Calculation of blind plate thickness?

1. Flat cover end caps can be used for pressure testing of small-diameter, low-pressure pipelines (for pipelines with DN200mm and PN 4.0 SPa or higher, elliptical end caps or flat covers with reinforcing ribs are recommended). There are three methods for calculation: the first is to calculate in accordance with Article 6.6 of GB50316 \"Code for Design of Industrial Metal Pipelines\", as shown in Equation (3); this method is applicable to pressure testing of pipelines with DN400mm and PN2.5 MPa or lower； Second, it is calculated in accordance with Article 7.4 of GB150—1998, as shown in Equation (4) ； Thirdly, the wall thickness of the end cap is determined according to the pipe designation Seh in GB12459; this applies to forged steel socket-welded pipe fittings with DN15–DN80 mm dimensions, and to end caps of the Seh80 and Schl60 grades for flat welding. =In equations (3) and (4), Kl is a structural characteristic coefficient, as shown in Table 6.6.1 of the GB50316 standard ； D — calculated diameter of the pipe/mm; generally, D = Di can be used ； K is the structural characteristic coefficient, see Table 7.7 of GB150. Under normal circumstances, the value calculated using formula (4) is higher than that obtained from formula (3). When using formula (4) to calculate flat-ended closures, since K = 0.44 ti/t, where ti is the calculated wall thickness of the pipe and can be approximated as the nominal wall thickness t of the pipe minus 2–3 mm, and t represents the effective wall thickness of the pipe which can also be approximated as the nominal wall thickness t, it is possible to approximate K as 0.44(t – 2)/t in order to simplify the calculations. 2. Calculation of the thickness of a flat head with reinforcing ribs: When calculating the thickness of such a head, the equivalent diameter D can be used in equation (4). Equation (5) can also be employed for pressure testing purposes. The equivalent diameter D is the diameter of the largest inscribed circle determined based on the support spacing as shown in Figure 1. 0·51 Dc √South + c (5) The flat cover head with reinforcing ribs shall meet the structural requirements: the thickness of the bottom plate shall be not less than 8 mm, the supporting reinforcing ribs shall be arranged symmetrically at equal intervals, the thickness of the rib plates shall be not less than 10 mm, and the height H of the rib plates shall satisfy the requirements of equation (6). H≥ +10 (6), where h is the allowable stress of the fillet weld in MPa ； 1 Weld height/mm. Figure 1: Flat cover head with currency reinforcement ribs. 2.4 Blind flanges – The thickness of these flanges is calculated using equation (7); standard flanges are used for the flange covers based on the design pressure. Plant-ij = 0.44D + c (7). YLJ = 2.5. Other considerations: Clean water or compressed air can generally be used as the testing medium; when the design temperature is ≤150°F, an additional thickness of 1–3rnm should be applied to the head walls. The allowable stress is 130 MPa for materials with a strength of 20R ； For 16Mn material, =170MPa ； (For 235 material, =120MPa. The structure of the pressure testing head should be selected appropriately based on the nominal diameter of the pipeline and the test pressure. The wall thickness of the head should be determined according to the pipe size specification or through calculation. All welds on the head must be fully penetrated; when the wall thickness deviation of the butt welds exceeds 3 mm, a 1:3 slope should be used for the transition. Medium and high-pressure heads must pass non-destructive testing before they can be used. Flat heads with reinforcing ribs are preferably welded in pairs using straight pipe sections, and then subjected to hydraulic testing before use.

Based on the data provided by the poster, 26MM thick blind plates of type 1# ybhx2009 are to be used

Flange blind plates like this do not require calculation; you can determine their thickness by referring to the thickness specifications for flange covers in HG20592, taking into account factors such as material, temperature, and pressure rating

Blind plates placed between two flanges; for reference on the calculation of blind plate thickness: http://bbs.hcbbs.com/thread-204519-1-43.html

Your approach is completely divorced from the actual conditions on site. The thickness of the flange or the 8-shaped blind plate can be used as a basis for selection, and this will certainly suffice to meet the required test pressure. However, if the thickness is too great, even for DN250 PN5.0, a thickness of 29 is needed; in practice, such thick plates are rarely used as they are neither convenient nor economical. It can be said that almost no one at construction sites determines the thickness of the pressure testing blind plate based on the flange thickness.

Take a look at the standard HG-T 21547-1993 for steel gaskets, washers, and tee blind flanges for pipes.