Section 1X p Nos

?

In what context?

Maybe you're referring to ASME Section IX, 'Welding and Brazing Qualifications'? If so, p numbers refer to classifications of materials, the ones you listed are all ferrous, if I recall. I no longer have access to the published code, but if you are working in that area, you need that access, available by purchase from ASME. As far as 'easily recognize', I'm not sure what you mean.

P Numbers are assigned to base metals for the purpose of reducing the number of welding and Bracing procedures qualifications required.

P Numbers are alphanumeric designation: Accordingly, each P number shall be considereda separated P Number,

See ASME IX QW-420

narasimha34:
P - Numbers are used to group materials to reduce the number procedure qualifications. For example, if you have qualified welding procedure for P1 material (SA 106 Gr.B) can be used for other P1 family materials as long as no change in F number (Electrode and filler wire classification) and A number (weld metal chemistry).You can find the complete list of listed materials and it's P-Numbers form ASME BPV Sec IX QW/QB 422.

You can only start recognizing them when you start working with them on frequent basis. Following should help you in remembering some groups you often do work with. Further detailed grouping is also available, if you want.