Development of Nippon Steel premium connection
Masao OgasawaraFujimasa KoyamaKazushi MaruyamaEiji TsuruYoichi YazakiToshitaro MimakiMasayoshi TanabeShuichi Takesue
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New premium connections for oil country pipes were developed and the gas tightness, anti-galling capability and joint strength were studied experimentally and theoretically. The sealing mechanism was the two-step-pin-nose radial metal seal and composed of two shoulders and stable gas tightness was ensured by the secondary reserve shoulder even if the primary shoulder was deformed. The stress relief mechanism was provided to alleviate the local pressure on the seal. The sealing area surface was processed by Cu, Zn plating or phosphating depending on the service environment to increase the anti-galling capability. The API Buttress type thread was used because of the easy application and sufficient joint strength. This connections were successfully applied to drill-strings used under severe conditions where stress varied much by thermal expansion and contraction, such as in steam injection wells containing heavy gravity crude oil in California, U.S.A. (13 figs, 3 tabs, 2 photos, 6 refs)Keywords:
Galling
Buttress
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Several pins fractured during service at the same position.Two of them were investigated.The failure cause of the pins was analyzed by fracture surface observation,chemical composition analysis,metallurgical structure and hardened case depth examination,and stress analysis by CAE.The results show that the fracture of the pins mainly resulted from the improper location of the oil holes.The oil holes were random located in the pins.If the oil hole was located in the side under the effect of the maximal bending stress,stress concentration effect of the oil hole would lead to overlarge stress at the port of the oil hole.As a result,fatigue cracks initiated at the port of the oil orifice.In addition,lower fatigue resistance resulting from thinner hardened case is another cause for the early fatigue fracture of the pins.According to the analysis above,the similar fatigue fracture of the pins can be avoided by locating the oil holes in the side under the effect of the lower bending stress and increasing the depth of the surface hardened cases.
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During the drilling in deep wells and extended-reach wells,non-uniform casing wear occurs due to the frequent contact between the drill pipe and the casing.While severe casing wear will lead to the reduction of casing collapse strength and internal pressure strength,this becomes a threat to drilling safety.Based on the recommended calculation formulae for casing collapse strength and internal pressure strength by the ISO 10400,the calculation models of casing collapse strength and internal pressure strength for non-uniform wear casing were derived,with the effects of casing eccentricity and ovality considered.Then the collapse strength and internal pressure strength of casing with different wear thicknesses were calculated.The results showed that the casing collapse strength and internal pressure strength will decrease as the casing wear-thickness increases.Under the same wear condition,the casing collapse strength decreases more rapidly than the internal pressure strength.From the comparison between the theoretical calculation result and the measured collapse strength of CS-110T worn casing,it is concluded that the relative error of this method is within 5%.This model will provide a new evaluation method for non-uniform casing wear in deep wells and extended-reach wells.
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Drill pipe
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Department of Materal Engineering of Jiujiang University China, Jiujiang 332005Abstract In this paper, the causes of slippage effect and thread gluing on the connection of oil well steel tube have been analyzed systematically. Force analysis of the oil well steel tube indicates that the first and second buckle of tube and coupler joggle and the front buckles of the coupler are stress concentration area. With the increase of torsion moment, the degree of stress concentration increased. So the first cause of tube failure is the stress concentration caused by over - tightened screw on and screw off that exceed the maximum rating one. Finally innovative approach and suggestion on thread slipping of oil well steel tube.
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Slippage
Buckle
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A slipping accident of 准177.8 × 10.36 mm N80Q EU casing was investigated. The failure analysis indicates that the coupling yield strength, yield strength and the tensile strength of the tube body can not meet the standard requirements. Because the casing pipe body strength is lower and the coupling tensile strength is higher, the material can not match appropriately. The lower plastic pipe body can cause yield, which can result in thread connection parts proning to galling, so the jointing strength reduces. Not qualified screw thread parameters and the poor anti-galling performance are the reasons for the failure of casing screw thread.
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Slipping
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Corrosion protection of fully grouted rock bolts has been the subject of considerable research in recent years. Corrosion protection is studied focusing on quantitatively determining how much encapsulation coating affect the bolt/resin bond capacity. Resin coating results in reduction of rib height and in turn causes a decrease in interlocking effect with the grout annulus. The laboratory tests performed have shown that there was a wide range of reduction in bonding strength (from 5 to 40 %), depending on the type of the bolt and media in which the bolt had been installed. The reduction of rib height was also responsible for lower lateral dilation during bolt pullout tests. This effect will make the confining medium become an important parameter, since higher confining medium results in higher confining pressure on the bolt surface which in turn, controls the bond capacity. INTRODUCTION For years, rock bolts have been a common method for ground reinforcement both at underground as well as surface rock structures. Effectiveness and ease of installation has been the main two advantages of this active support method as opposed to the usual passive ways of supporting broken rock. Most of the bolts are made out of steel which makes them good candidates for corrosion. Although fibreglass bolts have recently emerged into the market for special applications, nevertheless steel bolts have still remained the dominant type of rock bolt in daily practice. One of the main problems about rock bolts, especially underground, is corrosion. The main causes of this problem are underground water, humidity, stray currents and chemical interaction between the surrounding media and the steel. Grounds with sulphur content, when interacts with water, can produce strong acids which quickly reduce the effective diameter of the bolt. This problem in certain circumstances becomes so severe that can cause failure of the reinforcement. One of the temporary methods to overcome this problem is to apply a corrosion resistant coating on the surface of the bolt. Epoxy resin is one of these materials which have been widely used due to its relatively low price. Although this can be assumed only a temporary solution, but in many occasions, the lifetime of the tunnel which these reinforcements are to be used in is also short therefore their application is justifiable. For higher required life times, stronger protections are required. Double Corrosion Protection systems (DCP) utilizes a high density polyethylene tube as well as a layer of cement around the bolt as two corrosion protection layers, to ensure higher corrosion securities. One of the causes of epoxy coating is reduction of the effective rib height in the bolts which in turn, can reduce the bond capacity due to reduced interlocking effect with the grout annulus surrounding the bolt. The present paper tries to find a quantitative answer to this general feeling about reduced bond capacity. ROCK BOLTING IN MINES Rock masses contain natural discontinuities which may cause stability problems, therefore most underground openings need to be stabilized to maintain their integrity during their service life. As stated by Hoek and Brown (1980), “The principal objective in the design of underground excavation support is to help the rock mass to support itself”. The best way to achieve this is through the use of reinforcement (i.e. rock bolt) to help maintain the loadcarrying capability of rock masses near excavation boundaries. Beyl (1945) reported an early use of bolts in a longwall mine in 1912. The bolt was made out of wood and was used to prevent small pieces of rock from falling between the face and the main support system. Littlejohn and Bruce (1977) reported that the first use of rock anchors was in Cheurfas Dam, Algeria in 1934. Due to the success of bolting, fundamental studies on the bolting action were started by Rabcewicz (1955) and was continued by Panek (1956a, b,c,1962a,b) supported by U.S. Bureau of Mines. This research led to the concepts of suspension and beam building effects for bolts in bedded mine roofs. The arching effect of bolts was pointed out by Evans (1960). In jointed rocks, the importance of limiting displacement as the key parameter of the bolting action was explained by Palmer et al. (1976). This is because the opening of joints during excavation decreases the strength of rock due to the associated softening effect. This concept forms the basis of present pre-reinforcement concepts. 1 Associate Professor, School of Mining Engineering, The University of Tehran, Iran 2 PhD student, International Institute of Earthquake Engineering and Seismology, Iran 2008 Coal Operators’ Conference The AusIMM Illawarra Branch 118 14 15 February 2008 [ ]⎦ ⎤ ⎢ ⎣ ⎡ + − − + = 2 2 2 2 ) 2 1 ( ) 1 ( 2 o i i i o r d d v d d d v E k It was noted that pre-placement of bolts can decrease the deterioration of the internal rock mass strength resulting from joint dilation. Rock bolting is currently a usual practice in most of the coal mines due to the limited required length for the reinforcing rock layers and the request for high installation speed as a prerequisite for increasing production time. Most of the rock bolts use resin capsules as a bonding agent to the rock which facilitates faster process and reduces time for the whole supporting cycle. CORROSION MECHANISM Corrosion is defined as defect on material (usually metals) properties due to their interaction with the surrounding media. By this definition, wear, abrasion, scratch and fatigue which have mechanical cause are excluded. It is worth noting that the word “rust” is used only for Iron which is an interaction with water and Oxygen. In another words, other metals will corrode but do not rust. The main chemical mechanism in steel corrosion is as follows: So if anyone of the main three components (steel, water and oxygen) does not exist, the corrosion would not happen. In this mechanism, some parameters can have accelerating effects which the most important ones are as follows. Temperature: Usually the higher the temperature, the faster the corrosion would be. The hotter points in a material are usually more anodic than the other points so cause accelerated corrosion locally. Difference in galvanic potential: When two metals with different galvanic potentials are close to each other, the metal with higher galvanic number acts as anode and corrodes faster so protects the other metal from corrosion. Surface smoothness: Metals with rough surfaces usually corrode faster than shiny surfaces. Stress: When a material is under tensile stress, it corrodes faster which is believed to be due to the micro cracks generation in the metal. Corrosion will accelerate if the stress level is higher, especially if it is close to the material’s elastic limit. TEST SETUP AND SAMPLE PREPARATIONS The bolts used for tests consisted of two types, i.e. 28mm rebar and 28mm continuous thread bar from Dywidag company. The bond length in each sample was 15 cm and the water:cement ratio used for the grout annulus was 0.4. Some of the bolts were covered by epoxy resin while some others were left uncoated to enable comparison of bond reduction. The number of the bolts used in each test class is shown in Table 1. Table 1 The number of tests performed in each test category. Since the bolts are usually installed in 63.5 mm (2.5 inch) diameter borehole, the laboratory test was designed so that the bolts become surrounded by the same size mould. To confine the bolts, they were put in pipes with internal diameter of 63.5 mm (2.5 inch) and the space between the bolt and the pipe was filled with Portland Cement grout. This test was carried out “constant confining stiffness” condition, meaning that during pull test, the generated pressure at the outer surface of the grout will vary as a function of generated dilation due to ribs. These pipes were made of Steel, Aluminium and PVC, to simulate different rock mass qualities in the laboratory. To associate each pipe to a rock mass with known quality (i.e. Erm) equation (1) can be utilized. (1) Type of confining pipe PVC Aluminium Steel Type of bolt 4 4 4 CT bar Ф28 with Epoxy 3 3 3 CT bar Ф 28 without Epoxy 4 4 4 Rebar Ф28 with Epoxy 3 3 3 Rebar Ф28 without Epoxy 2 2 2 ) ( 2 1 OH Fe O O H Fe → + + 2008 Coal Operators’ Conference The AusIMM Illawarra Branch 14 – 15 February 2008 119 r v E k r r ) 1 ( + = 5 . 31 ) 25 . 0 1 ( 33 . 2110 + = r E In this equation kr is the radial stiffness of a pipe with di and do as its inner and outer diameters and E and v as the elastic properties of the pipe material. Table 2 shows the radial stiffness of the various pipes used as moulds. Figure 1 Sample preparation. Table 2 Radial stiffness of the pipes used as mould. E (GPa) v do (mm) di (mm) kr (MPa/mm) Steel 200 .25 58.4 45.5 2110.33 Aluminium 72 .25 59.6 50.0 504.81 PVC 3 .32 62.44 53.3 19.17 For a borehole drilled with radius r in a rock mass having deformation Modulus and poison’s ratio equal to Er and v respectively, the radial stiffness is: (2) therefore the steel pipe, for example, used in the tests is equivalent to a rock mass having deformation modulus equal to 83 GPa since;
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A steam pressure pipe broke into pieces in the course of normal operation. The chemical composition and mechanical property analyses proved that the material of the pipe was good. However,the metallographic examination and fractographic observation showed that there were some defects in the weld joint of the pipe and the fixed bracket,where there was a zone of high stress concentration. Furthermore,mechanical analysis of the weld joint explained the reason why there was high peak stress and it indicated that the wall thickness of the pipe was too thin to endure the severe stress condition. In addition,the possibility of steam hammer or water hammer and their possible influence were discussed. Based on these analyses,it was concluded that the cracking occurred first in the weld joint between a steam pipe and a fixed bracket. And then it lead to the rupture of the whole pipe. The cracking resulted from poor quality of the welding and inapposite design of the pipe thickness as well as the structure of the joint.
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During a routine preflight inspection at Ft. Hood, an outboard barrel nut was found to be cracked on an Army helicopter.The part was fabricated from UNS NO771 8 material according to AMS 5662F "Alloy Bars, Forgings, and Rings, Corrosion and Heat Resistant".Subsequent inspections at Ft. Hood and Ft.Rucker revealed an additional seven barrel nuts with large cracks.The components are used in many critical applications.The failures under investigation in this study were relegated to the vertical stabilizer of the aircraft.The failures were all attributed to hydrogen induced cracking.Galling between the unlubricated bolt and the nut threads provided the sustained hoop stress while galvanic corrosion of the carbon steel retaining clip in contact with the barrel nut generated hydrogen as a result of the corrosion process.Microstructural analysis of the material used to fabricate the nut revealed excessive banding consisting of a Widmanstatten phase and MC carbides which ran parallel to the fracture plane, The grains were almost completely surrounded by an undesirable acicular delta phase.No evidence of Laves phase was observed.Recommendations were made to utilize a corrosion inhibitive lubricant on the threads of the barrel nut and mating bolt to reduce galling and the consequential high stresses which result from metal to metal contact during torquing.A stress analysis of the part showed that the high strength level of the material could be reduced to increase fracture toughness and resistance to hydrogen cracking.The acicular delta phase should be avoided in accordance with AMS 5662F and the extrusion direction of the material should be parallel to the principal loading direction.Salt fog testing of the proposed barrel nut configuration revealed that the shoulder height base thickness should be increased.Future vendors should qualify their product by conducting a prescribed salt fog test incorporating the revised torque requirements.Finally, the material used to fabricate the retaining clip should be changed to prevent galvanic corrosion.
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During a routine preflight inspection at Ft. Hood, an outboard barrel nut was found to be cracked on an Army helicopter. The part was fabricated from Inconel 718 (UNS N07718) according to AMS 5662F, “Alloy Bars, Forgings, and Rings, Corrosion and Heat Resistant”. Subsequent inspections at Ft. Hood and Ft. Rucker revealed an additional seven barrel nuts with large cracks. The components are used in many critical applications. The failures under investigation in this study were relegated to the vertical stabilizer of the aircraft. The failures were all attributed to hydrogen induced cracking. Galling between the unlubricated bolt and the nut threads provided the sustained hoop stress while galvanic corrosion of the carbon steel retaining clip in contact with the barrel nut generated hydrogen. Microstructural analysis of the nut revealed excessive banding consisting of a Widmanstatten phase and MC carbides which ran parallel to the fracture plane. The grains were almost completely surrounded by an undesirable acicular delta phase. No evidence of Laves phase was observed. Recommendations were made to utilize a corrosion inhibitive lubricant on the threads of the barrel nut and mating bolt to reduce galling and the consequential high stresses which result from metal to metal contact during torquing. A stress analysis of the part showed that the high strength level of the material could be reduced to increase fracture toughness and resistance to hydrogen cracking. The acicular delta phase should be avoided in accordance with AMS 5662F and the extrusion direction of the material should be parallel to the principal loading direction. Salt fog testing of the proposed barrel nut configuration revealed that the shoulder height base thickness should be increased. Future vendors should qualify their product by conducting a prescribed salt fog test incorporating the prescribed torque requirements. Finally, the material used to fabricate the retaining clip should be changed to prevent galvanic corrosion.
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Fillet (mechanics)
Fillet weld
Spark plug
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