Laser Technologies of Gas Powder Surfacing and Heat Treatment of Drilling Equipment for Arctica Project Tasks
Nowadays our country faces the urgent problem of depletion of the largest, in particular, oil and natural gas mineral deposits. Such deposits include Megion, Samotlor, Urengoy, Yamburg and many others. According to the majority of expert estimates oil and gas reserves in these deposits will run short in as little as a few decades. Since nowadays the economy of the Russian Federation depends greatly on export of these mineral deposits, it is necessary to start development and exploitation of new deposits in a short space of time. For the time being these deposits are known to be located in Siberia, near the shelf of the Arctic Ocean and in a number of other arctic areas. Thereby, domestic manufacturing engineers specializing in the field of highly efficient processes of material processing, in particular, in the field of laser technologies, face the following tasks: to start rapidly development and sophistication of technologies for reconditioning, repair and enhancement of performance characteristics of the drilling equipment used for extraction of these mineral deposits.
First of all, such technologies include gas powder laser surfacing and laser heat strengthening. The major part of this paper is devoted to their consideration. In addition, main modifications of drilling equipment to be laser processed are summarized in the paper. Interoperation of essential components and assemblies of the drilling rig derrick in the course of drilling, oil well drilling chart with designation of key elements are shown in Fig. 1.
Bottom-hole assembly equipment is the most interesting for the laser processing specialist since such equipment needs to be primarily repaired and reconditioned; its performance characteristics need to be primarily enhanced while using highly efficient energy sources.
MAIN TYPES OF DRILLING EQUIPMENT SUITABLE FOR LASER PROCESSING AND DOMESTIC MANUFACTURERS OF THEM
A brief description of them is given further on. Let’s give examples of those types of drilling equipment which can be laser processed, surfaced and heat treated. But, first of all, let’s list domestic manufacturers of such drilling equipment:
• Drilling Equipment Plant (Orenburg);
• Mining Machines, JSC (Moscow, Krasnoyarsk, Ekaterinburg);
• Aleksandrov Drilling Equipment Plant, JSC (Moscow)
• BURSNAB, LLC (Moscow);
• Sovremennaya Burovaya Tehnika, NPC;
• Burovaya Technika – VNIIBT, OJSC SPA (Moscow);
• Bulanash Machine-Building Plant, JSC as part of Generation, Industrial Group (Sverdlovsk region);
• PromTehInvest, JSC (Saint Petersburg);
• Stroydormash, JSC as part of Uralinvestenergo, Industrial Holding Company (Sverdlovsk region);
• Integra, Group of Companies (Moscow).
Drilling stabilizer is a special-purpose drilling tool used to avoid damage to borehole walls caused by drill string while drilling. Stabilizer (Fig. 2) centralizes drill string and bottom-hole motor, stabilizes and changes well trajectory. Working surface (alternately referred to as a wall contact) is made of solid metals with diamond and tungsten carbide inserts. Working environment is as follows: alkaline medium; temperature ranging from ‒50 to 60 С°; hydro-abrasive wear.
Drill bit is the key element of the drilling tool designed for rock disintegration on the bottom hole while drilling. Drill bits are classified (Fig. 3) dependent on two ranking features: the purpose and nature of the impact on the rock.
Drill pipe is the major component of drill string designed to run in hole, lift a rock cutting tool, transmit rotation, generate axial load on the tool and convey drilling fluid to the bottom hole.
Drill pipes (Fig.5) are made seamless, of carbon or alloy steel, mainly upset. Drill pipes are 33.5–168 mm in diameter (drill pipes up to 60 mm in diameter are used mainly for exploratory core drilling).
Drill rod (Fig.6) is made of very strong high-carbon steel and used to transfer rotation from drilling rig to drill bit, auger. Moreover, drill rod serves to transfer impact force of the drilling installation to drill bit when percussive-rotary drilling is used. When fluid-circulation or air flushing drilling is used, drill fluid or air, respectively, is supplied through drill rods. Since drill rods are used under very high loads, they are made of very strong steel. Steel hardness is determined by the carbon content. Depending on the type of well drilling and dimensions of the drilling installation drill rods of various dimensions and strengths are used. There is no need to use expensive drill rods made of alloy steel, for example, for shallow water well drilling or when shallow-depth drilling installations are used. Meanwhile, when drilling deep oil or gas wells low-strength drill rods endanger the drilling process in view of the risk of breakdown of the auger system in the bore hole. The length of drill rod depends on the height of mast or drilling rig derrick. The height is directly proportional to the number of strokes of the drilling installation and, thus, the length of drill rod. Nowadays there are two basic drill rod hardening methods: water and oil hardening methods:
Water hardening – drill rod develops higher compression strength and at the same time it becomes more brittle. It is easier to process the item in contrast to oil hardening method. Drill rod or another item can hardly be welded when this hardening method is used.
Oil hardening is slower than water hardening; metal strength is higher. It is more difficult to process and weld oil-hardened drill rod.
When water hardening is used, a steel product is heated until it glows a cherry-red colour and then submersed into a container filled with water and left until cooled. This will makes it possible to get a tough, high-strength product, still treatable. Heating until the rod glows a cherry-red color with subsequent submersion in warm oil makes surface metalworking extremely difficult and may damage the cutting tool. Therefore, prior to oil hardening drill rods or other steel products have to be brought to readiness. Depending on the intended use some rods have to be less brittle and more ductile. For this purpose metal is tempered. Tempering is reached by slow heating after hardening. When steel is heated up to 450 degrees Celsius, metal hardness is getting lower. Thereafter, the product is left to be cooled in the air. Tempered metal can be grinded or polished.
The difference in water or oil steel hardening lies in the fact that water is better heat conductor than oil. Consequently, water cooling is faster, but uneven. It results in deformation due to uneven, from the surface to the depth, cooling. The said is essential to be considered when precision products are manufactured.
DRILLING EQUIPMENT RECONDITIONING BY LASER GAS POWDER SURFACING
Advantages of laser surfacing over traditional technologies
There are a number of advantages of laser surfacing over traditional surfacing methods. High energy concentration in the hot spot makes it possible to conduct the process at higher processing speeds. This, in turn, determines the following:
• Feasibility to form a pad with low mixing coefficient (0,05–0,15) due to slight base fusion.
• Minimal heat effect on base metal is especially important for the materials undergoing structural and phase transformations.
• Minor residual deformations of surfaced parts.
• Feasibility to surface small surfaces proportionate to the hot spot diameter when pulsed and repetitively-pulsed lasers are used.
• Higher performance characteristics of pads.
Thus, small deformations, on the one hand, and high performance characteristics, on the other hand, predetermine the use of this method not only while getting special performance characteristics of the product surface, but also while manufacturing machine parts.
Advantages of the use of broadband gas powder laser surfacing (broadband GPLS) when processing drilling equipment
Broadband GPLS is a more efficient technology than a traditional GPLS technology in which a circular beam spot is used since in the latter case sintered powder traces a narrow spiral-shaped curve on the work piece surface while in case of the broadband GPLS a rectangular beam is used and such a curve is 2–3 times as wide and the whole surface is covered in a much fewer passes at approximately the same cost of powder (Fig. 7). Thus, time and expensive laser source energy are saved.
Another important advantage of broadband surfacing over the traditional laser surfacing is the feasibility to reduce the volume of voids between rollers which makes it possible to obtain a more void-free pad structure, reduce dimensions of the overlap area  and substantially save powder material (Fig. 8):
The use of GPLS technology in which a rectangular beam is used is promising in both batch and mass production. High process efficiency makes it possible to replace plasma and arc surfacing with a laser one where pad quality is higher and there is less heat effect on the part. This technology is ideal for processing large parts due to high process performance. Moreover, it is fair to say that the GPLS with a rectangular beam has been developing namely in order to process large parts, such as shafts in motor vehicle and shipbuilding industry and drilling equipment.
Surfacing materials used for laser and traditional surfacing are the same. They include compact additives made in the form of wire or tape and powders.
• There are a number of advantages of powder materials over compact materials:
• Enhanced absorption of laser emission due to branched surface and multiple beam reflection from individual particles.
• Less (more than 1.5 times) energy needed melt powder material.
• Broad options to control chemical composition of the pad.
• Ability to deliver metal to hard-to-reach places.
• Ease of supply that is important while manufacturing irregular shaped parts.
The following examples of materials used in GPLS of drilling equipment can be given:
• INCONEL 625 UNS N06625 alloy ‒ nickel-chromium alloy with addition of niobium which in combination with molybdenum ensures increased strength without additional heat treatment. Operating temperatures of Inconel 625 alloy range from cryogenic temperatures to 980 °C. The alloy is resistant to a wide range of severe corrosive environment and especially resistant to pitch and crevice corrosion. It is resistant to gas corrosion resulted from the exposure to high temperatures. It is notable for high workability, in particular, weldability. ХН75МБТЮ alloy GOST 5632 can be considered as a domestic analogue of INCONEL alloy 625. It is used in chemical, petrochemical, aircraft and shipbuilding industries, nuclear reactors. According to ANSI/NACE MR0175 the material type for this alloy is 4d for annealed and cold-worked solid-solution nickel-based alloys used for any equipment and components.
• ХН65МВ alloy is used for manufacturing of welded chemical equipment used under the most severe conditions (reductive-oxidative environment) of chemical, petrochemical, pulp and paper and other industries at a wall temperature ranging from –70 to 500 ° and environment pressure amounting up to 5,0 N/ mmІ. The alloy is smelted in open induction furnaces.
• tungsten carbide is widely used in engineering for manufacturing of high-hardness and corrosion resistant tools, as well as for wear-resistant surfacing of parts used under conditions of intense abrasive wear and moderate impact loads. This material is used for manufacturing of various boring tools, abrasive discs, auger bits, mills, bore bits and other cutting tools. The hard alloy grade known as Pobedit is of 90% tungsten carbide. It is widely used in thermal spraying and surfacing in the form of a powder material aimed to make wear-resistant coatings. For example, cast tungsten carbide, being a WC-W2C eutecticum, is used to surface drilling tools and other items exposed to abrasive wear. It is one of the basic materials used to replace galvanic chrome plating by High Velocity Oxygen Fuel coating method.
To be continued