X stands rau pipeline steel, API yog American Petroleum Institute tus qauv, X sawv cev rau cov yeeb nkab, chav tsev yog kpsi (txhiab phaus ib square inch), K yog txhiab, psi yog phaus ib square inch, thiab lub siab chav tsev sawv cev yog dab tsi lub raj xa dej steel yuav tsum ua kom tiav Qhov tsawg kawg nkaus tawm lub zog yog feem ntau siab dua li cov ntaub ntawv xav tau, 1Mpa yog li 145psi, 1kpsi =6.897MPa.
