Design pressure and test pressure

I’ve never seen such a rule; you might as well post the entire clause

A hundred examples of problems in the design units for pressure vessels of categories 1 and 2. Through years of participation in the processes related to obtaining and renewing design qualifications for pressure vessels in various industries, the author has identified the common issues faced by such design units across different sectors; the surface area should be indicated as RF. 7.5 Only flange connections that are external connections shall have their connection standards and types specified. It’s not necessary to indicate it if it’s not connected externally. 8 Material Selection for Design 8.1 Preferred Materials The materials recommended in Chapter 2 of GB150 were not given priority. Many design drawings still use materials from Appendix A or materials that are not recommended; if substitutes are used, they must also comply with the provisions of Appendix A. 8.2 The selection of the corrosion margin is unreasonable. In some media, corrosion is severe and not uniform; it is unreasonable for designers to address this by increasing the corrosion margin. At this point, anti-corrosion measures should be considered. 8.3 The selection of welding rods is not consistent; sometimes design agencies specify welding rods by model, and other times by brand, but there should be uniformity within a single agency. 8.4 Improper material selection: Designs that use materials from abroad that are not intended for use in pressure vessels are unacceptable; in some cases, designs opt directly for materials from abroad that are not suitable for manufacturing pressure vessels, and then attempt to retest them using domestic standards for vessel steel – this is also not permitted. Even substitute materials are not allowed. 8.5 The selection of materials should proceed from lower to higher quality. The steel grades used in China for manufacturing containers include QZ3S—AF, QZ3S—A, B, C, 20R, 16MnR, etc. The design selection should proceed from low to high to make full use of the materials. 8.6 The material selection did not take the operating temperature into account; if the operating temperature is -19.8°C, A (Q 235-A) should still be chosen. As for Q235-A, its operating temperature range is 0~350°C. 8.7 For design and material selection, the old steel grade AS is still being used, while the new steel grades Q235-A, B, and C specified in Amendment 1 to GB150-89 are also employed. In cases where the operating conditions are not clear, such as when containers hold extremely hazardous media, Q235-A and B are still used for the vessel shells and heads; Q235-A is chosen when the pressure exceeds 1.0 MPa or when the thickness is greater than 20 mm. 8.8 For vertical vessel skirt supports, the material used for the shell is not the same as that used for the vessel shell itself; for example, the material used for tower vessel shells is 16MnR, while Q235-A is used for skirt support shells, which does not comply with the requirements of JB4710-92. 8.9 Manhole materials: Standard manholes shall be used; when P ≥ 1.6 MPa, the material for the flat cover section shall be changed to 16MAR. Some still use 16Mn, which does not comply with the GB150 regulations. 8.10 Using 16Mn steel plates as heat exchanger tube sheets does not comply with the requirements of GB151-89; when 16Mn steel plates are used for heat exchanger tube sheets and end caps, these standards specify that the design pressure should be P≤1.6 MPa and the design temperature should range from 0 to 350°C. 8.11 After the issuance of GB150-89, 16Mn steel plates were still used to manufacture the shells of pressure vessels; 16Mn continued to be the material of choice for the main pressure-bearing components of such vessels. The designer should follow HGJ 15—89, but since the publication and implementation dates of HGJ15-89 are both prior to those of GB150—89, the designer must adhere to GB150-89. 8.12 The tube sheet was directly selected as a forged part. When designing the heat exchanger tube sheet, the provisions of section 2.2.1.2 of GB 151-89 were not followed, and a forged part was chosen directly. As a result, when forged parts could not be obtained and container thick plates had to be used as substitutes, it became necessary to recalculate the tube sheet, and such substitution was not possible. Forgings can be used directly only when the thickness is less than 50 ram. 8.13 Inappropriate selection of gaskets: Asbestos rubber sheets should not be used in vacuum operations. When the medium is an organic solvent, oil-resistant rubber sheets should be used. 8.14 Incorrect selection of bolts and nuts: The combination of bolts and nuts should be selected in accordance with the recommendations in GB150—89. The hardness of the nut is slightly lower than that of the bolt. Some design units did not make the selection as recommended. The hardness of the nut is slightly lower than that of the bolt. Some design firms did not follow the recommendations; in some cases, the hardness of the nuts was even higher than that of the bolts. For carbon steel, whether the strength grades of bolts and nuts are specified separately or the material type is specified separately, the unit must be consistent throughout. 8.1 For cooling containers that come into contact with ammonia, 16MaR steel plate should not be used readily, as this can lead to stress corrosion cracking. Based on long-term usage experience, carbon steel proves to be a better choice than low-alloy steel. 8.16 Reinforcing ring: The material of the reinforcing ring is different from that of the housing, and its thickness is more than 1.5 times the nominal thickness. The reinforcement ring should generally be made of the same material as the housing during design, and its thickness should also be as similar as possible to that of the housing. Otherwise, difficulties in material selection and manufacturing will arise. 8.17 When the thickness of the steel plate selected is less than 6 mm, and the plate thickness is below 6 mm, 20R or 16MnR is still used. When container plates need to be selected, 20HE or 16MnHP can be chosen. Because when the thickness of 20R or 16MnR is less than 6 mm, no products are available for supply (the thinnest specified in GB6654 is 6 mm). 8.18 The use of high-quality carbon steel plates 10 and 20 for pressure vessel shells does not comply with the requirements of GB150-89. GB150-89 does not recommend the use of high-quality carbon steel plates for pressure vessels. 8.1 The use of 35 steel for welding structures in pressure vessel forgings violates Article 9 of the Pressure Vessel Regulations. When used in welded structures, its maximum carbon content should not exceed 0.25 (by melting analysis). 9 Design Calculations 9.1 Inconsistent Parameters The parameters in the technical specifications table on the drawings do not match those in the strength calculation sheet. This is a common occurrence in many pressure vessel design documents from various design firms. 9.2 Incomplete design parameters: The strength calculation document is lacking necessary design parameters, drawings, and calculation bases. The design parameters and the source of the data are not clearly specified. It makes it confusing when reviewing the calculation sheet. 9.3 Horizontal vessels are not considered; many horizontal vessels are excluded from consideration, and the wall thickness is designed solely based on the internal pressure of such vessels. 9.4 Corrugated tubes: When heat exchange elements are made of seamless steel pipes that are not recommended by GB151 (such as corrugated tubes), the calculation methods still follow those specified in GB151. Since there are neither enterprise standards nor industry standards providing recommended methods, there is a certain degree of arbitrariness in these calculations. 9.5 Determination of the mixing shaft diameter: There is no experience available for calculating or comparing the diameters of the mixing shafts in mixing equipment; it is not acceptable to simply assume a value for the shaft diameter. 9.6 External pressure design: Containers subjected to external pressure may be designed based on internal pressure, which can lead to instability. Some also experience both external and internal pressures, but when calculating, only one type of pressure is taken into account. During the external pressure and stability verification, the inner diameter was mistakenly used for the check. 9.7 Installation of expansion joints: Whether an expansion joint should be used in a fixed-plate heat exchanger can only be determined through calculations; it cannot be decided using empirical formulas or estimates. 9.8 Calculation of external pressure for horizontal vessels with a semi-jacket: Horizontal vessels with a semi-jacket are calculated for external pressure instability as if they had a full jacket. Under the same design conditions, the inner cylinder is most prone to instability when there is a half-jacket. Careful analysis is required during calculation. The calculation method for honeycomb jacketed vessels should be used for the calculation. 9.9 Calculation of reinforcement for openings – Calculation missing for reinforcement of openings. Especially in the case of large openings (such as manholes) or inclined openings, or when the ratio of the inner diameter of the opening to the inner diameter of the shell, d/d9, exceeds the limits specified in GB150, no calculations are carried out. Even if calculations are performed, it is not clear how reinforcement should be applied or what amount of reinforcement area is required. 9.10 Reinforcement for openings in standard manhole covers: When using standard manhole covers, it is unsafe not to carry out reinforcement calculations for the openings in those covers. 9. The weld coefficient in the calculations for reinforcement due to openings: In such calculations, for the welds of the reinforced cylinder and head, when performing local flaw detection, the weld coefficient is still taken as 0.85. For the cylinders and heads that are reinforced during reinforcement calculations, the weld coefficient shall be 1.0. 9.12 Design thickness: When performing strength calculations, the provisions of Amendment No. 2 to GB150-89 shall be applied. The design thickness is still considered to be the sum of the calculated thickness and the thickness addition (C1 + C2). 9.1 3 When there is a large difference between the calculated thickness, the design thickness, and the nominal thickness, in some cases these values are rounded to fit within two standard steel plate sizes. It causes unnecessary waste and increases manufacturing costs. 9.14 The method for determining the nominal thickness is incorrect. According to GB150-89, the nominal thickness is the design thickness plus the negative deviation of the steel’s thickness, rounded up to the thickness specified in the standard specifications for that steel. Some designers round down the nominal thickness to the standard specification for steel thickness. 9. The design pressure and calculated pressure of containers with a central jacket: When calculating the strength of containers with jackets, the design pressure of the inner cylinder is confused with the design pressure (calculated pressure) of the portion of the cylinder that is enclosed by the jacket, leading to a series of errors such as an excessively high hydrostatic test pressure. Errors are more likely to occur, especially when the working pressure of the inner cylinder is vacuum. 9.16 Stress verification in the absence of pressure testing: The design calculations include only the nominal wall thickness and stress calculations for the main pressure-bearing components when they are operating normally. However, there was no stress verification during the pressure test. This violates the provisions of GB150 and the ‘Allowance Regulations’. 9.17 During pressure testing, the stress checks do not take into account the additional thickness of the wall, nor do they account for the static pressure of the liquid column. 9.18 In the case of pressure testing on vessels with jackets, when checking the stability of the external pressure during jacket pressure testing, if the stability requirements are not met, designers blindly increase the thickness of the inner wall, resulting in unnecessary increases in manufacturing costs. The normal approach is to maintain a certain pressure in the inner cylinder during the jacket pressure test, with this pressure being no less than 25% of the designed jacket pressure. 9.19 The vertical waste heat boilers use thin, flexible tube sheets. When calculating the thickness of these tube sheets, JB3622 takes into account only the hypothetical circle in the area without tubes; however, it does not consider the hypothetical circles formed by the support tubes in the area with tubes. In such cases, it is possible that the hypothetical circle formed by the support tubes is larger than that formed in the area without tubes. The correct approach is to compare the two cases and use the larger value for the calculation. 9.20 The stirring power for glass-lined reactors equipped with agitators is not calculated, and there are no restrictions on the medium used; such reactors are supplied to the market as standard products. This approach of not calculating the power or the stirring shaft results in a high degree of arbitrariness. 9.21 Blindly adopting the tube sheet design for heat exchangers without performing strength calculations or using empirical formulas is highly arbitrary. 9.22 When a special steel plate specified in YB/T 40-87 is used for pressure vessels, C = 0.25 mm; if this value does not exceed 6% of the nominal thickness, then C = 0. However, designers still choose C = 0.25 mm, which is unnecessary. 9.23 The calculation documents are not properly formatted and are messy; when calculations are done using tables, the requirements outlined in Amendments 1 and 2 to GBI50 are not followed. When performed manually, complex calculations lack accuracy and reliability. 9.24 In the vast majority of design units for pressure vessels of categories 1 and 2, strength calculations are still carried out manually. Designers have very little knowledge of computers and their software. 10 Structure and Diagrams 10.1 Special node labels are not clear; the dimensions and angles of special nodes must be clearly indicated. 10.2 Vertical containers and jackets lack vent and drain ports. Gas and residual liquid cannot be discharged during operation. 10.3 The node structure in the assembly drawing differs from the actual structure of the component drawing. It causes unnecessary misunderstandings. 10,4 The web (6z) direction of the saddle support is reversed. Such errors have occurred in many places. 10. For components that require heat treatment followed by further finishing, there are no separate component drawings, nor are any specifications for dimensions and surface roughness provided. 10.6 The holes in the elliptical head are not located within the 0.8 range. During design, it should be kept within the 0.8D range as much as possible; if that’s not feasible, certain measures must be taken. (This new GB150 has been revised). 10.7 The liquid level gauge connections do not specify the installation tolerances. It causes difficulties in installation. 10.8 For pipe I=1, the orientation of the support and the orientation of the skirt base do not have their angles and elevations specified precisely. Unless an orifice orientation diagram is provided separately. 10.9 The height of the external takeover is not specified. It not only causes manufacturing difficulties but also complicates the process piping. 1O-10: When selecting pipe flanges and vessel flanges, the influence of temperature was not taken into account. The selection of flanges must take into account the influence of temperature. 10.11 For the same pressure vessel, its pipe flanges and vessel flanges are not selected based on the same design pressure and the same design temperature. This results in different grades of flanges within the same container. 10.12 For media that are extremely and highly hazardous, flat welding flanges are still used for the connection fittings; however, for media that are extremely and highly hazardous as well as those with explosion risks, butt welding flanges should be preferred. 10.1 3 When the takeover intersects tangentially with the cylinder or head, no detailed weld points are provided. At this point, a detailed node diagram must be provided, indicating parameters such as the notch dimensions and angles; the reinforcement rings must be drawn separately. 10.14 In equipment with jackets, the folded part of the jacket is welded to the reinforcement ring of the shell, which results in an unreasonable design. 10.1 5 The notation for bolts and nuts used in connectors: if commercial bolts and nuts are employed, the notation is not consistent. Some indicate the grade, while the same diagram also specifies the material. 10.16 Unclear design references and machining references lead to missing or incomplete dimensions, as well as difficulties in positioning. 10.17 Incomplete projections result in diagrams that fail to convey the intended meaning, making it difficult for those who view them to understand and prone to misinterpretation. 10.1B In the schedule, identical material grades are indicated with ellipses. It causes misunderstanding. 10.19 The terms for assembly drawings, component drawings, and part drawings are different. In the case of heat exchangers, they should be named in strict accordance with the names specified in Section 1.4 of GB151-89. 10.20 When the diameter of the container is 600 film and there is an access hatch, gasket welding is still used. For welds in containers of types A and B, double-sided welding should be preferred as much as possible to ensure full penetration; the use of backing plates is not recommended. 10.21 For vertical vessels that use gaskets, the fillet welds securing the gaskets are located at the bottom, which facilitates the accumulation of medium and can lead to corrosion as well as a high risk of explosion due to the accumulation of explosive substances. The proper approach is to weld the fillet welds on top of the gasket. 10.22 In cases of intergranular corrosion, only strength welding is used to connect the tube sheet of the heat exchanger to the heat exchange tubes. The correct approach is to use expansion bonding combined with strong welding; it is best to weld first and then expand. 10.23 The full penetration welding process is not clear. Full penetration refers to double-sided welding, or processes that achieve full penetration by using TIG welding for the root pass and manual or automatic welding for the cover pass, as well as single-sided welding that results in a double-sided finish, and welding processes that utilize shims which can be removed after welding. (The new GB150-95 provides new provisions on this). 10.24 Shut-off valves are not installed between the container and the safety valve for media that are extremely, highly, moderately hazardous or viscous. It violates Article 133 of the Code of Practice. 10.25 Selection of safety valves for media in different states should be differentiated. For gases or liquefied gases, a fully open safety valve should be used, while for liquids, a slightly open type is sufficient. 10.26 The selection of safety valves is not done based on the opening pressure; instead, the nominal pressure is often used as the basis for selection, which results in the safety valves not activating at the specified pressure. 10.27 The flange of the safety valve connection pipe and the throat area considered in the safety valve calculations are not the same thing; the throat area of a safety valve is generally two sizes smaller than the nominal diameter of the connection pipe flange. 10.28 The dimensions in the general layout or assembly drawing are incomplete. It is difficult to distinguish between external dimensions, assembly dimensions, characteristic dimensions, etc., which poses challenges for reviewers and manufacturers. 10.29 It is unclear when to indicate the design datum and when to indicate the machining datum when providing dimensioning. The design datum is sometimes the same as the machining datum, and sometimes it is different. 10.30 The total length of the horizontal storage tank is 10 meters, and there is only one access hole, which makes it difficult to clean the tank and remove flammable and toxic substances from it. Two manholes are required by regulations. 10. The designer of the nozzle flanges on the pressure vessel shell has selected the appropriate type based on factors such as pressure, temperature, and the medium used. But at the same time, reinforcement plates were added to the take over and flange, with one end of these plates welded to the reinforcement ring of this tube, resulting in the reinforcement ring having to bear additional torque, which is unreasonable. 10.32 For packed-bed shell-and-tube heat exchangers, the value of C representing the packing height is not taken as specified; this value is much lower than that stipulated in GB151, which makes sealing difficult. 10.33 With a design pressure of 6.3 MPa, the designer still chose a raised face flat welding flange (HGJ46—91). The designer mistakenly assumed that the stub of this flange was a necked (butt-welding) flange, resulting in an unnecessary error. 10.34 When oval manholes are provided on cylinders, some designers mistakenly align the long axis of the oval manhole parallel to the cylinder’s axis, resulting in an incorrect design; the correct approach is to have it perpendicular to the cylinder’s axis. 10.35 The manholes at the top and bottom of the horizontal container are located exactly in the middle of the two supports. The designer overlooked the fact that the exact center of the upper and lower parts of a horizontal container is the area subject to the greatest stress, which should be avoided as much as possible.

He means that this calculation method is incorrect, right? He didn’t say that it should be calculated in this way

Purely misleading nonsense! For pressure vessels, the relevant provisions in the standards adopted for design must be followed! ~~