What is Welded Steel Pipe

https://www.lordtk.com/pre-insulated-pipe/

Sizes: Out Diameter: 2-7/eight""-6-5/eight"", Wall Thickness: as much as zero.813"" Standard: API 5D Application: For well drilling Petroleum Cracking Tube Sizes: Out Diameter: 1.315""- 20"", Wall Thickness: zero.133""-zero