CA2883766A1 - Methods of building a pipe wall - Google Patents

Abstract

Methods of building up metal articles, such as pipes, by deposition of weld metal. The metal article or pipe may be made of stainless steel, such as non-magnetic stainless steel. Non-magnetic alloy may also be used as the metal article. A method of pipe build up includes: rotating a pipe about a pipe axis relative to a welding tip directed towards an external wall of the pipe; depositing weld metal circumferentially about the external wall using the welding tip; supplying coolant to an internal wall of the pipe; and in which the pipe comprises one or both a non-magnetic stainless steel alloy containing nickel, or a non-magnetic steel alloy containing nickel and magnesium.

Description

METHODS OF BUILDING UP A PIPE WALL
TECHNICAL FIELD
[0001] Disclosed are methods and apparatuses for building up a pipe wall.
BACKGROUND

[0002] Welding is used to build up and repair used valves and directional drilling tools made of carbon steel, which is magnetic. Build-up is also carried out on new and used tools made of non-magnetic material.
SUMMARY

[0003] Methods of building up metal articles, such as pipes, by deposition of weld metal. The metal article may be made of stainless steel, such as non-magnetic stainless steel.
Non-magnetic alloy metals may also be used.

[0004] A method of pipe build up comprising: rotating a pipe about a pipe axis relative to a welding tip directed towards an external wall of the pipe;
depositing weld metal circumferentially about the external wall using the welding tip; supplying coolant to an internal wall of the pipe; and in which the pipe comprises one or both a non-magnetic stainless steel alloy containing nickel, or a non-magnetic steel alloy containing nickel and magnesium.

[0005] Another method of pipe build up comprising: rotating a pipe about a pipe axis relative to a welding tip directed towards an external wall of the pipe;
depositing weld metal circumferentially about the external wall using the welding tip; supplying coolant to an internal wall of the pipe; and in which the pipe is non-magnetic and comprises metal.

[0006] In various embodiments, there may be included any one or more of the following features: Supplying flux to the external wall, in which weld metal is deposited as part of a submerged arc welding process. Shot peening the deposited weld metal to harden the deposited weld metal. Shot peening further comprises: rotating the pipe about the pipe axis relative to a shot peen nozzle directed towards the deposited weld metal;
and delivering shot peen under pressure circumferentially about the external wall using the shot peen nozzle. Coolant is supplied from a 360-degree nozzle located within the pipe.
Coolant is supplied at conditions sufficient to maintain the temperature of the external wall 100 degrees Fahrenheit or more below a maximum temperature limit of the pipe. Coolant is supplied at conditions sufficient to maintain the temperature of the external wall between 200 and 500 degrees Fahrenheit. The non-magnetic stainless steel comprises 3-8% nickel and 5-15%
magnesium. The external wall has an indented wear area, and the weld metal is deposited over the indented wear area to repair the pipe. The pipe is part of a drilling tool. Translating the pipe along the pipe axis relative to the welding tip.

[0007] These and other aspects of the device and method are set out in the claims, which are incorporated here by reference.
BRIEF DESCRIPTION OF THE FIGURES

[0008] Embodiments will now be described with reference to the figures, in which like reference characters denote like elements, by way of example, and in which:

[0009] Fig. 1 is a side elevation view, in section, of an apparatus used to perform a buildup method on a non-magnetic pipe.

[0010] Fig. 2 is a side elevation view, in section, of an apparatus used to perform a method of hardening a built up non-magnetic pipe by shot peening.

[0011] Figs. 3A and B are side elevation views, in section, of an apparatus used to perform a method of testing a built up pipe. The apparatus of Fig. 3A uses outer ultrasonic pads, while the apparatus of Fig. 3B adds inner ultrasonic pads.

[0012] Figs. 4 and 5 are side elevation views, in section of a built up pipe (Fig. 4) and a pipe (Fig. 5) with a faulty buildup portion removed.
DETAILED DESCRIPTION

[0013] Immaterial modifications may be made to the embodiments described here without departing from what is covered by the claims. % values for elements such as nickel and magnesium refer to volume / volume percentages.

[0014] Referring to Fig. 1, a method of pipe build up is illustrated. A
pipe 10 is non-magnetic and comprises metal. In one case pipe 10 comprises one or both a non-magnetic stainless steel alloy containing nickel, or a non-magnetic steel alloy containing nickel and magnesium. Example pipe compositions are given below. The pipe 10 is rotated about a pipe axis 12 relative to a welding tip 14. Pipe 10 may be rotated any number of suitable ways. For example, pipe 10 is mounted at an axial pipe end 20 to a rotating chuck 18. In other cases external wall 16 of pipe 10 may sit upon and be rotated by pipe rollers (not shown). Welding tip 14 is directed towards external wall 16 of pipe 10. Weld metal is deposited circumferentially about the external wall 16, for example over an indented wear area 21, using the welding tip 14. Indentation may be caused by wear from use. The deposition of the weld may create a collar 22 (build up) of weld metal about the hollow pipe 10.
While the deposition is occurring, coolant 24 is supplied to an internal wall 26 of the pipe 10.

[0015] The non-magnetic stainless steel may comprise 3% nickel or greater (for example 3-8% (such as 3%, 5% and 8% for example in the case of drilling tools) up to 15%, or more. Some inkaloids have 20-25% Ni. In some cases magnesium may be present, for example 5% or greater and in some cases 5-15% or up to 37%. Magnesium % may increase as nickel % increases. Magnesium may improve machining capability. Relative to carbon steel, stainless steel is more expensive but also more resistant to corrosion.
Thus, stainless steel is used in various pipes, including pipes 10 forming part of drilling tools used in the oil and gas industry. Various stainless steels are non-magnetic, including austenitic stainless steels.

[0016] Material preparation for welding may include cleaning off all foreign material from external wall 16. The base material should be clean, with no rust, scale, grease, dirt or product that may distort material bonding to the base material.

[0017] Weld metal may be deposited by a suitable welding method. Welding is a fabrication process that joins metals by causing coalescence. Welding is often done by melting adjacent workpieces and adding a filler material to form a pool of molten material (the weld pool) that cools to become a strong joint, with pressure sometimes used in conjunction with heat, or by itself, to produce the weld. Build-up material may include wire rod, flux, stick rod and powder. In the method shown in Fig. 1, weld metal, such as wire 30 from a wire loop 32, may be fed to the tip 14 and coalesced with external wall 16 at the welding site, which may be at an intermediate axial location along the pipe length as shown.

One or more motors (not shown) may be used to dispense wire 30 at a desired rate. The wire 30 may comprise similar or identical material as the material of pipe 10 to be welded, for example stainless steel.

[0018] A submerged arc welding (SAW) process may be used to deposit weld metal.
In such a method flux 28 is supplied to electrode 14 and external wall 16, for example via a flux hopper 32. In SAW processes the molten weld and arc zone are protected from atmospheric contamination by being submerged under a blanket of the granular fusible flux 28. Suitable flux material may be used such as lime, silica, manganese oxide, calcium fluoride, and other compounds. When molten, the flux becomes conductive, and provides a current path between the electrode and the work piece. The layer of flux covers the molten metal and prevents spatter and sparks as well as suppressing ultraviolet radiation and fumes.
Although SAW welding is mentioned, other types of welding may be used in the disclosed apparatuses and methods, for example plasma welding.

[0019] One or more or all aspects of the welding process may be automated.
For example, flux 28 and wire 30 may be dispensed at a desired rate proportional to one another and the rotation speed of the chuck 18. A processor, for example in the welding unit 34, may be connected to send control signals to tip 14, hopper 32, and wire loop 32 for control purposes. Welding unit 34 may also contain the components required to convert an electrical power input into the arc required to melt the weld metal and external wall 16 at the welding site. The welding unit 34 may also be connected to send control signals to chuck 18 to execute all parts of the process automatically, for example to carry out a pre-programmed welding process selected for the particular work piece 10 to be repaired. One or more processors or controllers (not shown) may be used to control the process.

[0020] Pipe temperature during the process may be maintained to support build-up material bonding to the base material. Temperature control may be maintained to support the core temperature and thus the base material (pipe 10) from distorting. The optimal temperature may vary per base material make up. Temperature may be controlled by fluid, air, or mist contact and removal. Coolant 24 may be supplied to internal wall 26 via a nozzle 36, which may be directed at a portion 42, of internal wall 26, that underlies an active welding site 44 on external wall 16. Nozzle 36 may be a 360-degree nozzle 36 located within an interior of the pipe 10. The nozzle 36 may be a perforated tube 38 as shown, with perforations represented by dotted lines in the figure. A 360 degree nozzle supplies coolant circumferentially about the internal wall 26, thus providing cooling at the active welding site 44 and even on portions of external wall 16 that are not being directly welded. The nozzle 360 may be changeable, to permit removal and installation of different nozzles sized according to the ID of the pipe 10 being welded. The position of the torch output point 36 may be adjusted throughout the process, for example moved along the axis 12 to correspond with relative motion of the welding tip 14.

[0021] In the example shown, the tube 38 is part of a supply line 39 that extends into the interior 46 of pipe 10 through a bore 49 in an annular seal 48, seal 48 being seated within or over end 20. In sonic cases nozzle 36 is positioned outside the pipe end 20 with or without seal 48. Seal 48 may itself be, or may have bore 49 lined with, a rubber gasket, about the supply line 39. Bore 49 may form a dynamic seal with the supply line 39, so that the pipe 10 rotates relative to the supply line 39. In other cases the nozzle 36 rotates in sequence with the pipe 10 and relative to the tip 14, and in other cases the nozzle 36 rotates independently of both the pipe 10 and tip 14 for example if the nozzle is designed to rotate under application of coolant fluid pressure.

[0022] In the example shown coolant runs into pipe via one end 20, along the pipe length, and exits pipe 10 via a second pipe end 50 opposite pipe end 20. In other cases the coolant may enter and exit the same pipe end 20, for example if a packer (not shown) or end plug (not shown) was positioned to block end 50 and seal 48 included an inlet for line 39 and an outlet for a spent coolant line.

[0023] Coolant is supplied to line 39 via a suitable coolant supply system, which may be open or closed, and may be once-through or recirculating. Coolant is pumped into line 39 using a fluid pump 54 drawing coolant from a coolant reservoir 52. Heated coolant 24 exiting pipe end 50 is expelled into a collection reservoir 56, and then pumped via a cooling pump 58, for example a vain type or propeller type pump, through line 60 into a cooling fluid tower or radiator 62. Cooled coolant passes through radiator 62 through line 64 and back into reservoir 52 for supply to line 39. Radiator 62 may incorporate a heat exchanger and a fan. Suitable devices other than radiator 62 may be used for reducing the temperature of the heated coolant. A fluid controller 66 may be used to regulate the operation of the coolant system. In one embodiment a processor or the welding unit 34 is connected to operate the coolant system.

[0024] A suitable coolant may be used, for example a liquid such as a non-water base or water, or a gas such as air. In one case antifreeze is used, for example selected with a boiling temperature above the maximum temperature of the interior wall 26 achieved during welding, to avoid coolant vaporization and unwanted deposition on the interior wall 26.
Temperature may be measured via a temperature sensor 19, and fluid control adjusted to maintain the operating temperature within a predetermined temperature range.
One example cooling fluid is an antifreeze type coolant, for example a green type coolant with components such as silicates and phosphates that inhibit corrosion, and having a 40/50 viscosity as measured using a Marsh funnel test. Higher viscosity means increased heat removal, but greater difficulty to cool the heated coolant. A gel may be used in some cases. Temperature may be monitored and one or more operating parameters adjusted to compensate, for example the parameters listed in Table 1, or other parameters such as welding parameters.

[0025] Coolant may be supplied at conditions sufficient to maintain the temperature of the external wall 16 to 100 degrees Fahrenheit or more below a maximum temperature limit of the pipe 10. Precise coolant monitoring and control may be required to regulate the external wall 16 temperature because the non-magnetic material absorbs height relatively fast compared to carbon steel. Coolant may in some cases be supplied at conditions sufficient to maintain the temperature of the external wall 16 to between 200 and 500 degrees Fahrenheit, for example between 200 and 400 degrees Fahrenheit. If temperature climbs outside of the predetermined range, coolant flow may be increased in response, or the action of the radiator 62 increased to reduce the temperature of the incoming coolant. By converse, if the temperature falls below the predetermined range, coolant flow may be decreased and the action of the radiator 62 reduced. An example predetermined range is from 200 to 100 degrees Fahrenheit below the maximum temperature limit of the pipe. Different materials have different maximum temperature thresholds, and above such limits, the material may start to distort the makeup of the material, shape and composition. The maximum temperature limit may be the lower limit of hot working, which is generally 60% of the melting temperature, beyond which crystal structure changes may begin to be observed.
With some inkaloids, temperature limits are higher, for example in the 900-1000 degrees Fahrenheit range. Temperature limits tend to increase as nickel % increases.
Limits of 200-350 degrees Fahrenheit were observed on the 3-8% Ni-containing materials tested.

[0026] During the welding process the pipe 10 may be translated along the pipe axis 12 relative to the welding tip 14. Translation may occur to reposition the tip 14 and apply a band of weld metal adjacent an already deposited band. Either the pipe 10 or the tip 14 may be moved to achieve the new orientation. Translation may occur during weld metal deposition or during an intermediate period where no weld metal is deposited, for example to create a spiral band pattern. The combination of rotation of pipe 10 and translation may be used to repair or otherwise build up a relatively larger section of the pipe 10.

[0027] Once the pipe 10 is built up and cooled to room temperature, further processing may be carried out. The build-up area may be treated to support hardness and remove contamination. An example process to decontaminate material includes an acid bath (for example 1-10% acid content) and shot peening.

[0028] Referring to Fig. 2, in the example shown shot peening is carried out on the deposited weld metal 68 to harden the deposited weld metal 68. Shot peening is a cold working process used to produce a compressive residual stress layer and modify mechanical properties of metals. It entails impacting a surface with shot, for example round metallic, glass, ceramic, sand, and nonferrous or non-magnetic particles, with force sufficient to create plastic deformation. In one example stainless steel fragments are used as shot and delivered to the metal 68. During shot peening the pipe 10 may be rotated about the pipe axis 12. For example, pipe 10 may be mounted at an axial pipe end 50 to a rotating chuck 70. Other suitable rotation mechanisms may be used. The shot peen 74 may be delivered to the weld metal 68 under pressure, for example circumferentially about the external wall 16, using a shot peen nozzle 76. A peen house 72 may be supported by one or more ground engaging members such as legs 86. One or more dust collectors (not shown) may be used with the shot peening system. Shot peening may be carried out to an extent required to raise the hardness of the build up (deposited weld metal 68) to within 20% of the hardness of the base material (pipe 10)..

[0029] The peen house 72 may be positioned partially or fully around the pipe 10, to shroud the portion of pipe 10 that contains the deposited weld metal 68 and to contain and collect shot expelled from nozzle 76. The peen house 72 may have a top wall 78, surrounding side walls 80, and a base 82, with an outlet 84, for example in the base 82, for collecting and removing expelled shot from house 72. The base 82 may be sloped to direct expelled shot by gravity into outlet 84. The pipe end 20, which extends into peen house 72, may be sealed with an end cap or plug 88, and a seal (not shown) may also be provided about pipe 10 at a pipe entry point 90 in the peen house 72, in order to prevent expelled shot from escaping the bounds of the peen house 72 except through outlet 84, which may be a perforated plate as shown by dashed lines. In some cases pipe 10 is entirely contained within the peen house 72 during shot peening.

[0030] Shot 74 may be cycled once through the system, or may be collected and recirculated as shown. The outlet 84 may be positioned at, or may be connected to a hopper 92 that collects expelled shot 74 into a shot basin 94, after which the shot 74 is pumped through one or more lines 98 by a shot pump 96 into and out of nozzle 76.
Thus, the shot peen is recycled during use. In other cases shot is supplied via one or more cartridge mechanisms, or a hopper. Fluid pressure, for example from air pressurized by pump 96, may be used to transport and expel the shot 74 throughout the system. Other suitable fluids may be used.

[0031] Shot peening is used to harden the deposited weld metal 68 to obtain a higher hardness rating. For example, shot pecning may be controlled to provide a hardness of 20 to 25 or higher on the Rockwell scale, although the Brinell scale may be used.
Shot peening provides an impact on the metal 68 surface intended to close up voids, densify the metal 68, and flatten the surface. In some cases shot of size 0.010" to .016" intensity is used, with a coverage of 150 % to 200%. C grade shot may be used, C grade having relatively sharp-edged beads in contrast to A grade, which is a round bead. Shot velocity may average 560-780 mm/second, at a coverage of 150%, and in some cases up to 200%. The greater the velocity, the greater shot impact on the surface, although shot peening above a threshold velocity will roughen the surface, potentially leading to erosion or non-sealing when pumping fluid during use of the tool. In some cases, to close up voids and keep the surface smooth, a velocity range of 120-200 ft/sec is used.

[0032] Referring to Figs. 3A and 3B, after deposition, and shot peening of the deposited weld metal 68, the weld metal 68 may be subject to quality control, such as a visual inspection for flaws, a dye test under black lights checking for cracks, or other testing.
For example the build-up area may be tested for the correct base and build-up material bonding and porosity. Testing may be destructive, non-destructive, or both.

[0033] In an example non-destructive test, the pipe 10 is subject to an ultrasonic bonding test. Ultrasonic testing is a family of non-destructive testing techniques based in the propagation of ultrasonic waves in the object or material tested. Ultrasonic pulse-waves are transmitted into materials to detect internal flaws or to characterize materials. An example is ultrasonic thickness measurement, which tests the thickness of the test object, for example, to monitor pipework corrosion. As shown one or both outer and inner ultrasonic pads 100 or 102, respectively, may be positioned adjacent the deposited weld metal 68 and connected to an ultrasonic control unit 104. A thickness profile may be generated and reviewed to identify defects, if any.

[0034] Example partial destructive testing includes an acid test, which is used to analyze compositional variance between the build up and the base material using wet chemistry. 10% HCI may be applied to the base material and the build up, and the color of the resulting solution compared. Higher Ni content generally produces a blue color, while lower Ni content produces a lighter green color. A color difference indicates a different composition, and if the difference is sufficiently large the process may be repeated using weld metal of a composition more closely aligned with the composition of the base material.

[0035] In some cases hardness may be tested. One non-destructive hardness test is the air injection test, where a head hits the material and the resistance is quantified to produce a Rockwell hardness amount. In a destructive hardness test a machine is used to put a dimple in the metal, and the depth of penetration is used to quantify hardness.

[0036] In some cases a test pipe may be subjected to destructive testing, of a nature that brings the pipe to failure, to determine if a particular welding program is suitable for the composition of the pipe. For example, a test pipe was subjected to a visual bonding inspection by slicing the pipe into pieces along planes perpendicular to the pipe axis, passing through the deposited weld metal 68 and the underlying pipe base. At the transition point where welding occurred the matrix is inspected, visually or by analytic methods, to check for any obvious differences in the matrix indicative of incomplete coalescence. In tests done on actual pipes, almost 100% bonding was achieved. In some cases a program is selected to achieve 100% bonding or within 1-3% deviance from 100%. The area of build-up may achieve bonding of 50% - 100%. Porosity sizes may range 0.001 - 0.010 and 0-30 inclusion per square inch.

[0037] After the build-up process is complete, excess build-up material may be removed to produce a smooth finish on deposited weld metal 68. The build-up area may be finished by a process that supports a smooth finish 10 plus, which is a micro finish quantifier based on voids per square inch. Referring to Figs. 4 and 5, if the build up fails during or after testing, the build up area 68 may be machined off, either partially (Fig. 5), or entirely to the base material. The process of correcting flaws may be carried out in stages.
For example, after machining off a portion of the weld metal 68, the remaining machined area 106 is inspected for flaws, and if the area 106 passes inspection, further build up may be carried out. If the area 106 does not pass, another skin of the material may be machined off, and the process repeated until the desired thickness and quality of deposited weld metal 68 is achieved. In some cases, prior to any welding the pipe 10 to be repaired may be machined down at the site to be welded, and then built up back to an outer diameter equal to or greater than the original outer diameter of the pipe, so that the build up area is flush with the adjacent area of the pipe 10.

[0038] Table 1 below illustrates parameters and test data for a sample test done on a non-magnetic alloy pipe made of stainless steel with Ni 3% and Mg 5%.
Table 1: Parameters and test data for non-magnetic alloy pipe Ni 3%
Mg 5%
OD - starting material 165mm 6.5"
ID - starting material 83mm 3.25"

wall thickness 42mm 1.62"
coolant rate 15-18 L/minute 4-4.5 gallons/minute wire diameter 0.05mm 1/16"
wire speed 381 cin/minute 150 inch/minute pipe rotation 60 revolutions / minute (30-40 in some cases) amperage 200-225 temperature of material 93-260 C 200-500 F
Build up thickness 35mm 1.5"

[0039] The methods disclosed here may be carried out on various pipes 10, including pipes used in the oil and gas industry, for example as part of a downhole tool such as a drilling tool or other oilfield tubular. Other applications include parts in valves, such as to repair non-magnetic stainless steel parts in ball or gate valves. Downhole parts often become worn over use, particularly those used with heavy oil or hydrocarbons carrying corrosive substances such as sand.

[0040] In one embodiment the welding is carried out on the internal wall 26 while supplying coolant to the outer wall 16. In one such example the pipe 10 may be positioned within a coolant bath (not shown) with a temperature sensor, a circulation device such as a stirrer, and a cooling device connected to maintain a desired temperature in the bath. In another example coolant may be sprayed upon the external wall 16, for example from a nozzle manifold extending up to a full circumference around the pipe 10 adjacent the active welding site.

[0041] In some cases a multi-:ayer build up may be produced. A single layer of weld metal may be deposited, by depositing weld metal in adjacent rings or a spiral pattern. The number of adjacent rings or the length of the spiral is selected to achieve the desired axial length of build up. After deposition, the pipe 10 is allowed to cool and may be tested, shot peened, and machined if necessary, before additional layers of weld metal are deposited. In some cases the deposited weld metal is machined down to a smooth surface, upon which one or more further layers of weld metal may be deposited. Each layer may be applied in the same or a similar fashion.

[0042] In the claims, the word "comprising" is used in its inclusive sense and does not exclude other elements being present. The indefinite articles -a" and "an"
before a claim feature do not exclude more than one of the feature being present. Each one of the individual features described here may be used in one or more embodiments and is not, by virtue only of being described here, to be construed as essential to all embodiments as defined by the claims.

Claims (12)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of pipe build up comprising:
rotating a pipe about a pipe axis relative to a welding tip directed towards an external wall of the pipe;
depositing weld metal circumferentially about the external wall using the welding tip;
supplying coolant to an internal wall of the pipe; and in which the pipe comprises one or both a non-magnetic stainless steel alloy containing nickel, or a non-magnetic steel alloy containing nickel and magnesium.

2. The method of claim 1 further comprising supplying flux to the external wall, in which weld metal is deposited as part of a submerged arc welding process.

3. The method of any one of claim 1 - 2 further comprising shot peening the deposited weld metal to harden the deposited weld metal.

4. The method of claim 3 in which shot peening further comprises:
rotating the pipe about the pipe axis relative to a shot peen nozzle directed towards the deposited weld metal; and delivering shot peen under pressure circumferentially about the external wall using the shot peen nozzle.

5. The method of any one of claim 1 - 4 in which coolant is supplied from a 360-degree nozzle located within the pipe.

6. The method of any one of claim 1 - 5 in which coolant is supplied at conditions sufficient to maintain the temperature of the external wall 100 degrees Fahrenheit or more below a maximum temperature limit of the pipe.

7. The method of any one of claim 1 - 6 in which coolant is supplied at conditions sufficient to maintain the temperature of the extemal wall between 200 and 500 degrees Fahrenheit.

8. The method of any one of claim 1 - 7 in which the non-magnetic stainless steel comprises 3-8% nickel and 5-15% magnesium.

9. The method of any one of claim 1 - 8 in which the external wall has an indented wear area, and the weld metal is deposited over the indented wear area to repair the pipe.

10. The method of claim 9 in which the pipe is part of a drilling tool.

11. The method of any one of claim 1 - 10 further comprising translating the pipe along the pipe axis relative to the welding tip.

12. A method of pipe build up comprising:
rotating a pipe about a pipe axis relative to a welding tip directed towards an external wall of the pipe;
depositing weld metal circumferentially about the external wall using the welding tip;
supplying coolant to an internal wall of the pipe; and in which the pipe is non-magnetic and comprises metal.