allowable bending stress = fy

huangyhg

allowable bending stress = fy'
i recently reviewed a simple-support steel beam design performed by an outside consultant.  the consultant used asd.  allowable stress he used to check a hp 10x42 was fy' = 29.4ksi.  why would this have been done?
i have never seen yet in practice or in books of fy' (value of when flanges become non-compact) be used as the allowable stress.
can someone possibly elaborate on maybe why this was done.  i don't have the opportunity to contact the consultant, hence why i'm asking here.
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if the calculations follow the typical design method and the only difference is fy' is it an issue?
rc
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    edmund burke

was he using 50 ksi steel?  was it laterally braced??
did he actually specify that he was using fy'?  or did he use a stress that just happened to be that number?
i need to clarify a couple things.
the beam was an hp 10x42.  aisc 9th edition lists fy' as 29.4 ksi.  the steel was a36 steel.
he actually substituted fy' = 29.4ksi for fy and made the allowable stress = 0.66(29.4ksi).
the beam i believe was not laterally braced in any appreciable way.
something to do with the hp being non-compact?
if i re  
i suppose the idea is that if the yield stress was 29.4 ksi, then the   
suggest that you ask the engineer if the hp is "used". lowering fy' may be his way addressing the possibility that the