Method for eliminating of longitudinal upset seams

In accordance with the invention, immediately after the completion of the upsetting process using an upset tool to form a pipe end of increased wall thickness, the upset half shells which have been pressed together are opened and the supporting mandrel is withdrawn. After the lifting of the pipe end out of the tool, the longitudinal upset seams formed during the upset operation are rotated through a predetermined angle in a plane to which the axis of the pipe is perpendicular and out of the parting plane of the upset half shells. The pipe end is again pressed into the working plane while maintaining its previous axial position to the tool. After the reintroduction of the supporting mandrel, the pipe end is additionally pressed radially to substantially eliminate the longitudinal upset seams.

FIELD OF THE INVENTION 
The present invention relates to a method of eliminating longitudinal upset 
seams which are formed when pipe ends are subjected to wall thickness 
enlargement by the application of axial pressure from an axially pressing 
support mandrel having an abutment collar and by the application of radial 
pressure from a pair of upset half shells. 
BACKGROUND OF THE INVENTION 
In the manufacture of pipes which are to be threaded to each other, for the 
petroleum and natural gas industry, it is necessary to increase the wall 
thickness in the end region depending on the stress in the field of use 
and the type of thread cut. This is done in known fashion in the manner 
that a given length at the end of the pipe is hot upset in an upset 
machine and its wall thickness thereby increased. In this process, 
longitudinal upset seams are formed in the upset region on the outside of 
the end of the pipe since tie rods which press the two upset half shells 
to each other are elastically stretched during the upsetting and material 
flows into the gap produced thereby between the two upset half shells. As 
a result of this flow, and furthermore with an increasing number of 
upsets, the edges of the upset half shells also gradually become worn 
within a given region, so that the gap becomes larger and larger. The 
longitudinal upset seams disturb the subsequent working to precise 
dimensions on a lathe since the undisturbed flow of chips is prevented at 
this place and the impact-like loading leads to increased wear of the tool 
and the mounting of the tool holder is also impaired. Even if the loading 
of the machine tool is tolerated, these seams are nevertheless disturbing 
since they lead to a radial offset of the pipe end to be machined within 
the chuck of the lathe. 
Up to now, as is known, the longitudinal upset seams which are formed have 
been eliminated by grinding. This manual cleaning of the hot-upset pipe 
ends is cost-intensive as a result of the expense for personnel, and the 
quality of the surface obtained is dependent also on the subjective 
judgment of the operator. For highly stressed pipe connections, manual 
grinding also constitutes a danger since, depending on the quality of the 
manual grinding work, injurious notches can be formed which may lead to 
failure of the thread connection. 
An object of the present invention is to provide a method which can be 
integrated into the manufacturing process and by which it is possible, in 
a cost-favorable manner, to eliminate the longitudinal upset seams formed 
upon the hot upsetting of pipe ends so that, with the better surface, the 
subsequent precision machining can be increased in quality and output and 
the permanence of highly stressed pipe connections is not reduced. 
SUMMARY OF THE INVENTION 
The invention provides a method for eliminating longitudinal upset seams 
which are formed when pipe ends are subjected to wall thickness 
enlargement by the application of axial pressure from an axially pressing 
support mandrel having an abutment collar and by the application of radial 
pressure from a pair of upset half shells. In accordance with the 
invention, immediately after the completion of the upsetting process using 
an upset tool, the upset half shells which have been pressed together are 
opened and the supporting mandrel is withdrawn. After the lifting of the 
pipe end out of the tool, the longitudinal upset seams formed during the 
upset operation are rotated through a predetermined angle, for example in 
a plane to which the axis of the pipe is perpendicular, and out of the 
parting plane of the upset half shells. The pipe end is again pressed into 
the working plane while maintaining its previous axial position to the 
tool. After the reintroduction of the supporting mandrel, the pipe end is 
additionally pressed radially to substantially eliminate the longitudinal 
upset seams.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT 
An upset machine for increasing the wall thickness of a pipe end generally 
includes (a) an induction coil, or some other type of heating element for 
heating the pipe end prior to working; (b) a support mandrel having an 
abutment collar for preventing unwanted distortion of the inner dimensions 
of the pipe end and for axially pressing the pipe end to cause an increase 
in the wall thickness thereof; and (c) a tool comprising a pair of upset 
half shells for radially pressing the pipe end into a predetermined 
configuration. Such upset machines, being well-known in the art, will not 
be further described. 
As noted above, when the upset half shells are pressed together a 
longitudinal upset seam is formed in the gap between them. In accordance 
with the invention such longitudinal upset seams are wholly eliminated or 
at the very least substantially eliminated in the manner described below. 
As used herein, the phrase "radial pressing" means the application of 
radial pressure using the upset half shells without applying axial 
pressure from the abutment collar of the support mandrel. 
As used herein, the phrase "upset pressing" means the application of axial 
pressure using the support mandrel with abutment collar in addition to 
applying radial pressure using the upset half shells. 
As shown in FIG. 1, when a prior art split tool is used to upset pipe ends, 
a sharp-tipped longitudinal upset seam is formed between the two halves of 
the upset tool as they come together during operation. In accordance with 
the present invention, the type of sharp-tipped seam illustrated in FIG. 1 
is to be avoided. 
As shown in FIG. 2, when the claimed methods are used, a lens-shaped or 
lenticular, i.e., relatively flat, longitudinal upset seam is formed which 
minimizes the need for subsequent machining of the pipe end following the 
upset operation. 
In the method of the invention, the longitudinal upset seams formed are 
eliminated immediately after the completion of the upset process in the 
form of a further manufacturing step under the same heat. For this 
purpose, after the upset half shells have been opened and the support 
mandrel withdrawn and the pipe end lifted out of the tool, the pipe is 
turned through a predetermined angle and then let down again into the 
working region. The upset seams then no longer lie in the original parting 
plane of the upset half shells but are displaced by said predetermined 
angle in the corresponding upset half shell. As an alternative to the 
turning of the pipe, it is also possible to turn the tool set. This, 
however, means a substantial expenditure in the construction of the upset 
machines and the machines already in existence would have to be refitted 
for this. After the closing of the upset half shells again, the protruding 
or bulge seam material is forced away radially, the support mandrel, which 
has been introduced, preventing ovalization of the inside diameter of the 
pipe end. It is important in this connection that the seams formed upon 
the upsetting process be so developed in their cross-sectional geometry 
that the forcing away is favored and no puckering can be produced. This is 
most easily achieved if the upset seam formed is developed in lenticular 
shape of only slight radial extent and with rounded transitions into the 
surrounding region. Furthermore puckering can also be avoided if the 
rotation of the pipe is effected within a region of around 90.degree. so 
that the apex region of the upset half shell presses, insofar as possible, 
symmetrically on the upset seam and, in the ideal case, the material flows 
away uniformly on both sides. In order to save expense, subsequent heating 
of the upset region of the pipe end is not provided for; rather the 
residual heat still remaining from the upset process is utilized for the 
elimination of the upset seams. 
Depending on the type of machine, two procedures are possible. In the case 
of an upset machine having only one set of tools and a hydraulically 
translatable support mandrel, the subsequent pressing is preferably 
effected in the same tool set, the support mandrel not being introduced 
entirely all the way so as to avoid even a slight axial initial upset in 
each case. It is important in connection with the turning of the pipe that 
the axial position of the end of the pipe with respect to the tool be 
retained since otherwise the contour which has already been initially 
upset is impaired. The introduction of the support mandrel is also 
preferable so that upon the subsequent pressing the inner contour is 
retained and the cross-section cannot be ovalized. 
In an upset machine with two tool sets, the subsequent pressing is 
preferably carried out in the second tool set which lies parallel thereto, 
in which connection one then has the possibility of modifying the inner 
contour of the upset half shells for an easier forcing away of the seams. 
Furthermore, in the case of such a combination, one can use a support 
mandrel without upset collar, so that the limiting of the introduction for 
the support mandrel is unimportant. 
The method proposed can, in the case of multiple upsettings, be carried out 
after each upset process in order to obtain the smoothest possible surface 
in the region of the pipe end and, in any event however, after the last 
upset process. The advantage of the method in accordance with the 
invention is that manual cleaning can be dispensed with. Another advantage 
of the method is that the existing upset machines can be used without 
change, and the required reconversion in the feed region is structurally 
simple and inexpensive. 
In the case of single-step and multi-step upset machines, the subsequent 
pressing does not mean any loss in cycle time since sufficient time 
remains for the cooling, cleaning and lubricating of the tool set for the 
radial subsequent pressing. In this connection it is to be born in mind 
that the actual cycle time for the hot upsetting of two pipe ends is not 
determined by the upsetting and the subsequent treatment of the tool set 
but by the heating of the pipe ends in the induction coils which are 
arranged in front. 
The problem of gradual wear of the edge of the upset half shells which has 
already been mentioned is unimportant in the method of the present 
invention since the geometry of the seams produced thereby accommodates 
the forcing away of the material with the greatest possible elimination of 
puckering. The size of the amount of material to be pressed away is of 
minor importance in the method of the invention, while upon manual 
grinding the time expended increases in direct proportion to the increase 
in volume of the seam. 
Thus in a more preferred embodiment of the invention, the inner contour, 
the supporting cross-section and the elasticity behavior of the tool are 
selected, as will be within the ability of persons skilled in the art, so 
that the upset seam formed is lenticular in shape, of only slight radial 
extent and with a rounded transition into the surrounding region of the 
pipe end. 
It should be understood that the preferred embodiments described are for 
illustrative purposes only and are not to be construed as limiting the 
scope of the present invention which is properly delineated only in the 
appended claims.