Pipe selection and thickness calculation
A piping designer work to design a crude oil piping system in an oil and gas plant. He selected the pipe size, pipe material, pipe thickness and make a recommendation to the logistics team to purchase the pipe according to the BOM – Bill of material. First of all, he get the technical data from the Process and Flow Diagrams made by the Process engineer. These data indicate that the pipe size is 18 in, with a design pressure of 300 Psi, a design temperature of 194 F and the pipe material specification using carbon steel.
Carbon steel pipes that can be used are API 5L grade B, ASTM A53 grade B and ASTM A106 grade B. If the pipe is used at high temperature and high pressure, then the choices are ASTM A335 Grade P11 or ASTM A335 grade P22 which is Cr-Mo Alloy Pipes. Alloy pipe is tubular with higher percentages, than standard carbon steel pipes like A106, of alloying elements as Molybdenum (Mo), Chromium (Cr). ASTM A335 covers “low-alloy” steel pipes that have a total amount of alloying elements below 5%.
Molybdenum (“Moly”) has benefit to increase the strength of the steel and its elastic limit, enhance the steel resistance to wear, its impact qualities, and the hardenability. Molybdenum also improves the resistance to softening, makes chromium steel less prone to embrittlement and prevents pitting. Chromium has benefit to prevent steel oxidation at elevated temperatures and increases the resistance of steel to corrosion. Chromium enhances the steel properties such as tensile, yield, and hardness of low-alloy pipes at room temperatures.
Since the Design temperature and design pressure is not high enough, so we can choose A106 grade B which is seamless pipe.
Minimum required thickness of pipe refer to ASME B31.3 calculation:
|1||Pipe Material of Construction||ASTM A106 Grade B|
|2||P : Design Pressure (Mpa)||2.067|
|3||Design Temperature (Deg. F)||194|
|4||D : Pipe Outside Diameter (mm)||457.2|
|5||S : Allowable Stress From Table A-1 (Ksi)||20|
|6||S : Allowable Stress (Mpa)||137.8|
|7||E : quality factor from Table A-1A or A-1B||1|
|8||Y : coefficient from Table 304.1.1||0.4|
|9||W : weld joint strength reduction factor per para. 302.3.5(e)||1|
|10||Y : coefficient from Table 304.1.1||0.4|
11. pipe thickness calculation : PD / 2(SEW + PY)
- thickness of pipe (mm) = 3.41
|12||corrosion allowance (mm)||3.00|
|13||minimum required thickness (mm) =||6.41|
|minimum required thickness (inch) =||0.252|
|14||refer to NPS chart|
|thickness of NPS 18 Sch 10 (inch)||0.250|
|thickness of NPS 18 Sch 20 (inch)||0.312|
|15||consideration of mill tolerance 12.5%|
|thickness of NPS 18 Sch 10 (inch)||0.219|
|thickness of NPS 18 Sch 20 (inch)||0.273|
|A106 Grade B, NPS 18 Schedule 20 with nominal thickness 0.312 in|
reference and excel sheet:
disclaimer: Please always refer to the new and latest ASME B31.3 edition for your work.