AD 2000 Merkblatt wall design safety factor

[Weng]

Accoding to B0 2003 edition, Table 2 - safety factors against yeild point, proof stress or creep rupture strangth, the safety factor S for the material at design temperature of rolled and forged steel is 1.5. Lately, I noticed that someone perform the required wall thickness calculation with enineering software by using the safety factor of 1.25. Is it acceptable or is there any changes to the code on 2006 or latest edition?

[*sessizlik]

you must use what is the standat write.
safety factor must be 1.5 for AD 2000

[AK5TASRT]

what is the significance of elastic and plastic buckling in B6?
actualy i am more familiar with asme.