In　order　to　investigate　the　strength　design　problem　of　the　brazed　aluminum　plate-fin　heat　exchanger　header　under　complex　external　piping　loads,　the　limit　load　interactions　of　the　header　under　combined　piping　loads　are　studied　in　this　paper.　To　establish　the　limit　piping　load　interaction　curves,　nonlinear　finite　element　analysis　assuming　the　elastic　perfectly　plastic　material　model　is　performed　by　using　the　commercial　finite　element　analysis　software　ANSYS　and　multiple　piping　load　combinations,　which　are　the　combination　of　orthogonal　bending　moment　components,　torque　component-shear　force　component,　bending　moment　component-axial　force　component,　compound　bending　moment-axial　force　component,　and　torque　component-compound　shear　force,　of　the　header　with　six　opening　ratios　ranging　from　0.5　to　1　are　explored.　The　results　of　the　interaction　diagrams　show　that　the　feasible　combined　piping　load　zone　of　the　header　derived　from　the　interaction　curves　can　be　simplified　as　a　triangular　zone　determined　by　the　individual　limit　piping　load　components　safely　and　the　simplified　feasible　zone　is　suggested　to　be　used　for　establishing　a　simplified　safety　assessment　method　for　the　header　under　combined　piping　loads.　©　2011　American　Society　of　Mechanical　Engineers.