The maximum value of the test pressure during hydraulic testing. Hydraulic and pneumatic testing of pipelines

One advantage is that hydrostatic testing in pipes is one of the most effective methods checks and checks for leaks at a specific location. During the test, you can find out exactly how intact the connections and tubes are. Its strength and resistance to the adversity of pressure are other remarks.

To carry out hydrostatic testing in pipes, it is necessary to hire companies with competent equipment and technicians. However, the analysis has a unique value, however, if a serious and compromised company is not chosen, it can be compromised. Several industry segments and even homes use the method of evaluating their pipelines.

To learn more about hydrostatic testing in pipes

Hydrostatic piping testing can test existing material defects, deformation corrosion, mechanical properties connections and identify possible puncture points when using a large number product. The rupture of a pressure vessel during a hydrostatic test in a region where at first there were no reasons for the rupture contributed to the search for root causes. This work presents a failure analysis methodology to determine the causes of a ship crash. At the end of the work, the results and discussions of the analysis are shown, and then the reason for the refusal is indicated. Pressure vessel failure analysis. Being a high responsibility equipment, its construction must be carried out according to international standards. The failure of pressure vessels during a hydrostatic test in a region where there was no reason for it at first stimulated the search for a cause. This work presents a failure analysis methodology that aims to identify the cause of vase failure. At the end of the work, the results and discussions of the analysis are shown, and then the reason for the gap is indicated. Strength of materials 03 Longitudinal stresses and circumferential stresses 04 Representation of the problem 06 Temperature and weld area 08 Pre-existing cracks 13 In this comprehensive definition, this group includes a simple pressure cooker and even the most advanced nuclear reactors. Vessels high pressure constitute a significant part of the manufacturing industries - the most important elements, large in weight, size and unit cost, and can reach up to 60% of the total cost of materials and equipment. Unlike most equipment, the vast majority of pressure vessels are not on the industrial production line, but are usually made to order and sized to suit a particular purpose or operating conditions. The design of a pressure vessel includes not only dimensions to withstand pressure and working loads, but also technical and economic choices. suitable materials, production processes, internal details and details. However, these standards are adequate for evaluating new ships; it is wrong to use these standards when checking used ships. Since they are pressurized elements, there is a problem with their structural integrity, because in their rupture, explosive decompression leads to material losses and can lead to human losses. Objectives The rupture of the pressure vessel shown in Figure 2, used as a light air compressor, fig. 1, during a hydrostatic test, drew attention to the study of failure analysis. The purpose of this analysis is to identify possible factors, which led to the destruction of this equipment, so that they can be understood and used as a source of data feedback for the designer. In this way, fault analysis functions as a working tool, and not just as an investigation that aims to find the cause of an incident. Figure 1: Vessel connected to a compressor. Figure 2: Vessel after rupture in a hydrostatic test. 2 Structure of the work The work is structured as follows: after the introduction presented in section 1, section 2 contains a bibliographic revision next to the theory needed to develop the work. Section 3 discusses the methodology used in the work, with a presentation of the problem and important data in its resolution. In Section 4, a fault analysis is carried out, where the cause of the gap is searched. Section 5 concludes with a discussion of the results obtained. Master by Carlos Alberto Kassou with the title "Failure Analysis Methodology". In this technique, we perform failure analysis step by step, starting from the first approach to the fracture, how to proceed, to the discovery of possible factors that led to the failure. Prior to the creation of the code that standardized pressure vessel design, pressure equipment accidents were common and usually had great consequences. This section, in turn, is divided into three parts. Section 1 contains rules for the construction of ships that do not require a more detailed analysis of labor forces, their integrity is ensured by a large safety factor in the calculations. Section 2 allows for a better analysis of operating stresses and allows thinner ships to be built because it uses more appropriate safety factors. Subsection 3 is used for very high pressure ships. Design codes were established not only to standardize and simplify the calculation and design of pressure vessels, but mainly to ensure minimum safety conditions for work. 3 Hydrostatic test Hydrostatic test is a test applied to pressure vessels and other industrial pressure equipment such as tanks or pipelines to check for leakage or some kind of rupture. These tests are carried out with the equipment turned off using overpressure, using an incompressible fluid, up to 1.3 times the maximum allowable working pressure, simulating more stringent conditions to ensure that no failure or leakage occurs during normal operation. Resistance of materials Elastic deformation and plastic deformation All material subjected to an external load undergoes deformation. These deformations occur both in the load direction and in the transverse direction. After removing the load, the material returns to its original size or follows with a deformation in the form. Figure 3 shows the strain graph. If the material is loaded from the initial point O to point A, and after the load is removed, the material returns to its original dimensions, this phenomenon is called elastic deformation. If a load is applied from point A to point B, when the load is removed, the material returns in a straight line parallel to line OA and will undergo a permanent deformation, expressed by point C, This phenomenon is called plastic deformation or flow. All ruptures of materials under loads in which the stress is greater than its mechanical resistance. Behavior in this whole process can classify 4 materials into two different groups. Materials that fail without sagging are classified as brittle, brittle fracture and consume little energy before breaking. Those that yield before failure are called ductile materials, exhibit ductile fracture, and have high energy consumption before they break. In the strain strain plot as shown in FIG. 3, brittle materials will fail before reaching point A and ductile materials after this point, that is, brittle materials will not flow. Longitudinal tensions and circular stresses Normal stresses σ1 and σ2 shown in figures 4 and 5 are the main stresses applied to the surface of the pressure vessel. Stress σ1 is known as hoop stress and stress σ2 is known as longitudinal stress. We conclude that the circumferential stress σ1 is twice the longitudinal tension σ. In the study of pressure vessels, this concept is fundamental, since welding and other work in the longitudinal direction should be avoided as much as possible. Working algebraically on expressions, one can put them in terms of characteristic stresses. However, it is known that often, even with a high safety factor, breakdown of components or structures occurs due to defects or cracks with a load significantly lower than the design load. From a mechanical point of view, this behavior is characterized as brittle, and it is at this point that the mechanics of destruction arise, acting as a tool of support and acceptance for projects with some failure. Fracture mechanics is an additional field to the strength of materials and is designed to study the criticality of defects. Fracture mechanics imposes concepts and equations to determine if defects can propagate catastrophically, i.e. unsustainably, or can be controlled and controlled in a stable evolution so that there is no need to replace this defective equipment. So fracture mechanics doesn't make a stress comparison to test the resistance of a material, and yes, it does make a comparison based on other parameters. This method consists of plotting a graph that represents two parameters. If the point is below the curve, the fault is not considered critical and the equipment may continue to operate normally. If the point is above the curve, then the gap is considered critical. To determine the type of crack or its safety, a straight line is drawn from the origin to the point. If this point is below the curve, then the distance between the curve and the point is considered equipment safety, if it is outside the curve, the point where the line crosses the curve indicates the type of collapse mechanism. Compressors are used for this, where they in turn need a reservoir, commonly referred to as an air lung. These devices have a pressure switch that turns on the compressor as soon as the pressure drops to the set value and turns it off as soon as the desired pressure is reached. As already noted, the vessel in question in this work is a light airspace designed for its dimensions to withstand certain pressures and loads. At the bottom of the body, the vessel has a drain that eventually drains into the walls of the vessel to condense water and, under the force of gravity, it drains to the bottom of the vessel if there is a way to drain it. This drainage must be done frequently because the water that forms at the bottom of the vessel facilitates the process of oxidation and corrosion. Effort can result in significant tearing over time, although the vessel is painted on the inside to discourage this corrosion. Other important detail of this light air is that it has a longitudinal seam along its side. The fact that this weld is on the side of the vessel was not accidental, given that the location of the weld is the most favorable region for initiating failures, since it is there that the material is subjected to microstructural changes and residual stresses. The fact remains that welding processes are prone to defects such as lack of penetration, lack of melting and others. For this reason, the longitudinal weld of this vessel is on its side, because if it were located at the bottom of the vessel, the effects of the weld could be added to the effects of corrosion, giving a greater chance of rupture. At the bottom there is still the pressure of the water column of the hydrostatic test, which, although in this case a very small load in relation to the internal pressure, is a more important fact, since this is the place where the ship experienced a fracture, 2 Check. When inspecting the vessel, an external visual inspection was carried out looking for deformation, corrosion or cracking, then the thickness was measured by ultrasound, followed by a hydrostatic test. When measuring the thickness, it was found that the pressure vessel was in the calculated dimensions, the wall thickness varied from 9 mm to 2 mm. Vessel calibration on its outside was also in accordance with the design, and the vessel was a horizontal cylinder in the form of a top. After an external inspection and thickness check, it was found that the ship was ready for hydrostatic testing. Then a test is performed during which the ship crashed. Figure 7 shows the large plastic deformation that occurred before failure. After the break, measurements of its thickness were again taken, especially in the area of ​​cracks, and a minimum thickness of about 2.4 mm was found, which can be seen in the figure. Figure 7: Fault zone severity. 3 Figure 8: Thickness measurement in the crack area. Data collection Figure 9 shows the data provided by the manufacturer on a label next to the vessel. Figure 9: Lung production label. Fault analysis investigates all possibilities of equipment failure. It will be seen in this section that there are many factors that can lead to a rupture in a pressure vessel. 1 Temperature and soldering area In high-pressure vessels with high pressure, runaway can occur, this is plastic deformation when the metal is subjected to constant loads and exposed to a high temperature environment above the melting point of the alloy. If the pressure vessel is at very low temperatures, this can result in the material having brittle material characteristics which are undesirable for pressure vessels. None of the temperature hypotheses apply to the ship in question, since the break was in hydrostatic testing and even in operation, it does not undergo major temperature changes. The area of ​​the weld is a place favorable for the occurrence of cracks, since this area is subject to changes in the microstructure and is the place where residual stresses are present, therefore great importance attached to both settlement calculations and checks. Since the current vessel broke into an area without welds, we can conclude that this is not the cause of the collapse. 2 Material defect Cutting the pressure vessel In order to perform all the necessary tests in the analysis of faults, it was necessary to cut a fracture in its contour, Figure 10, and also to remove a part of the vessel, which should be performed specimens for tensile testing. The cuts were made at a distance of 50 mm from the crack so that their analysis would not deteriorate. Figure 10: Parts cut from the analysis vessel. 9 Section selection and preparation for metallographic analysis. For metallographic analysis, two parts of a small vessel were taken, one in the longitudinal direction and the other in the transverse direction, and the two parts were embedded in Bakelite according to the figure. from bakelite, for the control of which there was a segment of longitudinal and transverse. After embedding, the pieces must be sanded by passing through different amounts of sandpaper, which vary with their roughness, that is, the greater their number, the less friction is created. Therefore, sandpaper is used in one direction, and when a person moves from sandpaper to another, Bakelite rotates 90°. Passing through all sandpaper, it is necessary to polish the surface to eliminate the grooves of the area to be analyzed, and then a chemical attack with 2% nitric acid in ethanol is carried out to visualize the microstructure in a microscope. Because it is a low carbon material, 13%, as can be seen from the chemical analysis below, the formation of ferrite and pearlite can be seen in the photographs taken by the microscope, Figure. In the photograph, we also see the direction of lamination of the plate into its microstructure. Chemical Analysis: Failure analysis is part of the chemical analysis of parts to ensure that the material meets the recommended specifications. Chemical analysis of a part does not require excellent preparation, as is done for microscopic analysis. In chemical analysis, only part of the material is removed, and if necessary, the paint is removed and cleaning is carried out. Figure 13 shows the material from which samples were submitted for chemical analysis. Figure 14 shows the percentage of each chemical present in the material, where the most important result is the percentage of carbon. If there is a slight difference between the results obtained and the specified composition, it should not be concluded that such a deviation is responsible for the failure. Figure 13: Photo of metal after chemical analysis. Figure 14: The concentration of elements in the alloy vessel. Hardness test: Vickers hardness was carried out to obtain the hardness value of the material. After that, the diagonals of the pyramid are measured using a microscope and the area of ​​​​the inclined surface is calculated. Vickers hardness is the result of charge separation and pyramid area. Figure 15: Photograph of the part after the Vickers hardness test. In pieces in the longitudinal direction of the vessel and five hardness measurements in the transverse direction, five hardness measurements were made. The results in the longitudinal and transverse directions of the cuts were very similar, from which it can be concluded that the hardness in both directions is the same. Tensile Strength Test: The main purpose in creating this tensile test is to compare the reduction in thickness of specimens with the reduction in thickness of a pressure vessel after collapse. Tensile testing required standard test specimens. The selected test specimens are of the type of connection and are made in accordance with specification 1 in FIG. 16. Figure 16: Format of tensile test specimens for tensile testing. The tensile test is a test carried out on samples of dimensions predetermined by the standard, where the pull is carried out to failure. With this test, several parameters can be measured, as can be seen from the table. In this table, you can see the tensile test results for the three test specimens. Table 1: Tensile test results. With specimen thickness values ​​after tensile testing, we achieve results very close to the thickness values ​​measured in the area of ​​the crack. In tensile testing, deformation is slower, so the reduction in thickness before fracture is expected to be greater than in hydrostatic testing, where the pressure values ​​rise very rapidly because the fluid used is incompressible. All material analysis results are in line with the values ​​or substances expected by the project. In fact, a very small number of failures are due to defects in the material or to its use in inappropriate cases. 3 Corrosion Insufficiency As noted earlier, in lightweight air compressors, water is generated due to air condensation. These are deposits of water on the walls of the vessel and, under the influence of gravity, sink to the bottom. To solve this problem, there is a drain in the bottom of the vessel so that water can often be withdrawn. It is known that often such drainage is not carried out at the desired frequency, and because of this it will be established whether internal corrosion can be the cause of the destruction. After the vessel ruptured, smaller thicknesses of its hull were found along the crack with a minimum value of 4 mm. Therefore, the calculation of the pressure vessel will be made as if it had a thickness of 4 mm throughout the hull, and thus, if the vessel does not break, the hypothesis of rupture due to loss of thickness due to corrosion is excluded. Even if the vertices are not faults, a quick calculation of the required minimum thickness will be performed. In this case, zero was used, since it is desirable to know the minimum thickness. Thus, the minimum thickness value at the tops is 2.07 mm. Therefore, even in the limiting case of a thickness of 2.4 mm, collapse will not occur on the entire ship. 4 Design error. In section 3, to withstand operating pressure, the container must have a minimum thickness of 2.07 mm at the top and 2.37 mm at the body. From the calculations, it was concluded that crack-type defects are not of decisive importance for a device with these design features, and the crack must be large enough to cause the pressure vessel to collapse. However, the required crack sizes will be shown in Table 2 for failure. Three main types of cracks were discussed: semi-elliptical, infinite, and propagation. If a crack of this size occurs during a hydrostatic test, it will be detected by a water leak. 6 Excessive pressure A significant decrease in thickness in the area around the crack is a clear indication that plastic deformation of the material occurred before the fracture. With the results obtained in the tensile test, where the decrease in the thickness of the samples reaches 29% and the measurement of the thickness in the vessel after rupture, reaching a 25% decrease, it can be concluded that this plastic conformation was due to internal loads in the pressure vessel exceeding the stresses material flow. This overpressure could be due to careless operators, poorly calibrated equipment, some blockage in the connections that reached the pressure gauge, or simply a malfunction of the pressure gauge. 15 In failure analysis, the steps described in this paper are followed to avoid settling when determining the cause of collapse. Early on, the main suspects for vessel rupture were corrosion and overpressure, as material defects were rare and the design of this pressure vessel was not an isolated design, the same equipment is used in numerous under the same conditions. Fatigue of welded structures. Lisbon: Calouste Gulbenkian Foundation, Introduction to Mechanics solid body. Analysis of hydrostatic test effects in a pressure vessel, master's thesis. Fault Analysis Methodology, master's thesis. Analysis of failures in a pressure vessel. . Do you need to find out if your cold, hot and thermal waters are really related?