If you have FEA Tools you can try to use it. Although it's not always a guarantee that it will reduce stress.

If still overstressed, try increasing section modulus by increasing bend thickness, but noting the welding requirements for dissimilar thickness from ASME (there is a limitation up to how much you can increase).

If you are sure of the number of cycles you can use 3125 cycles to use the 1.2 increase in expansion stress allowable, but note that this has limitations also and I think not applicable for high strength steel due to difference in fatigue properties (inferior I think in low cycle regime). Just make sure, you read the Code requirements before using this and check first if you can use it.

I have an idea before of exposing the portion with failure (not buried) to gain some flexibility (unrestrained). But check with your company standards and project requirements.

Warm Regards,