maximum erosion angle of the bend, the bends are read at a set of data points every 5° as shown in FIG. 4 , each of which contains Three data points are distributed on the solid line and the dotted line as shown in Fig. 5, and the interval between the solid line and the broken line is 0.5 mm, and the average of the three data points is taken as the wall thickness loss at the erosion angle.
From the data points averaged at the wall thickness of the bend under different particle sizes, the curve of the wall thickness loss of the bend along the bend section bending angle θ is shown in FIG. 6 . According to Figure 6, it can be seen that when 0°<θ<30° and 75°<θ<90°, the wall thickness loss of the outer half of the bend is small, and the erosion effect of different particle sizes on the wall is basically the same; When 30°<θ<55°, the wall thickness loss of the outer half of the bend increases with the increase of θ, and the effect of particle size on the erosion of the wall at 50 kg sand production : 60 mesh>80 mesh>35 mesh; when θ=55°, the particle has the largest erosion effect on the wall surface, which is the most likely to cause wear and tear and cause bend wear failure. The large erosion rate is 0.00372 mm/ Kg, which is basically consistent with the results of Lin et al. [29], where the simulated erosion bend’s maximum erosion wear position is around 50°; and when 55°<θ<75°, the wall thickness loss of the outer half of the bend follows. The increase in θ is getting smaller and smaller. For the same particle size, the maximum wall thickness loss of the bend does not change linearly at different sand production rates, but increases slowly with increasing sand production. This may be due to continuous impact of the material on the particles. Next, it shows a certain degree of work hardening, so that the material wear resistance.
20180629011749 10925 - Experimental Study on Local Erosion of 304 Stainless Steel Bends with Gas Carrying Sand

Fig.7 Morphologies of impinged surface for 80 (a), 60 (b) and 35 (c) mesh particle in entrance (0o~15o) (a1, b1, c1), upper middle (45o~60o) (a2, b2, c2) and exit (75o~90o) (a3, b3, c3) of bend

It can also be seen from Fig. 6 that the main wear area of the bend is 30°<θ<75°, and the following scheme can be selected to increase the service life of the bend: (1) The bend adopts variable wall thickness, especially the main wear Wall thickness or strengthening treatment of the area; (2) coating the erosion-resistant material coating in the main wear area; (3) setting the erosion-resistant and detachable baffle in the main wear area, which not only increases the service life of the bend, but also Can greatly reduce the labor intensity; (4) The arrangement of wear-resistant ribs in the main erosion area can greatly reduce the effect of particle erosion on the bend.
3.3 Microscopic morphology and mechanism of bend erosion
Figure 7 is a graph showing the erosion morphology of different wear parts after the bend is etched for 32 min under different particle sizes. It can be clearly seen that the erosion microscopic morphology of the different wear parts of the bend under the same particle size is quite different, because the erosion angle of the bend varies with the erosion position in the range of 0°~90°, but is different. The erosion mechanism of the particles under the erosion angle may not be the same.
Figure 7a shows the microscopic morphology of the different erosion areas of the bends after erosion by the 80-mesh particle, in which the entrance position and the upper middle position are covered with small scratches and pits, while the exit position has obvious cracks and is mixed with depressions. Pit, this is because irregular grit impacts the material surface at a low speed and angle at a low angle. On the one hand, furrows and scratches are formed on the material surface to cause material loss, and on the other hand, the surface of the material is deformed. In the form of “extrusion lip”, the material is abraded to form a number of eroded pits, in which deformation wear is the main mechanism of low-angle erosion wear, micro-cut wear is the secondary mechanism, and particles continuously impact and forge the material surface at high angles. The plastic deformation continuously accumulates. When the plastic deformation accumulates to a certain extent, cracks appear on the metal surface, accelerating the erosion loss of the material, and the wear mechanism is deformation wear. Due to the effect of gas turbulence, small particle size particles have a greater influence on the erosion area of the bend, but have a smaller influence on the wall thickness. This is the reason that the 80-mesh particle causes the largest mass loss of the bend and the wall thickness loss is not significant.
For Figure 7b, long cracks appear in the upper middle of the bend (45°~60°), accelerating the abrasion of the material, which explains the maximum wall thickness loss of the 60 mesh particles at 55°; for Figure 7c, It can be clearly seen that the surface of the erosion material has a large area but a relatively small number of erosion pits and scratches. Compared with the erosion of small particle size particles, the large particle size has less influence on the material, which is also large. The reason for the loss of bend mass loss and wall thickness after erosion is the smallest.
Comprehensive analysis of Figures 7a~c shows that as the particle size is larger, the erosion pit is larger, but the amount is relatively reduced; the main abrasive mechanism of the particle to the bend is deformation wear, and the secondary mechanism is low angle micro-cutting. Wear, their combined effects cause the failure of the bend (perforation puncture).
4 Conclusion
(1) The erosion of the ellipse by the particles is mainly concentrated on the outer half of the stainless steel bend. The mass loss of the outer half of the bend and the mass loss ratio of the inner half of the bend (α) increase with the increase of the particle size.
(2) The small particle size has a great influence on the stainless steel bend erosion area and has a relatively small influence on the wall thickness loss. The maximum erosion angle of the bend is 55°. At this time, the particle has the largest erosion effect on the wall surface. Causes wear and tear and causes bend wear to fail.
(3) The larger the particle size, the larger the erosion pit, but the quantity is relatively reduced; the main abrasive mechanism of the particle to the bend is deformation wear, and the secondary mechanism is low angle micro-cutting wear, their common influence Caused by the perforation of the bend.

Source: China Stainless Steel Bend Manufacturer – Yaang pipe fitting Industry Co., Limited (www.ugsteelmill.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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