ASME B31.4 Design condition
A piping designer work to design a transporting pipeline for crude oil from Gathering Station to Tank Farm. 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, design temperature of 194 F and the pipe material specification using carbon steel ( API 5L grade B ). Please note, the design temperature is < 250 ° F (120 ° C) so this is acceptable for using ASME B31.4 code.
additional concern : the pipeline will be cleaned regularly using foam pig and other pig types. Smart pig or ILI will be used to inspect the pipeline every 5 years.
minimum required thickness calculation as per ASME B31.4
| 1 | Pipe Material of Construction | API 5L grade B |
| 2 | Sy (Psi) | 35,000 |
| 3 | Sy (MPa) | 241 |
| 4 | D : Pipe Outside Diameter (inch) | 18.00 |
| 5 | P : Design Pressure (Psi) | 300 |
| 6 | Design Temperature (Deg. F) | 194 |
| 7 | F design factor | 0.72 |
| 8 | E : Weld joint factor | 1 |
calculate allowable stress for API 5L grade B as per ASME B31.4 design code:
| 9 | S : applicable allowable stress value (Psi) = | F E Sy |
| = | 25,200 |
pipe wall thickness calculation for straight sections of steel pipe :
| 10 | thickness of pipe (inch) = | PD /2S |
| = | 5,400 / 50,400 | |
| = | 0.107 | |
| thickness of pipe (mm) = | 2.72 |
| 11 | allowance (mm) = | 5.00 |
| 12 | minimum required thickness (mm) = | 7.72 |
| minimum required thickness (inch) = | 0.304 | |
| 13 | refer to NPS chart | |
| thickness of NPS 18 Sch 20 (inch) = | 0.312 | |
| thickness of NPS 18 Sch STD (inch) = | 0.375 | |
| 14 | consideration of mill tolerance 12.5% | |
| thickness of NPS 18 Sch 20 (inch) = | 0.273 | |
| thickness of NPS 18 Sch STD (inch) = | 0.328 | |
| 15 | decision | |
| API 5L Grade B, NPS 18 Schedule STD with nominal thickness 0.375 in | ||
other consideration for ILI in transporting pipeline ASME B31.4 :
To be honest, I don’t see code requirement for 3D bends and running ILI tools, it depends on what the Client / owner wants to do. If they want to inspect the line using ILI tools, they will make the bends 3D otherwise the line will be difficult to inspect with ILI (at least the conventional ILI tools, the odd tool can negotiate 1.5D on 12″ or larger). If there is a “smart” pigging requirement, I would challenge them on how they intend to pass ILI tools. If it is just maintenance pigs e.g. foam pig, they will pass through 1.5D bends (generally speaking). Have a look at this document NACE Standard RP0102-2002, “Standard Recommended Practice, Inline Inspection of Pipelines”, Appendix A. It gives the 3D guideline with some tools able to make it through 1.5D in larger diameters, though they would have to locate the ILI vendor with this capability/be limited in the tools they can run. The valve that will be installed in this line shall use full bore type to make sure the smart pig can pass smoothly.
related article and excel sheet:
- Pig cleaning system
- minimum required thickness as per ASME B31.4 design code
- ASME B31.4 minimum required thickness calculation (excel sheet )
disclaimer: Please always refer to the new and latest ASME B31.4 edition for your work.