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Multi-layer wrapped high-pressure vessel 1: Why is this equipment designed with a multi-layer tubular section wrapping structure? Is a single layer okay? Why not use a multi-layered integral wrapping structure? 2. Octagonal gaskets are used for connection flanges; why are metal flat gaskets used for manholes? 3 Technical Requirements, Article 10: What are the issues with UT testing of the circumferential weld joints of the cylinder shell and those of the cylinder’s spherical shell? 4 The drawing lacks information on the head forming method and heat treatment process; please provide details on these How is the heat treatment temperature calculated? 5 Mechanical prototypes of the Latin American formula. 6 What does the special coefficient K for flat heads depend on? 7 What are the differences between Tables 5-9 and 5-10 for flat heads? Spherical tanks. 1 Regarding Clause 6 of the technical requirements, “Magnetic particle testing of butt joints between nozzles and flanges where DN≤250”: what’s the problem with this? There are too many national standards; even for spherical tanks, Article 11 of the RT 2 technical requirements stipulates that magnetic particle testing should be carried out after cleaning the back side of the weld joint. What’s the problem with that? Penetrant testing 3: What are the problems with the embedded nozzle having the same thickness as the shell thickness? What are the components of the maximum vertical load on the 4 supports? 5 How to determine the heat treatment location for test plates? 6 What are the two important basic dimensions before tank installation? 7 Define and explain the purpose of welding process qualification, identify the factors involved, and provide some examples. 1. Can the safety valve of a nitrogen tank be installed on the pipeline? What needs to be considered? Answer: It can be installed on pipelines; those used for releasing gas can be placed at the top of containers and on pipelines, while those used for releasing liquid are installed below the liquid level. Points to note: 1. The flow area of the pipeline must not be smaller than the relief area. 2 The discharge volume takes into account the entire system of containers and pipelines. 3 The pipes are unobstructed. 4 Leaks at the sealing surface may occur due to the weight of the safety valve itself, the impact caused by high-speed gas flow during discharge, as well as pipe thermal expansion and being suspended; in such cases, brackets can be designed for fixation. 2. Are the discharge pressure and temperature of the safety valve determined? Answer: The discharge pressure includes the design pressure and the overpressure limit; for a single safety valve, the overpressure limit is the higher of 0.1 times the design pressure and 20 kPa. (In the case of multiple relief devices, it can be increased to the greater of 0.16 times and 30 kPa; see Appendix B3.2.2 of 150.1 for details.) Discharge temperature: Liquefied gases are generally considered to be in a saturated state. Refer to the medium parameter table based on the discharge pressure to obtain the corresponding temperature. For gases, calculations are generally carried out using Clapeyron’s equation PV=nRT. 3. Principles for selecting expansion joints – how to choose expansion joints for high-temperature and high-pressure heat exchangers? When should expansion joints be used? What is the function of expansion joints? Expansion joints should be placed away from high-temperature areas, preferably below the supports; generally, a single-layer pipe made of stainless steel is used. If either the axial stress of the shell, the axial stress of the heat exchange tubes, or the pulling force between the heat exchange tubes and the tube sheet is not within acceptable limits, an expansion joint should be installed. Function of expansion joints: Installed on container shells or pipelines to compensate for the additional stresses caused by temperature differences and mechanical vibrations; they serve as elastic compensating elements that can expand and contract freely. 4. How is heat treatment carried out for fixed-tube-sheet heat exchangers? Stress model of fixed tube sheet heat exchangers? There are two types of post-weld heat treatment: one is segmented heat treatment, where the shell is treated first, followed by local heat treatment after welding the tube sheets to the shell, and the tubes to the tube sheets. This method has a long cycle time, high energy consumption, and requires heavy labor. The other method is overall heat treatment. This method primarily involves controlling thermal differential stresses. When the materials of the shell and the tube bundle are the same, the shell heats up quickly while the tube bundle heats up slowly. Under the effect of this temperature difference, the shell undergoes significant thermal expansion; however, this expansion is restricted by the tube bundle. As a result, the tube bundle experiences tensile stress, while the shell is subjected to compressive stress. After the heat treatment, the cooling process is the reverse of the heating process. Therefore, during both heating and cooling, the thermal differential stresses must be kept below the material’s yield strength. Typically, the heating and cooling rates are controlled at 65°C/h; to ensure quality, overall post-weld heat treatment is generally not employed. Force application model: The tube bundle is treated as an elastic support, while the tube sheet is considered a circular plate placed on an elastic foundation; the bending stress of the tube sheet is then determined based on the magnitude of the load, the stiffness of the tube bundle, and the surrounding supports. 5. What are the requirements for the main bolts of high-pressure vessels, including material selection and structural inspection requirements? 6. What are the requirements for the material of manhole bolts? 7. What is the difference between embedded nozzles and inserted nozzles? a. Insert-type nozzles are easy to align and center, allow for full penetration during welding, are simple to manufacture, and can easily meet structural size and inspection requirements. However, they require a large amount of welding, leading to significant stress concentration; they are commonly used in medium and low-pressure equipment. b. Fixed-type nozzles require less welding, result in less deformation and lower stress. It is necessary to ensure that the sheet metal at the opening site does not suffer from delamination, and drilling is required after welding; the precision required for processing is high. It is difficult to process these nozzles when their diameter is small, so they are generally used in high-pressure equipment. c. Embedded splices are commonly used in fatigue vessels and spherical tanks; as butt joints, they require high welding quality. Since the weld joint is of type A, the inspection requirements are high, which increases the manufacturing cost. For use in fatigue and high temperature gradient conditions. 8. Differences between thick-walled and thin-walled containers; are high-pressure containers necessarily thick-walled? What about stress distribution? When K≥1.2, it is a thin-walled structure; otherwise, it is thick-walled. For high-pressure vessels, the pressure range is 10 Mpa≤p＜100, and there is no direct relationship between these factors – high pressure does not necessarily mean thick walls. Thin-walled biaxial stress; radial stress is not considered, the circumferential stress is twice the axial stress, with a uniform distribution. Thick-walled 3-directional stress, axially uniform, otherwise non-uniform; larger inner wall, smaller outer wall. 9. What are the requirements and composition specifications for low-hydrogen welding electrodes used for spheres and tanks? According to 4.6.3.3 of GB12337, for shell welds and welds that are directly welded to the shell, low-hydrogen flux-cored electrodes should be used, and the diffusion hydrogen content of the weld metal shall be measured on a batch basis; the values for diffusion hydrogen content are shown in Table 15. 10. What are the layout requirements for spherical shell versions? Firstly, the spherical shell version must not be assembled; it has to be formed by cold pressing. Defects such as cracks, bubbles, scars, folds, and inclusions are not allowed, nor is delamination permitted. Secondly, in terms of layout, it should: a. meet the requirements of the materials in terms of capacity, pressure, and temperature, and be safe and reliable. B. It has a good stress condition. C. Control the geometric dimensions of the press-formed shell plates; opt for larger shell plates to minimize weld length and reduce installation efforts. d. The steel grade should be appropriate to improve plate utilization. The specifications should be limited to improve interchangeability. The plate size of the spherical shell shall be no less than 500 mm. E. Adjacent welds are offset. F. The weld pattern is designed to minimize assembly stresses, restraint stresses, and residual stresses, ensuring a uniform distribution of these stresses. 11. Which components are mainly affected by wind loads and seismic loads in terms of stress? 12. How are the design temperature values determined, and how is the design pressure set? P11 in GB150.1: The design temperature is the metal temperature specified under normal operating conditions. Its values are as follows: A. It must not be lower than the highest possible temperature during operation; if it is below 0°C, it must not be higher than the lowest possible temperature. B. When the temperatures of various parts differ, separate design temperatures can be set. C. Determined through heat transfer calculations, measured from similar containers that have been used, or specified based on the medium temperature and environmental conditions. D. The minimum design metal temperature takes environmental effects into account. The lowest values of the monthly average temperatures over the years are primarily considered. The design pressure is the highest pressure at the top of the container; it is generally not lower than the operating pressure, and when there is a safety relief device, it should also be higher than the overall pressure. For the rest, see 150’s P10.13: Thinning structure for the connection between the cylinder and the spherical head? According to GB150.4, for grade P325 with different thicknesses, when the difference in thickness exceeds a certain value (for thin plates with a thickness of ≤10 mm, the difference is greater than 3 mm; or for thick plates with a thickness greater than 10 mm, the difference is greater than 0.3 times the plate thickness or 5 mm), it is necessary to perform thinning on one side or on both sides. Attention should be paid to a 1:3 slope ratio and a smooth transition; generally, thinning is carried out on the side that is thicker. 14. What are the problems with octagonal pads, and what are the requirements for their hardness and material? What are the requirements for the annular groove surface? The hardness of the gasket material is 30~40 HBW lower than that of the groove, and the gasket material is used for forging grades III or IV. The surface roughness of the inclined surface (23° inclined surface) in the annular groove that comes into contact with the octagonal gasket is not higher than 3.2 μm. The advantages are good sealing performance and a simple structure. The disadvantage is that when the diameter is large, it is somewhat difficult to machine the octagonal gasket and the ring groove. 15. What considerations are taken into account in the design of liquid ammonia containers? What is stress corrosion, and what are the requirements regarding material selection, structural fabrication, and inspection? Liquid ammonia is not highly corrosive in itself, but the medium can easily become contaminated by air (oxygen and carbon dioxide) during loading and unloading of the containers; this subsequent contamination can cause stress corrosion in the steel. Therefore, it is generally required that the water content be slightly above 0.2%, with water being used as a corrosion inhibitor. For designs subject to stress corrosion, 100% non-destructive testing must be considered; ultrasonic testing should be carried out on the sheets. The yield strength of the material should generally not exceed 355, and its tensile strength after testing should not be greater than 630. For normalized sheets, the carbon equivalent must be controlled (≤0.43 for carbon steel, ≤0.45 for low-alloy steel); selenium and lead shall not be added, and post-weld heat treatment is required. 16. Requirements for steel plate impact, mainly Clause 4.1.6 in GB150.2? For quenched and tempered steel with a thickness greater than 36, and for normalized or normalized + tempered plates with a thickness greater than 80, impact testing is performed on samples taken at 1/2 of the thickness. Personally, I think the requirement for impact energy should remain the same as in normal conditions. In 150.2, section 4.1.11 specifies stricter impact requirements for thicknesses greater than 100; generally, a) the temperature is set at its lowest value, resulting in an increased impact energy, or b) if the temperature is below the lowest value, the impact energy remains unchanged. The reason for conducting impact tests on thick plates on a sample basis is that their properties are unstable; generally, the surface quality is good while the quality in the middle is poor, so impact tests are performed at a point halfway through the thickness. 19. Understanding the minimum design metal temperature? The minimum design metal temperature is, in container design, the lowest value of the metal temperature expected for that container under various possible operating conditions (including normal, abnormal, environmental, etc.). The materials and welded joints must meet the impact requirements at that temperature, primarily to prevent brittle fracture at low temperatures. 20. What are the differences in stress between towers and spherical tanks? The tower is an elastic continuum or a multi-degree-of-freedom system, subjected to high bending stresses and bending vibrations, with the pull stresses on the foundation bolts also needing to be considered. The spherical tank is a single-degree-of-freedom system with shear vibration, and the shear force on the foundation bolts is calculated. 21. What are the design considerations for chromium-molybdenum steel? 22. Difference between high-pressure fasteners and atmospheric-pressure equipment. 23. What is the impact test process? The impact test is carried out on a pendulum impact testing machine. The specimen, which has a notch cut in it (usually a Charpy V-notch), is placed on the testing table, and then struck by a pendulum. The energy released at the moment of fracture is measured; the energy absorbed during impact indicates the material’s ability to undergo rapid plastic deformation. A higher capacity to absorb impact energy corresponds to better plasticity, while otherwise the material may be better suited for slow deformation. 24. What are the special requirements for fixed-type connectors? A. The steel plate at the opening must not delaminate (UT). B. Machining and boring are required after welding. 25. What are the various situations of equipment failure? Brittle fracture (such as low-temperature brittle fracture, temper embrittlement), ductile fracture (overpressure cracking), excessive deformation (joint leakage, such as flange leakage), elastic or plastic instability (external pressure instability and instability in the transition zones of elliptical heads and disc heads under internal pressure), creep (fracture at high temperatures, excessive deformation, and instability), corrosion, environment-induced cracking (stress corrosion, hydrogen-induced cracking), fatigue failure, etc. 26. What is the comparison between TOFD and conventional UT? TOFD (using a dual-probe setup with one transmitter and one receiver, based on time-independent amplitude) offers a higher detection rate, provides more information, is intuitive, allows for recording, can be stored for long periods, can operate in semi-automatic or fully automatic mode, has minimal human error, and exhibits good repeatability. However, using two probes results in poor flexibility; it is not suitable for objects with complex structures, the detection performance for metals with coarse grains is not ideal, and there are certain blind areas. (This question is outside our area of expertise.) Tower equipment: 1. What are the different operating conditions for tower equipment, and what loads need to be taken into consideration for each condition? ； Operating conditions, testing conditions, installation conditions, and maintenance conditions. Loads: A. Pressure loads, gravitational loads, eccentric loads, vertical seismic forces (for areas with seismic intensity of 8 and 9 degrees), wind loads, and seismic loads (during operation, the greater of wind + eccentric force or seismic force + 0.25 times wind + eccentric force; during testing, 0.3 times wind + eccentric force). 2. Why are spherical heads used? What processing methods are employed for spherical heads? How is the degree of deformation calculated? Why is it necessary to specify a minimum thickness for molding? ； Spherical heads have good stress resistance, thin walls, and are also cost-effective. Spherical heads are generally formed first and then joined together, through cold forming. The deformation rate is calculated according to 8.1.1 in GB150.4 (biaxial tension formula). The processing involves thinning, and it is necessary to maintain the minimum thickness required to ensure strength after molding; this also facilitates manufacturing plants in carrying out the processing according to their own techniques. 3. What types of containers require the preparation of welding test plates ； There are Class A connectors, and: A. Extremely high hazard ； B.Rm≥540 low-alloy steel ； c. Low-temperature container ； d. Heat treatment is required to improve or restore material properties ； e. As required by the drawings. 4. What form of reinforcement is used for opening reinforcement, and why was this method chosen? Strengthen with a solid forged piece. High pressure (≥4 MPa) and large thickness are the reasons for its selection. 5. What type of heat treatment is required for post-weld heat treatment? Heat treatment processes that alter the microstructure and properties of weld joints or reduce residual stresses (commonly referred to as stress-relief heat treatment, though not entirely accurate). 6. How is the reinforcement range B calculated for opening reinforcements, and which thickness is used in the calculations for the shell? For the transverse reinforcement range, take the larger value between B=2dop and B=dop +2δn+2δnt; for the axial reinforcement range (external and internal protrusion of the tube), h is the smaller of the two values: the square root of dopδnt and the actual protrusion height of the fitting. The calculated thickness for the shell is the nominal thickness at the opening.