Satish Lele

Fabrication and Installation of Piping
Piping General Arrangement drawings are provided showing equipment location and piping configuration. These drawings shall be adhered to for the erection and installation of pipe spools. Fabrication of pipe spools shall be in accordance with the Piping Isometric drawings which are provided for all lines size DN 50 and above. Small bore piping DN 40 and below are field run in accordance with the General Arrangement drawings.
Pipe support location plans may be provided for complex piping systems but generally pipe supports will be located on General Arrangement drawings and Isometric drawings. The pipe supports shown will be a minimum requirement. Additional supports may be required to comply with standards and codes. Where pipe supports need to be manufactured detail drawings are provided. Fabrication of pipe spools and supports shall only commence after issue of Approved for Construction (AFC) drawings. Subsequent revisions of AFC drawings will supersede all previous drawings and the Contractorís procedures shall ensure all fabrication is carried out in accordance with latest revision of each drawing.

Pipe Cutting and Bevelling: Pipe shall be cut accurately to the measurements on the drawings or field fit conditions and shall be worked into place without springing or forcing. Stainless steel material shall be segregated from other piping materials during all stages of machining and fabrication to prevent surface contamination with carbon steel leading to localized corrosion. Cutting of pipes shall preferably be done by mechanical means. Flame cutting is acceptable within the limits as listed below:

  • For carbon steel, flame (or arc) cutting and bevelling is acceptable only if the cut is reasonably smooth and true and all oxides are removed from the flame-cut surface by grinding.
  • For alloy steel, flame-cut bevels are acceptable only where machine cutting is not feasible. After flame cutting approximately 2mm of material must be removed from the surface of the bevel by grinding.
  • Bevelling by mechanical means (ie. shearing) requires work hardened areas to be removed as above.
  • Stainless steel and non-ferrous metals shall be prepared by machining, grinding or plasma arc cutting and grinding.
Grinding of stainless steel and non-ferrous metals shall be done with a non-carbonaceous, iron free non sulphur bonded grinding wheel. Chipping, filing, cutting with hacksaws or wire brushing using carbon steel brushes is not permitted on stainless steel.
Burrs and other objectionable defects shall be removed by reaming, machining or grinding.
All cuts shall be made at right angles to the longitudinal axis of the pipe. All pipe ends shall be remade to the full bore of the pipe.
All cuts shall be carefully bevelled and accurately matched to form a suitable groove for welding and to permit complete penetration of the welds at all points. Reference is to be made to the relevant section of the Code.
Defective or damaged weld ends shall be examined in order to determine the nature and extent of damage. Any bevelled edge of pipe that has been damaged shall be machined to minimum tolerances. All bevels shall be cleaned to bright metal finish.
Repairs shall not be made on weld preparation of pipes or fittings without written permission from the Superintendent.
Repairs to weld preparations shall only be carried out using repair procedures which have been reviewed and approved by the Superintendent. Repair procedures must be submitted in writing for the Superintendentís review and approval.
End Preparation: Surfaces to be welded shall be ground free of rust. Grinding is to extend 10mm past the toe of the weld preparation and is to be done immediately prior to welding.
Butt Welding: End preparation for butt-welding shall be in accordance with ANSI/ASME B16.25. Cleaning and end preparation shall be in accordance with the Code and in accordance with this Standard. Stainless steel materials shall be cleaned using degreasing compounds free of chlorides and sulphur for a distance of 75mm from the prepared edge of inside and outside surfaces. Stainless steel wire brushes shall not be used for carbon steels.
Fillet Welds: Pipes for insertion in slip-on flanges and for socket-weld joints shall be cut square, to within the tolerances specified in ANSI/ASME B16.11. Prior to welding of socket connections, the pipe shall be backed off 1.5mm from the seat of the socket. Socket welds and the external welds of field welded slip-on-flanges shall always be carried out using a minimum of two passes with staggered stops and starts. Shop welded slip on flanges may require two passes on the external weld, depending on the welding process, to ensure good root fusion.
Welding Procedure Specification: Manual, semi-automatic, or automatic electric arc welding processes shall be used on all piping. The preparation and procedure for welding shall conform to the requirements of the Code. Welding of carbon steel pipe shall be performed by either: Submerged Arc (SAW), Manual Metal Arc (MMAW), Gas Tungsten Arc (GTAW), or a combination of these processes. Flux Cored Arc (FCAW) maybe used for workshop welding only. Welding processes other than these are prohibited. Weld passes thicker than 10mm are prohibited. Welding of stainless steel or alloy shall be performed by either Gas Tungsten Arc, or Manual Metal Arc Welding, or a combination of these processes. Root pass must be made using Gas Tungsten Arc process with inert gas purge on inside of pipe. Flux Cored wire may be used. Procedure for welding dissimilar metals (e.g. carbon steel to stainless steel 304L or 316L, etc) shall be submitted and approval obtained prior to any welding.
Qualification of Welding Procedure: All Welding Procedure Specifications shall be qualified in accordance with the Code and ASME Section IX.
Welding Types : All welds shall be full penetration welds except:
  • reinforcing pad, peripheral fillet welds
  • structural attachment fillet welds
  • socket welds, which shall be welded to the Code
All butt welds DN 50 and below shall be made with the Gas Tungsten Arc process.
Estimation: Engineers often need to predict the cost of piping and pipe fittings associated with a process unit. Even though detailed prices are available, finding and organizing them takes time and costs money. For those needing a quick method of approximation (such as for a pre-design estimate), a short-cut piping cost method of Inch diameter x length is used.

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