Hi 2ndchild,
May be your're right, but be aware that these requirements differs depending on the applicable design code.
ASME B31.3 may stipulate that z=0.85 in case of ET, but do the EN standards use the same safety factors?
From the Outokumpu site you are refering to it seams that the EN standard do accept a factor of 1.0 in case of ET.
ASME B31.3 only allows for 1.0 if 100% RT, but it is not clear (sofar) if they accept ET as an alternative for RT.
Regards.