EP3389918A1

EP3389918A1 - Process of butt-welding a laminated item, and an assembly comprising a butt-welded laminated item

Info

Publication number: EP3389918A1
Application number: EP16813162.1A
Authority: EP
Inventors: Simon Kam-Sang Yuen; Duane Go SERATE; Johannes A DE JONG; Etienne LJM AGGENBACH
Original assignee: G C C Holding BV; GCC Holding BV
Current assignee: G C C Holding BV; GCC Holding BV
Priority date: 2015-12-18
Filing date: 2016-12-12
Publication date: 2018-10-24
Also published as: NL2015990A; NL2017980B1; NL2015990B1; NL2017980A; CA3006950A1; WO2017105226A1

Abstract

Process of butt-welding a first item and a second item to each other at edges of these items that face one another, wherein at least the first item is a laminated item comprising a first, base layer (102a) of a first material and a second, cladding layer (102b) of a second material, wherein the first material is different than the second material, wherein the second item has at least a first layer (102b) of a material that is butt-weldable to the material of the first, base layer of the first item, the process comprising the steps of: -- placing an insert (107) between the facing edges of the first and second items at the transition zone of the base layer and the cladding layer of the first item, wherein the insert is of a material that is non-fusible at the temperature(s) used in this process of butt-welding, wherein the insert is placed such that it is in contact with the facing edges of the first and second items and defines a bottom of a welding groove; and -- butt-welding the first layers of the first item and the second item to join the facing edges of these first layers in the welding groove.

Description

Process of butt-welding a laminated item, and

an assembly comprising a butt-welded laminated item

BACKGROUND OF THE INVENTION

[0001] The invention relates to a process of butt-welding items, in particular plates or strips, with either a flat or curved surface, the latter such as e.g. in transport pipes or vessels with clad walls. At least one of the items is laminated, comprising a first or base layer of a strength-providing first material and, on at least one side thereof, a second, cladding layer of a wear-resistant and/ or corrosion-resistant second material that is dif- ferent than the material of the base layer, which second layer may be bonded to the first layer, for instance by means of roll-bonding, explosion-bonding or pressure-temperature bonding. The first material and/ or the second material can comprise an alloy, e.g. an alloy that is a mixture of metals (e.g. iron and any of e.g. manganese, nickel, chromium, molybdenum, vanadium, silicon, boron, aluminium, cobalt, copper, cerium, niobium, titanium, tungsten, tin, zinc, lead and zirconium) or a mixture of a metal and another element (example: an iron-carbon alloy, steel).

[0002] Further, the invention relates to an assembly of items comprising a laminated item that is butt-welded according to the process of the invention.

[0003] When welding the first or base layer, dissolution or cross-contamination of its material with the material of the second or cladding layer needs to be avoided. The same applies to dissolution or cross-contamination of the materials of the layers into the weld root deposit.

[0004] It is known to avoid contamination by controlling the depth of the root weld by means of a specific weld procedure followed by monitoring the actual weld depth after welding using non-destructive test methods such as phase-array and time-of -flight (TOFD) diffraction techniques. This process, however, is complex and time-consuming. The same is true for other butt-welding processes that include combinations of welding and grinding sequences.

[0005] According to another known approach - as disclosed in patent publication US- 3.629.932 and relating to two laminated items that are butt-welded to each other, where- in both items each comprise a base layer of steel and a cladding layer of titanium - a re- cess is formed by removing material at the two opposing base layer edges so that the two opposing cladding layer edges project beyond the base layer edges and each cladding layer edge forms a support for an insert. The insert is manufactured from the same base layer and cladding layer material and is fittingly inserted in the recess between the base layers. The insert is laminated in accordance with the items which are to be butt-welded, and it thus consists of a steel base layer and a titanium cladding layer. The insert is positioned with its cladding layer against the inner surface of the cladding layers of the two items, after which the base layer of the insert is root-welded to the base layers of the two items. Subsequently, two welds are made, with one weld joining the three cladding-layer portions and the other weld joining the three base-layer portions.

SUMMARY OF THE INVENTION

[0006] It is an object of the invention to provide a relatively simple process of butt- welding a laminated item of the type mentioned in the introductory part of the descrip- tion.

It is an object of the invention to provide a process of butt-welding a laminated item of the type mentioned in the introductory part of the description, which process provides reliable and consistent results.

It is an object of the invention to provide a process of butt-welding a laminated item of the type mentioned in the introductory part of the description, by which process dissolution and/ or cross-contamination of the materials of the welds, base layers and/ or cladding layers is prevented as much as possible.

It is an object of the invention to provide a process of butt-welding a laminated item of the type mentioned in the introductory part of the description in order to obtain welding zones which produce a satisfactory and effective bond throughout.

It is an object of the invention to provide a process of butt-welding a laminated item of the type mentioned in the introductory part of the description, which process provides a bond which is free of brittle zones of inter-metallic alloys formed during heating.

It is an object of the invention to provide a process of butt-welding a laminated item of the type mentioned in the introductory part of the description, which process provides a bond which is free of brittle zones in order to avoid the formation of cracks when exposed to mechanical stresses and any resultant rupturing of the welding bond. [0007] According to one aspect of the invention there is provided a process of butt- welding a first item and a second item to each other at edges of these items that face one another, wherein at least the first item is a laminated item comprising a first, base layer of a first material and a second, cladding layer of a second material, wherein the first material is different than the second material, wherein the second item has at least a first layer of a material that is butt-weldable to the material of the first, base layer of the first item, the process comprising the steps of:

— placing an insert between the facing edges of the first and second items at the transi- tion zone of the base layer and the cladding layer, wherein the insert is of a material that is non-fusible at the temperature(s) used in this process of butt-welding, wherein the insert is placed such that it is in contact with the facing edges of the first and second items and it defines a bottom of a welding groove; and — butt-welding the first layers of the first item and the second item to join the facing edges of these first layers in the welding groove.

[0008] When following the process of butt-welding according to the invention, the insert will not become or form part of the weld or bond of the two items. Because of the non- fusible nature of its material at applicable welding temperatures, the insert will not melt or dissolve or leave any contaminating traces in the material of the root weld deposit. As the insert will be of a non-reactive material, it will not be affected by the weld deposit. As such, the insert will not contribute to the mechanical strength of the bond. The insert will form a barrier between the weld groove and the root weld and the material of the cladding layer.

[0009] In other words, the material of the insert does not dissolve in the weld deposit. A technical advantage of this feature is that mixing or (cross-) contamination of weld deposit material in the material of the cladding layer and vice versa is prevented. Another technical advantage is that because the insert itself does not form a fused part of the weld it does not affect the root properties of the weld.

[0010] A further technical advantage is that the process makes it easy to hold precise bond-line tolerances. This makes tighter tolerances in comparison with prior-art processes achievable. [0011] Yet another technical advantage is that the weld preparation will result in a smooth, flawless root weld finish between the two items. This has been shown to provide a better impact toughness of the weld joint as the root roundness is maintained throughout the welding process. The insert can also function as a spacing element between the two items.

[0012] The insert may be a non-metal insert. In particular, the insert may be a ceramic insert. A suitable metal insert is e.g. a tungsten insert or a molybdenum insert. The essen- tial requirement of the insert material is that it has a higher melting temperature than the melting temperature of the material(s) of the items that are to be welded according to the invention and that of the weld deposit or filler material.

[0013] The material of the first layer and/ or the material of the second layer may be an alloy. Any or all of the alloys of the layer(s) of the first and second items should be understood to comprise a mixture of metals or a mixture of a metal and another element, e.g. a metal-carbon alloy. An alloy within the meaning of the present invention should be understood to be a solid-state compound exhibiting metallic bonding, and with a defined stoichiometry and ordered crystal structure. An alloy should be understood to be a (solid) solution of metal elements, either as a single-phase compound, a multi-phase compound or an inter-metallic compound.

[0014] The base layer may be made of a metal-carbon alloy. [0015] The material of the cladding layer may comprise any of the group consisting of ferritic and austenitic stainless steels, nickel-based alloys, copper-nickel alloys, martensit- ic (stainless) steels, Duplex 55, nickel-chromium alloys, and chromium alloys e.g. high- chrome white iron. Alternatively, the cladding layer may comprise nickel or titanium. [0016] In a further development of the process of the invention, both the first and the second items are laminated, each item comprising a second, cladding layer of a material that is similar, and preferably identical, to the material of the cladding layer of the first item. A technical advantage of this feature is that full-penetration welding can be achieved at the facing edges of both layers. [0017] In one embodiment of this process, the first and second items are similar, and preferably identical, in regard of the compositions of the materials and the thicknesses of their first and second layers. [0018] In an alternative further development of the process of the invention, the second item does not comprise a cladding layer that is similar to or equivalent to the cladding layer of the first item, and in particular it does not comprise a cladding layer at all. The second item can be monolithic, i.e. comprise just a single layer and not comprise a second, cladding layer. In an embodiment, the base layer of the second item has a thick- ness which is greater than the thickness of the base layer of the first item, and preferably (almost) equal to the combined thicknesses of the base layer and the cladding layer of the first item.

[0019] The process according the invention may include the step of:

— shaping at least the facing edges of the two base layers of the two items for forming a recess or welding groove between the two items.

[0020] In the above-mentioned process in which both the first item and the second item are laminated, it may include the steps of:

— shaping at least the facing edges of the two cladding layers of the two items for forming a second welding groove between the two items, and butt-welding the second layers of the first item and the second item to join the facing edges of these second layers. This embodiment of the process results in a full-penetration weld.

[0021] The facing edges can be shaped with a groove face and a root face between the groove face and the recess. [0022] In a further development of the process according to the invention, the process includes the step of:

— making a first recess for fittingly accommodating at least a portion of the insert at the transition zone of the base layer and the cladding layer of the facing edge of the first item, and placing the insert with at least said portion in the first recess. [0023] The recess facilitates the positioning of the insert so that it may be easily and purposefully placed in a correct position. In addition, the recess may contribute to keeping the insert in its correct place during the actual butt-welding.

[0024] In one embodiment, the first recess is made at the transition zone and in both the base layer and the cladding layer.

[0025] These advantages can be enhanced when the process includes the step of:

— making a second recess in the second item for fittingly accommodating at least another portion of the insert in the facing edge of the second item opposite the first recess in the first item, and placing the insert with at least said another portion in the second recess. [0026] The second recess in the facing edge of the second item may be made at the transition zone of the base layer and the cladding layer of the facing edge of the second item.

[0027] Together, the recesses form a void prior to welding, which void is filled with at least a portion or preferably the whole of the insert.

[0028] At least at the start of the butt-welding step the insert may be kept in its place through a form-fit in the recess or recesses, with or without the application of pressure forces to hold the items close to each other. It may then not be required to bond or otherwise adhere the insert to the item or items as long as the position of the insert does not change significantly or, preferably, not at all during the welding step.

[0029] In the above-mentioned process in which both the first item and the second item are laminated, the facing edges of the cladding layers may be kept spaced from each other so as to form a gap until after butt-welding. The result may then be a partial- penetration weld of the two items. Here, too, the insert can function as a spacing element.

[0030] According to another embodiment, in an assembly of two items at least the first item comprises a base layer of a first material, in particular a first alloy, and a cladding layer of a second material, in particular a second alloy, wherein the first material and the second material are different materials, and the second item comprises at least a base layer of a material that is butt-weldable to the first material of the base layer of the first item, in particular comprises a base layer of said first material, wherein the base layers of the two items have been butt-welded to each other at their edges that face one another, and wherein an insert is present at the transition zone of the base layer and the cladding layer at the facing edge of the first item where it forms the welding groove, and wherein the insert is made of a material that is non-fusible at the temperatures that arise during the butt-welding of the two items and the insert is not fused with any material of both items.

[0031] According to another embodiment, in an assembly of two items, at least the first item comprises a base layer of a first material, in particular a first alloy, and a cladding layer of a second material, in particular a second alloy, wherein the first material and the second material are different materials, and the second item comprises at least a base layer of material that is butt-weldable to the first material of the base layer of the first item, in particular comprises a base layer of said first material, wherein the base layers of the two items have been butt-welded to each other at their edges that face one another, and wherein an insert is present of which at least a portion form-fits in a recess at the transition zone of the base layer and the cladding layer at the facing edge of the first item where it forms the welding groove, and wherein the insert is made of a material that is non-fusible at the temperatures that arise during the butt-welding of the two items, and the insert is not fused with any material of both items.

[0032] Both the first item and the second item may each comprise a base layer of a first material and a cladding layer of a second material. The insert may be placed in a position such that it is in contact with both the base layer and the cladding layer of the first item.

[0033] The base layer and the cladding layer of the first item and/ or of the second item may bonded to each other. A technical advantage is that the welded product can be very strong mechanically.

[0033A] The process according to the invention also comprises the following embodiments as described in paragraphs [0033B], [0033C], [0033D], [0033E], [0033F] and

[0033G]. [0033B] A process of butt-welding a first item and a second item to each other at edges of these items that face one another, wherein at least the first item is a laminated item comprising a first, base layer of a first material and a second, cladding layer of a second material, wherein the first material is different than the second material, wherein the second item has at least a first layer of a material that is butt-weldable to the material of the first, base layer of the first item, the process comprising the steps of:

— placing an insert between the facing edges of the first and second items at the transition zone of the base layer and the cladding layer of the first item, wherein the insert is of a material that is non-fusible at the temperature(s) to be used in this process of butt- welding, wherein the insert is placed such that it is in contact with the facing edges of the first and second items and it defines a bottom of a welding groove; and

— butt-welding the first layers of the first item and the second item to join the facing edg- es of these first layers in the welding groove, wherein the insert has a melting point that is higher than that of the first material and is higher than that of the second material and also is higher than that of the material with which the weld is made.

[0033C] A process of butt-welding a first item and a second item to each other at edges of these items that face one another, wherein at least the first item is a laminated item comprising a first, base layer of a first material and a second, cladding layer of a second material, wherein the first material is different than the second material, wherein the second item has at least a first layer of a material that is butt-weldable to the material of the first, base layer of the first item, the process comprising the steps of:

— butt-welding the first layers of the first item and the second item to join the facing edges of these first layers in the welding groove, wherein the insert is a tungsten insert or a molybdenum insert. [0033D] A process of butt-welding a first item and a second item to each other at edges of these items that face one another, wherein at least the first item is a laminated item comprising a first, base layer of a first material and a second, cladding layer of a second material, wherein the first material is different than the second material, wherein the second item has at least a first layer of a material that is butt-weldable to the material of the first, base layer of the first item, the process comprising the steps of:

— butt-welding the first layers of the first item and the second item to join the facing edg- es of these first layers in the welding groove, wherein the insert is a non-metal insert.

[0033E] A process of butt-welding a first item and a second item to each other at edges of these items that face one another, wherein at least the first item is a laminated item comprising a first, base layer of a first material and a second, cladding layer of a second material, wherein the first material is different than the second material, wherein the second item has at least a first layer of a material that is butt-weldable to the material of the first, base layer of the first item, the process comprising the steps of:

— placing an insert between the facing edges of the first and second items at the transi- tion zone of the base layer and the cladding layer of the first item, wherein the insert is of a material that is non-fusible at the temperature(s) to be used in this process of butt- welding, wherein the insert is placed such that it is in contact with the facing edges of the first and second items and it defines a bottom of a welding groove; and — butt-welding the first layers of the first item and the second item to join the facing edges of these first layers in the welding groove, wherein the insert is a ceramic insert.

[0033F] A process according to an embodiment as described in either of paragraphs [0033B], [0033C] and [0033D], wherein the second item is laminated and it com- prises a second layer of a material that is butt-weldable to the material of the cladding layer of the first item, further comprising the step of butt-welding the second (cladding) layers of the first item and the second item to join the facing edges of these second layers, wherein the insert is of a material that is non-fusible at the temperature(s) to be used in this butt-welding step.

[0033G] A process according to the invention as described in any of claims 1-22 and 29-31, wherein as seen in a plane of cross-section with respect to the direction of extension of the facing edges of the first and second items, the insert has a cross-section with a curvilinear peripheral surface, in particular a circumambulating convex peripher- al surface, more particular an ellipse-shaped, oval or circular cross-section.

[0033H] An assembly according to the invention also comprises the following embodiments as described in paragraphs [00331] and [0033J]. [00331] An assembly according to any of claims 23-27, wherein as seen in a plane of cross-section with respect to the direction of extension of the facing edges of the first and second items, the insert has a cross-section with a curvilinear peripheral surface, in particular a circumambulating convex peripheral surface, more particular an ellipse- shaped, oval or circular cross-section.

[0033J] An assembly according to any of claims 23-27, wherein only the first layers have been joined to each other and the second layers have a gap between them. This is particularly pertinent when only the first layers of the first item and the second item are butt-welded to join the facing edges of these first layers in the welding groove ac- cording to any of the embodiments described in claims 1-8.

[0033K] It is emphasized that the invention provides the technical advantage of an increased fracture toughness. This can be attributed to a blunting effect of the non-fusible insert. Put differently, a laminated item butt-welded according to the invention provides a joint that blunts any crack tip. Furthermore, the non-fusible insert acts as a shield preventing a plate, e.g. a hard martensitic plate, on the second layer to be in contact with the weld pool on the first layer, thus decreasing the probability of the second layer softening or cracking. The blunting effect referred to above leads to an enhanced shockload-bearing capacity of the butt-welded item. The invention also provides the technical advantage of an improved low-temperature impact toughness or improved fracture resistance in comparison with sharp edges as also referred to in paragraph

[0050] below.

[0034] The aspects and measures described in this description and the claims of the ap- plication and/ or shown in the drawings of this application may possibly also be used individually. Said individual aspects may be the subject of divisional patent applications relating thereto. This particularly applies to the measures and aspects that are described per se in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The invention will be elucidated with reference to examples of processes depicted schematically in the attached drawings, in which:

Figures 1A-D depict consecutive steps in performing a first embodiment of a process according to the invention;

Figures 2A and 2B depict consecutive steps in performing a second embodiment of a process according to the invention;

Figures 3A-3B and 3C-3D depict consecutive steps in performing a third embodiment and a fourth embodiment of a process according to the invention; and

Figures 4A-4C depict illustrations evidencing the presence of a non-fused insert between two items that have been butt-welded in accordance with a process of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0036] In Figure 1A, two laminated plates la and lb are shown, each comprising a base layer 2a, 2b of a first metallic alloy and a cladding layer 3a, 3b of a second metallic alloy. The layers 2a and 3a and the layers 2b and 3b are metallurgically bonded to each other at an interface (transition zone). The base layers 2a, 2b comprise a lower alloy in comparison with the alloy of the cladding layers 3a, 3b. [0037] According to the invention, the facing edges of both laminated plates la, lb are machined to make recesses, see Figure IB. At the transition zone, the edges 12a, 12b of the cladding layers 3a, 3b and the edges 14a, 14b of the base layers 2a, 2b are provided with recesses 4a, 4b that - in this example - are curvilinear. These recesses have a shape and size, in this example expressed as their circumferences, that match the shape and size, in this example expressed as the circumference, of an insert 7 of a ceramic material (or any other suitable material, for that matter) which in non-fusible at the welding temperatures required for butt-welding the plates la, lb.

[0038] In a direction facing away or pointing away from the cladding layers 3a, 3b, the edges 14a, 14b have a non-machined edge portion 5a, 5b, connecting to the recesses 4a, 5b and extending perpendicularly with respect to the longitudinal direction of the plates. The edge portions 5a, 5b merge into machined bevelled groove faces 6a, 6b.

[0039] In Figure 1C, the two laminated plates la, lb are shown as placed in a position ready for butt-welding, wherein the insert 7 has been fitted into the recesses 4a, 4b. Due to the insert 7, the edges 12a, 12b remain spaced from each other leaving a gap 8 free. The edges 5a, 5b leave a root opening 9 free and the groove faces 6a, 6b define a welding groove 10. The laminated plates la, lb are now ready for the welding process. [0039A] In the drawings, the insert is shown to have a circular cross-section. It should be clear that the insert can be curvilinear at least in part. An insert can thus also be e.g. oval- or ellipse-shaped. It should also be clear that the weld groove itself can be curvilinear at least in part. [0040] In Figure ID, the weld 11 is shown has having been made, with several passes done for filling the groove 10. The insert 7 is not fused and is not been affected e.g. by fusion with any of the layer materials, and it prevents mixing and contamination of weld deposit material with the material of the cladding layer and vice versa. The weld is of good quality and the cladding layer is unaffected.

[0041] In Figure 2A, the laminated plates 101a, 101b - having the same structure and materials as the plates la, lb - are also shown with a weld preparation for welding the base layers 102a, 102b and the cladding layers 103a, 103b. To this end, the outer portions of the edges 112a, 112b are bevelled to make groove faces 113a, 113b. The shapes of the edges of the base layers 102a, 102b are similar to those of the base layers 2a, 2b according to the example depicted in Figures 1A-D.

[0042] After bringing together the two plates 101a, 101b and fitting the insert 107 in the recesses 104a, 104b, both groove 110 and groove 116 are filled with weld deposits 111, 117 so as to make a full-penetration weld encompassing the ceramic insert 107 which may function as a barrier between the weld deposits and the various layers of the items.

[0043] In Figure 3A, the laminated plates 201a, 201b - having the same structure and materials as the plates la, lb or 2a, 2b - are shown without a weld preparation for welding the base layers 202a, 202b (not indicated) and the cladding layers 203a, 203b. An insert 207 is held between the plates 201a, 201b and the plates are then pressed against each other so as to clamp the insert 207 between them at the transition zone of 212a, 212b and 214a, 214b. Fig. 3B shows both groove 210 and groove 216 filled with weld deposits 211, 217 so as to make a full-penetration weld encompassing the ceramic insert 207 which functions as a barrier between the welded items.

[0044] In Figure 3C, the laminated plates 301a, 301b - having the same structure and materials as the plates 3a, 3b - are shown with an alternative weld preparation for weld- ing the base layers 302a, 302b (not indicated) and the cladding layers 303a, 303b. To this end, the outer portions of the edges 312a, 312b are bevelled to make groove faces 313a, 313b. Then, an insert 307 is held between the plates 301a, 301b and the plates pressed against each other so as to clamp the insert 307 between them at the transition zone of 312a, 312b and 314a, 314b. When the material of the insert is harder than that of either plate, e.g. when an insert comprising titanium, tungsten or zirconium is used, then the plates will possibly yield a little at where the insert is held between them depending on the amount of pressure used to press the plates against each other. Fig. 3D shows both groove 310 and groove 316 filled with weld deposits 311, 317 so as to make a full- penetration weld encompassing the ceramic insert 307 which functions as a barrier be- tween the welded items.

[0045] Figure 4A depicts an x-ray scan of an assembly according to Figure 4B. Figure 4A shows a section of the assembly according to Figure ID as rotated over 90 degrees in an anti-clockwise direction as compared with the depiction in Figure ID. Figure 4B depicts an assembly according to Figure ID that has been rotated over 90 degrees in an anticlockwise direction as compared with the depiction in Figure ID. Figure 4C depicts a photograph of a section of a real-life embodiment of an assembly according to Figure ID, also shown as rotated over 90 degrees in an anti-clockwise direction as compared with the depiction in Figure ID. Figures 4A-4C are shown with the interface between the two items aligned on the same horizontal line on the plane of the drawing. [0046] Starting with Figure 4B and as seen from left to right, the items 401a, 401b are shown with their base layers 402a, 402b and cladding layers 403a, 403b and a part of the interface between the cladding layers formed by an air gap 420. In practice, the air gap is less than 0.5 mm wide. The insert 407 is shown as having a circular cross-section. Figures 4A, 4B and 4C are not drawn to the same scale. The insert in this example has a diameter of approx. 3 mm. The ellipse 422 schematically indicates a root weld. The space between the bevelled faces 412a, 412b of the items 401a, 401b are shown as filled with a number of weld passes 424.

[0047] Now with reference to Figure 4A: the dark horizontal band indicates an air gap A between the two items. This dark band A will only show up in the case of a partial-weld penetration as in this example. This dark band will not show up in the case of a full-weld penetration as the weld filling on the other side of the insert will show its diffraction pat- tern and obscure the dark band. The lighter horizontal band B immediately below the dark band A is the diffraction pattern of the insert 407. Finally, the band C indicates (the breadth of) the weld on the outside and across the interface between the two items.

[0048] Figure 4A shows how precise bond-line tolerances can be held. The linearity of the bond line is markedly constant, more so in comparison with that of bond lines obtained by the application of prior-art butt-welding processes.

[0049] Figure 4C depicts a short-side view of a (real-life) partial-penetration weld around a non-fusible insert. The two items are indicated as 401a, 401b. The thin horizon- tal line indicates the interface between the two items. The insert is indicated as 407. The weld itself is indicated as 430. There is no fusion between neighbouring atomic layers of the insert and the materials of the first and second items as evidenced by insert 407 which can readily fall out under influence of the gravitational force when the assembly is held such that the insert extends in a substantially vertical orientation.

[0050] The shape of the insert and the corresponding shape of the recesses may vary depending on the specific circumstances. Cracking in the butt-weld can be prevented from occurring through a judicious choice of the geometry of the insert and the void in which at least a portion of the insert is to be form-fitted according to the invention. There should preferably not be any sharp edges or angles in or around the weld groove. Pre- ferred forms for the weld groove are curvilinear forms, e.g. circular, oval and elliptical forms as these forms improve low-temperature impact toughness or fracture resistance in comparison with sharp edges as also referred to in paragraph [0011] above. [0051] It will be clear to the skilled person that the sequence of welding both the base layers and the cladding layers together will not matter in the case of full-weld penetration as long as both layers are welded to each other.

[0052] It may be the case that when butt-welding the base layers of two items to each other and butt-welding the cladding layers of the two items to each other, butt-welding is limited to a or the high-wear zone of the assembly of the two items.

[0053] It will also be clear to the skilled person that any suitable welding method can be applied, such as arc welding, shielded-metal arc welding, gas-metal arc welding, flux- core arc welding, gas-tungsten arc welding, submerged arc welding, plasma arc welding, percussive arc welding, resistance welding, oxyfuel gas welding, electron-beam welding, laser-beam welding, electroslag welding, inertia welding and ultrasonic welding.

[0054] The non-fused nature of the insert inside or under a weld deposit according to the invention can be identified and validated by visual inspection and by taking e.g. ultrasonic thickness measurements of the area around and including the insert.

[0055] In regard of visual inspection: depending on the accessibility and orientation of the weld, the non-fused insert will be clearly visible and the beginning or the end of a longitudinal weld connection. See Figure 4C for an example.

[0056] Radiographic inspection can provide a film record of weld quality which is easy to interpret. With reference to Figure 4A: a partial-penetration weld will show up as a sharp line x. A flawless full-penetration weld will be marked by the absence of the sharp line x.

[0057] Ultrasonic inspection, e.g. by means of phased-array diffraction, can be used to determine the approximate location and approximate depth and size of a non-fused insert in an assembly of items that are subjected to a butt-welding process according to the invention. Each (subsequent) perpendicular cross-sectional view of the weld across the length of the weld will give a (similar) fairly constant reading (which is normally classified as a weld defect). In the case of a full-penetration weld - where a reading as described for a partial-penetration weld will be classified as a welding flaw-, it will not appear as a continuous and steady flaw. Additionally, or alternatively, time-of -flight diffraction ultrasonic technique can be used to determine the approximate location and approximate depth and size of a non-fused insert in an assembly of items that are subjected to a butt-welding process according to the invention.

[0058] Destructive inspection is another possibility. A weld can be sampled by means of grinding, gouging, cutting, drilling or any other suitable means in order to inspect the root of a partial-penetration weld deposit or full-penetration weld deposit. Once opened, the presence of a non-fused insert can be clearly established. Depending on the sample size, the insert bit may fall out of the weld zone on its own, or otherwise readily be pushed out manually with the aid of pointed object.

[0059] The insert does not form an integral part of the butt-weld. It does not contribute either mechanically to the strength of the butt-weld.

[0060] The process according to the invention provides a controllable and reproducible root penetration depth with both partial-penetration welding and full-weld penetration welding of the base layer and the cladding layer.

[0061] The risk of planar flaws at the root of the welds and at the transition zone is eliminated.

[0062] Mixing and subsequent contamination of weld deposits and the base layer and the cladding layer is avoided.

[0063] With the process of the invention, a smooth flawless butt-weld root design is ob- tained.

[0064] Clad butt-welding and procedures are simplified by eliminating intermediate weld deposits and subsequent grinding of the intermediate weld deposit. [0065] The present invention, which teaches the use of a non-fusible weld insert in a butt-welding process, can be applied advantageously and in general for all structures with types of clad plates that comprise a base material and a cladding material. The cladding material preferably comprises any of ferritic and austenitic stainless steels, nickel, nickel-based alloys, copper, copper-nickel alloys and titanium.

[0066] Typical fields in which the present invention can be applied advantageously include: the refinery, petrochemical and chemical industries; oil and gas production; power plants and e.g. flue-gas desulphurization plants.

[0067] Some examples of assemblies obtained by a butt-welding process according to the invention include: fractionators, vacuum towers, coke drums, process pipes, process columns, pressure vessels, reactors, washers, heat exchangers; clad flow lines, catenary riser pipes, slug catchers, line pipes and accumulator tanks.

[0068] The above description is included to illustrate the operation of some preferred embodiments of the invention and not to limit the scope of the invention. Starting from the above explanation many variations that fall within the spirit and scope of the present invention will be evident to a skilled person in the art.

Claims

C L A I M S

1. Process of butt-welding a first item and a second item to each other at edges of these items that face one another, wherein at least the first item is a laminated item com- prising a first, base layer of a first material and a second, cladding layer of a second material, wherein the first material is different than the second material, wherein the second item has at least a first layer of a material that is butt-weldable to the material of the first, base layer of the first item, the process comprising the steps of: — placing an insert between the facing edges of the first and second items at the transition zone of the base layer and the cladding layer of the first item, wherein the insert is of a material that is non-fusible at the temperature(s) to be used in this process of butt- welding, wherein the insert is placed such that it is in contact with the facing edges of the first and second items and it defines a bottom of a welding groove; and

— butt-welding the first layers of the first item and the second item to join the facing edges of these first layers in the welding groove.

2. Process according to claim 1, wherein the insert is a non-metal insert.

3. Process according to any of claims 1-2, wherein the insert is a ceramic insert.

4. Process according to any of claims 1- 3, wherein the second item is laminated and it comprises a second layer of a material that is butt-weldable to the material of the clad- ding layer of the first item.

5. Process according to claim 4, wherein the first and second items are similar, and preferably identical, in regard of the compositions of the materials and the thicknesses of their first and second layers.

6. Process according to any of claims 1-3, wherein the second item does not comprise a cladding layer that is similar to or equivalent to the cladding layer of the first item, and in particular it does not comprise a cladding layer.

7. Process according to claim 6, wherein the base layer of the second item has a thickness that is greater than the thickness of the base layer of the first item, and is preferably (almost) equal to the combined thicknesses of the base layer and the cladding layer of the first item.

8. Process according to any of the preceding claims, including the step of: shaping at least the facing edges of the two base layers of the two items for forming a recess or welding groove between the two items.

9. Process according to claim 8, when dependent on any of claims 4- 5, including the steps of: shaping at least the facing edges of the two cladding layers of the two items for forming a second recess or welding groove between the two items, and butt-welding the second layers of the first item and the second item to join the facing edges of these second layers.

10. Process according to any of claims 8-9, wherein the facing edges are shaped with a groove face and a root face between the groove face and the recess.

11. Process according to any of the preceding claims, including the step of: making a first recess for fittingly accommodating at least a portion of the insert at the transition zone of the base layer and the cladding layer of the facing edge of the first item, and placing the insert with at least said portion in the first recess.

12. Process according to claim 11, wherein the first recess is made at the transition zone and in both the base layer and the cladding layer.

13. Process according to claim 11 or 12, including the step of: making a second recess in the second item for fittingly accommodating at least another portion of the insert in the facing edge of the second item opposite the first recess in the first item, and placing the insert with at least said another portion in the second recess.

14. Process according to claim 11, when dependent on either of claims 4-5, wherein the second recess in the facing edge of the second item is made at the transition zone of the base layer and the cladding layer of the facing edge of the second item.

15. Process according to any of claims 11-14, wherein at least at the start of the butt- welding the insert is kept in its place through a form-fit in the recess or recesses.

16. Process according to any of the preceding claims, when dependent on either of claims 4-5, wherein the facing edges of the cladding layers are kept spaced from each other so as to form a gap until after butt-welding.

17. Process according to any one of the preceding claims, wherein the base layer is made of an alloy.

18. Process according to claim 17, wherein the base layer is made of a metal-carbon alloy.

19. Process according to any one of the preceding claims, wherein the cladding layer is made of an alloy.

20. Process according to claim 19, wherein the material of the cladding layer comprises any of the group consisting of ferritic and austenitic stainless steels, nickel-based alloys, copper-nickel alloys, martensitic (stainless) steels, Duplex 55, nickel-chromium alloys, and chromium alloys.

21. Process according to any one of the claims 1-18, wherein the cladding layer comprises nickel or titanium.

22. Process according to any of the preceding claims, wherein the insert is placed in a position such that it is in contact with both the base layer and the cladding layer of the first item.

23. Assembly of two items, wherein at least the first item comprises a base layer of a first material, in particular a first alloy, and a cladding layer of a second material, in particular a second alloy, wherein the first material and the second material are different materials, and the second item comprises at least a base layer of a material that is butt- weldable to the first material of the base layer of the first item, in particular comprises a base layer of said first material, wherein the base layers of the two items have been butt- welded to each other at their edges that face one another, and wherein an insert is pre- sent at the transition zone of the base layer and the cladding layer at the facing edge of the first item where it forms the welding groove, and wherein the insert is made of a material that is non-fusible at the temperatures that arise during the butt-welding of the two items and the insert is not fused with any material of both items.

24. Assembly of two items, wherein at least the first item comprises a base layer of a first material, in particular a first alloy, and a cladding layer of a second material, in particular a second alloy, wherein the first material and the second material are different materials, and the second item comprises at least a base layer of material that is butt- weldable to the first material of the base layer of the first item, in particular comprises a base layer of said first material, wherein the base layers of the two items have been butt- welded to each other at their edges that face one another, and wherein an insert is present of which at least a portion form-fits in a recess at the transition zone of the base layer and the cladding layer at the facing edge of the first item where it forms the welding groove, and wherein the insert is made of a material that is non-fusible at the temperatures that arise during the butt-welding of the two items, and the insert is not fused with any material of both items.

25. Assembly according to any of claims 23-24, wherein both the first item and the second item each comprise a base layer of a first material and a cladding layer of a second material.

26. Assembly according to any of claims 23-25, wherein the base layer and the cladding layer of the first item and / or of the second item are bonded or otherwise adhered to each other.

27. Assembly according to any of claims 23-26, wherein the insert lies such that it is in contact with both the base layer and the cladding layer of the first item.

28. Fractionator, vacuum tower, coke drum, process pipe, process column, pressure vessel, reactor, washer, heat exchanger; clad flow line, catenary riser pipe, slug catcher, line pipe or accumulator tank according to any of claims 23-27.

29. Process according to claim 4, further comprising the step of butt-welding the se- cond (cladding) layers of the first item and the second item to join the facing edges of these second layers, wherein the insert is of a material that is non-fusible at the temperature^) to be used in this butt-welding step.

30. Process according to claim 1, wherein the insert has a melting point that is higher than that of the first material and is higher than that of the second material and also is higher than that of the material with which the weld is made.

31. Process according to claim 1, wherein the insert is a tungsten insert or a molybdenum insert.

32. Process according any of claims 1-22 and 29-31, wherein as seen in a plane of cross-section with respect to the direction of extension of the facing edges of the first and second items, the insert has a cross-section with a curvilinear peripheral surface, in particular a circumambulating convex peripheral surface, more particular an ellipse-shaped, oval or circular cross-section.

33. Assembly according to any of claims 23-27, wherein as seen in a plane of cross- section with respect to the direction of extension of the facing edges of the first and second items, the insert has a cross-section with a curvilinear peripheral surface, in particular a circumambulating convex peripheral surface, more particular an ellipse-shaped, oval or circular cross-section.

34. Assembly according to any of claims 23-27, wherein only the first layers have been joined to each other and the second layers have a gap between them.