Helical Strakes

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Helical strakes installed on stacks in Alaska.

Helical strakes installed on stacks in Alaska.

Helical Strakes at Chicago Metal Rolled Products checked for size on a full-sized template

Helical strakes at Chicago Metal Rolled Products checked fro Size on a full-sized template.

Stacks with strakes installed

Stacks with strakes installed.

Helical Strakes from Flat Bar

Chicago Metal Rolled Products employee producing helical strakes from 3/16 x 3 flat bar.

Chicago Metal Rolled Products has developed the technology to produce thousands of helical steel strakes in short order for the most demanding schedules and with tight tolerances.

Capacity to Produce Helical Strakes

Helical strakes can be made from steel bars of various sizes. The ideal size to use depends on the engineering of the stack itself.  Best practice for the design of strakes or spoilers on stacks can be found at ASME STS1-2011. General guidelines include:

  1. Use three-set of helical strakes 120 degree apart attached to the stack circumference;
  2. The pitch of the helix should be five times the stack diameter over a 360 degree rotation;
  3. The strake width should be one-tenth of the stack diameter.  Common thicknesses can range from 10 gauge to 3/8", and widths from 2" to 12".  Strakes outside of these dimensions are also able to be produced.

It is critical in the production of strakes that the flat bar be as close to perpendicular to the stack as possible.  We have the ability and experience to do critical fitment checks insuring tight tolerances are met.

Chicago Metal Rolled Products has produced strakes for jobs varying in size from a small section of one tower, to thousands of pieces covering hundreds of structures.  For large or small jobs, Chicago Metal can meet your helical strake bending needs.

Helical Strakes: Value-Added Services

Chicago Metal can shear, saw, or torch cut the ends of helical strakes.  It can provide unique markings for ease of installation in the field.  And it can kit various sizes of strakes to match the requirements of each varying tower.  Shipments can be staggered for a timely delivery at the customer's plant or job site.

Chicago Metal Rolled can also provide clips to attach the strakes to the stacks.

Helical Strakes Applications

The most common application of helical strakes is to decrease the vortex shedding that causes unacceptable vibration in towers.  The strakes "confuse" the wind and reduce the movement to acceptable levels of oscillation.  Tall structures for various purposes can use helical strakes.  Power lines, power plants, exhaust stacks (alternately called "smoke stacks" and "chimney stacks"), aerial towers, weather stations, and wind turbines are some possible applications.

One large project involved attaching strakes to electrical transmission towers.  Under heavy winds, the towers were vibrating so violently that they cracked and crashed to the ground.  A team of engineers studied the issue, made the necessary calculations and used wind-tunnel testing to confirm that the attachment of helical strakes to the towers would solve the problem.

Chicago Metal Rolled Products provided the samples for the wind-tunnel testing at Texas Tech University.  After successful testing, additional samples were sent to the job site to develop the best method to attach the strakes to the poles in the field.  Engineers, welders, erectors, suppliers and others all gathered 20 miles north of Las Vegas.  Methods of attachment included welding the strakes directly to the towers, welding clips to the tower and then welding the strakes to the tips, and welding the strakes to the tower and then welding the clips to the tower and the strakes.  This last method proved to be the fastest and easiest method.

Before the vibration issue had been identified, towers of various heights had been delivered to sites evenly spaced along miles of highway.  The strakes and clips were kitted for the special requirements of each tapered tower.

Another application involved helical strakes installed in Alaska to mitigate the vibration of stacks for generators at a missile defense site.

Contact us for more information on manufacturing helical steel strakes.