Monthly Archives: September 2011

Bending Stainless Steel Tubing: A Few Considerations

A variety of methods can be used for bending stainless steel tubing.  If the bend has a large radius, the tubing can be curved with three-roll benders (also called section benders, profile benders, or angle rolls.)  If the bend has a tight radius, the tubing can be bent on a rotary-draw bender through a process called mandrel tube bending.

Both welded and seamless tubing can be curved.  When the desired radius is very tight, seamless usually bends better.

Recently we bent 8 pieces of 304 seamless stainless steel tubing 1.5 OD x 0.083 wall (14 ga) to a 5.25in inside radius with 81 degrees of arc and with 6in tangents on each end. These are prototypes for a vacuum pick-up tube system in a food processing plant.

Since the application of bent stainless tube often involves products for the pharmaceutical and food industries, care must be taken to avoid carbon contamination of the steel.  The machinery and tooling should be cleaned and prepared to avoid such contamination.  Furthermore, care should be taken to avoid having metal strapping in contact with the stainless parts.  Cardboard, wood or plastic can be used to protect the tubing during transit.

After bending stainless steel tubing, a nut and sleeve can be slid over the ends which then can be flared.  Process piping is often supplied this way.  For example, 316 seamless stainless steel tubing 1.5 OD x 0.065 wall (16 ga) was bent with two 90 degree bends into a flat-back U. The ends had a 37 degree JIC flare.  JIC (Joint Industry Council) fittings are widely used in fuel delivery and fluid power applications, especially where extremely high pressure is involved. Other tubing of the same size and grade was bent with an offset.

37 degree JIC flare

A full size template was made to allow for 100% inspection of the prototypes.

The pictures below show the final product which in this case will carry hydraulic fluid.

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Mandrel Bending of Pipe for Bollards

A common application of mandrel bending of pipe is for pipe bollards.  A bollard is one of a series of posts preventing vehicles from entering an area.  Bollards can be as simple as a straight pipe embedded vertically in the ground, or they can be made of pipe with four bends in two planes.  The most common bollards that utilize pipe bending are those with a U shape or a flat-back-U design. Painted yellow, these are often seen protecting the pumps in gas stations or guarding equipment in factories.

In order to provide maximum protection in the horizontal length of the bollard, the two 90 degree bends are often done with a tight radius.  Such bending requires using an internal support or mandrel to ensure that there will be no ovality or other distortion at the bend.  Common pipe sizes for bollards are 4, 5 and 6in OD pipe.

The flat-back-U pipe bollard shown above is made of 6in outside diameter, Schedule 40 pipe with two 90 degree 12in center-line-radius bends.  The width of the bollard is 10ft; the above-ground height of the bollard is 2ft minimum; and the bollard will be embedded 3ft deep into a concrete footing.

The two bends are 2D, i.e. the center-line radius (12in) is two times the outside diameter of the pipe (6in).  Such bends are prone to rippling on the inside radius of the pipe, but with the proper tooling, material, and process, a very smooth, ripple-free bend can be achieved.

This particular order called for 110 pieces to be shipped on one flatbed, a challenge because the load was at both the dimensional and weight limits without permits.  The shipping department nested one bollard within the other and stacked them horizontally to the height limit allowed.  An unusually long 53ft flatbed was used to carry the load.  And the shipping team secured the load with considerable strapping and wood blocking to create a safe means of transport.

Pipe bollards are just one example of a product employing mandrel bending of pipe.  Other applications include roll-over protection (ROPS), elbows for process piping, handrails, and exhaust tubes.

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Rolled Angle Rings: Standard vs. Blowpipe

One of the most common applications of angle bending is to form complete rings which are called rolled angle rings, angle flanges, or companion angle rings.  Such rings are made of angles as small as ½ x ½ x 1/8 and as large as 8 x 8 x 1.  These rings are used as flanges to connect pipe, as stiffeners on cylinders, and as housing frames among other applications.

Over the decades, two types of angle rings were developed as stock items:  standard angle rings and blowpipe rings.  The two types of rings differ in their inside diameter, the angle size used, the bolt circles, the number of holes and hole sizes, and the weight of a ring.

For example, a 16in standard angle ring has an inside diameter of 16-1/4in, is made of 1-3/4 x 1-3/4 x 3/16 angle with a 18-1/8 bolt circle for 16 ea. 13/32 holes, and weighs 9.50lbs.  A 16in blowpipe angle ring has an inside diameter of 16-1/8in, is made of 1-1/2 x 1-1/2 x 3/16 angle with an 18in bolt circle for 8 ea. 7/16 holes, and weighs 8lbs.

Standard angle rings tend to be a little heavier with a larger angle and more bolt holes. Standard angle rings are used in heavier applications, for example, in conveying grain.  Blowpipe rings are used in lighter applications, for example, in conveying air, dust or other light particulate. Both types of rings work well in pneumatic conveying systems. They are welded to the outside of the pipe and therefore cause no interference to the flow inside the pipe.

The differences can be seen on charts that are provided by angle ring producers: one for standard rings and one for blow pipe rings.

Angle rings are available in most cases within a day of order placement.  Since they do not involve custom fabrication, they can be purchased very economically.  The inside diameters of the angle rings can accommodate welded, lock-seam and spiral pipe.

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Section Bending at Steel Day: September 23, 2011

Benders and Rollers, companies specializing in section bending for the construction market, will be supporting the efforts of the American Institute of Steel Construction (AISC) to promote the use of steel in construction on Steel Day, September 23, 2011.

Lectures, shop tours, and other activities will be taking place all across North America, and Benders and Rollers will be giving demonstrations, presentations, and networking with structural steel fabricators, engineers, architects, and general contractors.

For example, Chicago Metal Rolled Products will be bringing its steel sculpture to Chicago’s Steel Day at the State of Illinois Building.  The sculpture is comprised of a wide flange beam 6 inches tall and weighing 16 pounds per foot rolled into a “C” shape against the strong axis (x-x axis or the hard way).  Viewers always marvel at the very tight 14 inch radius, an example of minimum radius bending. They ask if the beam was bent with heat.  In fact, it was bent cold and shows no distortion.  Another beam is also bent the hard way into something like an omega shape.

Chicago Metal Rolled Products will also be promoting steel at two other Steel Day locations: at the Bi-State Fabricators Association in St. Louis and at PKM Steel Service, Inc.  in Salina, Kansas.

Steel Day is billed as the industry’s largest educational and networking event and returns now for a third successive year. As AISC says, “There’s always a solution in steel.”

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Profile Bending for the Ornamental and Miscellaneous Metalworking Industry

When the job requirements for curved steel exceed their capabilities, members of the ornamental and miscellaneous metalworking industry often turn to companies that specialize in steel profile bending.  Although the miscellaneous metal workers can fabricate beautiful and complex railings, gates, fencing, furniture, balconies and sculptures—and many times with steel sections they curve themselves– they sometimes need to outsource the bending to a bender/roller.

For example, the designers of a bar at the new Four Seasons Hotel in Baltimore sketched out a decorative, bell shape that would hang over the bar tenders and hold glassware. The miscellaneous fabricator turned to us as a bender/roller to create the complex curves out of 6,268 pounds of heavy tubing.

Seven 6 x 2 x 5/16 tubes were curved the hard way to radii from 44in to 47ft.

Twelve 6 x 3 x ¼ tubes were curved the hard way to multiple radii of 66in and 140in within each piece.

And four 6 x 3 x ¼ tubes were rolled the easy way to radii from 109in to 43ft.

The two companies worked together to create ellipses easier for both companies to fabricate while still producing a quality product for the high-end hotel.  The miscellaneous metal fabricator is considering submitting the software solution in a competition among the SDS2 user group members.

With the help of some sophisticated software, the collaboration between a bender/roller and a miscellaneous metal fabricator provided the solution to the customer’s challenging requirements.

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Structural Beam Bending: How to Ship Long, Heavy Loads

Once structural beam bending is completed, challenges arise regarding how to ship what can be very long and very heavy loads.  Major steel mills like Nucor Yamato and SDI often employ pole trailers to ship their jumbo beams in lengths up to 105ft. and beyond.

A pole trailer is an unpowered dolly or rig towed behind a powered vehicle for transporting long or irregular loads.  The loads generally can sustain themselves as beams between the towing vehicle and the trailer.  Straight poles, pipe, logs and structural members are often transported with pole trailers.  But pole trailers can also carry curved structural members including curved beams.

Depending on the radius, length of beam, and weight, a load of curved steel can be put together on a pole trailer for safe and cost-effective transport.  A load of curved beams was recently shipped this way from Chicago to Texas for a pedestrian bridge.

Four W36 x 160# x 65ft, and one W36 x 160# x 60ft were loaded with one W36 x 194# x 65ft.  All of the beams had both sweep and camber (i.e. they were compound bends) and one had a reverse camber.  And each one had a different radius.  Nevertheless, after being carefully loaded, 53,410 pounds of steel was transported on the pole trailer with the beams supporting themselves.

The beams were loaded in a fashion that we sometimes call a “smiley face,” i.e. with the concave side to the sky.  Since there was more sweep than camber, the load looks most like a load of easy way beams.  The major benefit of using the pole trailer is that it can carry a greater load than a flatbed trailer.  A normal flatbed might have a maximum weight limit of 48,000 pounds while a pole trailer can carry as much as 53,500 pounds.

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Tube Bending: Where to Locate the Weld Seam

Except for seamless tubing and pipe, the other grades of tubing and pipe have a longitudinal weld seam.  When tube bending is done for OEM parts, the question often arises about where to locate the weld seam.

Possibilities include putting the weld seam on the inside radius of the bend, on the outside radius of the bend, and on the centerline radius of the bend.  Further complicating the issue is the fact that the location of the weld seam is not necessarily centered on the side of a square tube or rectangular tube although it is usually located some distance from the corners for structural reasons.

The weld seam on rectangular tubing may be put on either the short side or the long side: different tube mills vary in this regard.  Under some circumstances, a mill will accept an order with some restrictions regarding the location of the weld seam.  In the case of tubes telescoping one within the other, e.g. a 1-1/2 x 3/4 tube telescoping into a 2 x 1 tube, it may be actually desirable to have the weld seam close to a corner.

Unless there is a reason to do otherwise, most often the weld seam on round tubing and pipe is located on the centerline radius which is the neutral axis of the bend.  Depending on the design of the parts, there may be top and bottom locations for the weld seam.

An example of an OEM requesting the location of the weld seam on square tube bending are these “tongue tubes” that function as a connection between a tractor and a wagon, for example.  Here a drawing specifies that the seam be on the center line diameter located on a side defined by the miter cut, drilled hole and straight tangents.

Often when appearance is most important, the weld seam is hidden on the “back” side.  For the arms supporting a bucket on a front-end loader, the customer wanted the 5 x 2 x 1/4 tubes bent such that the seam was hidden from view from either side of the vehicle.

OEM design engineers, OEM fabricators and subcontractors specializing in tube and pipe bending often work together with tube mills to create the optimal solution for a given bent or curved component part.  Further welding information can be found at

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Steel Tube Bending: Trial and Error to Achieve Minimum Radii

The best way to determine if steel tube bending can achieve a given radius for given steel sections curved in a given orientation is probably through trial and error.  Companies that specialize in curving steel often keep records of what can be done and with what success.  With all the sizes of tubing available that could be rolled in innumerable ways, however, it is inevitable that a rolling company will encounter requirements that it has not seen before whether the request comes  from an original equipment manufacturer (OEM) or from a structural steel fabricator.

OEMs seek to continually improve their products while reducing lead time (including R&D lead time), reducing cost, and improving quality.  It seems like the larger the OEM, the more demanding the requirements, but these challenges are often offset by the potential reward of  large volume, repeat orders for a rolling house.

Design engineers often specify bent or rolled tubing to become component parts of the equipment they are manufacturing.  In the best of circumstances the engineers at the OEM work closely with the bending suppliers to develop the optimal design for manufacturing and for the final product.

For example, a series of designs were developed with samples provided for the steering mechanism on a zero-turn mower.  The final design called for a 3 x 2 x 1/8 rectangular tube bent to form a flat back U with a 4-1/8in radius on two 90 degree bends.  Unlike most tube bending, however, the design called for  significant concavity on the inside and outside of each of the two bends.

Through trial and error, the design engineers working with the rolling house created a part that with its concave bends was actually stronger for its application that without the concavity.

To a certain degree, the decision of whether a radius can be achieved can be answered by interpolation.  For example, since we have rolled an 8 x 8 x 1/4 tube to a 15ft radius and to a 25ft radius with no distortion, we can assume we can roll this tube to a 20ft radius with no distortion.

But when you start pushing the limits on minimum bending radius and start varying the wall thickness, for example, interpolation doesn’t always work that well.

Benders and rollers are always trying to curve parts that they had never done before.  The result is that new solutions are discovered every day that add value  to projects.

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Steel Beam Bending For a Ski Jump

When a small town in the northwest corner of Connecticut decided to replace their 85-year-old wooden ski jump with a modern concrete and steel one, the design required steel beam bending.

What spurred the construction of a new ski jump was the opportunity for Salisbury, Connecticut, to host the 2011 United States Junior Olympic ski jumping championships. Although the town had hosted this event twice before, officials now required a new ski jump.

Components included 16 W12 x 45 beams curved the hard way to a 267ft radius in lengths from 27 to 29ft and 2 W8 x 31 beams curved the hard way to a 22ft radius in lengths of 21ft.

In order to meet the championship deadline, the town of 4000 had to obtain local approval, raise $700,000 through donations, obtain a line of credit from a bank, and design and build the structure–all in a period of 22 months.

With an expedited delivery from Chicago Metal Rolled Products, the curved beams arrived in Connecticut in time for the fabricator and erector to finish the 65-meter (213ft) jump in time for the Junior Olympics.

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