Small Bore Tubing (SBT) runs must be designed to accommodate Large Scale Deformations (e.g. due to Main Line thermal expansion). Traditionally, this type of movement was always enabled by incorporating ‘pigtails’ (multiple circular coils of tubing) within the SBT runs One of the most radical recommendations within the new guidance notes is the replacement of ‘Pigtails’ with ‘Rectoils’.
Laboratory testing by Xodus has shown that Pigtails are not the most effective method of reducing SBT stresses caused by large scale deformations. In contrast, the rectangular coil design of the ‘Rectoil’, when applied in the correct way and with the correct geometry can offer superior performance.
The design of the Rectoils is covered in great detail in the guidance notes and is very prescriptive, including:
- Precise minimum lengths for all Rectoil sections R1, R2 & R3
- Precise minimum lengths for all pipe straight sections A, B & C
- Precise orientation (short side of Rectoil must be in 1st pipe run (line A)
- Precise spacing between the coils of the Rectoil
- Precise orientation of Rectoil such that the direction of expected largest deformation will cause separation of coils within the Rectoil.