Method and apparatus for testing pipes

A method and an apparatus for testing the tightness of a threaded connection between an oilfield pipe and a tapped connector. An annular space along the threaded connection is sealed with a test head, and only the threaded connection is thus subjected to internal hydraulic pressure via this connection.

BACKGROUND OF THE INVENTION 
The present invention relates in general to the testing of pipes, and more 
particularly to method and apparatus for testing tubings and casings used 
in oilfield applications. 
According to API Spec. 5A, Section 5.1, it is required that tubings and 
casings for oilfield applications and having a "power-tightened" threaded 
connecting sleeve of a diameter up to 133/8 inches (=339.7 mm), are 
required to undergo a hydraulic internal pressure test. For this purpose 
the tubings and casings, inclusive of the sleeve, are usually transported 
to a water-pressure testing machine, in which the entire assembly is 
filled with a water/emulsion mixture and pressurized to the required 
pressure level which must be maintained for a period of 5 seconds. 
A problem with this approach is that it is quite elaborate and 
cost-intensive, since a complete water-circulation system must be 
installed. Another problem is that the brief five second time is not 
adequate to determine whether the threaded connection itself is actually 
tight, due to the fact that water dripping off the machine from the 
previously emptied pipe tends to obscure any leakage at the threaded 
joint. Moreover, if leakage does occur at the threaded joint, the quantity 
will be so small as to not cause any perceptible drop in the test 
pressure. Finally, the water-pressure testing machine itself is very 
expensive, especially because it must be connectable to both ends of the 
pipe and since both connecting heads of the machine must be capable of 
withstanding the quite enormous axial thrust of the pressurizing medium. 
Also known in the prior art are methods and installations which make it 
possible to test a completed installation-ready connection of two oilfield 
pipes with external threaded connecting sleeve, either from the exterior 
(the Gather Hauck method) or from the interior at the site (in the 
drilling tower). However, both of these approaches can be used only in 
installation-ready applications. It is not possible to adapt either of 
these methods for use in factory (as opposed to on-site) testing, because 
after the completed test one of the two pipes would have to be unscrewed 
from the connecting sleeve which, as is known, usually results in a 
destruction of (or at least damage to) the threads involved. 
SUMMARY OF THE INVENTION 
It is, accordingly, an object of the invention to overcome the prior art 
disadvantages. 
A more particular object of the invention is to provide an improved method 
and arrangement for testing threaded oilfield-pipe connections for 
tightness at the manufacturer's site of operation. 
Another object is to provide such an improved method and arrangement which 
makes it possible to identify leakage at the threaded joints with simple 
equipment and while having to maintain the pipes pressurized only for a 
brief period of time. 
A comcomitant object is to require as little pressure medium as possible 
and to avoid any damage to the threads involved. 
The invention is based upon the realization that each pipe per se is 
normally thoroughly pressure tested for tightness while its ends are still 
smooth, i.e. before they are formed with threads. All that needs to be 
finally tested, therefore, are the final steps involved; i.e. threading of 
the pipe end, manufacture of the tapped connecting sleeve, mating of the 
connecting sleeve with the threaded pipe end, and checking the threaded 
joint for tightness. Accordingly, the present invention purposes to 
subject only the threaded pipe end and the tapped connecting sleeve to an 
internal pressure test to determine tightness. 
According to a further concept of the invention the volume of pressure 
medium required for this--already substantially reduced by the inventive 
concept--can be reduced still further by utilizing as the pressure chamber 
for the pressure test only an annular space at the pipe end/connecting 
sleeve wall. 
Having resort to the present invention, the entire quantity of pressure 
medium needed to carry out the pressure test on a 133/8 inch (339.7 mm) 
oilfield pipe, amounts to about two liters. This contrasts with the 
conventional water-pressure test of a 14 m long oilfield pipe of the same 
133/8 inch diameter, where 1,270 liters of water/emulsion (i.e. pressure 
medium) are required just to fill the pipe. 
Aside from the tremendous savings in pressure medium which are realized 
with the invention, the small volume of pressure medium needed to fill the 
annular space according to the invention can be introduced and removed so 
rapidly that the times required for this purpose now constitute merely a 
negligible part of the test-procedure time. 
Further, it is advantageous to utilize the test pressure in order to attain 
axial locking (i.e. arresting of the position) of the testing head. The 
locking pressure increases as the testing pressure does. In this manner 
the cylinder needed for advancing of the testing head can be made of 
relatively small dimensions, which reduces its weight and cost. 
Incidentally, this combination (i.e. where the test pressure equals the 
locking pressure) can be used with particular advantage if, according to 
another concept of the invention, oil is used as the pressure medium, 
because this eliminates corrosion danger for the components of the 
installation as well as for the threads at the pipe end and in the 
connecting sleeve. 
As explained above, the quantity of pressure medium needed is very small 
and this brings with it certain advantages which have already been 
mentioned. Another advantage resulting directly from the small quantity of 
pressure medium is the fact that even a slight leakage at a defective 
threaded joint will result in a noticeable drop of the indicated test 
pressure, so that the difference between nominal test pressure 
(drag-indicator needle) and actual pressure is readily visible. 
The arrangement according to the present invention requires only a test 
head which surrounds the threaded joint and thus seals the 
earlier-mentioned annular space. This eliminates the need (and cost) for a 
second test head (counter-pressure head) and the expensive water/emulsion 
supply installation with its requisite low-pressure and high-pressure 
supply systems. 
It is advantageous to seal the annular space against the outer 
circumferential surface of the connecting sleeve, because a seal adjacent 
the end of the sleeve would be structurally much more difficult to 
achieve. Moreover, this outer seal of the sleeve, ahead of the pipe end 
provided with the thread, prevents due to the pressure equilibrium inside 
and outside at the sleeve end that an unintentional expansion of the 
sleeve might take place (with the resulting danger that the screw 
connection could be spread partly open and the leakage indication thereby 
falsified). 
It goes without saying that if oil is used as the pressure medium, the 
seals used must not be subject to attack by the oil. 
The type of seal used permits an absolute sealing of the annular space by 
the fact that increasing spreading of the seal legs occurs with increasing 
test pressure, with simultaneous yielding of the seal legs when the test 
head is pushed onto the pipe end respectively onto the connecting sleeve. 
Still another advantage of the rather small annular pressure space is that 
the reaction forces resulting from the test pressure and the effective 
"piston surface" and acting upon the axial locking and/or the test-head 
advancing cylinder, remains small. This allows the entire aggregate to be 
constructed less massively than would otherwise be required and saves the 
high costs involved in such a more massive construction. 
By construction of the sleeve the oilfield pipe is held in position without 
requiring tension due to frictional pressure on the pipe surface; this 
eliminates the otherwise sometimes unavoidable damage to the pipe surface 
or deformation of the pipe from round to oval cross section. 
It is advantageous if individual defective parts of the test head--or 
indeed the entire test head itself--can be replaced. Replacement of the 
complete test head would be advantageous in e.g. the case of dimension 
changes, i.e. if pipes of different dimensions need to be tested. 
It is also an advantage to mount the test head and the clamping device, so 
as to be height-adjustable in the event a new (and different) pipe 
diameter is to be tested. This is simpler than the heretofore customary 
height adjustment of the pipe support grids, bars or similar elements. 
Circular guides are preferable for the axial shifting of the test head, 
because they are inexpensive to produce and require little maintenance. 
Despite this light-weight inexpensive construction, the necessary rigidity 
is assured. Due to the manner of axial clamping these circular 
guides--given the light-weight overall construction--are able to fulfill 
additional functions, and in addition it is possible to use commercially 
available sleeves. 
The simplest manner of indicating leakage losses through the threaded 
connection is via the manometer which must in any case be present to 
indicate the test pressure. If a pressure indicator is used having a 
drag-pointer, then it is possible to determine at a single glance both the 
initially selected test pressure as well as any possible pressure loss due 
to leakage. 
The invention will hereafter be described with reference to an exemplary 
embodiment as illustrated in the appended drawings. However, this should 
be understood to be for purposes of explanation only and it is not to be 
considered limiting in any sense.

DESCRIPTION OF PREFERRED EMBODIMENTS 
In the embodiment illustrated in FIGS. 1-3 an oilfield pipe 1 to be tested 
is provided at its end portion 2 with threads. A tapped connecting sleeve 
(FIG. 1) has been threaded onto the end portion 2. An axial roller 
conveyor (not shown) is used to transport the pipe 1 and sleeve 3 into the 
hydraulic pipe handling device, until the sleeve 3 has passed in its 
entire length through the region of the illustrated clamping jaws 30. 
Thereupon, clamping cylinders 29 are operated to close the clamping jaws 
30 (which are held by threads 31) so that they engage and centrically hold 
the pipe 1, but do not fixedly clamp the same. The entire hydraulic pipe 
handling device is mounted on a not-illustrated carriage which, once the 
pipe is engaged, is axially retracted until the jaws 30 abut behind the 
sleeve 3. Now, cylinders 28 are operated to move the test head 4 over the 
pipe end portion 2 carrying the sleeve 3. 
Head 4 is centrally mounted via screws 21 on flange 43 in the housing 20. 
The latter, in turn, is axially shiftably mounted via its flanges 42 and 
43 (and guide rings 24) on three guides 27 which are distributed over 
120.degree. on the circumference. Three clamping rings 25 arranged on the 
guides 27 behind the guide rings 24, serve to arrest the head 4 where 
desired. The guides 27 are mounted on a guide plate 39 and on clamping 
cylinders 29. The latter are mounted on a support 32 which is 
height-adjustable together with the guide plate 39 (via lifting spindles 
39 and handwheel 36) relative to the frame 37; the purpose of this measure 
is to be able to adapt the arrangement to work with pipes of different 
diameters. Once a height has been set, the support 32 is arrested via lock 
34 on the plate 33. 
Depending upon the diameter of the oilfield pipes 1 to be tested, 
differently sized testing heads 4 must be used; each such head can, 
however, be used for substantially the entire range of pipe 
wall-thicknesses that are permissible for use with the particular pipe 
diameter. To exchange one head 4 for another it is merely necessary to 
release the screws 21 and the oil connection 16. 
Each test head 4 (shown in more detail in FIG. 2) is composed of an inner 
"mandrel" 5 and an outer ring 23 secured thereon via screws 22. To save 
weight the inner mandrel 5 is hollow; it also has several different 
stepped outer diameters, to assure that the annular space 13 between the 
sleeve 3 (and pipe end portion 2) and the surface of the mandrel 5 is as 
small as possible. This annular space 13 is delimited within the interior 
of the pipe by a U-shaped sealing ring 6 which is pushed onto the mandrel 
5 and is of rubber or synthetic plastic material (for example 
"Vulcolan"/TM). A nut 14 and support rings 8 and 10 fix the sealing ring 6 
against displacement in axial direction. 
The leg 40 of the sealing ring is made flat at the outer side, to have the 
largest possible contact surface relative to the pipe wall so that, when 
pressure builds up in the annular space 13, the leg 40 will lie flat 
against the pipe wall and cannot fold over. 
At the outer side of the sleeve 3 the annular space 13 is similarly 
delimited by a sealing ring 7 (clamped in the outer ring 23 between 
support rings 9, 11 and nut 15) having legs 40 which are constructed as 
described in the preceding paragraph. 
An abutment ring 12 is arranged at the line of separation between the outer 
ring 23 and mandrel 5, directly in front of the sleeve 3; its purpose is 
to serve as an abutment for the stroke of the cylinder 28 and, in 
addition, to reduce the hydraulic pressure acting upon the above-mentioned 
line of separation. Ring 12 has several grooves to assure that the test 
(pressure) medium can freely flow in the space 13 from the outer side of 
the sleeve 3 to the inner side thereof. 
The arrangement of the guide rings 24 (two sets of three rings each) on the 
guides 27 is shown in FIG. 3. Each guide ring is composed of a housing 46 
and a slide sleeve 45 which is guided in the housing 46. Each two guide 
rings 24 on a guide 27 are surrounded by a sleeve 44 which protects them 
against contamination. For purposes of stabilization they are welded to 
the flanges 42, 43 of the guide housing 20. 
Clamping rings 25 are flanged behind the housing 20. A pressure space 48 
exists between the clamping-ring housing 47, the oil connections 49 and 
the sleeve 26. The latter, incidentally, consist of an elastomeric 
material (rubber or synthetic plastic) which has embedded steel lamellae 
as reinforcements. All of the pressure spaces 48 are connected with the 
annular space 13 of test head 4 via oil line 17 and oil connector 16 (FIG. 
1). The oil pressure can be read off the manometer 18 as an absolute value 
as well as a differential value between two pressure conditions. 
The oil circuit can be vented via a venting valve 19 and hose 41. Oil 
issuing from the hose 41 is collected in the oil receptacle 38. The entire 
hydraulic system is supplied by a not-illustrated central hydraulic 
aggregate. 
Once the test head 4 has been moved in position over the sleeve 3, the 
valve 19 is opened and a high-pressure pump of the central hydraulic 
aggregate is switched on. The valve 19 is closed once the oil issues from 
the hose 41 free of air bubbles; the pressure of the test medium is then 
increased to the preselected test pressure (e.g. 500 bar) and the 
high-pressure pump switched off. After the prescribed holding time (e.g. 
five seconds) at constant pressure the valve 19 is opened, so that the oil 
can flow off into the receptacle 38 via hose 41. Thereafter the cylinders 
28 are operated to retract the head 4, the cylinders 29 open the jaws 30 
and the tested pipe 1 (with sleeve 3) can then be axially withdrawn from 
the device via the not-illustrated axial roller conveyor. 
The invention has been described and illustrated with reference to a 
specific embodiment. However, modifications ans variations will offer 
themselves to those skilled in the art and, therefore, should and are 
intended to be encompassed within the scope of the appended claims.