Time for MEP Pros to Start Prefabricating

September 8, 2017 Ron King

This time of economic uncertainty emphasizes the need to maximize your profits, and prefabrication is one proven technique construction firms can use to accomplish this.

Although larger mechanical contractors have been maximizing prefabrication processes for many years, smaller companies can utilize the same principles to reduce field crew size and the time required for material handling on the jobsite.

What are the benefits of prefabrication?

Proven benefits of prefabrication include:

  • Improved material quality

  • Lower cost

  • Streamlined schedule requirements

Let’s dig into each of these benefits with examples and recommendations for successful implementation:

Improved material quality

As seen in the chemical, pharmaceutical, and food industries, where strict government and industry guidelines set the bar for quality, critical tolerances can be more consistently maintained in a fabrication facility. This ensures quality is not compromised as it could be if materials are fabricated in the field, in a non-controlled environment.

Inspection and testing can also be performed more efficiently in the shop, identifying problems that can be corrected before even reaching the field.

Lower cost

Work is performed more efficiently in a fabrication shop than in the field, which reduces cost. Much of this efficiency and speed is due to automation, machinery, and the assembly line process, which can produce layouts, cuts, and welds faster than is possible in the field.

Additionally, once a subassembly or module is assembled and tested in the shop, it can often be safely transported to the jobsite and installed as a single unit, saving time and, in many cases, shipping cost.

Streamlined schedule requirements

The construction schedule can be optimized by utilizing the fabrication shop, reducing the number of labor hours expended in the field. Shop activities can begin long before mobilization to the jobsite, so multiple jobs can be scheduled and prioritized as need dictates. Reduction of field hours relieves jobsite congestion and stacking of trades.

How to effectively plan for prefabrication

Planning the prefabrication is one of the most important steps. It allows the contractor to step back and consider the whole job and then decide how to proceed in a way that will allow as much cost control as possible.

The planning process identifies what portion of work is to be done in the shop based on many factors, including:

  • Pipe size

  • Access to the site for finished product

  • Trucking requirements

  • How quickly the fabrication is needed.

Once exactly what to fabricate has been determined, the field measurements and fabrication drawings can begin.

The importance of field measurements

Verifying field measurements may be the most critical step in the process. If measurements are incorrect, the fabrication won’t fit, requiring it to be cut and rewelded in the field at a very high cost. The locations of field welds are of paramount importance. They need to be located where the welder can easily access, or they’re going to end up costing too much.

Fabrication drawings

  1. The field dimensions are used to create isometric drawings

  2. Spool drawings are produced based on the isometric drawings.

  3. The spool drawings are typically printed on 11” x 17” paper and used by the craftsmen in the shop as fabrication instructions.

  4. Plan views are also produced with elevation views as needed for clarity.

Material inventory

Materials can be ordered and delivered to the fabrication shop “bagged and tagged” per spool sheet or isometric drawing. This reduces the time required to find all the necessary parts to fabricate each spool. The craftsmen simply looks for the bag identified by the spool number instead of going through boxes or crates of fittings to gather the items.

The optimized prefabrication process

From there, an efficient prefabrication process runs like a well-oiled machine:

  1. The work typically starts at the pipe feed rack, or conveyor, where lengths of pipe from the storage yard are loaded for the pipe cutting station.

  2. The conveyor loads each length of pipe to the cutting torch head, where the operator monitors the automatic cutting and beveling of the pipe.

  3. The cut piece is labeled and removed from the cutting conveyor by overhead crane or jib and placed on pipe stands which can be rolled to the layout station, where assembly begins.

  4. The cut lengths of pipe and the “bagged and tagged” fittings are assembled and tack-welded together according to the spool drawing. (Layout jigs and adjustable-height work tables help the craftsmen assemble the part efficiently. Jigs can be labeled and used to assemble future projects as well.)

  5. The spool is then rolled or moved from the layout station to the welding station for final welding.

  6. Depending on the welding procedure required by the customer, the correct method is used, which could be stick, MIG, Heliarc, STT, or submerged arc, to name a few. A turntable will facilitate the rolling of as many welds as possible, reducing the number of position welds.

  7. The spool is then rolled or moved from the welding station to the testing station for final inspection and quality testing. This stage can involve hydrotesting or non-destructive radiographic testing (based on the requirements of the customer and service in which the pipe is to be used).

  8. The finished spool is then loaded directly on a flatbed trailer for scheduled delivery to the jobsite.

Additional prefabrication tasks that are better in the shop than in the field

There are many other tasks that can be performed more efficiently and effectively in the shop than in the field, such as:

  • Hydraulic punching or shearing of steel plate or angles and shapes

  • Punching of holes (which is much quicker than conventional drilling.)

  • A pulling tee station is used to pull a nozzle onto the side of a pipe (thus eliminating the fitting and joint required to attach a conventional branch connection.)

  • A grooving or threading station is used to place a groove or thread on the end of a pipe.

  • A hanger station is used to fabricate hangers to be shipped to the jobsite as a completed piece.

And that just scratches the surface. Be creative and think of other labor saving stations you could utilize to cut fabrication costs in your respective markets.

 

What if you want to start your own prefabrication facility from scratch?

Contractors interested in starting a prefabrication facility should visit as many existing fabrication shops as possible during the planning process.

A good method to gain facility access is through peer groups or contractors you meet while attending educational seminars or conventions across the country, not in your geographical market. Just ask, and chances are they would love to show off their facility. Additionally, material suppliers and equipment vendors should be a good source of information.

Deciding to prefabricate requires a great deal of thought and commitment. If you’re leaning that way, be sure to involve your craftsmen in the planning process for their good ideas and to mitigate any possible negative attitudes they may have at the outset. Buy-in from management will also have a strong influence on the success of the prefabrication facility.

Once labor and management ideas are aligned, the decision to fabricate can quickly boost your bottom line. Prefabrication can be considered at the estimating stage to gain a competitive edge, and will no doubt become commonplace in your workflow.

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