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Thursday, July 31, 2014

Designing Effectively for Large-Scale Metal Fabrications

Credit: Chicago Metal Fabricators

Credit: Chicago Metal Fabricators

For job shops that do fabrication and machining, effectively designing a large-scale fabrication project requires some highly detailed planning and not just engineering. Installation and transport are critical factors that, if not assessed correctly, can drive up cost well beyond the quoted price and cut into profits. These factors are well known to most engineers faced with large projects, but they often get lost in specification constraints and design revisions.

Every fabricator knows what their shop’s work envelope is or how much their gantry crane can handle. But what about when the assembly leaves the shop? Knowing what happens once the product has gone out the door is a critical cost consideration. Poor planning of this can have serious implications on the project’s overall success.

Here are a few points to consider when designing for large-scale metal fabrications.

Will It Fit on the Truck?

The U.S. Department of Transportation (DOT) rules that no state may impose a length limitation of less than 48 feet, while stating overall load width will not exceed 102 inches (8.5 feet) and that gross vehicle weight is limited to 80,000 pounds. Load height varies from state to state and can range from 13.6 to 14.6 feet. A good rule of thumb is 13 feet from the pavement to the top of the load. Regulations in individual states vary, so it’s a good idea to get in touch with your local DOT or a trusted carrier to get the specifics.

Oversize loads pose even greater challenges and are heavily restricted, with each state having its own regulations on what constitutes an oversize load. From predefined routes to special trailers for oversize and overweight loads, being under the maximum allowable dimensions is certainly a goal worth achieving from a cost standpoint.

As restrictions vary from state to state, so do fines for non-compliance; in addition, your assemblies could be held up for days or weeks. If an oversize load is unavoidable, get in touch with a fully insured, reputable heavy hauler that will work with you to avoid surprises.

Rigging and Placement Considerations

If your installation requires a crane, then creating rigging drawings is an SOP — standard operating procedure. Proper load distribution is a critical factor for level placement; skids and vessels need to place level on pads to ensure safe installation and not damage mounting hardware. This is even more important when placing in tight with adjacent equipment that requires interconnection with flanges or process piping, for example.

If offloading requires righting, create detailed drawings and plans for the riggers. If your design goes through multiple revisions, make sure your rigging plans follow along, and always make sure that site plans are up to date.

Another must-have is an experienced rigging crew. Though detailed documentation will make a big difference, an experienced rigger can save the day if something is overlooked or if site circumstances change. Verify that your rigger is fully qualified and accredited by the U.S. Occupational Safety and Health Administration (OSHA), insured, certified, and licensed to work in the state that your site is located.

Installation Takes Coordination 

The plant is on a planned shut down, and the trucks have arrived with no load damage. The riggers are ready along with mechanical and electrical contractors on site. Everyone’s ready to go — that requires a lot of planning and coordination. Most riggers and contractors charge by the day, so you have eight hours before you begin incurring overtime.

A really good design takes into account every aspect of a project, from meeting the customer’s requirements and specifications to service-life issues such installation, serviceability, and decommissioning.

To maximize your installation budget, take into account options such as welding versus fastening. If components can be assembled on site with fasteners rather than welding, there is one less trade that needs to be involved in the process.

Understand how adjacent equipment will affect the work that needs to be done — not just during installation but throughout the life of the assembly. Are serviceable areas close to hot equipment? How easily can connections be made? Consider not just structural elements but flanges and electrical connections, as well.

If your assembly includes mechanical or electrical systems, can they be accessed easily for installation and service? If insulation is a consideration, make sure to leave ample room for the installers as well as for the removal of blankets in serviceable areas. Perform a comprehensive design review and a hazard and operability (HAZOP) study with as many qualified reviewers as possible.

The keys to any project are planning, thoughtful design, and execution. Taking the extra time and resources early in the design and planning phase will eliminate cost overruns and unnecessary delays.

 

Randal Hauser is president of Chicago Metal Fabricators, a fully integrated fabrication shop that specializes in heavy components and large assemblies. Its services include welding and assembly, press brake forming, laser cutting, plate rolling, and CNC machining and saw cutting. For more, visit www.chicagometal.com.

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