Clamp

A clamp for forming a seal on a pipeline section, the clamp comprising a pair of complementary clamp members to be clamped together, each clamp member having an inner surface with a pair of axially spaced, circumferentially extending circumferential seals, and one clamp member having a pair of circumferentially spaced longitudinal seals which extend axially to bridge the gaps between the opposed circumferential ends of the pair of circumferential seals to define four junction zones where the circumferential seals and the longitudinal seals abut, and retention means at each junction zone to connect the circumferential and longitudinal seals together in the retention zones, and at the same time connect the seals to the clamp member at the junction zones. The clamp includes corner seals to provide back-up sealing for the junction zones. The clamp includes heat protection grooves to protect certain of the clamp seals. The clamp may include a pipe branch to provide a hot tapping facility. Embodiments of the clamp have an optimised body design to provide for weight minimization.

This invention relates to a clamp. More particularly this invention relates 
to a clamp for use in forming a seal on a pipeline section. The clamps of 
this invention are particularly adapted to serve as repair clamps for use 
in repairing leaks or weakened zones in high pressure pipeline sections. 
They may also be used to reinforce pipeline sections in weakened zones or 
in zones which are vulnerable to damage or to additional stress. 
Known high pressure pipeline repair clamps are generally expensive because 
of the high cost of manufacture, are frequently not as reliable as 
required by the function which they serve, and are often difficult and 
clumsy to install. 
Clamps which are intended to be mounted onto existing pipeline sections, 
such as, for example, repair clamps, branch clamps, tapping clamps, and 
the like, comprise separate components which can be fitted together to 
complete the clamp. Such clamps are therefore usually split clamps which 
are split into circumferential sections to enable them to be mounted onto 
a pipeline sections. The seals of such clamps thus cannot be 
monolithically constructed to surround the pipe circumference. 
Difficulties are therefore often encountered in locating seals in the 
clamp members or sections of such pipeline clamps. This is in contrast to 
full annular seals which can often be retained in seal grooves simply by 
interference. The seals in the components of such pipeline clamps, 
experience significant loads as the clamp is installed on a pipe section 
due to the interference which is necessarily designed in the seals. The 
most prominent forces exerted on the seals tend to occur at the split 
seams between the clamp members where friction from squeezing and sliding 
the seals into position tends to slide the seals out of position during 
installation. 
Attempts have been made to retain the seals of such clamps, particularly of 
repair clamps, in position by using retainer rings which are mounted on 
the clamp members and compress portions of the seals onto the bodies of 
the clamp members. These retainer rings can be effective at retaining the 
seals in position. However, the retainer rings can sometimes damage the 
seals. Sometimes the retainer rings can be so effective at seal retention 
that the seals do not have sufficient freedom of movement necessary to 
fill imperfections in a pipeline surface or to engage sealingly with 
adjacent or abutting seals. Other attempts have been made to provide 
dovetail seal grooves in the repair clamp member to locate correspondingly 
shaped seals. Dove tail seal grooves require special machining during 
manufacture and are more costly to manufacture due to the additional 
detail of cutting the reverse angle groove walls. 
Where seals are located securely on clamp members of repair clamps, a large 
effort is often necessary to replace the seals. Many users of pipeline 
repair clamps use them temporarily. When conditions permit, the pipeline 
is permanently repaired and the repair clamp is recovered for future use. 
This requires replacement of the used seals with new seals. It is 
desirable, therefore, that repair clamps have seals which are readily 
replaceable when desired. Where the seals are difficult to replace, users 
often discard the entire clamp rather than incur the cost charged for 
refurbishing such repair clamps. 
It is an object of one aspect of this invention, to provide a clamp, 
particularly a pipeline repair clamp for repairing high pressure 
pipelines, which can overcome or at least reduce the disadvantages of the 
prior repair clamps discussed. 
In accordance with one aspect of this invention, there is provided a clamp 
for forming a seal on a pipeline section, the clamp comprising at least 
two complementary clamp members to be clamped together on a pipeline 
section to complete the clamp; each clamp member having an inner surface 
with a pair of axially spaced, circumferentially extending circumferential 
seals; at least one clamp member having at least one longitudinal seal 
which extends axially to bridge the gap between a pair of circumferential 
seals and define two junction zones where the two circumferential seals 
and the longitudinal seal abut; and retention means at each junction zone, 
each retention means penetrating at least one of the seals to connect the 
seals together in the junction zone. 
The clamp is particularly suitable as a high pressure repair clamp for 
repairing leaks or defects in high pressure pipeline sections. 
Each retention means may preferably be connected to a clamp member to 
connect the seals with which it is engaged, to such clamp member. 
In a preferred application of the invention, each retention means extends 
through one of the seals and penetrates the adjacent seal to thereby 
connect the two seals together at that junction zone. 
The retention means may be in the form of various types of mechanical 
devices which can positively connect abutting seals together to form a 
seal, for example, nails, pins, brads or shafts. In a preferred embodiment 
of the invention the retention means comprises a self-tapping screw which 
extends through one seal and is screwed into the adjacent seal. In this 
embodiment of the invention, the clamp member preferably has bores through 
which the screws extend to thereby secure the seals with which they are 
engaged, in position on the clamp member. 
The seals may be located in appropriately positioned seal grooves in the 
clamp members. The clamp may include one or a plurality of additional 
retention means which connect the seals to their respective clamp members 
in one or a plurality of connection zones to thereby retain the seals in 
position. 
In an embodiment of the invention, the clamp members may have heat 
protection grooves in their inner surfaces between selected peripheral 
edges of the clamp members and selected seals, to protect the seals from 
heat flow towards the seals during welding of such peripheral edges during 
use. 
The clamps of this invention may have corner seals positioned to abut the 
junction zones and provide secondary sealing for the junction zones during 
use. 
The clamp may have one clamp member with a pipe branch extending therefrom. 
In this embodiment of the invention, the clamp member may have an annular 
gasket to seal a peripheral zone proximate the pipe branch to a pipeline 
section when the clamp is sealingly engaged with such a pipeline section. 
In this aspect of the invention, the clamp may also have one clamp member 
with a test port. 
Users of high pressure pipeline repair clamps sometimes prefer to weld the 
clamps onto a pipeline section subsequent to repair of the leak with the 
clamp. This makes the clamp a permanent fixture of the pipeline and 
eliminates the dependence of sealing integrity on the elastometric seals 
of the clamp. The usual procedure is that the repair clamp is installed to 
seal the leak. Then the area is cleared of any combustible products which 
may have leaked from the pipeline. The pipeline is brought up to steady 
flow conditions to dissipate welding heat and thereafter the seams and 
openings of the clamp are welded. 
Seal welding of a repair clamp does present certain dangers. If the heat 
produced by welding conducts to the seals in sufficient quantity to exceed 
the temperature capabilities of the seal material, the seal material may 
fail prior to completion of the seal welding procedure. If the pipeline 
product is combustible, this can create a hazard. 
Attempts have been made to combat this problem by adding excess steel to 
the axial ends of the clamp to absorb the welding heat when those axial 
ends are welded to the pipeline section, and thus prevent excessive 
quantities of heat being conducted to the seals. Usually the amount of 
added metal is approximately three inches on each axial end. This added 
metal is heavy, adds to the cost of the product, and is wasteful where 
seal welding is not employed. 
It is accordingly an objective of a further aspect of this invention, to 
provide means for overcoming or reducing the problem presented by heat 
conduction to seals during seal welding of repair clamps and other clamps. 
In accordance with this aspect of the invention, there is provided a clamp 
for a tubular member, the clamp having an inner wall surface, having a 
sealing groove in the inner wall surface to house seal means, the sealing 
groove being spaced from a peripheral zone of the clamp, and the clamp 
having a heat protection groove, the heat protection groove being provided 
in the inner wall surface between the peripheral zone of the clamp and the 
sealing groove to interrupt heat flow from the peripheral zone to the 
sealing groove to thereby partially protect seal means when housed in the 
sealing groove during use, against heat flow from the peripheral zone 
during welding thereof. 
The invention further extends to a clamp for pipeline repair, the clamp 
comprising a plurality of clamp members to be clamped to each other about 
a pipeline to be repaired to complete the clamp, each clamp member having 
a sealing zone for receiving seal means, and each clamp member having a 
heat protection groove between the sealing zone and a peripheral zone of 
the clamp member to interrupt heat flow from the peripheral zone to the 
sealing zone during welding of the peripheral zone and thereby provide 
protection of seal means when positioned in the sealing zone. Moreover, 
heat protection grooves may be extended axially to protect the 
circumferential seals and the longitudinal seals, or a portion of the 
longitudinal. 
The heat protection grooves may have depths generally corresponding to the 
depths of the sealing grooves. They may, however, have greater or lesser 
depths depending upon the configuration of the clamp members and the 
proposed welding conditions. If desired, insulation material may be housed 
or fixed in the heat protection grooves to provide further heat 
insulation. 
Since repair clamps require both circumferentially extending and axially 
extending seals, and since repair clamps comprise two or more clamp 
members which are clamped together to complete the repair clamp on a 
pipeline section, a plurality of seal junction zones occur where separate 
seals abut. These are the most sensitive areas for sealing reliability in 
leak repair clamps. 
These junction zones are generally areas where seal-to-seal contact occurs. 
In other areas of the clamp in accordance with this invention, the seals 
can generally be arranged so that seal-to-metal contact is utilized. Where 
the seals are in direct contact with metal, seal performance is very 
predictable and reliable. However, extensive seal-to-seal contact can tend 
to be unreliable. 
It is a further object of this invention to provide means for improving the 
reliability of sealing in such junction zones. 
In accordance with this further aspect of the invention, there is provided 
a clamp for forming a seal in a pipeline section, the clamp comprising at 
least two complementary clamp members to be clamped together on a pipeline 
section to complete the clamp, each clamp member having an inner surface 
with a pair of axially spaced, circumferentially extending circumferential 
seals, at least one clamp member having at least one longitudinal seal 
which extends axially to bridge the gap between the ends of a pair of 
circumferential seals and define two corner junction zones, and at least 
one clamp member having at least one corner seal positioned to abut a 
junction zone during use and provide back-up sealing for the junction zone 
when the clamp is completed during use. 
The clamp preferably has a corner seal positioned at each corner junction 
zone to embrace the outwardly directed edges of the seals in the corner 
junction zones. 
The corner seals are preferably located in corner recesses provided in the 
clamping members to allow an appropriate degree of compression of the 
corner seals during use. 
Particularly, for example, when using conventional high pressure sealing 
materials, the corner recesses may be such in relation to the designed for 
compression of the seals, that the corner seals can be compressed by 30 or 
40 percent during completion of the repair clamp. 
The corner seals are preferably employed for very high pressure 
applications. They will tend to be less important or unnecessary in medium 
or high pressure applications. 
The clamp preferably includes retention means to retain the corner seals in 
position on the clamp members. 
In an embodiment of the invention, the retention means may comprise the 
retention means used for retaining the circumferential and longitudinal 
seals in position. 
Pipeline repair or leak repair clamps are often used in hot-tapping and 
line-stopping applications. Such variations are often used in line 
maintenance and construction projects as well as in those cases where 
pipeline leaks are to be repaired or pipe sections are to be replaced. 
Prior art clamps of this type are generally simply a leak repair clamp with 
a pipe branch attached to extend from the clamp. 
These prior art branch clamps have certain disadvantages and create certain 
concerns. 
First there are concerns about the reliability of the seals and the high 
cost of failure in the event of leakage. Often no leak exists (at the tap 
location) prior to tapping into the pipeline. A fitting may therefore be 
successfully installed with no indication of a leak since the pipeline has 
not yet been tapped. However, after the line is tapped, pipeline pressure 
is applied to the interior of the fitting. At this critical time a leak 
may be observed for the first time. Since a hole, which can be of a 
significant size, has by then been bored through the pipe, the fitting 
cannot practically be removed, and no convenient method exists to stop the 
leak. This, therefore, usually necessitates taking the pipeline out of 
service in order to replace the leaking fitting. 
A further concern is based on the fact that, after a tap is effected, the 
pipeline fluids are free to circulate in the annular space formed between 
the interior of the tapping fitting or branch fitting, and the outside of 
the pipe. Pipeline fluids may be corrosive or damaging to seals. Pipelines 
usually have internal coatings applied to resist the deleterious effects 
of the pipeline product. However, the exterior of the pipe does not 
usually have the same protection. It is often, therefore, considered 
undesirable to have free movement of the pipeline product on a region of 
the pipeline exterior. 
It is accordingly a further objective of this invention, to provide a clamp 
which can serve as a branch clamp, and which can reduce or overcome some 
of the discussed advantages. 
In accordance with this further aspect of the invention, there is provided 
a clamp for clamping sealingly onto a pipeline section, the clamp 
comprising at least two clamp members to be clamped together on a pipeline 
section to complete the clamp, each clamp member having seal zones for 
receiving seal means to provide a sealing engagement between the clamp and 
a pipeline section during use, one clamp member having a pipe branch 
extending therefrom for the clamp to serve as a tapping saddle or branch 
clamp, and that clamp member having an annular gasket to be positioned 
within the clamp member about the inner periphery of the pipe branch for 
sealing engagement with a pipeline section during use. 
The gasket preferably comprises a pliant gasket which can conform closely 
with the pipeline surface during use, and can isolate the pipe branch zone 
from the remainder of the interior of the clamp. 
In a preferred embodiment of the invention, the gasket comprises a 
perforated elastomer sheet which is relatively pliant to be tolerant of 
pipe dimensions and pipe surface defects. 
In the clamp of this aspect of the invention, at least one clamp member may 
include a test port to provide access to the interior of the clamp to a 
zone between the annular gasket and the seal means of the clamp members 
during use. 
The seals and annular gasket used in the clamps of this invention, may be 
made of any conventional or suitable materials which can serve the 
required purpose. There are a number of standard materials of different 
types which are commercially available. Appropriate seals can be purchased 
off the shelf, can be extruded to specification, or can be molded to 
specification. 
Various synthetic rubbers are, for example, available which are suitable 
for seals in the clamps of this invention. 
For line temperatures below about 300.degree. F. buna nitrile synthetic 
rubbers are generally preferred. For temperatures at 300.degree. F. or 
higher, fluoro elastomers, such as those for example available under the 
trademark "VITON" are currently preferred. 
Silicon seals are also sometimes used. 
The particular seal material depends on the chemical composition in the 
pipeline, the operating temperature, and the operating pressure. From 
these parameters, persons of ordinary skill in art can readily select 
appropriate seal materials from those commercially available, and can 
readily design the dimensions and compression ratios from the ratings 
which are available for various applications. 
Seal materials are graded by a standard, referred to as a durometer 
reading, which gives an indication of the stiffness of the rubber. 
The preferred seal material for average conditions for a repair clamp of 
this invention, is a buna nitrile seal operating at a temperature of less 
than 250.degree. F. For an ANSI class 600 rating (that is 1,480 psi at 
ambient temperatures) a durometer reading of 70 to 75 is preferred. 
The materials from which the clamp members are made, are well-known to 
persons of ordinary skill in the art. They may be selected from the 
various steels which are listed in available piping and pressure vessel 
codes. 
Where welding will be employed for the clamp of this invention, the 
material of the clamp must be selected that neither the material of the 
clamp nor the material of the weld will be compromised during welding. 
The clamp materials may for example comprise carbon steel casting ASTM 
A-216-grade WCA, WCB or WCC. Applicant's presently preferred grade is 
grade WCC. 
While the clamps of this invention can have various applications, they are 
particularly suitable for and adapted for use in pipeline repair and high 
pressure pipeline repair or sealing operations. 
A further concern is based on the fact that the clamps for use in forming a 
seal on a pipeline section, particularly where the pipeline to be clamped 
is of large diameter, are quite heavy and additionally, quite bulky. It 
has generally been thought that in order to combat the high pressures and 
temperatures associated with pipeline repair clamps, it was necessary to 
add additional weight to the clamp. Clearly, however, such weight costs 
money. Material costs are significant to the cost of the product. 
Transportation charges are directly related to shipping weight. 
Additionally, installation is made more difficult by the high weight. 
Accordingly, the present invention also provides clamps of reduced weight 
which are rated to withstand the same at higher operating pressures. This 
weight reduction, while retaining or increasing the clamp performance, is 
due to a reduction in bending loads in the clamp body that result from 
internal pressure. Such reduction in bending loads is achieved by 
adjusting the primary path of tensile loads in the clamp body and in the 
bolts. 
The primary tensile loads associated with a pipe clamp having a pair of 
complementary clamping members to be clamped together to form a clamp 
body, are defined radially around a tensile load centerline of the clamp 
wall and laterally along a bolt force centerline defined by the bolt 
positioning on the bolting flanges. Therefore, by adjusting the relative 
positioning of the two tensile load forces, that is, the bolting force 
centerline and the wall tensile load centerline, clamps may be designed 
which achieve a minimized weight yet which meet at least minimum 
acceptable criteria for clamp wall thickness, clamp body bending stress 
and bolt bending stresses. 
The wall tensile load centerline, commonly referred to herein as a wall 
centerline may generally be defined as being projected along a radial path 
extending from a mid point between the inner and outer surfaces of the 
clamp walls, the radial path generally corresponding to the curvature of 
the curved inner wall surface. In the completed clamp, that is, a clamp in 
a closed or clamped position, the wall centerline may generally be 
envisioned as an annular tensile load defined radially around a central 
point, the central point generally being defined as the axial center of 
the clamp body bore, alternatively, the axial center of the pipe to be 
clamped. 
The bolt force, or tensile load, centerline is generally defined by the 
bolt hole or bolt bore, more specifically, the axial center of the bolt 
hole or bore. 
It will be appreciated that adjustment of the bolt force centerline with 
respect to the wall centerline may result in a clamp body cavity with a 
non-circular bore. Pipes are nevertheless sealing engaged by the present 
clamps through the use of axially spaced sealing flanges which extend from 
the clamp walls and have radii roughly corresponding to the radius of the 
pipe. 
Embodiments of the invention are now described by way of example with 
reference to the accompanying drawings.

With reference to FIGS. 1-4 of the drawings, reference numeral 10 refers 
generally to one preferred embodiment of a clamp in accordance with this 
invention for forming a seal on a pipeline section. 
The clamp 10 is in the form of a repair clamp for the repair of high 
pressure pipeline sections to stop leaks or repair defects. 
The clamp 10 comprises two complementary clamp members 12.1 and 12.2 which 
are designed to be clamped together on a pipeline section to complete the 
clamp 10. 
Each of the clamp members 12 (that is 12.1 and 12.2) has inner flange 
surfaces 14 which are generally semi-annular. 
The clamp members 12 are generally semi-annular because two clamp members 
12 are used to complete the clamp 10. It would be appreciated, however, 
that more than two appropriately shape clamp members 12 could be used to 
complete the clamp 10. A pair of clamp members 12 is however the present 
preferred configuration. 
Each of the flange surfaces 14 of the clamp members 12, has a pair of 
axially spaced circumferentially extending circumferential seal grooves 16 
wherein circumferential seals 18 are located. These circumferential seals 
18 of each clamp member 12 are thus axially spaced and extend 
circumferentially. They are provided in the inner flange surfaces 14. 
Only one of the clamp members, namely the clamp member 12.2, has a pair of 
circumferentially spaced, axially extending, longitudinal seal grooves 20. 
The longitudinal seal grooves 20 are provided at the circumferentially 
opposed ends of the circumferential seal grooves 16 and thus of the clamp 
member 12.2. 
Each seal groove 20 has a longitudinal seal 22 positioned therein. 
The longitudinal seals 22 abut the circumferential seals 18 to define four 
junction zones 24. 
The inner flange surfaces 14 of the clamp members 12 are defined along the 
inner peripheries of inwardly extending flanges 26 which are axially 
spaced from each other to define recesses 28 between the flanges 26. 
Each clamp member 12 has a clamp flange or bolting flange 30.1 (for the 
clamp member 12.1) and 30.2 (for the clamp member 12.2) at the 
circumferentially opposed ends. The flanges 30 are used for bolting the 
clamp members 12 together to complete the clamp 10. 
Each flange 30 has a plurality of bolt holes or bores 32 for receiving 
bolts or studs to clamp the clamp members 12 together. 
Each flange 30 has a seating face 34. 
The seating faces 34 of the clamp member 12.2 have the longitudinal seal 
grooves 20 provided therein. The longitudinal seals 22 therefore cooperate 
with he seating faces 34 of the clamp member 12.2 and with he seating 
faces 34 of the clamp member 12.1 when the clamp 10 is completed on a 
pipeline section. 
Each clamp member 12 has a curved outer wall surface 36 and a curved inner 
wall surface 38 between the flanges 26. Each flange 30 has a bolt surface 
40. 
During use the clamp members 12 are clamped together by means of 
appropriate bolts. In the preferred embodiment illustrated in the 
drawings, the bolts are in the form of socket head cap screws 42 having 
socket heads 44. Hexagonal nuts 46 are used with the screws 42. 
Since the socket head cap screws 42 are tightened with a male driver key, 
it is not necessary to provide excess spacing around the bolt head 44. The 
bolts may thus be spaced more closely to each other, and more closely to 
the outer wall surfaces 36 of the clamp members 12. This can lead to a 
significant reduction in the size of the flanges 30 of the clamp 10. 
The offset between the bolt or capscrew 42 center lines and the center line 
of the clamp body, may be minimized for the same reason, leading to less 
bending loads on the clamp body. 
Since the socket head 44 diameters are less than the width across the flat 
portions of the nuts 46, the flanges 30 are conveniently shaped so that 
the nuts 46 cooperate with corners formed between the junctions of the 
bolt surfaces 40 and the outer wall surfaces 36 to prevent the nuts 46 
from rotating during installation. This therefore eliminates the need for 
a back-up wrench during bolt torque procedures. 
While socket head cap screws of any conventional materials may be used, the 
present preferred screws 42 are those produced under ANSI B18.3 which 
specifies material according to ASTM A-574. The material specification 
specifies a minimum 0.2% offset yield strength of 153,000 psi and a 
minimum ultimate tensile strength of 170,000 psi. A minimum elongation 
(before fracture) of 8% is also specified for the material. Because of the 
higher strength, the length of pipeline section encapsulated may be 
increased without using larger bolts or screws 42. Alternatively, the same 
length may be encapsulated or sealed using smaller bolts. This is 
important since an increase in bolt size also increases the size and 
weight of the clamp 10. 
The cumulative weight savings which can result from the use of socket head 
cap screws of high strength, attributable to the weight of the screws 42 
and the reduced possible dimensions of the bolting flanges 30, and the 
concomitent lesser bending loads on the clamp body from an optimized 
design in accordance with this invention, can provide a weight saving of 
typically from about 15% to a saving which may be as high as 40% in some 
cases. 
The clamp member 12.2 includes retention means 48.1 which connect the 
longitudinal seals 22 to the circumferential seals 18 in the four junction 
zones 24. At the same time, the retention means 48.1 serve to secure the 
longitudinal seals 22 and the circumferential seals 18 in position to the 
clamp member 12.2. 
Each retention means 48.1 comprises a self tapping screw 48.1 which extends 
through a bore 50 in the flange 26, which is screwed through the 
circumferential seal 18, and into the longitudinal seal 22. (As can be 
seen particularly in FIG. 4.) 
Each retention means, or self-tightening screw 48.1, thus positively 
secures the circumferential seal 18 to the longitudinal seal 22 in the 
junction zone 24, while at the same time positively locating the junction 
zones 24 in position on the clamp member 12.2. 
The clamp members 12 include additional retention means 48.2 which likewise 
extend through bores 50 in the flanges 26, and penetrate the 
circumferential seals 18 in connection zones to connect the 
circumferential seals 18 to the clamp members 12 in those connection 
zones. 
The additional retention means 48.2 will be provided at spaced intervals 
along the length of the circumferential seals 18, with the spacing 
depending upon the diameter of the clamp 10. Receiving bores may be 
provided at appropriate intervals in the flange 26 to receive the free 
ends of the retention means 48.2 which pass through the circumferential 
seals 18. 
The embodiment of the invention as illustrated in FIGS. 1-4 of the 
drawings, provides the advantage that the retention means 48 effectively 
locates the circumferential seals 18 in position in the seal grooves 16 of 
the clamp members 12. In addition, the retention means 48.1 secure the 
ends of the circumferential seals 18 and longitudinal seals 22 together in 
the critical junction zones 24 to improve the sealing effect in the zones, 
while simultaneously locating the ends of the circumferential seals 18 and 
of the longitudinal seals 22 in position in these junction zones. 
The seal retention means 48 effectively supports the seals during 
installation, and does not restrict the seals from filling imperfections 
in the pipe surfaces during use. Additionally, the seal retention means 
allows easy replacement of the seals when required. 
The use of the retention means 48 in accordance with the aspect of the 
invention described with reference to the preferred embodiment of FIGS. 
1-4, provides several advantages. This aspect of the invention provides 
simplicity. Conventional self threading screws are used to penetrate the 
seals and provide a firm holding power on the seals. The retention means 
48.1 comprises a single self-tapping screw per corner junction 24, and 
serves the dual purpose of locating the seal in position while keeping the 
number of screws to a minimum. Installation of the seals is simplified. 
The labor savings resulting from the ease of installation of the seals and 
the retention screws, and the ease of replacement, reduces the cost of 
manufacture and can decrease delivery time. 
Applicant was surprised that retention means in the form of self-tapping or 
threading screws could be used for the purpose disclosed. Applicant 
believed that such screws would weaken the seals and that the tendency to 
leak at the penetration points would be great. Surprisingly, the elastomer 
materials of the seals create tight seals along the retention means 48 and 
test have shown that leaks are unlikely in these regions. In addition, the 
retention means 48.1 create effective seals at the junction zones of the 
circumferential and longitudinal seals thereby resisting leakage in the 
corner junction zones 24. In fact the retention means 48.1 reinforce the 
seals in the leak sensitive corner or junction zones 24 and do not appear 
to have any harmful effect on the sealing properties of the seals. 
Each clamp member 12 further has circumferentially extending heat 
protection grooves 52 provided in the inner surfaces of the flanges 26. 
The circumferentially extending heat protection grooves 52 are provided 
between the circumferential grooves 16 and the axial ends of the clamp 
members 12. The heat protection grooves are clearly visible in FIGS. 3 and 
4 of the drawings. 
The purpose and function of the heat protection grooves 52 is demonstrated 
more particularly with reference to FIG. 3 of the drawings. 
The repair clamps of this invention are often welded to a pipeline section 
once they have been mounted in position. At the same time the clamp 
members 12 are welded together. The clamp 10 thus becomes a permanent part 
of the pipeline section to which it is welded. The sealing reliability of 
the repair clamp it is thus no longer dependent upon the sealing effect of 
the elastomer seals 18 and 22. 
In FIG. 3 a typical weld 54 is shown welding the axial end of the clamp 
member 12 to a high pressure pipeline section 56. 
During the welding operation, heat is generated. If the quantity of heat 
which is conducted along the flange 26 towards the circumferential seal 
18, becomes excessive, the seal 18 can lose its sealing effect during the 
welding operation. During the welding operation, fluids are conveyed 
through the pipeline 56 to dessipate heat generated during welding. 
Deterioration of the seal 18 is undesirable and can thus be harmful if it 
occurs during the welding operation. It can also, of course, be dangerous 
if combustible materials are be conveyed in the pipeline section 56. 
The heat protection groove 52 interrupts the heat flow path thereby 
limiting the quantity of heat conducted from the weld zone 54 to the 
circumferential seal 18 during welding. 
The heat protection groove 52 conveniently has a width of about 1/8", and a 
depth generally corresponding to the depth of the circumferential seal 
grooves 16. 
The heat protection groove 52 provides advantages over the prior art 
systems of increasing the axial widths of the flanges 26 by about 3 inches 
to absorb the heat generated and thus protect the seals. The heat 
protection grooves 52 do not add to the weight of the clamp 10 and provide 
a more effective barrier to the transfer of heat than additional material 
in the clamp members 12. 
The clamp 10 includes a plurality of corner seals 58. The corner seals are 
illustrated in detail in FIGS. 5 and 6 of the drawings. For the sake of 
clarity, the corner seals 58 have been omitted from FIG. 1 and from FIG. 
4. 
With particular reference to FIGS. 5 and 6 of the drawings, therefore, four 
corner seals are provided on the clamp member 12.2 at the four corner 
junction zones 24. 
The corner seals 58 are positioned in the appropriate recesses 60 in the 
sealing face 34. The recesses 60 communicate with their adjacent 
circumferential seal grooves 16 and longitudinal seal grooves 20. 
Each corner seal 58 is shaped to be located in its recess 60, and to 
embrace the adjacent circumferential seals 18 and longitudinal seals 22 
where they join at the corner junction zones 24. 
The corner seals 58 are positioned so that the retention means or 
self-tapping screws 48.1 also pass through the corner seals 58 before 
penetrating and passing through the circumferential seals 18, and then 
penetrating the longitudinal seals 22. The retention means 48.1 thus serve 
to additionally locate the corner seals 58 in position, and to secure them 
to the seals 18 and 22. 
The junction zones 24 are the most sensitive zones for sealing reliability 
in repair clamps. These are the areas where leaks are most likely to occur 
because the longitudinal seals abut the circumferential seals in these 
areas. In addition, in these junction zones, seal-to-seal contact occurs 
during use, as opposed to seal-to-metal contact. The clamp members 12 are 
specifically designed to provide seal-to-metal contact in most areas. That 
is why the longitudinal seals 22 are provided on the clamp member 12.2 
only, so that they can co-operate with the sealing faces 34 of the clamp 
member 12.1. 
The corner seals 58 do not eliminate the seal-to-seal contact, but 
completely surround the area in question with metal-to-seal contact. The 
corner seals 58 therefore provide a relatively reliable sealing geometry 
as a back up or secondary sealing system to the primary seal provided by 
the seals 18 and 22. 
The corner seals 58 may conveniently be installed as circular pads which 
are located in the recesses 60 and are then cut so that they do not extend 
over the seal grooves 16 or 20 in the junction zones 24. 
In practice, for average conditions, the longitudinal seals 22 and 
circumferential seals 18 would project about 1/4" or so above the surfaces 
of the clamp members. The recesses 60 are therefore conveniently made so 
that, upon proper compression during use, the corner seals will have 
compressed by about 30 to 40 percent of their original height. 
With reference to FIG. 7 of the drawings, reference numeral 62 refers 
generally to an alternative embodiment of a clamp in accordance with this 
invention for forming a seal on a pipeline section. 
The clamp 62 corresponds substantially with the clamp 10 of FIGS. 1-6. 
Corresponding parts are therefore indicated by corresponding reference 
numerals. 
The clamp 62 is in the form of a tapping saddle or branch clamp which may 
be used to provide a tap into a pipeline section, or which may be used to 
provide such a tap when a repair is made. 
The clamp member 12.1 of the clamp 62 has a pipe branch 64 extending 
thereform. 
The clamp 62 includes an annular gasket 66 which is positioned within the 
clamp member 12.1 proximate the inner periphery of the pipe branch 64 to 
provide a sealing engagement with the pipeline section 56 during use as 
shown in FIG. 7. 
The clamp 62 further includes a sealable test port 68 which is provided in 
the clamp member 12.1. 
The annular gasket 66 is preferably made of a material which corresponds 
with that of the longitudinal and circumferential seals 22 and 18 as 
discussed in the specification. As such the gasket is pliable and tolerant 
to pipe dimensions and surface defects in the pipeline section. 
The gasket is located in an annular gasket recess 70 along the inner 
surface of the clamp member 12.1. 
Since the annular gasket 66 closely surrounds the tapping area once the 
tapped hole 72 has been formed in the pipeline section 56, access by the 
pipeline fluids to the exterior of the pipe section 56 will be restricted 
to the very small area around the tapped hole 72. The external surface of 
the pipeline section 56 is therefore protected by the annular gasket from 
any corrosive action of the pipeline fluids. 
The clamp 62 provides a more important benefit in that it allows testing of 
the clamp 62 for sealing integrity prior to actual tapping of the pipeline 
section 56. By using the test port 68, hydrostatic pressure may be applied 
between the gasket 66 and the conventional circumferential and 
longitudinal seals of the clamp 62 to test the seals and verify that the 
seals are effective. This practically insures that no leakage will occur 
when the pipeline section 56 is tapped. Without the annular gasket 66 of 
the clamp 62, it is generally only possible to determine whether or not 
the conventional seals are effective once the tapped hole 72 has been 
formed and the fluid under pressure enters the interior of clamp 62. If a 
leak is detected at that stage, after the tapped hole 72 has been formed, 
it is a serious disadvantage. 
The clamp 62 provides the further advantage that if a leak occurs in the 
clamp 62 sometime after installation, the test port 68 may be used to 
inject an appropriate sealant into the cavity defined by the outer 
periphery of the gasket 66, and by the outer peripheries of the 
longitudinal and circumferential seals 22 and 18. A leak may therefore be 
repaired without taking the pipeline out of service. This is generally not 
possible if no such annular gasket 66 is included, because the sealant 
will then flow into the bore of the pipe and will not be effective in 
sealing the leak. 
Referring now to FIGS. 8-10, there is shown cross-sectional views of 
various repair clamps. FIG. 8 shows the basic body shape of a conventional 
repair clamp 70. Note that the clamp body bore 72.8 of the clamp 70 is 
basically circular. The dash lines displayed therein indicate the primary 
path of the wall tensile load centerline 74.8. It should be observed that 
a significant distance results between the bolt force centerline 42.8 and 
wall centerline 74.8 at the clamp seam 76.8 defined by the seating faces 
34.8. Arrows (78.8) illustrate the off-set distance between the wall 
centerline 74.8 and bolt centerline 42.8. 
It will be appreciated that the product of the off-set distance 78.8 and 
the tensile load along the bolt centerline 42.8 is the value of the 
bending moment induced in the shell of the clamp. Further, this moment is 
constant and continuous from one side of the shell to the other. 
Therefore, where the off-set distance 78.8 is a large value, the bending 
moment is also a large value. Such large bending moments are undesirable 
in that these loadings must be resisted by the clamp body which leads to 
an increase in the body wall thickness or alternatively to the use of 
expensive stiffening ribs. Additionally, the clamp may not deflect 
significantly without endangering the loss of proper seal loading. 
Moreover, it is possible to design the clamp such that the stresses 
resulting from high bending loads are acceptable, while the deflections 
that result from the high bending cause leakage of the clamp. Excessive 
deflections of the clamp body induce high bending stresses in the bolts as 
well. High bending stresses in the bolts, since the bolts are generally 
seated on the side flanges which will deflect annularly with increases in 
clamp curvature deflection. 
Therefore it is generally desirable to design a clamp which meets three 
criteria. That is, the clamp must meet at least the minimum acceptable 
criteria for clamp wall thickness, clamp body bending stress and bolt 
bending stress. This may be achieved in accordance with the present 
invention by adjusting the off-set distance 78 and the body wall thickness 
to achieve a clamp having a more desirable bending moment and having a 
decreased weight. 
In general terms, the minimum criteria for clamp wall thickness may be 
computed according to accepted or standard codes such as, for example, the 
ASME codes or their equivalent for cylindrical vessels of the same 
diameter and material as the clamp body. AMSE, Section 8, Division 2 gives 
additional criteria for safe bending stress levels. Under these rules a 
basic stress allowable may be established for any material used. 
Furthermore, the allowable level of the sum of membrane (tensile) stress 
and bending stress is 11/2 times the basic allowable stress. It will be 
appreciated that the bolting material will generally have a different 
limit of allowable stress than the clamp body since different materials 
are used and different methods exist for computing basic allowable limits 
for bolting than for vessel materials. 
Once the basic allowable stresses are established, the allowable criteria 
for bending plus tensile stresses will result. 
FIG. 9 displays a clamp 80 having an off-set distance 78.9 between the wall 
load centerline 74.9 and bolt force centerline 42.9. The clamp is composed 
of opposing clamp members 12.9 and 12.10. In that the off-set distance 
78.9 is equal to 0, then the bending load or bending moment is equal to 0 
because the bending moment is equal to the product of the off-set distance 
and the bolting force. Although the bending loads have been eliminated in 
clamp 80, this configuration is not the lightest possible since the side 
or bolting flanges 30.9 and 30.10 must be greatly increased in order to 
provide the necessary space for the bolting. It is thus better to have 
some bending moment than no moment. As the bolting flanges 30 are moved 
out away from the wall centerline 74, the side flanges 30 may be shortened 
to accommodate the clamp wall 36, therefore resulting in a decreased clamp 
weight. However, as the off-set distance 78 is increased, bending loads 
become greater and thus the required wall thickness to resist the bending 
loads. Therefore, the off-set distance 78 must be optimized to achieve a 
minimized clamp weight. 
It will be appreciated that although a fully minimized (minimum) clamp 
weight is generally preferred, it may nevertheless be desirable, for 
certain applications, to provide a clamp having a partially minimized 
weight (i.e., a partially optimized off-set). 
In order to determine the optimum geometry (lightest weight), data 
processing, preferably in the form of a computer program, may be utilized 
to iteratively design a clamp. Such data processing is discussed in 
greater detail below. 
FIG. 10 shows a typical clamp 82 made in accordance with the present 
invention. The clamp has a pair of complementary clamping members 12.11 
and 12.12 to be clamped together to complete the clamp, each clamping 
member 12 having a clamp wall 84.11 and 84.12 defining an outer wall 
surface 86 and a curved inner wall surface 38.10. The clamp wall 84.12 
defines a wall centerline 74.10 projected along a radial path extending 
from a mid point between the inner surface 38.10 and outer surface 86. It 
will be appreciated by those of skill in the art that the mid point 
referred to is not necessarily a geometrical mid point per se, rather this 
refers to a force mid point within the clamp wall 84. However, the wall 
load centerline 74.10 will follow a radial path which generally 
corresponds to the curvature of the curved inner wall surface 38.10. 
Bolting or side flanges 30.11 and 30.12 are laterally spaced at opposed 
circumferential ends of the clamp wall 84 for use in bolting the clamping 
members 12.11 and 12.12 to complete the pipe clamp 82. Each bolting flange 
30 has at least one bolt hole 32 for receiving a bolt 40, the bolt hole 32 
defining a bolt force centerline 42, wherein the distance between the bolt 
force centerline 42 and the wall centerline 74.10 represents a centerline 
off-set distance 78.10. 
It will be appreciated that by decreasing the off-set distance 78.10, a 
non-circular bore 72.10 or 72.9 will result. Such non-circular bore 72.10 
is generally characterized by opposing curved inner wall surfaces 38.10 
and 38.11 and opposed planar inner wall surfaces 88.10 and 88.11. However, 
such inner wall surfaces 88.10 and 88.11 are not necessarily planar. 
Therefore, such inner wall surfaces 88 may be defined more generally as an 
inner flange wall surface 88. 
Therefore, it will be appreciated, that the present invention may be 
defined in terms of the shape of a cross-section of the clamp body bore 
72, with the non-circular shape generally indicating an optimized clamp 
body shape. Moreover such shape may be further defined with reference to 
the relative distances between opposing clamp body inner wall surfaces 
88.10 and 88.11 as compared to the distance between opposing curved inner 
wall surfaces 38.10 and 38.11, with the curved inner wall diameter being 
generally greater than the diameter between the planar, or alternatively, 
the flange inner wall surfaces 8.10 and 88.11. 
In a preferred embodiment the distance between opposing curved inner wall 
surfaces 38.10 and 38.11 is at least 1% greater than the distance between 
opposing inner flange surfaces 88.10 and 8.11. A still more preferred 
embodiment may be realized by providing up to a 25% difference between 
opposing inner flange diameter and opposing curved inner wall diameter. It 
has been found that an optimized body shape for smaller clamps generally 
exhibits a greater difference between these distances than in larger 
clamps. For example, 2" clamps (that is, clamps designed for 2" pipes) 
have been prepared which exhibit a 25% difference. Moreover, 16" clamps 
made to the same specification were found to exhibit a 10% difference 
whereas 48" clamps may demonstrate only a 3%. However, optimized clamps 
made for different applications may vary. 
Pipe clamps made in accordance with the present invention may similarly be 
defined by comparing the radius of the generally annular wall force 
centerline 74 to the radius (i.e., half) of the distance between opposing 
flange inner wall surfaces 88.10 and 88.11. Accordingly, the wall 
centerline radius may be defined as by the radius of the annular wall 
force centerline 74.10. Thus, the advantages of the present invention may 
be realized by maintaining the radius of the distance between opposing 
flange inner wall surfaces 88.10 and 88.11 at a value which is less than 
the wall centerline radius. 
In a preferred embodiment the flange radius is within 1% less than the wall 
centerline radius. 
In a more preferred embodiment the flange radius is within 5% less than the 
wall centerline radius. 
In still more preferred embodiment, the flange radius can be 25% less than 
the wall centerline radius. 
It can be appreciated from the foregoing that an important part of the 
present invention is the clamp weight optimization which is achieved by 
varying tensile load off-sets 78. 
FIG. 11 illustrates a chart which demonstrates the advantages which may be 
realized. Shown therein is a graphical display of changes in clamp weight 
(along the Y) axis versus changes in off-set distances (along the X axis). 
It is particularly noteworthy, and particularly surprising, that a unique 
optimum off-set dimension exists. As illustrated, an off-set distance of 
zero results in a clamp weight which is somewhat greater than the clamp 
weight achievable at the optimum off-set distance value. The totally 
circular body of the conventional repair clamp (for example see FIG. 8) 
gives a clamp of high weight relative to both the optimum off-set distance 
and the zero off-set distance. 
In order to generate the optimization data as generally illustrated by FIG. 
11, it is preferable to utilize data processing, preferably in the form of 
a computer software program. 
FIG. 12 illustrates a logic circuit for minimization of clamp weight. Those 
of skill in the art will recognize that such logic circuit may be 
adaptable by those of skill in the art to perform within the framework of 
a computer software program. However, it is not absolutely necessary to 
utilize computer software, as calculations for the various stresses, 
deflections and physical dimension may be achievable by non-software 
related means, such as manual calculation. However, it will be generally 
recognized that computer software has the advantage of being much less 
time consuming and potentially more accurate, in arriving at proper 
optimized clamp dimensions. 
In a very general manner, the logic circuits of FIG. 12 iteratively designs 
a clamp. The program starts by designing for the case where there is no 
off-set (i.e., off-set equals zero). The logic circuit computes all of the 
appropriate parameters for the clamp design and then computes the weight. 
The program then increases the off-set dimension by a small increment and 
completes the process again. After each design iteration, the following 
weight is compared to the weight for the preceding step. As long as the 
weight continues to decrease, the process is repeated. After a sufficient 
number of times, a minimum clamp weight will be found. Such an iterative 
logic circuit can be used to demonstrate the finding that a unique optimum 
off-set dimension does exist and that this optimum can be approached 
"smoothly" by the logic circuit (i.e., no radical changes in the weight 
were observed with small changes in the off-set dimension). These 
conditions were successfully met and therefore the procedure works 
effectively at finding an optimized geometry for any given clamp design 
requirement. 
In particular, the logic circuit of FIG. 12 begins at input block 90 by 
inputting the pipe size 92 (in terms of the pipe's outer diameter) and the 
sealing length 94, which is the minimum distance between the laterally 
spaced circumferential seals 18 which will accommodate, for example, a 
hole in the pipeline to be repaired. Additional inputs include the 
pressure rating 96 of the clamp to be produced and the number of bolts 98. 
The number of bolts is generally based upon the determined bolt area 
requirements and by the preferrence of the designer. In practice, a 
resonable number of bolts can be selected. Once the minimized weight has 
been determined, the number of bolts can be varied to alter the diameters 
of the individual bolts. This will alter the bolt centerline position. The 
minimized weight can then again be determined and so on until the best 
number of bolts to give the best weight has been determined. The print key 
is set to 0 as an internal counter. 
After inputting the four above-mentioned variable inputs, the logic circuit 
then proceeds to logic box 100 which computes the clearance of the sealing 
flange inner wall surfaces 14 over the pipe to be repaired. Generally, for 
example, a 3/16" inch clearance is typical for a 4" pipe. However, 
formulas which take into account potential pipe expansion and unevenness 
may be used to generate such clearance data, and such formulas are 
well-known to those skilled in the art of clamp manufacturer. Generally, 
the clearance may be set at the maximum acceptable tolerance of the pipe. 
In a preferred embodiment, the clearance is set at twice the maximum 
acceptable tolerance. 
The next logic step 102 involves locating the longitudinal seal along the 
seating face 34 of the clamp member 12 in line with the positioning of the 
ends of the circumferential seals 18. 
Next, at logic circuit box 104, the pressure loading on the clamp is 
determined with reference to American Society of Mechanical Engineers 
(ASME) codes. In particular, gasket retention loading must be sufficient 
to produce enough squeeze on the seal to maintain the pressure. Thus the 
pressure applied over the rectangular area as defined by a cross-section 
of the clamp load bearing cavity (i.e. the cross sectional area sealed as 
defined by the outer edges of the longitudinal and circumferential seals) 
defines the total load and therefore determines bolt loading which is also 
definable as the pressure loading. 
At logic box 106, the cross-sectional bolt size necessary to counteract the 
pressure loading is established by the allowable tensile stress for the 
bolt material as determined from the pressure loading information at logic 
box 104. This is a generally standard computation known to those of skill 
in the art. 
Logic circuit box 108 locates the bolt centerline 42 wherein the inner edge 
of the bolt hole is located just outside of the longitudinal seal. 
Logic circuit box 110 sets the centerline of the body shell 74 equal to the 
bolt centerline 42 (therefore setting the off-set distance equal to 0). 
Logic circuit boxes 112-120 are concerned with computing the physical 
dimensions of a clamp which meets minimum criteria for clamp wall 
thickness, clamp body bending stress and bolt bending stress. At box 112, 
the shell wall thickness is computed according to standards for clamp wall 
thicknesses necessary to meet specified pressure loadings. For example, 
Section 8, Division 1 of the ASME codes specifies the general rules 
relating to wall thickness for pressure vessels. However, other 
specifications may be referred to where appropriate. Accordingly, box 114 
computes physical dimensions of a clamp having the selected off-sets and 
shell wall thickness. Such physical dimension computations include, for 
example, considerations of the fact that bolt nuts 46 will normally wedge 
against the outer clamp body 36 in order to obtain the maximum advantages 
of the present invention. 
Logic circuit box 116 computes the internal stresses and deflections of the 
clamp having the physical dimensions previously determined. This includes, 
for example, the tensile stress on the body due to pressure. The bending 
stress on the body is determined by dividing the moment (the product of 
the load and the offset) in the clamp shell by the section modulus of the 
clamp, wherein the moment is equal to the pressure loading per each clamp 
member 12. The section modulus of bending is a conventional calculation 
whereby the shell is considered a beam. 
Allowable tensile stress in the body may be determined with respect to ASME 
codes, Section 8, Division 2 which specifies more specific operating 
criteria. Whatever tensile stress allowable is determined to be 
appropriate with reference to the codes, the sum of the tension and 
bending stress is allowed to be approximately 11/2 times greater. 
Therefore, whatever primary membrane allowable stress for the material is, 
11/2 times that allowable stress can be used for the sum of tension and 
bending stress. These are criteria for bending stress in the bolts and 
bending stress in the body. 
The appropriate ASME codes are the codes currently preferred for 
determining the specified criteria. 
At logic box 118 the stresses and deflections calculated at box 116 are 
checked against ASME standards, and if they do not the wall thickness is 
incrementally increased at box 120 and the computations of boxes 114-118 
repeated. 
Once a clamp which meets the specified minimum requirements is generated by 
boxes 112-120, the weight of the resultant clamp is computed at box 122. 
Logic box 124 is a print key test which is acuated only when a clamp of 
minimum weight is achieved. 
At logic box 126 a further test is undertaken to determine if the weight of 
the clamp generated at the present iteration is less than the clamp 
achieved at the previous iteration. Basically, this test requires that the 
computations be continued until a clamp of minimum weight is achieved. 
At logic box 128 the clamp weight of the present iteration is saved for 
comparison with the clamp achieved at the next iteration. At logic box 130 
the off-set distance is incrementally increased and the next iteration is 
begun. 
Iterations are continued until a clamp is generated which has a greater 
weight than the previous iteration (determined at box 126). When this 
occurs, the logic circuit drops back to the previous iteration which 
generated a clamp of decreased weight and the off-set distance is again 
set at the previous value at logic box 130 (wherein the print key is set 
equal to 1). During this final iteration, the print key test at box 124 is 
actuated and the design data printed at box 132. 
Further modifications and alternative embodiments of the apparatus of this 
invention will be apparent to those skilled in the art in view of this 
disclosure. Accordingly, this description is to be construed as 
illustrative only and is for the purpose of teaching those skilled in the 
art the manner of carrying out the invention. It is to be understood that 
the forms of the invention herewith shown and described are to be taken as 
the presently preferred embodiments. Various changes may be made in the 
shape, size and arrangement of parts. For example, equivalent elements or 
materials may be substituted for those illustrated and described herein, 
parts may be reversed, and certain features of the invention may be 
utilized independently of the use of other features, all this would be 
apparent to one skilled in the art after having the benefit of this 
description of the invention.