Failures bolts

Ceramics cannot be bolted or riveted the contact stresses would cause brittle failure. Instead, ceramic components are bonded to other ceramic or metal parts by techniques which avoid or minimise stress concentrations. 

The problem could be maintenance, operation, or design, or a combination of any or all these factors. In all honesty, you should never. see this set of evidence marks because it indicates a lack of control. Now because the mechanic cannot control operational problems or design problems, the first phase to correct this situation is to control the mechanical maintenance factors, like alignment, proper bolting and torque. sequences, be sure shafts are straight and round, and dynamically balance all rotary components. Reinstall the pump and wait for the next failure. Once the maintenance factors are under control, there should appear a clear vision and path to resolve any operational and/or design weaknesses. 

The principal failure modes of bolted joints are (1) bearing failure of the material as in the elongated bolt hole of Figure 7-44, (2) tension failure of the material in the reduced cross section through the bolt hole, (3) shear-out or cleavage failure of the material (actually transverse tension failure of the material), and (4) bolt failures (mainly shear failures). Of course, combinations of these failures do occur. 

Net-tension failures can be avoided or delayed by increased joint flexibility to spread the load transfer over several lines of bolts. Composite materials are generally more brittle than conventional metals, so loads are not easily redistributed around a stress concentration such as a bolt hole. Simultaneously, shear-lag effects caused by discontinuous fibers lead to difficult design problems around bolt holes. A possible solution is to put a relatively ductile composite material such as S-glass-epoxy in a strip of several times the bolt diameter in line with the bolt rows. This approach is called the softening-strip concept, and was addressed in Section 6.4. 

Bonded-bolted joints generally have better performance than either bonded or bolted joints. The bonding results in reduction of the usual tendency of a bolted joint to shear out. The bolting decreases the likelihood of a bonded joint debonding in an interfacial shear mode. The usual mode of failure for a bonded-bolted joint is either a tension failure through a section including a fastener or an interlaminar shear failure in the composite material or a combination of both. 

Bonded-bolted joints have good load distribution and are generally designed so that the bolts take all the load. Then, the bolts would take all the load after the bond breaks (because the bolts do not receive load until the bond slips). The bond provides a change in failure mode and a sizable margin against fatigue failure. 

Why did they not report the failures If they had reported them would anything have been done The accident would not have occurred if the foreman or the engineer, on their plant tours, had noticed the broken bolts and asked why there were so many. 

Many companies now insist that if use of the wrong grade of steel can affect the integrity of the plant, all steel must be checked for composition before use. This applies to flanges, bolts, welding rods, etc., as well as the raw pipe. Steel can be analyzed easily with a spectrographic analyzer. Other failures caused by the use of the wrong construction material are described in Section 16.1. 

Corrosion usually results in a leak or failure of a support because a vessel or support gets too thin. It is then not strong enough to withstand the pressure or load. However, rust can cause failure in another way. It occupies about seven times the volume of the steel from which it was formed. V/hen rust occurs between two plates that have been bolted or riveted together, a high pressure develops. This can force the plates apart or even break the bolts or rivets (see Section 9.1.2 g). Corrosion of the reinforcement bars in concrete can cause the concrete to crack and break away. 

High-strength a-0 brasses containing up to about 5Vo A1 (with small amounts of Fe, Mn, Sn, etc.) used for propellers, parts of pumps, nuts and bolts, etc. usually give good service but occasionally suffer intercrystalline failure, for instance in contact with sea-water. Examination of such failures usually reveals thin dezincified layers along the cracks, but it is difficult to decide whether the crack or the dezincification occurred first. 

While ideally structures should be designed and fabricated so that environment-sensitive cracking is avoided, in practice it is sometimes necessary to live with the problem. This implies an ability to detect and measure the size of cracks before they reach the critical size that may result in catastrophic failure. Such inspection has important implications for plant design, which should be such as to allow inspection at relevant locations. The latter are regions of high residual stress (welded, bolted or riveted joints) and regions of geometrical discontinuity (notches, crevices, etc.) where stress or environment concentration may occur. 

Blast loaded structures produce high reaction loads at column supports. This usually requires substantial base plates as well as high capacity anchor bolts. Achieving full anchorage of these bolts is of primary importance and will usually require headed bolts or plates at the embedded end of the bolts to prevent pullout. When anchor bolts are securely anchored into concrete, the failure mechanism is a ductile, tensile failure of the bolt steel. Insufficient edge distance or insufficient spacing between bolts results in a lower anchorage capacity and a brittle failure mode. 

D.T. Hill, S.A. Cobbs, and J.P. Bolte. Using volatile fatty acid relationships to predict anaerobic digester failure. Trans. ASAE, 30 496-501, 1987. 

Consider the case of a component failure in a physical system, such as a bolt or a gasket. Wben an unexpected failure occurs, it is for one of two reasons ... 

Some cadmium-plated bolts and nuts were purchased and installed as a test in the plant. More bolts were purchased and eventually some of the cadmium-plated bolts were installed on the outlet piping flanges of a cracking furnace. The high temperature outlet flanges on the furnace started to weep a bit. An experienced, intelligent pipefitter attempted to snug up a few bolts and the nuts crumbled. (The cause of the failure was later determined to be due to corrosion phenomena called liquid metal embrittlement. )... 

The alert mechanic informed the operations supervisors of the failures. Operations shut down the furnace. Maintenance mechanics replaced the bolts with the properly-specified high-strength stud bolts prior to any serious releases. 

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