Shan,

1.8kNm ? That's a small bending load, equating to about 19MPa in 4" Sch 160 pipe. What exactly is limiting your bending to this value ?

Assuming the direction ofthe moment shows it is due to well movement and not deadweight, to reduce it will mean adding some pipe flexibility in an appropriate plane. In your case I would add pipe in the Z direction

You should discuss this with your lead engineer or client ... you might get your imposed moment accepted.