Novelty Steel Is An Experienced Piping and Pipe Spool Fabricator for Both Carbon Steel and Stainless Steel Applications.

This article has enlisted a comprehensive list of tips for piping fabrication and pipe spools covering both workshop and site environment.

Table of Contents

1. General

  • Piping fabrication work shall be carried out in accordance with standards, codes, specifications and special requirements of the project.
  • Prefabricated spools for installation shall be 100% dimensionally controlled.
  • The general tolerance normally permitted in piping fabrication is ± 1.5 mm for pipes up to 1.5 meters and ±3mm for pipes longer than 1.5 meters.
  • Maximum angular deviation of bolt holes shall not exceed 1.5 mm measured across bolt pitch circle.
  • Length, height and width of completed piping spools shall be within limits of road transport and handling constraints unless specifically requested otherwise by the Client.
  • All welds require visual inspection to ascertain contour, reinforcement, undercut and other surface opening defects on weld

2. Workshop Environment

  • Adequately covered workshop facility with side cladding is absolutely essential to protect welding works from wind and other adverse weather conditions that have a direct impact on weld quality.
  • In case a radiography testing is planned during regular production shifts, then area specified for the test shall be located at a safe distance from piping spool fabrication area to conduct RT without interrupting piping spool fabrication.
  • The area where radiography tests are conducted shall comply with all statutory and safety requirements set forth by the Atomic Energy Board of the country.
  • Tools containing carbon steel and grinding discs containing carbon steel particles shall not be used on stainless and other high-alloy steels.
  • Tools to be used only for fabrication of stainless steel piping and piping components shall be stored separately to avoid accidental switching with tools previously used on carbon steel fabrication work.
  • A dedicated partition or workshop should be arranged to conduct stainless steel piping works and no carbon steel work should be performed in this area.

3. Coating

  • Pipe spools shall be pressure tested prior to galvanizing.
  • Galvanized piping and fittings NPS 80 (3″) and larger shall be fabricated as flanged spools and then hot dip galvanized
  • Stainless steel piping shall not be painted.
  • Flange gasket faces shall be protected against damage and paint deposits during entire surface preparation and painting process.
  • Pipe spools shall remain identifiable at all times, even during surface preparation and painting phases.
  • After painting, open ends are properly protected to avoid entrapment of debris during storage.

4. Joints

  • Bevel preparation is required only for butt weld joints. For socket weld and threaded connections, square cutting is good enough.
  • End preparation is acceptable only if the surface is reasonably smooth and free of slag.
  • Valve stems shall be kept in fully open position prior to commencement of welding to prevent distortion of valve seat.
  • Threaded joints in piping system shall be made up using PTFE pipe tape or thread seal compound applied on male thread.
  • Threaded joints shall also be ensured that a sufficient number of threads have already been engaged per ASME B 1.20.1
  • Shop fabrication of flanged spool pieces for connection to existing pipework or equipment shall have the mating flange tack welded to spool. An additional allowance of 50–100mm of pipe shall also be provided for taking care of any probable adjustments required during fit-up at field

5. Bending

  • Pipe NPS 40 and smaller shall be bent only where cold bending is indicated in piping drawings
  • Unless otherwise specified, centre line radius of bends shall be five times nominal pipe diameter
  • Butt welds in arc portion of the bend shall not be permitted.
  • Bending shall not reduce pipe wall thickness below the minimum wall thickness required by design
  • No bending shall be performed at metal temperatures less than 4°C (40°F).
  • Mandrel and die used in bending stainless steel piping shall be free of zinc.
  • In case of welded pipes, pipe longitudinal welds shall not be located within 30° of the plane of bend measured axially from pipe centreline
  • Flattening or ovality of a bend, difference between maximum and minimum diameters at any cross section, shall not exceed 8% of nominal outside diameter
  • Wall thinning in piping shall not exceed 20% for bend radius of up to 3 pipe diameters; 10% for Bend radius of 5 pipe diameters and larger.

6. Preheating

  • Concerned engineer/supervisor shall ensure that required preheat is applied to the joint prior to start of weld if preheating is required in the WPS.
  • Preheat temperature shall be established over a minimum distance of 50–75 mm on either side of the weld.
  • It is also essential to ensure that preheat temperature measured is the true “through thickness temperature” and not skin temperature.

7. Welding

  • Cleaning to a distance of 15–25mm on either side of bevel on both internal and external surface is required for welding.
  • Butt-welded joints in piping systems are primarily of the single-V configuration and are welded from pipe outside surface. Larger diameter pipes, which can be accessed from inside will often be welded from both sides using a double-V type of joint preparation
  • When a thicker part needs to be welded to a thinner pipe, thicker section are machined or ground down to match thinner pipe wall. The excess thickness tapered, either internally or externally.
  • For fillet welds a maximum of 2 mm difference between legs is considered acceptable, with the lowest leg having the minimum specified leg size.

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