Selecting Line Pipe Grades for Transmission Projects
How API 5L grade, delivery condition and toughness requirements interact when specifying transmission line pipe.
18 May 2026
Grade is only the starting point
API 5L defines grades from Gr. B through X80, but two pipes of the same grade can behave very differently depending on delivery condition, chemistry restrictions and supplementary requirements.
PSL2 introduces mandatory chemistry, mechanical and toughness limits that PSL1 does not, which is why most transmission specifications call for PSL2 even when the grade is modest.
Toughness and fracture control
Charpy energy and DWTT requirements govern whether a running fracture will arrest. These are properties of the pipe as delivered, not of the grade name, and they must be stated explicitly on the purchase order.
Where the line carries dense-phase CO2 or hydrogen, fracture arrest requirements are typically more demanding than for natural gas at the same pressure.
Practical procurement consequences
Confirm delivery condition, supplementary tests and hardness caps before enquiry, because they change the eligible mills and therefore the lead time.
Group the requirement by grade and wall thickness rather than by construction section, then release deliveries in the sequence the spread needs.
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