Thanks for the comments.

As I read the bases of the Factor B graphs I take the B value from the vertical A to Upto 300 F line in all cases where there is intersection. If there is no intersection then it is Step 7. There is commercial software where Step 7 is used for all A values if the temperature is below 300 F. So I had my opinion in conflict with the software. Literature is totally silent on this issue.

I will contact the software supplier and will ask them to look into this issue.

I cannot use the Code case but I had a look. Step 2: "Move vertically to an intersection with the material temperature line for the design temperature" 300 F is the lowest curve. What to do if the temperature is 250 F? My argument is that the word "Upto" on 300 F line (CS-2) is "Design temperature" line for all temperatures <=300F. I understand that your opinion is the same.