What is the difference between API 5L PSL1 and PSL2?

API 5L offers the same grade designations (X52, X65, X70) at two product specification levels, and the level changes what the mill must control and report.

PSL1 gives a minimum yield strength and basic chemistry. There is no maximum yield, no carbon equivalent limit, no impact testing requirement and no yield-to-tensile cap.

PSL2 adds: maximum as well as minimum yield strength, a yield / tensile ratio limit (0.93 max), mandatory Charpy V-notch testing with specified absorbed energy, carbon equivalent limits (CEpcm or CEIIW), tighter sulphur and phosphorus, mandatory non-destructive inspection, and a stricter certification and traceability regime.

Those additions are what make the pipe weldable and predictable in the field, which is why transmission, offshore and sour service lines specify PSL2 as a matter of course. For sour service, PSL2 is combined with NACE MR0175 / ISO 15156 and HIC testing to NACE TM0284.

When enquiring, state the PSL level, whether sour service applies, the end finish (bevelled, plain, threaded) and any coating requirement (3LPE, 3LPP, FBE) — these drive both price and lead time more than the grade itself.