At present, the scholars of the High Pressure manifolds damage, failure, assessment methods and strength analysis of many studies have been carried out. But the pressure load case study is generally below 40 MPa, 40 MPa for pressure load is greater than the few studies. From the results of published studies, the use of the finite element method of stress analysis is limited to the range of elastic deformation, the current domestic research work is mainly focused on the assessment of defects in equipment, and most of the research, analysis, experimental work focused on starting split assessment, and safety analysis of the structure to consider crack initiation, fracture, instability of the whole process, so for High Pressure manifolds especially the pressure exceeds the strength analysis and fatigue life prediction of 40 MPa of High Pressure manifolds are virtually nonexistent.
As for the HPF Erosion problems, study erosion-corrosion behavior of single-phase system has attracted the attention of many scholars, now use more American Erosion Wear formulas proposed standard API-14E, but the study is relatively liquid-solid two-phase flow less. Multiphase flow containing solid particles and a relatively high velocity, Erosion role can not be ignored, is more difficult to predict, because it involves fluid flow, particle size distribution and pipe diameter, shape and other parameters.
In recent years, although the country has been developed for the evaluation of Sand Erosion behavior of fluid metal material testing equipment, and the two-phase fluid Erosion mechanism and its influencing factors were studied extensively, but almost did not relate to the internal manifold pressure High Pressure manifoldsErosion impact damage. In view of this, the authors experimentally studied interior, explore the impact of High Pressure manifolds internal pressure on the High Pressure manifoldsErosion Wear, and provide guidance for the design and manufacture of High Pressure manifolds.
1.High Pressure manifoldsErosion Features
For High Pressure manifolds, the most prone position Erosion damage is Swivel joint, Integral Fitting (long sweep elbow, right angle elbow, Tee, Y-tee, manifold Tee, cross tee) as a result of changes in direction and velocity of the fluid Location. Referring to the publication in 1964 of the tube system design manual, when subjected to internal pressure, Swivel joint will produce hoop and axial stress, which is calculated as
σθ = (2R + rmsinξ) rmp / 2 (R + rmsinξ) (1)
σs = rmp / t (2)
Where: σθ for stress Swivel joint of the ring; σs Swivel joint of the axial stress; P Swivel joint is subjected to internal pressure; t Swivel joint representative wall thickness; R is the radius of curvature of the Swivel joint; rm Swivel joint for inside and outside average diameter; ξ Swivel joint for an arbitrary vertex of the angle between the cross-sectional axis.
To 7.6 cm in the elbow by 140MPa pressure, for example, the main parameters are: elbow outer diameter 140 mm, inner diameter of 76 mm, the radius of curvature 190mm, ξ is 90 ° elbow that is outside the arc vertex position, by equation (1), (2) calculate the hoop stress and axial stress where about 210MPa and 118MPa, we can see that the hoop stress is significantly greater than the axial stress.
And because the full-size High Pressure manifoldsErosion Wear difficult to carry out the experiment, high degree of risk, taking into account the state of High Pressure manifolds pressure, the hoop stress is greater than the axial stress characteristics, the authors studied the hoop stress is tensile stress on High Pressure manifoldsErosion Wear impact.
2.Experimental section
2．1.Experimental section
Experimental apparatus used in the experiment is independent research laboratory can be applied tensile stress Erosion Wear test machine, the device shown in Figure 1. Sand and water with stirring by a stirrer, after mixing, the sand-laden fluid mortar pump pumped through conduit Erosion chamber nozzle, and then sprayed onto the surface of the sample, which Erosion cavity principle shown in Figure 2, the angle of the sample Erosion can be adjusted by the inclination means, in the range of 0 ~ 90 ° adjustment, suffered a tensile stress is applied to the sample by stretching a pump, which tension in the range of 0 ~ 100 kN, while the size of the force can be obtained by the tension sensor, sand-carrying fluid flow rate can be adjusted by changing the mortar pump inverter, the flow rate in the range of 0 ~ 50 m / s.

Fig1 Schematic diagram of the erosion wear testing system

Fig2 Impact test mechanism
2．2.Sample Preparation
Experiment, High Pressure manifolds common materials 42CrMo, its geometry shown, after modulation processing, its chemical composition and mechanical properties parameters in Table 1 shown in Figure 3. After each sample processing is completed, all use fine sandpaper surface of the sample, eliminating machining marks the sample surface, to ensure that each specimen surface smooth. Before and after the experiment, the sample cleaned with acetone, and then placed in a drying oven using the quality Mettler precision balance ML503 Erosion measured before and after the sample, the measurement accuracy of 1 mg, linearity error 2mg, each set of experiments do 3 times, the final results averaged.

Fig3 Schematic representation of the sample used in erosion weal-test(mm)
Table 1 Chemical composition of 42CrMo material ％

Table 2 Mechanical properties of 42CrMo

2．3.Experimental parameter settings
Erosion Erosion Wear medium used for water with sand, which is a new type of sand used in fracturing proppant coated sand particles range in diameter 450-550μm, such sand with a high temperature high pressure, corrosion resistance, high strength, sphericity, strong conductivity and other advantages. During the experiment, each time before the start of the experiment were replaced with new sand, to ensure that each time the same experimental parameters. According to fracturing conditions fracture site, and the toughness of the material at an angle of about 30 ° Erosion when, Erosion Wear largest law, binding properties Erosion Wear testing machine, setting experimental parameters shown in Table 3.
Table 3 The main parameters of the tests

3.Experimental results and analysis
According to the experimental design of the parameters in Table 3, a total of five experiments, each experiment done three samples, each set of three computing Erosion average weight loss of the sample, the results shown in Figure 4.

Fig4 The relationship of the erosion wear rate and the tensile stress
As can be seen, 40CrMo of Erosion Wear rate substantially increases the tensile stress increases linearly. Since 40CrMo yield strength greater than 930 MPa, and the course of the experiment, the surface of the sample has not been found to yield phenomenon, indicate that the experiment did not occur during the plastic deformation of the material, has been in the elastic deformation range.
Depending on the material of the elastic deformation of the microscopic processes diatomic model, when the external force is increased, the material lattice ions to increase the distance between the stress and the repulsion between the ions reasonable increases, reduced ability to resist damage when subjected to the impact of gravel , it is prone to breakage, thus reflected in the macroscopic material Erosion Wear rate increases with increasing stress.
After the end of the experiment, cut Erosion Wear parts, scanning electron microscopy Erosion parts of the surface topography. Choose 0,300,500 MPa conditions the surface observation image of the central part of the specimen Erosion pit red, as shown in Figure 5-7, they have in common is, Erosion surface of a large number of furrows and a small pit, This formation morphology is due at low Erosion angle, material damage in the form of micro-cutting based, consistent with the theory Erosion Wear.

Fig5 SEM micrographs of worn surface of wears pecimens at30°with no stress

Fig6 SEM micrographs of worn surface of wear specimensat 30°under 300MPa

Fig7 SEM micrographs of Worn surface of wear specimens at 30°under 500MPa
In addition, from the scanned image can be seen obviously different points, i.e., with increasing tensile stress, scratches become increasingly clear, the width and depth of the scratch increases, and because the number of cutting lips generated and size also increases. Described in Erosion angle of 30 °, the tensile stress increases, the ability of the material weakening anti-Erosion, easily peeled from the surface.
4. Conclusion
(1) When the angle is 30 ° when Erosion, 40CrMo of Erosion Wear rate increases with stress, a linear relationship.
(2) increasing the stress does not affect the main failure mode at 30 ° Erosion angle of the material - micro-cutting.
(3) With the increase of stress, anti Erosion ability 40CrMo material weakening, Erosion depth and width of the surface scratches to increase.
Test surface, when the High Pressure manifolds material selection 40CrMo, the Swivel joint, Integral Fitting (long sweep elbow, right angle elbow, Tee, Y-tee, manifold Tee, cross tee) and so easy to change the position of the fluid flow, the tube should be increased thickness of sinks to reduce risk Erosion damage points. Through this study, for High Pressure manifolds production enterprises High Pressure manifolds have some significance.