Stsndard gives criteria to design the line for the internal pressure, collapse due to external pressure and the propogation buckling.

Thickness requirement for the buckle arrestor is decided based on buckle propogation criteria however I am unable to find out the criteria to find out the span at which the buckle arrestors are to be provided.

External pressure design is affected by the length of the component into the consideration and ASME gives consideration to the same to select the thickness/ stiffener calculation and I believe that the same principal shold be applicable in case of DNV code also.