Shan,

It is not possible to have zero moments at a wellhead connection. Either you have modelled this nozzle as an X,Y,Z force restraint only (should be an anchor), or as a nozzle with displacements, but left the rotational displacements free (these should be zero).
I agree with MoverZ that 1.8 kNm is a small moment for this size and pressure rating of pipe, and the manifold should be well capable of handling this moment.