Existing (in operation) or a new production plant?
A very important aspect is where the work must be done: Into a existing (in operation) or a new production plant?
During the construction of a new plant, the work can generally be carried out in the same way as for example in a fabrication shop. Installation and making field welds require no special authorisation. Transports with, e.g., a forklift truck and lifting with cranes require no special permits, etc.
During the construction of a new plant, the work can generally be carried out in the same way as for example in a fabrication shop. Installation and making field welds require no special authorisation. Transports with, e.g., a forklift truck and lifting with cranes require no special permits, etc.
In an existing plant in operation, the conditions are totally different as during construction of a new plant.
In general, for all activities work permits are necessary. For activities with open flames (welding, cutting etc.) and also for combustion engines, so called Hot-Permits are required.
The contractor often can not determine when a scheduled task can be performed, because it depends on plant operators, who should or should not give permission for a particular job.
In short, in an existing plant in operation, high risks are present, and the contractor can probably scheduled tasks do not always perform according to his planning.
In general, for all activities work permits are necessary. For activities with open flames (welding, cutting etc.) and also for combustion engines, so called Hot-Permits are required.
The contractor often can not determine when a scheduled task can be performed, because it depends on plant operators, who should or should not give permission for a particular job.
In short, in an existing plant in operation, high risks are present, and the contractor can probably scheduled tasks do not always perform according to his planning.
Shop fabrication and install
Shop fabrication is, generally speaking, any pipe, fittings and components that are assembled by welding into spool assemblies at the fabricator's facility. The spools are then labeled with an identifier and transported to the job site for installation.
Each spool piece needs its own identifier marked on the piece itself in some fashion that will make it easy to know where its destination is in the facility and/or where it belongs in a multi-spool system of pipe. This will allow the installer to efficiently stage the piece and ready it for installation.
As part of the process of developing spool sections field-welded joints need to be designated. These are welded joints that connect the pre-fabricated spools. In doing this the designer or fabricator will identify two different types of field-welded joints.
Each spool piece needs its own identifier marked on the piece itself in some fashion that will make it easy to know where its destination is in the facility and/or where it belongs in a multi-spool system of pipe. This will allow the installer to efficiently stage the piece and ready it for installation.
As part of the process of developing spool sections field-welded joints need to be designated. These are welded joints that connect the pre-fabricated spools. In doing this the designer or fabricator will identify two different types of field-welded joints.
One is a Field Weld (FW) and the other is a Field Closure Weld (FCW). The FW indicates a joint in which the end of a pipe segment is prepared for the installer to set in place and weld to its connecting joint without additional modification in the field. This means that the length of pipe that is joined to another in the field is cut precisely to length and the end prepared in the shop for welding.
The FCW provides the installer with an additional length of pipe, usually 100 to 150 mm longer than what is indicated on the design drawings, to allow for field adjustment.What has to be considered, and what prompts the need for a FCW, is the actual, as-installed, location of both the fixed equipment that the pipe assemblies may connect to and the actual installed location of the pipe assembly itself. Odds are that all equipment and piping will not be installed exactly where indicated on design drawings.
The dimensional location of the equipment items given on design drawings is not a finite location, they are merely intended locations, as are drawings for building steel, pipe supports and others. What factors into the installation of shop fabricated pipe is the actual location of the equipment nozzle it will be connecting to in relation to the pipe's installed location.
In connecting to equipment there is a build-up, or stack-up, of tolerances that will effectively place the actual, or final, location of the nozzle at some point in the xyz geometry of three-dimensional space, other than where the design drawing indicates. The tolerance stack-up comes from the following:
- Manufacturing tolerances in material forming, nozzle location, and vessel support location.
- The actual set-in-place location of the vessel.
- Load cell installation (when applicable).
- The actual set-in-place pipe run-up location.
In order to allow for these inevitable deviations between the drawing dimensions used to fabricate the vessel, set the vessel, and install the pipe assembly, and the actual installed location of the connecting points, a field closure piece, or two, will be required for that final adjustment.
The field closure piece is a designated section of the pipe assembly in which a field weld has been indicated. The section with the field closure weld would be the length required to agree with that indicated on the design drawing, plus an additional 100 to 150 mm (more or less depending on fabricator's comfort level with the equipment locations). What this does is allow the field to make the final determination in the adjustments when connecting to fixed equipment.
Field installation of Pipe Spools
Good work... great article.. keep it up
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