ASME Section I Code Calculations PDF

Code Calculations - ASME Section I • Chapter 2 ^ OBJECTIVE 2 Given the material specification, construction method, and other necessary parameters, use the formulas in ASME BPVC Section 1, PG-27.2.2 to determine the minimum required thickness and/or maximum allowable working pressure for boiler dr...

Code Calculations - ASME Section I • Chapter 2 ^ OBJECTIVE 2 Given the material specification, construction method, and other necessary parameters, use the formulas in ASME BPVC Section 1, PG-27.2.2 to determine the minimum required thickness and/or maximum allowable working pressure for boiler drums, headers, or piping. PIPING, DRUM, AND HEADER CALCULATIONS PG-27.2.2 gives the formulas that are used to calculate the minimum required thickness or the MAWP offerrous piping, drums, and headers. Note that a different pair of equations is used for tubing in PG-27.2.1 and piping in PG-27.2.2. Piping and tubing have slightly different formulas because of the specific factors and coef&cients used. The equation for tubing is limited for use on tubing with a maximum outside diameter of 125 mm. Above 125 mm, PG-27.2.2 must be used. The size of each component may be stated as the outside diameter or as the inside radius. The formulas that are applied differ in each case, and are as follows: To Find Minimum Required Thickness If the outside diameter is given, use the following: t = PD 2SE + 2yP +c If the inside radius is given, use the following: t = PR SE-{l-y)P +c To Find MAWP If the outside diameter is given, use the following: p - 2SE(t-C) D-2y(t-C) If the inside radius is given, use the following: p = SE(t-C) R+(l-y)(t-C) 3rd Class Edition 3 - Part A2 77 Chapter 2 • Code Calculations - ASME Section I Example 3: Calculate the mmimum required thickness of a boiler drum Calculate the minimum required thickness, in millimetres, of a welded boiler drum with an inside diameter of 1.5 m. The drum plate is carbon steel, SA-516-65, and the metal temperature will not exceed 250°C. The MAWP is 4500 kPa gauge. The efficiency of the ligaments between the tube holes is 0.5. Solution 3 From PG-6, the spec SA-516 is pressure vessel plate, carbon steel." This is a ferritic steel. We need this information to determine the value for y. The inside diameter is given, so the formula (from PG-27.2.2) for inside radius is required. Given: P = 4500 kPa = 4.5 MPa R = — = ""1"" = 0.75 m = 750 mm. Note: R refers to inside radius 2 2 E = 0.5 (ligament efficiency stated in question From PG-27.3, C = 0 (PG-27.4.3, use C= 0 as there are no threads mentioned, see Note 1) S = 128 MPa (Section II, Part D, Table 1A for SA-516-T56 at 250°C) y = 0.4 (see Note 2) Note 1: For the value of C, note that PG-27.4.3, does NOT specify a value of C for anything other than threaded pipe. For non-threaded, welded components, the value of C is zero, unless a corrosion allowance is specified. Note 2: To find the value for y, refer to PG-27.4.6. Carbon steel is ferritic and the operating temperature is 250°C. Choose the column marked 480°C and below and read off the y- value as 0.4. Substitute these values into the equation: t ._^_,C SE-[l-y)P 4.5 MPa x 750 mm t = ——— ... — — — _^_ o j^^ 128 MPa x 0.5 - (1 - 0.4) x 4.5 MPa 3375 64 - 0.6 x 4.5 3375 61.3 = 55.06 mm (Ans.) 78 3rd Class Edition 3 • Part A2 Code Calculations - ASME Section I • Chapter 2 ^ Example 4: Calculate MAWP of a boiler drum Calculate the MAWP for a welded drum if the plates are 25 mm thick and of material SA-299-B. The inside diameter of the drum is 988 mm and the joint efficiency is 100%. Assume the steam temperature will not exceed 400°C. Solution 4 From PG-6, the spec SA-299 is pressure vessel plate, carbon steel, Mn-Si." This is a ferritic steel. We need this information to determine the value for y. The inside diameter is given, so the formula from PG-27.2.2 for inside radius can be used. SE{t-Q R+(l-y)(t-Q Given: t = 25 mm R = D = 494.0m 2 E =1.0 (efficiency stated in question) Find factors for formula C = 0 (From PG-27.4.3 no threads involved) S = 107 MPa (Table 1A, SA-299-B, with ^ < 25 mm) y = 0.4 (PG=27.4.6. ferritic steel, T is less than 400°C) Substitute these values into the equation p = SE{t-Q R+(l-y)(t-Q 107 MPa x 1 (25 mm - 0 mm) 494 mm + (1 - 0.4) (25 mm - 0 mm) 2675 509 = 5.26 MPa (Ans.) 3rd Class Edition 3 - Part A2 79 Chapter 2 • Code Calculations - ASME Section I Example 5: Calculate the minimum required thickness of a header Calculate the minimum required thickness, in millimetres, of a superheater outlet header operating at 510°C with a MAWP of 17 MPa. The header material is SA-335-P5 and the outside diameter is 457.2 mm. Solution 5 PG-9 states that SA-335 is seamless, ferritic, alloy steel pipe for high temperature service" We need to know that we have seamless pipe in order to calculate efficiency £ below. To determine)/, the temperature coeffident, we need to know if the steel is ferritic or austenitic. The outside diameter is given, so the formula from PG-27.2.2 for outside diameter should be used. ( - PD 1C 2SE +-2yP Given: P = 17.0 MPa D = 457.2mm C = 0 (From PG-27.4.3 no threads involved) S = 46.4 MPa (From Table 1A) E = 1.0 (PG-27.4.1, for seamless cylinders) As stated in PG-9, the spec number SA-335 is a ferritic alloy steel. From PG-27.4.6, for ferritic steel at 510°C, we find the value as y = 0.5. Substitute these values into the equation: t =_ro^C 2SE + 2yP 17 MPa x 457.2 mm (2 x 46.4 MPa x 1) + (2 x 0.5 x 17 MPa) 7772.4 109.8 = 70.79 mm (Ans.) 80 3rd Class Edition 3 • Part A2 + 0 mm Code Calculations - ASME Section I • Chapter 2 Example 6: Calculate the minimum required thickness of a high-pressure boiler pipe Calculate the minimum thickness required for a seamless steel feedwater pipe of material SA-335-P1. The outside diameter of the pipe is 168.28 mm and the operating pressure is 5200 kPa and the temperature is 510°C. The pipe is plain-ended. Neglect the manufacturers tolerance (see note below). Note: Plain-end pipe does not have its wall thickness reduced when joined to another pipe. For example, pipe lengths welded together rather than threaded are classed as plain-end pipes. Solution 6 PG-9 states that this material is "seamless ferritic alloy steel pipe." From Table 1A, we find that SA-335-PlisC-l/2Mo. The outside diameter is given, so the formula from PG-27.2.2 for outside diameter should be used. ( = 2SE _^ ^C + 2yP Given: P = 5.2 MPa D = 168.28mm C = 0 (from PG-27.4.3 no thread involved) S = 41.7MPa(fromtablelA,SA-335-Plat525°C) y = 0.5 (PG-27.4.6 for ferritic alloy steel at 510°C) E = 1.0 (PG-27.4.1, seamless pipe as per spec in PG-9) Substitute these values into the equation: t = .._PD_+C 2SE + 2yP 5.2 MPa x 168.28 mm (2 x 41.7 MPa x 1) + (2 x 0.5 x 5.2 MPa) + Omm 875.06 88.6 = 9.88 mm (Ans.) Side Track All of the thickness questions in this objective have asked for the calculation of minimum required thickness using the appropriate formulas from the ASME code; the examples in this book are valid and correct. ® However, when pipe thickness is in question, consideration must be given to a manufacturer's tolerance before the correct size of pipe can be arrived at. This may involve adding additional thickness (above the minimum required thickness) to the pipe when ordering (see PG-27.4.7). The topic of manufacturer's tolerance and related calculations for piping will be covered in another chapter. 3rd Class Edition 3 • Part A2 81 ?& Chapter 2 • Code Calculations - ASME Section I Case Study 1: Monitoring Corrosion I work as a non-destructive examination (NDE) technician and was performing an inspection in a turnaround one day. A packaged watertube steam boiler had been prepared for maintenance, and I discovered corrosion on the inside of the shell while inspecting the internal metal of the steam drum. I investigated the corrosion further by taking depth measurements and determined the remaining wall thickness. Then,I gathered information about the boiler and used the equation from the ASME BPVC I PG-27.2.2 to ensure that the minimum shell thickness had not been reached with the corrosion. I then gave my findings and the calculation to the inspection department for their records so that the corrosion could be monitored and the boiler could continue to be operated in a safe manner. 82 3rd Class Edition 3 • Part A2