ASME B31.1 Steam Piping

Not sure, but maybe you are looking for this ( From ASME B.31.1 par 100.1.2 and Fig´s):

Piping between the terminal points and the valve or

valves required by para. 122.1 shall be provided with

Data Reports, inspection, and stamping as required by

Section I of the ASME Boiler and Pressure Vessel Code.

All welding and brazing of this piping shall be performed

by manufacturers or contractors authorized to

use the appropriate symbol shown in Figs. PG-105.1

through PG-105.3 of Section I of the ASME Boiler and

Pressure Vessel Code. The installation of boiler external

piping by mechanical means may be performed by an

organization not holding a Code symbol stamp. However,

the holder of a valid S, A, or PP Certificate of

Authorization shall be responsible for the documentation

and hydrostatic test, regardless of the method of

assembly. The quality control system requirements of

Section I of the ASME Boiler and Pressure Vessel Code

shall apply. These requirements are shown in Appendix J

of this Code.

The "one" refers to the second stop valve, if it is required, which depends on circumstances and the Code being followed.