WO1999054126A1

WO1999054126A1 - Bias longitudinal weld

Info

Publication number: WO1999054126A1
Application number: PCT/US1999/008411
Authority: WO
Inventors: Robert E. Stagg
Original assignee: Individual
Current assignee: Individual
Priority date: 1998-04-20
Filing date: 1999-04-16
Publication date: 1999-10-28
Anticipated expiration: 2000-10-20
Also published as: AU3649299A

Abstract

A bias longitudinal weld for forming pipe and tubing from metal skelp (10). An edge plane disposed on each side (30, 35) of metal skelp (10) forms an acute angle with respect to bottom longitudinal surface (25) of the skelp (10) and correspondingly forms an obtuse angle with respect to top longitudinal surface (20) of skelp (10). The opposite edge plane forms an obtuse angle with respect to bottom longitudinal surface (25) of the skelp and correspondingly forms an acute angle with respect to skelp's top longitudinal surface (20). When this skelp (10) is formed into pipe (100), the planar sides (30, 35) form a biased line comprising a longitudinal welded seam (50).

Description

1

BIAS LONGITUDINAL WELD

Background of the Invention This invention relates to manufacturing of tubes and pipe, and more particularly relates to means for manufacturing tubes and pipe using a bias longitudinal weld.

It is well known in the prior art that welds generally have a dual nature — passive and active. The passive nature of a weld, of course, is to permanently bond two metallic members together into a reconfigured joinder. The active or dynamic nature of a weld, on the other hand, is its ability to withstand a diversity of conditions of forces and related pressures. As will be understood by those skilled in the art, most properly executed welds produce a joinder of metals or alloys that has superior tensile strength than either of the welded members. Simultaneously, however, such a joinder typically has an inferior shear strength. Thus, welds typically are stronger than either of the welded members regarding withstanding the effect of longitudinal forces, but are weaker regarding withstanding the effect of perpendicular forces.

It is also well known in the art that welds are generated by a diversity of processes which cause local coalescence of metallic members over a wide range of pressure and temperature conditions. For instance, traditional welds are generated by welding processes including tungsten inert gas ("TIG") welding, prevalent for light-metal gages and for high-precision bonding; metal insert gas ("MIG"); plasma welding; and electric resistance welding (ΕRW). Such welding processes inherently produce a broad heat affected zone ("HAZ") and concomitantly change the microstructure of the welded metals thereby adversely affecting the mechanical properties manifest by the joinder. 2

Laser welding, by contrast, produces a narrower HAZ and concomitantly engenders minimal changes to the joinder's microstructure.

It will be appreciated by those skilled in the art that in all weld processes the portion of the HAZ adjacent the weld per se constitutes a region of weakness which is susceptible to load stresses. For instance, in pressurized pipelines in which loads are applied perpendicularly of pipe walls, shear stresses are imposed upon the HAZ and the weld. In such pipelines or under similar shear stress circumstances, it would be advantageous if such shear stresses could be ameliorated to avoid the likelihood of deterioration and rupture at the welded joints.

There have been many attempts in the art to improve the formation of the joinder of metals or metal alloys via welding processes. For example, in U.S. Patent No. 5,446,257, Sakamoto et al. disclose a method and apparatus for promoting the formation of high quality welds during conventional straight or vertical laser welding of two jointing members using a filler wire which is applied to the locally heated portion of each jointed member. To promote formation of such quality laser welds, the difference between the welding plasma intensities measured from both sides of the locally heated portion is minimized and kept below a predetermined value, by correcting the relative position between the filler wire and the local heat supply.

As another example, in U.S. Patent No. 5,399,834, Guth discloses a method and device for butt welding metal sheets using a laser beam while lateral pressure is applied towards the plane adjoining the flat sheets. As will be appreciated by those skilled in the art, this is an alternative means for conventional strip joining methods such as flash welding and dual bias welding, which is taught by the instant inventor 3 in U.S. Patent No. 5,456,405. Guth teaches that, for effectively joining by butt welding at least two metal sheets of different thicknesses, wherein the mechanical strength of the joinder is optimized, the shape of the joint is improved if a laser beam forms an acute angle in a prescribed degree-range with respect to a vertical axis passing through the focal point of the laser beam. Similarly, U.S. Patent No. 5,456,405 teaches a technique of butt welding metal strips by forming a bias seam at the joinder.

There have also been attempts in the art, recognizing the susceptibility to fracture of welds due to HAZ and the like, to reinforce the joinder. For example, Findlan et al. disclose, in U.S. Patent No. 5,430,270, a laser beam method and apparatus for repairing the internal surface of a damaged tube. By add ng filler metal to build up the internal surface where a focused laser beam contacts this surface, a smooth clad welding repair may be achieved that restores the original strength of the tube and also creates no crevices for future corrosion attack.

While, as hereinbefore exemplified, practitioners in the art have attempted to improve the means for producing welded joints, there has been less effort expended to inherently produce a stronger joint — subjected to both tensile and shear stresses — that minimizes HAZ and other disadvantageous characteristics. In U.S. Patent No. 5, 191,911, Dubois teaches a method for making seam-welded tubing from shorter lengths of flat metal strip which are spliced end-to-end and formed into a tubular configuration, and then seam-welded. Adjoining ends of two successive lengths of the strip are trimmed at supplementary angles and then abutted and welded. Similarly, Dubois, in U.S. Patent No. 4,863,091, teaches a method and apparatus for producing continuous lengths of coilable tubing from shorter 4 lengths of flat metal strip.

These improvements in the art address welding means and methods for joining metal strips, but not means for enabling the closure of metal skelp longitudinally into pipes, tubes and the like. Accordingly, these limitations and disadvantages of the prior art are overcome with the present invention, and improved means and techniques are provided which are useful for forming bias longitudinal welds from metal skelp to form pipe and the like.

Summary of the Invention

The present invention provides an improved weld for joining edges of metallic sheets or skelp to be formed into tube, pipe, and the like. More particularly, the present invention provides a bias longitudinal weld that enables joining edges of metal skelp in a manner heretofore unknown in the art.

As will be described in detail, it is a feature and advantage of the preferred embodiment that the weld bias structure disclosed inherently removes the HAZ weld region from shear stresses, thereby minimizing any mechanical property differences between the welded joint and the member metals comprising the pipe or tube walls. Thus, the present invention teaches a weld with performance that effectively approaches the performance of seamless pipes and tubes.

In accordance with the present invention, a longitudinal bias weld is disclosed that enables closure of metal skelp to form essentially seamless pipes, tubes, and the like having surprisingly enhanced capacity to withstand both tensile and shear stress at the joints. An edge plane disposed on each side of metal skelp forms acute angle with respect to bottom longitudinal surface of the sheet and correspondingly forms an obtuse angle with respect to top longitudinal surface of the 5 skelp. The opposite edge plane forms an obtuse angle with respect to bottom longitudinal surface of the skelp and correspondingly forms an acute angle with respect to top longitudinal surface. When this skelp is formed into pipe and the like, the planar sides form a biased line comprising a longitudinal welded seam.

It is an object of the present invention to provide a means for manufacturing tubes and pipe that inherently reduces inseam stresses.

It is also an object of the present invention to provide a means for manufacturing tubes and pipe that are flash- abated or at least flash- minimized regardless of size considerations.

It is a further object of the present invention to provide a means for manufacturing tubes and pipe that requires no flash removal process steps supplemental to the basic steps commonly occurring during tube and pipe formation.

It is also an object and feature of the present invention that a means is provided that enables tubes and pipe to be manufactured with no or minimal coolant contained in the finished tube and pipe product. It is another object of the present invention to provide a means for manufacturing tubes and pipe that engenders minimal spume contained in the finished tube and pipe product.

It is still another object of the present invention to provide a means for manufacturing tubes and pipe that negates the need for use of an D. scarfing tool and thereby reduces set-up time.

It is an object of the present invention to provide a means for manufacturing tubes and pipe that inherently reduces the generation of scrap.

It is another object of the present invention to provide a means 6 for manufacturing tubes and pipe with a greater life expectancy than heretofore known in the art.

It is yet another object of the present invention to provide a means for manufacturing tubes and pipe that reduces re-inspection and prove-up costs attributable to open seam or scarfing.

It is still another object of the present invention to provide a means for manufacturing tubes and pipe that maximizes throughput.

It is yet another object of the present invention to provide a means for manufacturing tubes and pipe that produces the equivalent of seamless tubes and pipes.

It is a specific object of the present invention to provide a bias longitudinal weld for forming pipe from a continuous coil of flat metal skelp having: a longitudinal axis, a first longitudinal planar surface, a second longitudinal planar surface disposed oppositely of and parallel to said first longitudinal planar surface, a first edge planar surface disposed between said first planar surface and said second planar surface, and a second edge planar surface disposed between said first planar surface and said second planar surface, and disposed oppositely of and parallel to said first end planar surface, said bias longitudinal weld comprising: a first angle formed by said first edge planar surface and said second longitudinal planar surface; a second angle formed by said first edge planar surface and said first longitudinal planar surface, a third angle formed by said second edge planar surface and said second longitudinal planar surface; a fourth angle formed by said second edge planar surface and said first longitudinal planar surface, a permanent joinder of said first edge planar surface and said second edge planar surface when said first edge planar surface and said second edge planar surface are disposed in an abutment relationship.

It is another specific object of the present invention to provide a bias longitudinal weld for forming pipe from a continuous coil of flat metal skelp having: a longitudinal axis, a first longitudinal planar surface, a second longitudinal planar surface disposed oppositely of and parallel to 7 said first longitudinal planar surface, a first edge planar surface disposed between said first planar surface and said second planar surface, and a second edge planar surface disposed between said first planar surface and said second planar surface, and disposed oppositely of and parallel to said first end planar surface, said bias longitudinal weld comprising: a first acute angle formed by said first edge planar surface and said second longitudinal planar surface; a first obtuse angle formed by said first edge planar surface and said first longitudinal planar surface, a second acute angle formed by said second edge planar surface and said second longitudinal planar surface; a second obtuse angle formed by said second edge planar surface and said first longitudinal planar surface, a permanent joinder of said first edge planar surface and said second edge planar surface when said first edge planar surface and said second edge planar surface are disposed in an abutment relationship. These and other objects and features of the present invention will become apparent from the following detailed description, wherein reference is made to the figures in the accompanying drawings.

In the Drawings FIG. 1 depicts a frontal perspective view of a flat metal coil or skelp prior to being formed into welded tubing known in the prior art. FIG. 2 depicts a frontal perspective view of a flat metal coil or skelp prior to being formed into welded tubing embodying the present invention. FIG. 3 depicts a cross sectional frontal view of a portion of the metal skelp depicted in FIG. 1.

FIG. 4 depicts a cross sectional frontal view of a portion of the metal skelp depicted in FIG. 2.

FIG. 5 depicts a frontal perspective view of the formation of a longitudinally welded tubing constructed from the metal skelp depicted 8 in FIGS. 1 and 3, prior to seam -welding as known in the art,.

FIG. 6 depicts a frontal perspective view of the formation of a bias longitudinally welded tubing constructed from the metal skelp depicted in FIGS. 2 and 4, prior to seam-welding embodying the present invention.

FIG. 7 depicts a cross sectional end view of the metal pipe formed as depicted in FIG. 5.

FIG. 8 depicts a cross sectional end view of the metal pipe depicted in FIG. 6. FIG. 9 depicts a simplified schematic of a pipe formed with a conventional weld subjected to shear stresses.

FIG. 10 depicts a simplified schematic of a pipe formed with a bias longitudinal weld taught by the present invention, subjected to shear stresses. FIG. 11 depicts a simplified schematic of a pipe formed with a conventional weld subjected to x-ray inspection.

FIG. 12 depicts a simplified schematic of a pipe formed with a bias longitudinal weld taught by the present invention, subjected to x- ray inspection. FIG. 13 depicts a simplified schematic of a pipe formed with a conventional weld subjected to ultrasonic inspection.

FIG. 14 depicts a simplified schematic of a pipe formed with a bias longitudinal weld taught by the present invention, subjected to ultrasonic inspection.

Detailed Description Now referring to FIGS. 1- 8, there is depicted, on a comparative basis, the conventional weld well known in the art and the bias longitudinal weld taught by the present invention. Specifically 9 referring to FIGS. 1, 3, 5, and 7, there are depicted frontal perspective, cross- sectional, and frontal views of formation of conventional weld 6 formed from metal skelp 10. As clearly shown, weld 6 known in the prior art is constructed normally as edge 3 is adjoined with edge 5 of skelp 10 to form pipe 100.

Referring now specifically to FIGS. 2, 4, 6, and 8, there are depicted frontal perspective, cross- sectional, and frontal views of formation of a preferred embodiment of bias longitudinal weld 50 constructed from coiled flat metal skelp 10 as contemplated by the present invention. More particularly, FIG. 6 depicts a frontal perspective view of a flat portion of metal skelp 10 to be formed into pipe 100 with bias longitudinal weld 50. This portion of metal sheet 10 comprises top planar surface 20, longitudinal edge planar surfaces 30 and 35, respectively, and transverse or end planar surfaces 40 and 45 (not shown), respectively. Also shown is top and bottom planar surfaces 20 and 25, respectively, and longitudinal edges 30 and 35. Pipe 100 comprises interior surface 110 and exterior surface 105 formed by bias longitudinal weld 50 joining edges 30 and 35 hereinbefore described. As will be appreciated by those skilled in the art, pipe 100 is formed by the joinder of planar edges 30 and 35. Planar surface 30 of a side of metal skelp 10 is defined by line LI disposed along top longitudinal surface 20 being offset to line L2 disposed along bottom longitudinal surface 25. Edge plane 30 forms acute angle α with respect to bottom longitudinal surface 25 and correspondingly forms obtuse angle β with respect to top longitudinal surface 20. Similarly, planar surface 35 of opposite side of metal skelp 10 is defined by line L3 disposed along top longitudinal surface 20 being offset to line L4 disposed along bottom longitudinal surface 25. Edge plane 35 forms 10 obtuse angle β with respect to bottom longitudinal surface 25 and correspondingly forms acute angle α with respect to top longitudinal surface 20.

According to the present invention, when metal skelp 10 is formed into pipe 100 and the like, planar sides 20 and 25 form a biased line comprising longitudinal welded seam 50. It should be evident that angles α and β are supplementary to each other. It should be appreciated by those skilled in the art that the weld taught by the present invention inherently assures that maximum weld is emplaced along the longitudinal joinder thereby establishing a stronger joinder than has been heretofore known in the art.

It should be evident to those skilled in the art, that as shown in FIG. 3, conventional welds are formed by a perpendicular relationship between edge plane 30 and bottom longitudinal surface 25 and correspondingly forms a like perpendicular relationship with respect to top longitudinal surface 20. Thus, a weld heretofore known in the art suffers from being disposed perpendicularly with respect to the joinder of proximal edge plane segments 30 and 35.

Referring now to FIGS. 9 and 10, there is depicted how the preferred embodiment of the present invention tends to mitigate the adverse characteristics of the heat affected zone (HAZ) that is a routine by-product of the welding process. In particular, FIG. 9 depicts the HAZ associated with conventional weld 6 wherein the HAZ is disposed symmetrically and circumferentially on each side of weld 6. It is well known in the art that pressurized pipelines and the like are susceptible to damage when subjected to shear stresses in the proximity of the HAZ and implicated weld. FIG. 10 depicts how the bias longitudinal weld taught by the present invention tends to ameliorate the resistance to shear stresses at the juncture of the HAZ and the weld. Since weld 11

50 is inherently disposed on a bias, the HAZ is protected from the influence of shear stresses. That is, since shear stresses are engendered in pressurized pipelines and the like by load thrust perpendicularly against the walls of the pipe, such stresses are minimized because the force is not perpendicular to either weld 50 or the HAZ, and is uniformly distributed across both the weld and the HAZ. The reduction in shear stress effectuated by the weld of the present invention may be seen by considering the basic formula for stress, i.e., pressure:

Force Stress = (1)

Area

Thus, referring to FIGS. 7 and 8, if the area manifest by conventional weld 6 (FIG. 7) is taken to be 1.0 for convenience, then the corresponding area manifest by bias longitudinal weld 50 (FIG. 8) will be comparatively larger depending upon the acute angle α. If, for example, angle α is taken to be 45 ° , then the comparative area for weld 50 would be 1.414, i.e., \/2. The reduction in stress would be represented by the formula:

F Pl - P2 = F - —— = 0.2927 (2)

1.414

which is approximately 30%. As another convenient example, if angle α is taken to be 30°, then the comparative area for weld 50 would be

1.155. The reduction in stress would be represented by the formula:

F PI- P2 = F- —- = 13.14% (3)

which is 50%. As yet another convenient example, if angle α is taken to be 60°, then the comparative area for weld 50 would be 2.0. The reduction in stress would be represented by the formula: 12

F

P\ - P2 = F = 50% (4) 2.0

which is approximately 60%. The shear stress reduction may be tabulated as follows:

Acute Angle Conventional Bias Longitudinal Shear Stress α Weld Area Weld Area Reduction

45 1.0 1.414 30%

30 1.0 1.155 13%

60 1.0 2.0 50%

It will be evident that the greater acute angle α, the more elongated the

resultant weld will be.

It will be appreciated by those skilled in the art that it is a feature

and advantage of the present invention that the properties of the weld

seam produced are virtually the same as the properties of the

remainder of the non-joined pipe. Accordingly, the bias longitudinal

weld of the present invention emulates seamless pipes and the like in

a manner heretofore unknown in the art.

It is another advantage and feature of the present invention that

the entire profile of the pipe weld may be viewed using conventional

inspection techniques such as x-ray and ultrasonic testing. Now

referring to FIGS. 11 and 12, the improvement in x-ray inspection is

depicted on a comparative basis. Specifically referring to FIG. 11, as

will be appreciated by those skilled in the art, since x-rays are typically 13 applied perpendicularly, i.e., vertically, to the pipe wall, only the outer

edge of a conventional circumferential weld may be scanned.

Accordingly, it will be appreciated that radiography can only see the

top edge of a vertical weld. As clearly shown in FIG. 12, however, since

the weld taught by the present invention engenders a bias longitudinal

seam as hereinbefore described, a vertical x-ray scan exposes the

entire profile across the bias.

Similarly, FIGS. 13 and 14, schematically comparatively depict

another advantage and feature of the present invention, wherein

conventional ultrasonic inspection is also rendered more thorough.

Specifically referring to FIG. 13, as is known to those skilled in the art,

since ultrasonic signals are typically applied 45° to the pipe wall, only

a limited portion of a conventional circumferential weld may be

inspected. As clearly shown in FIG. 14, however, since the weld taught

by the present invention engenders a bias longitudinal seam, the

ultrasonic signal tests the integrity of the entire profile across the bias.

Indeed, for a bias longitudinal seam having an acute angle of 45°, such

ultrasonic testing would perpendicularly penetrate the weld. In

addition, pipe welds formed using laser welding processes are

inherently more controllable and finite so that non-destructive testing

such as magnetic eddy current testers could be finely tuned to a

higher standard of inspection. 14

It will be appreciated that the preferred angle α for biasing the

longitudinal seam taught by the present invention depends upon wall

thickness, tube diameter, and intended goal for stress reduction. Wall

thickness, of course, is generally the most critical factor. A thicker

tube wall requires a longer weld which would, in turn, require higher

energy input. Currently, lasers have the ability to weld up to V2 inch

metal (with a 25 KW energy source), which would cover most of the

commodity- sized diameter pipes and the like up to 36 -48 inches in

diameter. Nevertheless, as will be understood by those skilled in the

art, it is currently possible to weld a 1 inch wall by using two welders,

i.e., one welder inside and one welder outside, that are applied along

the same line of fusion. Accordingly, it is contemplated that the

present invention would encompass virtually every pipe, tube, and the

like that is currently being manufactured.

It will be understood that since smaller acute angles α will tend

to be directed toward the pipe wall, it is important that the bias

longitudinal weld of the present invention be passed from the outside

to the inside of the resultant pipe to achieve the thorough joinder

contemplated by the present invention. On small diameter pipe, a

small angle α would pass through the wall and not into the inside

diameter. Therefore, an angle α of 45° would probably be the preferred

angle for producing production quantities and simultaneously 15 attaining economic optimization of energy required, traditional edge

machining techniques, and stress reduction.

As will be evident to those skilled in the art, manufacturing

techniques for production of tubes and pipes from roll forms are well

known. Tube mill equipment and roll manufacturers typically have

proprietary designs. While such manufacturers focus on specific

d fferences of sub-component designs, roll form pipe and tube

manufacture is essentially fraught with conventionally- accepted

practices and procedures.

In order to form the biased seam under the present invention by

conventional techniques such as weld fusion and other popular

processes, certain modifications are preferable. For example, to form

a bias longitudinal weld via weld fusion, the edge of the input metal

skelp or sheet should be finished to the combination of acute and

obtuse angles. It will be appreciated that, while such edge-fufishing

may be achieved by offset positioning via traditional slitting, shearing,

or metal-processing mills, edge-finishing contemplated by the present

invention should be preferably be performed via milling or like

machining operations. As is well known in the pipe manufacturing art,

such edge-finishing, of course, should be performed in-line to minimize

the possibility of adversely affecting the precise fit of the pair of

longitudinal skelp edges as hereinbefore described. 16

Traditional roll-form tube mills and the like cold-form the skelp

through a series of mill stands. This series of rolls have full contact

with the outside of the forming- tube and the associated edges to be

fused together. It will be appreciated that, ideally, these edges should

be receiving a slight upset to their shape in the fin pass area so that

parallelism of both edges may be assured as the edges enter the weld

box. It will be appreciated that each of these mill stands imparts a

reforming shape or profile to the metal sheet passing therethrough.

The resultant profile is determined by the combination or cumulation

of this series of individual profiles. The fin-pass rolls guide and,

occasionally, assistance form the edges to a common mating fusion

plane. Thus, it would be advantageous for this series of rolls to be

configured to assure this the mating line is effectuated on a bias.

These fin rolls prevent the forming-tube from rotating or slipping,

thereby maintaining control of mating planes being fused together.

The commonly used weld box is a rollered containment point,

wherein two edges of metal skelp are brought together. In a typical

high frequency induction process or electric resistance process, there

is usually an excess width generated. Thus, the resulting longitudinal

seam produced by weld fusion is formed by forcing the heated edges

together in the weld roller box. This, in turn, causes excess welded

material, commonly referred to as "O.D. weld flash" and "LD. weld 17 flash," to be forced both outwardly and inwardly of the pipe wall. As

will be appreciated by those skilled in the art, such flash is typically

removed by using suitable O.D. and LD. scarfing tools while the O.D.

and LD. weld flash is still hot. Accordingly, pipe contemplated by the

present invention is produced having the intended shape and having

uniform thickness. It should be evident that the weld box roll should

preferably be configured to assure that the mating plane is on a bias.

In common high frequency induction and electric resistance

processing mills, the roll stands, fin-passes, and weld boxes contain

and guide the two edges to a mating plane. If laser weld applications

were used to manufacture pipe and the like, a tracking or guidance

system would be preferable to precisely locate the energy beam along

this mating plane, thereby compensating for any minor movements

deviating from the prescribed pipe profile. Once the bias longitudinal

weld of the present invention is formed, the newly produced, post-

scarfed pipe may be passed through a re-heat process ("seam-

annealing'') to relieve stress existing at the weld seam. Such post weld

seam-annealing is, of course, not always performed; it's application

depends from the intended use of the pipe and the like.

As will be understood by those knowledgeable in the art, if the

bias longitudinal weld of the present invention is formed via a laser

welding process, then the HAZ is substantially narrower than for 18 fusion welding and the like. Accordingly, it would be advantageous to

limit this seam -annealing to the HAZ so that the grain structure of the

underlying metal is not affected, thereby assuring the integrity of the

metal's innate mechanical properties. Inclined mills should preferably

be used to prevent mill coolant, commonly used to reduce heat

attributable to friction on roll former machines, from being carried

downstream inside of the produced pipe. Using such inclined mills

also prevents tramp byproducts, e.g., mill scale, grease, and oil, from

contaminating or enhancing pipe deterioration due to corrosion and

pitting, not to mention preventing coolant waste. Such tramp

byproducts are, of course, prevalent in most steel processing

operations.

It will be understood by those skilled in the art that, if welds

taught by the present invention were produced by a laser welding

process, it is possible to minimize the resultant O.D. and LD. weld

flash. Indeed, according to the teachings of the present invention, the

existence of weld flash may be so attenuated that it even becomes

possible to completely eliminate the manufacturing step of removing

weld flash — especially LD. weld flash. As will be appreciated by those

skilled in the art, removing LD. flash, particularly on high frequency

induction and electric resistance processing mills, is difficult for

smaller diameter profiled tube and the like. The core impedance 19 structure of tooling limits the internal space required for such removal.

As is well known in the art, a conventional cylindrical impeder

constructed of ferrite is disposed concentrically within the forming-

tube and is disposed in a specific distance relationship relative to the

outside weld coil which does not contact the outside of the forming-

tube. The magnetic field created by the high frequency weld coiled is

repelled by the ferrite impeder core and thereby induces electricity to

flow and concentrate on the VEE area just prior to the weld tolls step.

LD. flash removal tools, attached to the impeder and positioned

immediately downstream of the joining weld box, use a tungsten

carbide insert member that scrapes off the internal flash. Since an

impeder is water-cooled, the components prerequisite for inducing the

heat required for weld fusion are proportionately smaller in large

tubing and tend to consume more space as the tubing diameter

decreases. It will be apparent to those skilled in the art, that there is

insufficient space within small diameter tubing to provide a substantial

flash removal tool. Accordingly, if flash must be removed, it is

performed as a secondary machining process on short lengths of pipe,

i.e., lengths of pipe on the order of 20 feet or less. Thus, tubing

products such as conduit and seamless extruded pipe are typically

manufactured in short lengths.

Other variations and modifications will, of course, become 20 apparent from a consideration of the structures and techniques

hereinbefore described and depicted. Accordingly, it should be clearly

understood that the present invention is not intended to be limited by

the particular features and structures hereinbefore described and

depicted in the accompanying drawings, but that the concept of the

present invention is to measured by the scope of the appended claims

herein.

What is claimed is:

Claims

21 1. A bias longitudinal weld for forming pipe from a continuous coil of flat metal skelp having: a longitudinal axis, a first longitudinal planar surface, a second longitudinal planar surface disposed oppositely of and

parallel to said first longitudinal planar surface, a first edge planar surface disposed between said first planar surface and said second planar surface, and a second edge planar surface disposed between said first planar surface and said second planar surface, and disposed oppositely of and parallel to said first end planar surface, said bias longitudinal weld comprising: a first angle formed by said first edge planar surface and said

second longitudinal planar surface; a second angle formed by said first edge planar surface and said first longitudinal planar surface, a third angle formed by said second edge planar surface and said second longitudinal planar surface; a fourth angle formed by said second edge planar surface and said

first longitudinal planar surface, a permanent joinder of said first edge planar surface and said

second edge planar surface when said first edge planar surface and said second edge planar surface are disposed in an abutment relationship.

2. The weld recited in Claim 1 wherein said first angle and said third 22 angle are disposed in a congruent relationship.

3. The weld recited in Claim 1 wherein said second angle and said fourth angle are disposed in a congruent relationship.

4. The weld recited in Claim 1 wherein said first angle and said second angle are disposed in a supplementary relationship.

5. The weld recited in Claim 1 wherein said third angle and said fourth angle are disposed in a supplementary relationship.

6. The weld recited in Claim 1 wherein said first angle is an acute angle.

7. The weld recited in Claim 1 wherein said second angle is an obtuse angle.

8. The weld recited in Claim 1 wherein said third angle is an acute angle.

9. The weld recited in Claim 1 wherein said fourth angle is an obtuse angle.

10. A bias longitudinal weld for forming pipe from a continuous coil of flat metal skelp having:

a longitudinal axis, a first longitudinal planar surface, a second longitudinal planar surface disposed oppositely of and parallel to said first longitudinal planar surface, a first edge planar surface disposed between said first planar

surface and said second planar surface, and

a second edge planar surface disposed between said first planar surface and said second planar surface, and disposed oppositely of and parallel to said first end planar surface, 23 said bias longitudinal weld comprising: a first acute angle formed by said first edge planar surface and said second longitudinal planar surface; a first obtuse angle formed by said first edge planar surface and said first longitudinal planar surface, a second acute angle formed by said second edge planar surface and said second longitudinal planar surface; a second obtuse angle formed by said second edge planar surface and said first longitudinal planar surface, a permanent joinder of said first edge planar surface and said second edge planar surface when said first edge planar surface and said second edge planar surface are disposed in an abutment relationship.

11. The weld recited in Claim 10 wherein said first acute angle and said second acute angle are disposed in a congruent relationship.

12. The weld recited in Claim 10 wherein said first obtuse angle and said second obtuse angle are disposed in a congruent relationship.

13. The weld recited in Claim 10 wherein said first acute angle and said first obtuse angle are disposed in a supplementary relationship.

14. The weld recited in Claim 10 wherein said second acute angle and said second obtuse angle are disposed in a supplementary relationship.