how to identify cor ten 9weathering steel0 in the field

huangyhg

how to identify cor ten (weathering steel) in the field
i am looking at an existing pedestrian bridge.  
how do i know if the bridge is constructed using weathering steel or if it is just rusting?  
overall the level of corrosion does not appear alarming.  
a secondary question is if it is weathering steel and i need to do some repairs, what are the durability issues with drilling holes or welding the existing weathering steel.  would i be compelled to use weathering steel for any steel repairs or supplementary structural members?
thanks,
garry  
when was it built?  where is it located (dry/humid)?
hg
located over a stream in connecticut (humid).  i do not know the construction date, but it looks an awful lot like a pre-engineered pedestrian bridge - so it may not be too terribly old.  
see attached photo.
look on the bridge for an identification plate or plaque.  if it identifies the manufacturer, call and ask questions.  i know continental pedestrian bridges have plates on an end post at each end of the bridge.
the attached file is an example of an identification plate from a pedestrian bridge.
it looks like unpainted steel to me.
i also want to say it looks like unpainted steel but it's really hard to tell just from looks. i would suggest having a sample cut from the bridge and sending it away for a metallurgical analysis which should be able to tell you what it's composed of. if it has a large amount of copper (2%) than it's weathering steel, probably astm a588 if it's recent.
eit with bs in civil/structural engineering.
it's unpainted, the question is what kind of unpainted.
i would find it hard to believe that a modern "pre-engineered" ped bridge manufacturer would ship an unpainted nonweathering bridge.
if it is weathering steel, then yes, you need to have similar corrosion protection for the rest of the bridge.  you *could* replace parts with painted nonweathering steel, but i don't see why you would do that.  use weathering steel and weathering fasteners (a 325 type 3 bolts, etc.), weathering welding electrodes (aws d1.1 table 3.3).
hg
looks like weathering steel.that usually had rust that is fairly tightly adhering.
our bridge across the delaware here has cor-ten griders but the outside, visible parts are painted because the public doesn't want to see a new bridge rusting !!!!
your bridge looks like a continental bridge.  i worked on a similar bridge.  it was a bit heavier in order to carry golf carts but the details look very similar.  it was weathering steel.
and another picture.