TDS Clamps

Types of Clamps

The nature of the leaking or defective hardware drives the design of the clamp to be used. Leaking components may include flanges, straight lines, tees, 45°s and 90°s, screwed or welded fittings, valves, defective welds, and many more.

Page Contents

Bar Clamps

Laminated Box

Solid-Block Clamps

Pipe Clamps

Welded Plate Box

Flange Clamps

Hub Clamps

CNC Clamps

Hot Taps

Strongbacks

Bar Clamps

The simplest enclosures are generally bar clamps. They are typically used on small diameter pipes, 4” and less. They are most often used for covering bad welds and leaking threads where pipes are mated to various types of fittings like 90s, unions, couplings, and valves. Bar clamps are typically made from common bar stock sizes. They are quick to design and fabricate, and are usually the least expensive of clamps.

Laminated Box

Laminated boxes consist of four plates stacked in layers. The two inner layers will have a cavity profile cut out of them. The two outer layers will be solid plates that cover the cavity openings in the inner plates. A ¼ fillet seal weld is run around the cavity perimeter where the inner plate and cover plates touch. Because flat plates are not as efficient at containing internal pressure as circular cavities, such as the case with pipes, the cover plates and perimeter wall thickness can become very thick as clamps get larger and pressures get higher. If a perimeter seal style of clamp is desired, the cover plates are cut to the size of the cavity cut out in the inner rings and inset so that they are flush with the outside face of the inner plates. Full penetration welds are then used to secure the covers to the inner plates.

Solid-Block Clamps

Solid block clamps have their cavity either square milled into each half of the clamp or circular bored through the clamp. For small clamps and relatively low pressure, square milled cavity blocks may be used in place of a laminated box to avoid having any welds present. Where pressures get in the 1500 psi and up range, flat plates and pipes may not have enough strength to handle the stresses and a circular cavity through two plates will be used to get a greater cover thickness and to keep the pressure boundary as tight as possible to the existing hardware to reduce bolting loads. The main difference between these and typical CNC clamps is that there is no machining of the exterior of the clamp.

Pipe Clamps

As the name implies, these are created using pipe to form the wall of the main cavity. Circular plates are welded to each end and machined to match the diameter of the closing surfaces. Ears, formed with bar stock, are welded along the split lines of the clamp sections to hold everything together. If the material thicknesses start getting large, then post weld heat treatment may become necessary, which adds more time and expense to the fabrication process. They are typically used when dealing with leaking pipes 3” O.D. and up. They are used for line to line enclosures, 90 enclosures, tee enclosures, and valve enclosures.

Welded Plate Box

In general, a round cavity is preferable to a cavity with flat surfaces. Flat surfaces require much greater wall thicknesses than do circular walls to contain a given internal pressure. However, there are times where it is not practical to use pipe. In such a case, the clamp is formed using flat plates to form the body of the clamp and bar stock for the ears. These can become very large in a hurry even for moderately high pressure jobs. They will often require post weld heat treatment as well.

Flange Clamps

As the name implies, these are used where the leak source is in the gasket area between flanges. In every case, the “gap” between the flanges will be pumped with sealant, filling the voids around the studs in the gap and in the body of the flanges. There are various styles of flange clamps used depending on the specific geometry of the flanges involved. The clamps are pattern burned from plate material of common thicknesses and then machined depending on the type of seal desired.

Hub Clamp

There are times when a full enclosure is not possible. In these cases a clamp may be pushed or pulled up against a curved or flat hub face. Packing or Tubing will be used between the clamp and hub face. Jack bolts or straps may be used to hold the clamp in place. These are common on large headers with small stub out lines and tanks with nozzles.

CNC Clamps

It is often desirable to avoid having any welded joints in a clamp. Certain services may attack welds and cause them to lose integrity. Certain sizes and types of metal must always be post weld heat treated (PWHT), which adds more time and expense to the fabrication process. Welds may also require time consuming inspections and repairs to meet the standards of end users. Most of these issues can be avoided by using CNC fabrication. CNC stands for Computer Numerical Control. CNC machines use files based on 3D design models to guide the machines use of different tools to create clamp sections from solid pieces of material by milling away the unwanted metal, leaving behind a completed part. So long as the original 3D models are accurate and the machines are setup correctly, the end results are very accurate and easily repeatable. Designs are limited by the sizes of material that can be accommodated by various CNC machines.

Hot Taps and Line Stops

Many facilities frequently need to create a branch line off an existing line without interrupting the service of the existing line. This is commonly done with a hot tap clamp. A "Tee" clamp is attached to the line, either bolting it on or by welding. The tee branch will have a flange where a special machine is attached to the clamp that cuts into the existing line. A valve is used to control the flow from the existing line into the new line. It may also be necessary for the flow in an existing line to be temporarily diverted so a bad section of line can be removed or perhaps a control valve installed in the line. Hot tap clamps are used to create both the temporary flow path and the line stops. A different machine is used in conjunction with a hot tap clamp that inserts plugs into the line on either side of the area to be isolated. The change in the existing line is made, the plugs are removed, flow is restored to the existing line, and the temporary flow path is removed.
We recommend watching this video as a visual reference for how hot tap clamps may be installed and this video to experience the time and man power required.

Strongbacks

Strongbacks are non-leak sealing devices used to constrain the movement of existing equipment or clamps resulting from axial loads. They generate their holding power in two ways, in bearing against other surfaces or by using crunch teeth that bite into the O.D. of the closing surface to prevent the strongback from sliding along the pipe length. Where the loads are small and vibration is not a concern, cup tip and/or cone tip setscrews may be used to secure the clamp.

When total failure, differential-thrust, or flange-stud overload is a concern, some form of strongback is incorporated into the clamp itself or added as additional hardware to secure all the existing components so they cannot move.