Annually, millions of feet of T&C (threaded and coupled) pipe and various length pipe nipples (ASTM A733) are manufactured from ASTM A312, A333, etc. pipe that are used in high temperature, very corrosive applications. These grades of pipe are threaded with NPT tapered pipe threads. The threads must fully conform to ASME B1.20.1 thread tolerances including thread crest truncation limits. Currently, ASTM A999 Table 1 permits the OD of the pipe to be 1/32 under the nominal outside diameter for NPS sizes 1-1/2 and smaller. When the pipe OD is run at the current allowed A999 minimum OD requirements (1/32 under nominal) it is physically impossible to produce fully formed threads conforming to the ASME B1.20.1 requirements. Such pipe, threaded at 1/32 under nominal OD pipe, will result in excessive flat threads that can leak in service. For consistency and harmonization purposes, I recommend that the OD under tolerance of Table 1 of ASTM A999 be revised from (1/32 under) for NPS 1-1/2 and smaller pipe to the exact same outside diameter tolerances (1/64 under)for NPS 1-1/2 and smaller pipe as specified by ASTM A53 and A106. Thanks.
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