Regarding the calculation of Sch.No

Go and check ASME B31.3; it contains explanations regarding what correction factors are required.

Using Sch to calculate the wall thickness is a lazy approach; it is recommended to use the formula from 50316 for a proper calculation

The Sch value reflects the pressure-bearing capacity of steel pipes to a certain extent. To illustrate this, Sch40 means that when the allowable stress of the material is 100 MPa, the pressure-bearing capacity of the steel pipe is 40 bar. The allowable stress of ordinary low-carbon steel at room temperature is around 130 MPa; therefore, the pressure-bearing capacity of the steel pipe is approximately 40×113=52 bar. The minimum pipe thickness is calculated using the allowable stress of the material at the design pressure and design temperature, and then rounded up to a specific Sch value specified in the standards. Therefore, the Sch value does not represent the allowable stress of the material at the design temperature.

SCH is an abbreviation for Schedule, commonly found in American steel pipe standards; it serves as a prefix for a series number. For example: SCH10, SCH40, SCH80, and so on. Corresponding to these series numbers, you can find the wall thickness for each specification of steel pipe in the steel pipe size table. This is a great way to standardize and serialize steel pipe sizes. Convenient and practical! A size chart is attached for reference! -------------------------------------- The classification of steel pipe wall thickness: The methods used to denote the grades of steel pipe wall thickness vary across different standards. But there are mainly three ways of expressing it. 1. The wall thickness series is indicated by the pipe schedule (Sch.). This was specified in the 1938 American National Standards Institute standard ANSI B36.10 (Welded and Seamless Steel Tubes). The pipe schedule (Sch.) is the value obtained by multiplying the ratio of the design pressure to the allowable stress of the material at the design temperature by 1000, and then rounding it off. That is, Sch. = P/t × 1000 (1-2-1), where P is the design pressure, in MPa ； t—allowable stress of the material at the design temperature, MPa. The pipe designations for seamless steel pipes and welded steel pipes can be determined by referring to available information. The pipe designations in ANSI B36.10 and JIS standards are ； Schl0, 20, 30, 40, 60, 80, 100, 120, 140, 160. The pipe designations for stainless steel pipes in ANSI B36.19 are: 5S, 10S, 40S, 80S. The tube designation (Sch.) is not the wall thickness, but rather a wall thickness series. For the actual wall thickness, at the same pipe diameter, it varies among different pipe grades. The wall thicknesses for pipes of different nominal sizes in the United States and Japan are determined using the Barlow formula for calculating the thickness of thin-walled pipes under internal pressure, taking into account a corrosion allowance, the thread depth, and a negative wall thickness deviation of -12.5%, as shown in equations (1-2-2) and (1-2-3). tB = D0P / 2t (1-2-2)
t = t] + 2.54 (1-2-3)
Where, tB and t represent the theoretical and calculated wall thicknesses, respectively, in mm; D0 is the outer diameter of the pipe, in mm; P is the design pressure, in MPa; and t is the allowable stress of the material at the design temperature, in MPa. The actual wall thickness is obtained after rounding the calculated wall thickness value. If the pipe grade of the steel pipe is known, the design pressure to which it can withstand can be calculated using equation (1-2-1), namely P = Sch… × t/1000 (1-2-4). For example, for Sch40 carbon steel seamless pipes in stock, the design pressure they can withstand at a design temperature of 350°C is: P = 40 × 92/1000 = 3.68 MPa. The standards set by Sinopec, SHJ405, specify the wall thickness categories for seamless pipes, namely Sch.5S, Sch.10, Sch.10s, Sch.20, Sch.20s, Sch.30, Sch.40. 40s, Sch.60, Sch.80, Sch.100, Sch.120, Sch.140, Sch. 160, as shown in Table 1-2-9. 2. Wall thickness series expressed in terms of pipe weight – The methods specified by the American MSS and ANSI for expressing wall thickness in terms of pipe weight classify pipe wall thicknesses as follows: ； Type: (1) Standard weight tubes are denoted as STD ； (2) Thickened pipes are indicated as XS ； (3) Extra-thick pipes are denoted by XXS.

Thank you for your reply. You might have misunderstood me; I’m not trying to calculate the wall thickness, I’m just unsure about the value of S in the formula

In the formula for HGT20553, the value of S clearly denotes the allowable stress of the material at the design temperature; yet it is stated later that 10,000 Psi should be used, which is confusing

You should use the allowable stress of the material at the design temperature for the calculations. The value of 10,000 Psi comes from the earliest definitions of Sch; it allows for an approximate estimation of the pressure-bearing capacity of pipes. For example, when the allowable stress of the material is 100 MPa, the pressure-bearing capacity of a steel pipe is 40 bar. However, the allowable stress of metal materials decreases as temperature rises. Different operating conditions involve different design temperatures and pressures; therefore, it is not possible to simply use 100 MPa – instead, the allowable stress at the corresponding temperature for that material must be used.