Pipe fabrication can be defined as the process of cutting, bevelling, and welding piping components such as pipes, tees, elbows, flanges, reducers, etc., as dictated by the design documents. In the process and power piping industry, Piping fabrication is a highly critical activity as it involves hundreds of components and thousands of steps and requires a high degree of precision. In any construction project wherever piping networks are involved, piping fabrication needs to be properly planned, scheduled, and executed as per design requirements. To maintain the system integrity, proper functioning of each item, and minimize accidents, It is required to ensure maximum quality of work during pipe fabrication. In this article, we will explore more details about piping fabrication.
Piping fabrication involves various activities like piping material storage and handling, cleaning, cutting, bevelling, welding, inspection and testing, painting, insulation installation, etc.
Types of Piping fabrication
Depending on the location of the pipe fabrication work they are classified in to two groups.
- Shop Pipe Fabrication and
- Field Pipe Fabrication.
There are various factors that determine whether pipes will be shop fabricated or field fabricated or both method will be used. In most of the cases, both shop and field pipe fabrication is used. The major deciding factors are profitability, type and size of the project, piping material and size, post-fabrication surface treatment, environmental condition, accessibility of equipment, skilled personnel availability, time requirement and availability, etc.
In general practice, small bore pipes, threaded and socket welded pipes are field fabricated whereas butt welded pipes, pipe bending, modular items, etc are shop fabricated.
In the Shop pipe fabrication process pipe, fittings and components are assembled by welding into spool assemblies at the fabricator’s facility or a workshop normally known as a pipe fabrication shop. The spools are then labeled using an identifier and transported to the construction site for installation. Whereas in the field pipe fabrication all these assemblies are done at the construction site.
Tools/Equipment used for Pipe Fabrication
During pipe fabrication, various equipment and tools are used that helps in the fabrication process. The widely used equipment is listed below:
- Pipe Jacks
- Adjustable Pipe Rollers
- Welding Machine
- Pipe Rigging and transport equipment
- Chain Clamps/ C Clamps
- Pipe Fit up Tools
- Pipe Purging Equipment
- Pipe Cutting and Bevelling Equipment
- Torque Wrench/Adjustable Wrench/Combination Wrench/Hammer Wrench
- Flange Alignment Tools and Pins
- Center Punch
- Compass/Contour Marker
- Pipe Threader
- Fork Lift
- Wraparound Tapes
- Hydraulic Crane/Tower Crane
- Pipe Bending Machine, etc
Preparation for Pipe fabrication
In this stage, pipe fabricators are required to calculate various parameters from the drawing specifications. They are required to take into consideration welding and tack welding processes along with any distortion that may arise from welding. The tools required for the fitting-up of pipes and flanges, such as pipe supports and clamps will also need some thought. Then they need to prepare a simple wire model of the pipe spool from the drawings. Material take-off and client’s fabrication specification is also supplied to the pipe fabricators.
Piping Fabrication Procedure
The pipe fabrication process requires to assemble pipes and pipe fittings according to the spool drawing. Pipe fabricators must take into consideration the size of the assembly, as transportation could be a problem. In such cases, Sub-assemblies are an effective way of transporting large projects. Piping fabrication is done as per the below-mentioned steps:
- Marking and Cutting: As per the design drawing requirement, Marking shall be done and the same shall be verified by the concerned supervisor prior to cutting. Pipe cutting is normally done as follows:
- Carbon Steel pipes – By gas cutting & grinding.
- Alloy Steel pipes – By grinding or flammable cutting.
- Stainless Steel Pipes – By grinding or plasma cutting.
- Tagging: Using dye stamping, Paint marking, or Tagging, pipe heat numbers are transferred to the cut pieces before cutting the pipe.
- End Preparation: In the next step, End preparation (bevelling) and fit-up are done following an approved Specification and WPS.
- Welding Pipes: Extra precaution must be exercised to ensure that longitudinal seams on the joining pipes do not come in one line in a butt-welded joint. Seams must be staggered at least 100 mm apart and also will clear the branch connections. Care is taken to make sure that longitudinal seams are not resting on the steel structure.
- Welding Pipes and Fittings: Pipes and Fittings for fit-up are then placed on a temporary pipe bed and supports are properly secured properly. Next, the arrangement is inspected for quality Fit-Up. Once inspection clearance is received, Joints are welded by qualified welders.
- Details Marking: Various details line pipeline No., Component Heat No., Joint No., Fit-up inspection signature, Welder No., Visual inspection signature, and welding date are marked near to the joint using a metal paint marker.
- The pipe Spool Number is marked with a paint marker and an aluminum tag is tied to the spool.
- Heat-treatment: As per project-specific requirements, Preheating and PWHT will be done at the shop or field.
- Fabricated pipe spools are then shifted from the pipe fabrication shop to the laydown area.
- Inspection: As per the requirement of the project specification or guidelines, NDT is performed. Once NDT clearance is received, spools are released for erection/painting with a release notice.
- Spools rejected in the NDT process are identified with yellow and black tags and sent for the repair work. NDT has performed again on the repaired weld areas as required.
- Documentation: After painting, field inspection is executed for QC and the same is recorded in the prescribed format. After painting inspection, the spool is released for erection.
- Fabrication of Stainless Steel Pipes: Stainless Steel piping fabrication is normally done in the shop with an isolated area from carbon steel and alloy steel. The equipment and tools which are used for CS fabrication shall not be used for SS. Tools for SS must be differentiated clearly by marking “For Stainless Steel” only. For Stainless steel materials, stainless steel tools will be used for grinding, brushing and clamping, etc.
- Protection: For the protection and temporary storage till the erection, all flanged raised faces of completed pipe spools are fitted with plywood blinds and spool ends shall be fitted with proper caps.
Pipe Fabrication Shop
Pipe fabrication Shop is basically a workshop where all the prefabricated pipe spools are developed. All the pipe works for spool preparation are normally performed inside this shop using highly skilled pipe fabricators. Generating pipe spools in the Pipe Fabrication shops are the best economic way for reducing site installation costs for big size projects. All equipment, tools and manpower are available in the pipe fabrication shop and pipe spools are produced with high quality.
Pipe Fabrication Specification
Pipe fabrication Specification is an engineering documents that provides all guidelines to be followed by pipe fabricators for spool pipe fabrication. The specification for piping fabrication provides the minimum requirement of preparation of detail shop drawings and the fabrication, requirements for inspection and testing. It lists down all applicable codes and standards.