mud pump broken bolts factory

A 2011 model year car is "generally" too new to have a bolt so stuck that it is broken on removal. It is possible the mechanic encountered a stuck bolt but simply used the wrong technique to remove it (common mistake). It is possible, but less likely, that the bolt was defective. Either circumstance can be determined, in a forensic examination of sorts, by examining what remains of the bolt, the amount of corrosion, and other standard engineering factors. Again, though, simply due to the newness of the vehicle I would be very suspicious of any "reasons" (or excuses) given to you for a bolt breaking. Unless the car is more than 10 years old, the real "reason" is almost always improper disassembly. Furthermore, charging $1,100 to fix a broken bolt is unheard of, unless you are working on the Space Shuttle, and so obviously there is more to this story. YourMechanic can take over the job, if the car were towed to your residence but then, of course, you would have to disentangle yourself from the present shop. Keep the old broken segment of the bolt and take photographs of the stub that is stuck in the head or block and the area upon removal. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.

A circulating water pump is a key equipment of cooling systems in nuclear power plants. Several anchor bolts were broken at the inlet rings of the same type of pumps. The bolts were turned by a special material for seawater corrosion protection. There were obvious turning tool marks at the root of the thread, which was considered as the source of the crack. The fatigue crack extended to the depth of the bolt, causing obvious radiation stripes on the fracture surface, which was a typical fatigue fracture. Obvious overtightening characteristics were found at the head of the broken bolt. Fracture and energy spectrum analysis showed that the bolt was not corroded. The axial vibration of the pump was measured. The static tensile stress along the bolt axis caused by the preload, the axial tensile stress caused by the axial vibration, and the torsional stress were calculated, respectively. According to the fatigue strength theory, the composite safety factor of the bolt fatigue strength was 1.37 when overtightening at 1.2 times the design torque, which was less than the allowable safety factor of 1.5-1.8, so the bolt was not safe, which further verified the conclusion of fracture analysis. The reason for the low safety factor was caused by the overtightening force. The improvement method was to control the bolt preload or increasing the bolt diameter.

A cooling water pump is a very important equipment in nuclear power plants. During overhaul, it was found that the fixing bolts of the embedded parts of four CR1QS1 pumps were broken. The pump is a single-stage, vertical, bottom-suction concrete volute centrifugal pump. The pumps were fixed on the concrete embedded parts with 8 hexagon socket bolts through the mouth ring, as shown in Figure 1. The purpose of the protective cap is to protect the bolt from erosion. The working medium of the pump is sea water.

The common failure modes of bolt fracture are fatigue fracture, stress corrosion cracking, and overload fracture. Due to the large stress concentration of a bolt thread, it is easy for a fatigue source to form at the root, and the possibility of fatigue fracture is high. The bolt fracture studied by González et al. occurred at the second turn of the screw thread, which was caused by hydrogen embrittlement [1]. The bolt studied by Shafiei and Kazempour-Liaisi had M23C6 carbide, which was the source of the fatigue crack. The crack propagates along the grain boundary, and finally, fatigue fracture occurs [2]. Li et al. found that surface decarburization of the bolts and stress concentration at the bolt thread neck decreased the fatigue strength [3]. Wu et al. studied the corrosion fracture mechanism of cable bolts [4]. The fracture had general fatigue fracture characteristics. There were corrosion fatigue crack sources and radial fatigue crack propagation traces. Hydrogen-assisted stress corrosion cracking was the main fracture mechanism of cable bolts failure. The fatigue crack source of the bolt-sphere joint was pitting caused by corrosion [5]. Wen et al. [6] studied the fracture of a 20MnTiB steel high-strength bolt. Microdefects were found near the bottom of the thread. Considerable stress and corrosion accelerated the crack propagation of the bolt. The working capacity of a rock bolt decreased by 25-50% when it worked under the condition of rock and groundwater corrosion [7].

It is generally believed that the fatigue strength of bolts is only related to the stress amplitude. The fatigue strength only studied the stress amplitude of bolt tensile stress [7–10]. For example, the bolt fatigue strength condition was that the allowable stress amplitude was equal to 90 MPa [8], and the fatigue curve studied was the curve [9]. However, in practice, many examples showed that the failure of bolts was related to the average stress (i.e., bolt preload) [11, 12]. The reason for a bolt fracture was that the safety factor is insufficient due to excessive preload [11, 12]. The safety factor of static strength is obtained by preloading, the safety factor of variable stress is obtained by strain, and the safety factor is modified by Goodman’s theory [13].

In this paper, the fracture analysis, mechanical property analysis, and energy spectrum analysis of the broken bolt are carried out. At the same time, the fatigue strength of the bolt is calculated, the failure causes are found out, and the improvement suggestions are put forward. Finally, the calculation method of the bolt fatigue strength is proposed.

The bolts in service are shown in Figure 2, in which Nos. 1 and 2 were the unbroken bolts, Nos. 3-6 were the head of the broken bolts, and Nos. 7-11 were the rest of the broken parts of the broken bolts. Compared with the spares, their surfaces were the same as the serviced bolts, indicating that there was no corrosion.

The fracture of No. 3 bolt in Figure 2 is representative. Take it as an example to illustrate the fracture form of bolts. Figures 3(a) and 3(b) are the overall morphology and local morphology of the No. 3 bolt, respectively. There are obvious radial lines on the edge of the thread teeth, which is the fracture source as the point indicated by the arrow. The fracture source extends to the core, and then the bolt breaks when the crackle reaches the middle. This is the instantaneous fracture zone region, where the section is rough and uneven. The instantaneous breaking zone occupies a relatively large area, indicating that there is a large residual pretightening force when the bolt is broken.

Figure 5(a) is the morphology of the inner hexagon of the head of No. 3 broken bolt. The top of the bolt head is damaged when the sample was taken on site, as shown by the arrow. But the inner hexagon area is damaged during tightening, as shown in the region. Figure 5(b) shows the morphology of the unbroken bolt head, with the inner hexagon of the screw head intact. The comparison shows that the broken bolts have overtightening behavior when they were installed.

Figure 7 shows the macroimages of four unbroken screws through dye penetrant inspection, and no cracks are found on the surface. The metallographic structures of the unbroken and broken bolts are, respectively, shown in Figures 8(a) and 8(b), which show an austenite + ferrite structure. This conforms to the characteristics of dual phase steel, without obvious abnormality.

The bolts were made of a special material for seawater corrosion protection. Due to the small quantity, they were manufactured by turning. The chemical composition meets the ASTM s32760 standard, see Table 1. Using the XHB-3000 Digital Brinell Hardness Tester, the average hardness of bolts is 230-240 HBW, equivalent to grade 8.8 (Chinese national standard GB3098.1), which also meets the requirements of ASTM s32760 of less than 310 HBW.

By the AG100KNG universal testing machine, the tensile properties of sample bolts were tested, as shown in Table 3. The results all meet the requirements of standard values, and the mechanical properties are normal. According to the empirical formula recommended in the mechanical design manual, the symmetrical cycle fatigue limit and torque yield limit are estimated as follows:

Table 4 shows the composition of the fracture surface after cleaning by Energy Disperse Spectroscopy (EDS). The result is the same as the previous conclusion in Section 2.1, that is, as can be seen in Figure 2, the broken bolts were as glossy as the spare parts, and there was obviously no corrosion.

The bolts should be tightened when they are installed; that is, they are subject to the preload (tension) and friction torque. When working, it may be subjected to the variable stress of axial tension. In this paper, the finite element method is used to calculate the tensile stress and torsional stress by ANSYS Workbench 15.0 software.

The pump and the foundation ring are connected by 8 bolts. The finite element model takes 1 bolt and one eighth of the foundation including the ring and concrete, as shown in Figure 9. According to the equipment maintenance manual, the installation torque of the bolt is 40.5 Nm, the torque coefficient is 0.258, and the calculated preload is 13081 N.

The axial tensile stress and torsional stress of the bolt are shown in Figures 10 and 11, respectively. The axial tensile stress is 434.05 MPa, and the torsional stress is 59.29 MPa at design torque. If the overtightening torque reaches 1.2 times the design value, the axial tensile stress is 520.86 MPa, and the torsional stress is 71.41 MPa. The inner hexagon of the broken bolt head has been seriously damaged, and the actual torque is far greater than 1.2 times the design value.

When the pump runs, the impeller will have a working load, acting on the bolt axis direction. The stress is a symmetrical cyclic strain produced by the axial vibration when the pump is running. The axial load was obtained by actual measurement. A speed sensor was installed at the bearing, and the excitation spectrum load was the relationship between the speed and the frequency spectrum, as shown in Figure 12.

(1)There are obvious crack sources at the root of the thread, and there is an obvious fatigue fracture zone and an instantaneous fracture zone at the cross section. The fatigue fracture zone is typically radial and has typical fatigue fracture characteristics(2)The bolt safety factor at 1.2 times the design torque is 1.37, which has been less than the allowable safety factor of 1.5-1.8. Therefore, the fatigue strength of bolts is insufficient, and a bolt fracture is due to fatigue failure when the bolt is overtightened(3)The failure of bolts is not caused by seawater corrosion. The surface of the broken bolt is bright, and there is no trace of corrosion(4)The key cause of a bolt fracture is too much preload. The measure to improve the safety factor is to control the bolt preload or increase the diameter of the bolt

as far as the broken bolt goes, i have had many many bolts break off, i have worked on cranes that are offshore on barges and rigs, and they were rusted so bad the bolt would fuse itself to the piece of metal it was going thru and even heating it with a "Rose Bud" would not get it out. i found that if you soak it in penetrating oil for a few hours and then drill it out with a masonry bit it goes a little easier as the masonry bit will not dull as fast as a metal bit, i swear by this method because in alot of the rigs the bolts are made of spring metal which is much much harder than stainless to drill out. i would avoid heating the aluminum/cast if possible, it doesnt take much heat to compromise the integrity of aluminum/cast. if i understood what you were saying the bolt was almost out when it broke, so i would drill a small hole thru the bolt and use an extractor to get it out, that way you dont damage the aluminum/cast housing. also, someone mentioned welding another bolt to the broken one to get it out, i would be very cautious, if your motor has ANY electronics on it as the welder can short them out, if you do choose this route, be sure to disconnect the battery (both cables) as the welder can short out anything connected to the electrical sytem on the entire vessel. Good Luck

How many times are pump operators forced to modify fasteners that are used to secure motors and/or pumps to baseplates? A warehouse spare is ready to be installed and nothing fits, i.e alignment is not successful, major piping does not bolt up cleanly, and operations are anxiously awaiting their new equipment.

During shop maintenance performed—probably at a well qualified OEM or independent repair facility—the solution would be to enlarge the through holes for hold down bolts. While not a perfect solution to frustrating installation issues, my experience has been that this simple modification can often provide almost instant relief.

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So everything has been going pretty well with what I have been working on, granted I haven"t done any major projects. Well last night when I was going to reinstall my fuel pump after changing out the internals (went well), I snapped one of the fuel pump bolt heads off. The frustrating part is even having over torqued it, it never felt like I was applying that much more pressure than the torq specs (80-97 in/lbs). Either way, I read that this has been an issue occasionally for others and they recommended changing out the bolts anyway, a few people having done that before breaking one.

The 6 factory pressure plate mounting bolts have captive lock washers and should be torque to 11-15 ft-lb using a diagonal pattern (see FSM page 2-13 Chassis and Body Repair Manual). Apply the torque in 5 ft-lb increments and make sure you use a thread sealer similar to Locktite. To get the proper torque, it is best to use a tap to chase the threads to remove the sealant from the previous installation.

Lock washers are not used with the factory 2F flywheel bolts. The torque for the six 2F flywheel bolts is 59-61 ft-lb applied in a diagonal pattern (see FSM page 3-44 2F Engine Repair Manual). Apply the torque in 10-15 ft-lb increments and make sure you use a thread sealer similar to Locktite. To get the proper torque, it is best to use a tap to chase the threads to remove the sealant from the previous installation.