It seems as per the article that they are (or were not) entirely forbidden. However see what Bruneau has to say...
Partial Penetration Splices
A half penetration butt weld connecting two heavy jumbo
steel sections, and tested in pure bending, has been able to
develop and exceed its nominal design capacity. However, it
failed in a very brittle manner partly as a consequence of a
severe stress concentration created by the unwelded part of
the flange, as well as due to a series of concurrent
metallurgical and welding factors inherent to these type of
details when used for heavy steel section splices. Continuous
visual inspection during welding and ultrasonic testing of the
base metal and welds was not sufficient to avoid this
undesirable failure mode.
Where such welds are to be used, care must be taken to
ensure that (1) splices would not be expected to yield under
realistic loading conditions or (2) a brittle failure of the
splice would not impair the stability of the structure."
I personally would try to avoid the partial penetration flange splices. Ensure that all the combinations and fatigue, stress concentration, size effects etc are well represented in your factored forces -or ASD equivalents- prior to accept the detail.
A normative answer to your question reduces to examination of the ruling code respect welds, normally the weld chapter in AISC 360 and seismic spec ... I have not looked at them at the moment.