Every profession uses concepts and words that may have special meaning within the profession. Understanding these commonly used concepts and words allows for clear communication and reduces potential for misunderstanding. The following is a list of those commonly used in the leak sealing industry. It is not exhaustive. If you have other suggestions, please contact us and we can include your suggestions.
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Used in flange clamps to keep the clamps centered on the gap between the flanges. It is a smooth lip that sticks down into the area between the flanges, usually only ¼” below the OD of the flange ().
In cases where the flange diameters are different, a differential thrust will exist that will push the clamp in the direction of the smaller flange. Here the alignment tongue also serves as a strongback.
These are ears attached to flange clamps to provide more bolting force where a single bolt is insufficient. They may also be used to allow for the installation of injectors between the split line and ears on larger diameter clamps where the distance across the split line between the ears makes it difficult to get sealant into the gap near the split lines ().
These are thin sections of metal that are usually .015" thick, .110" tall from top to bottom, spaced 1/16" apart in concentric circles and, and machined into the sides of tongues on some flange clamps ().
They make a metal-to-metal seal and are designed to bend or deflect sideways as the tongue is forced into the gap between flanges. It is important to understand the difference between blade and crunch teeth. Blade teeth are NEVER used for strongbacks.
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The planar area defined by an internal pressure boundary, seen when looking at the split line ().
The internal pressure of the clamp acts against this area, generating a load that wants to separate the clamp bodies. This load is resisted by bolting the bodies of the clamp together. Multiple bolting areas can be present in a clamp design.
For clamps designed using pipe, there is often a long distance between the ID of a bore and the OD of the endplate. This region is unsupported at the split line where the two halves of the endplate come together. This is sometimes solved with additional ears, welded to the face of the endplate along the split line to ensure a good seal at the bore (). Typically, these bolts are NOT included in overall clamp bolting calculations.
The minimum required thickness of material necessary to withstand the internal pressure of the clamp ().
For clamps made of pipe, it is determined by a hoop stress calculation in the pipe wall. The same is true for clamps made from solid bars or plates where the cavity is formed by circular boring and is determined by the thickness present at the thinnest point in the cavity. For plate clamps, flat plate calculations determine the thickness of plate necessary to prevent deformation of the clamp.
Crunch teeth are concentric rings of sharp triangular shaped "teeth" that form a mechanical interference fit with the surface on which they are closing. They are used for sealing in clamp bores and for anchoring existing hardware where structural failure is a concern ().
The depth of penetration changes with the intended function.
Crunch teeth can be machined into the tongue of a flange clamp (), a clamp’s bores (), and through a strongback ().
It should be recognized that both functions can not be utilized in a single application of crunch teeth. Therefore, crunch teeth machined in a bore can NOT be used to anchor the existing structure. Additional components, known as strongbacks, must be used in such a situation.
All clamps are held together using bolts. The material through which the bolts pass is called an "ear". For many clamps, this will be standard sized bar material welded to the outer edges of the clamp along the split line. It may also refer to walls in plate clamps where the bolts pass through the walls (). They may sometimes be referred to as "flanges".
When a flange clamp is installed to stop a gasket leak, the pressure boundary contained by the flange studs changes. In the worst case scenario, the new pressure boundary will extend out to the OD of the flange. The load from pressurizing this additional donut shaped area between the gasket OD and the flange OD can result in the existing flange studs carrying a load beyond their rating. Evaluating the existing flange studs to determine if an overload condition exists is part of the design process for every flange clamp. In cases where there is an overload, a strongback is always recommended ().
These are small valves, machined from round or hex stock. The most frequently used sizes are 1/8 NPT, 1/4 NPT, and 3/8 X 16 UNC. They are threaded into tapped holes in the body of a clamp or into half couples that are welded to the body of a clamp. The valves are used both to vent leaks while a clamp is being installed and as a means for inserting sealant into the the internal cavity of a clamp, the perimeter seal grooves, or both. They may also be referred to as Shut Off Valves.
The peening lip is a thin piece of metal formed by cutting into the face of an endplate around the outside of a bore. The result is typically a “lip” that is 1/8” thick. A chisel/punch is then used to bend this lip down against the face of the surface on which the bore is sealing ().
A perimeter seal clamp is used when it is determined that a void fill cannot be used. This may be driven by the presence of holes in the existing hardware that would allow sealant to enter the flow of service and cause contamination, down stream clogging, or even damage to down stream equipment. There might also be a concern that the pressure on the sealant could collapse the damaged existing pipe. Whatever the reason, there are several styles of perimeter seals used, but all involve creating a seal between mating faces of the split lines and connecting this seal to the bores to form a continuous perimeter gasket.
The most common types of perimeter seals use either crunch teeth, tubing, or packing in the bores. There is a sealant groove sitting between an inner and outer seal. The inner seal prevents sealant from extruding into the interior of the clamp and the outer seal prevents it from extruding outside of the clamp. The sealant groove in the bore is then taken out into one face of the split line where the endplates come together and into the ears, connecting all the bores. A peening lip is often added to the outside of the bore for any of these types of clamps. These will be seen noted on the data sheets as P.S. Crunch, P.S. 3-1 tbg, or P.S. 3-1 pkg. If a peening lip is desired, png will be added to the end of those. The 3-1 refers to the number of grooves in the bore and ear, so three grooves in the bore and a single groove in the ear ().
A less common style of perimeter seal with tubing or packing is a P.S. 3-3 tbg or pkg (with or without a peening lip). Here all three grooves in the bore are carried out into one face of the split line. The tubing/packing groove in the face of the split line will be milled to a depth that leaves 1/16" of the tubing or packing sticking out of the groove to make contact with the other face of the split line. A draw back to this style of perimeter seal is that it requires wider ears to make room for the extra grooves. Having to use larger than normal ears can sometimes cause the clamp to need post weld heat treating where the use of a typical 3-1 style of perimeter seal might not. thicknesses that will require post weld heat treatment ().
The last style of perimeter seal commonly used is a single groove in the bores and ears. The groove is deep enough to allow ALL of the packing to sit flush inside the groove and still have 1/16" of space behind the packing for sealant to be injected behind the packing, pushing it out of the groove against the sealing surface. These bores are kept tight to the OD of the sealing surface to prevent the packing from being pushed out of the bore by the sealant. This style of perimeter seal bore is frequently combined with a peening lip. A typical sealant groove in either a P.S. crunch, P.S. 3-1, or P.S. 3-3 is only 1/8" deep. The deeper groove needed for the pumpable packing requires a thicker ear which can result in thicknesses that will require post weld heat treatment ().
Many clamps are designed with a perimeter seal as the primary method of sealing, but also include blind-half couples welded to the cover. This allows field technicians to later install injectors to pump the cavity in the event that the perimeter seal fails.
A mechanism that prevents movement of the clamp and existing hardware caused by thrust. Strongbacks may be a part of the clamp body (e.g. a lip in a bore to catch against the end of fittings) or a separate component anchoring the clamp and existing hardware ().
A circular metal ring that fits in the gap of a flange () or against other existing hardware.
It may have a tight fit, as in a case when it is designed to form a seal, or a loose fit, as in a case when it is designed as a strongback or alignment-tongue.
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