Intermediate head subjected to test pressure at convex side (test pressure is larger than MAEP)

[fraccionadora]

I design a Div.1 combination unit column with two independent pressure chambers in which intermediate ellipsoidal subjected to the upper chamber design internal pressure at concave side and bottom chamber design internal pressure plus FV pressure at upper chamber. With these design pressures at concave (22.4bar) / convex(23.5bar) sides, MAEP@test_temperature for the intermediate head is 27bar. Since the independent pressure chambers are tested as seperate vessels, the intermediate head is subjected to bottom chamber test pressure at convex side which is UG-99(b)-->1.3*MAWP*LSR=29bar. According to UG-99(e)(1), the min. test pressure for the common element (intermediate head) shall be design differential pressure times the LSR (26.6bar) in addition to the UG-99(b) requirement. The test pressure by UG-99(b) already satisfy this, however the test pressure (29bar) is above the MAEP@test_temp=27bar. Since UG-99(d) does not suggest any limit on the maximum test pressure, how to justify the test pressure at convex side of intermediate head? Or, what should be the appropriate design margin between the intermediate head test pressure at convex side and MAEP@test_temperature? The failure mode is no more plastic collapse like in internal pressure, it is buckling for pressure at convex side.Thanks.