Phosphating of CS pipe for Oxygen Service

A. What is the oxygen application? What material & cleanliness standards apply? Grade of steel? Phosphating both internal and external surfaces? Anything applied over the phosphate?

For applications such as liquid nitrogen, medical nitrogen and semiconductor gas piping, the HCl pickling & phosphating issues are irrelevant since carbon steel is unacceptable piping material.

For medical oxygen service, ASTM B819, 'Standard Specification for Seamless Copper Tube for Medical Gas Systems' applies in the USA and possibly Canada. Similar to ASTM B88, Type K, but requires specific internal cleanliness/residue limits, that tubes be capped or sealed to maintain these limits, and properly labeled by the manufacturer.

There are many specifications regarding oxygen service, including:
AFNOR BP E86-002 004-APR-01 Oxygen piping systems - Design, operation and maintenance [French]

ASME B31 Standards of Pressure Piping
   ASME B31.3 (2002) Process Piping

ASTM D2512 Standard Test Method for Compatibility of Materials with Liquid Oxygen (Impact Sensitivity Threshold and Pass-Fail Techniques)
ASTM G88 Standard Guide for Designing Systems for Oxygen Service
ASTM G93 Standard Practice for Cleaning Methods and Cleanliness Levels for Material and Equipment Used in Oxygen-Enriched Environments

G-4 Oxygen [issued by the Compressed Gas Association]
   CGA G-4.1 Cleaning Equipment for Oxygen Service
   CGA G-4.3 Commodity Specification for Oxygen
   CGA G-4.4 Oxygen Pipeline Systems (EIGA Doc 13/02)

MIL-DTL-24800 [on DLA] CLEANING COMPOUND - AQUEOUS - OXYGEN SYSTEMS COMPONENTS
NFPA 51: Standard for the Design and Installation of Oxygen-Fuel Gas Systems for Welding, Cutting, and Allied Processes.
NFPA 53: Recommended Practice on Materials, Equipment and Systems Used in Oxygen-Enriched Atmospheres.
NFPA 99C [Ed. note: now superceded by NFPA MGHB18 Standard on Gas and Vacuum Systems
(US) 29 CFR § 1910.253 Oxygen-fuel gas welding and cutting.
(US) 49 CFR § 56.60-1 Acceptable materials and specifications [allowable carbon steel piping includes seamless ASTM A106, seamless or welded ASTM A53 [affil. link] Types S, F, and E steel pipe (with restrictions) or welded ASTM A134, ASTM A135 or ASTM A139 (with restrictions).]
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A. Dear Shridhar
CGA G-4.4 and NFPA 51 should give you the required answers. I gather this is for oxygen line to a steel plant. There are commercially available solutions or pastes for example from Avesta which you can use for pickling.