A stepped downcomer apparatus for use in a vapor liquid contact apparatus, comprising: a radially interior inlet downcomer panel which, in conjunction with a boundary downcomer wall, defines an inlet opening of a downcomer vapor-liquid flow through passageway; a step section replacing a lower portion of the downcomer panel, comprising a substantially horizontal step platform extending radially outward with respect to said radially interior inlet downcomer panel at an intermediate level of the downcomer vapor-liquid flow through passageway and having a radially converging profile towards an outer chordal edge; a step wall arrangement (51, 53, 55) extending in a downward direction from the outer periphery of said step platform, said step wall arrangement (51, 53, 55) having a central chordal step wall panel extending vertically downward from the outer chordal edge of the step platform and step wall panels (51, 53), extending to opposite sides of said central chordal step wall panel whereby the step wall panels (51, 53, 55) are arranged for preventing, in operation, vapor bypassing through downcomer step openings (O 1, O 2, O 3) between the outer chordal edge and platform edges (48, 50) of the step platform and the vessel wall; said step wall panels (51, 53) comprising a first flange extension and a second flange extension with the first flange extension extending out away from a first of said step wall panels toward the vessel wall and the second flange extension extending out away from a second of said step wall panels toward the vessel wall so as to define liquid flow-through passageways with respect to the underlying tray along a lower edge (88', 86') of said first and second flange extension (88, 86). a radially interior inlet downcomer panel which, in conjunction with a boundary downcomer wall, defines an inlet opening of a downcomer vapor-liquid flow through passageway; a step section replacing a lower portion of the downcomer panel, comprising a substantially horizontal step platform extending radially outward with respect to said radially interior inlet downcomer panel at an intermediate level of the downcomer vapor-liquid flow through passageway and having a radially converging profile towards an outer chordal edge; a step wall arrangement (51, 53, 55) extending in a downward direction from the outer periphery of said step platform, said step wall arrangement (51, 53, 55) having a central chordal step wall panel extending vertically downward from the outer chordal edge of the step platform and step wall panels (51, 53), extending to opposite sides of said central chordal step wall panel whereby the step wall panels (51, 53, 55) are arranged for preventing, in operation, vapor bypassing through downcomer step openings (O 1, O 2, O 3) between the outer chordal edge and platform edges (48, 50) of the step platform and the vessel wall; said step wall panels (51, 53) comprising a first flange extension and a second flange extension with the first flange extension extending out away from a first of said step wall panels toward the vessel wall and the second flange extension extending out away from a second of said step wall panels toward the vessel wall so as to define liquid flow-through passageways with respect to the underlying tray along a lower edge (88', 86') of said first and second flange extension (88, 86).