Caculate Velocity

No, it is not possible yet.

There should be a Process Flow Diagram in existence, created by the Process Engineer at the facility, and the nominal, minimum and maximum flowrates in each line will be on that document.

You have answered your own question with the last two words you wrote.

Flow meter.

Pipe Flow Calculation

No. You also need oxygen flow rate, mass flow, standard or normal flow, or (less likely) actual flow, and temperature. Similarly for how you want to express velocity.

There are various types of gas flow meter. I prefer thermal mass type, depending on the sort of flow/pipe size you're talking about. Then there's differential pressure (orifice plate, Pitot tube....), vortex shedding, Coriolis, positive displacement.....

There are a great number of system piping flow resistance dynamics that must be known in order to accurately calculate the velocity of any fluid flowing through it.

The available flow capacity of the fluid source must also be known.

It is possible to take two separate pressure readings at a measured distance apart then using the differential-pressure drop between the two points, a reasonable estimate of velocity can be calculated.

If you need an ideal number, I believe this is covered in the collection of physical laws known as "The Gas Laws". Bernoulli, Avogadro, Boyles, Charles and others developed them. (we called them Gazz Laws in engineering at PSU due to the overabundance of people with the Philadelphia accent)

It has been too long since Mech Engineering 101 for me to reference the exact law you need, but it is out there if you Google.

Exact numbers needed then you're using the flow meter. The above laws don't cover pipe rugosity very well.