Nozzle cracking

NDE inspection at a planned shutdown revealed significant nozzle cracking. A replica-based investigation and engineering analysis identified the nature, quantity and significance of the creep cracking and cavitation damage. Creep ... 

No external primary loop piping. The use of a natural circulation driven integrated reactor vessel eliminates the potential for hot and cold leg breaks, pressurizer surge line nozzle cracking and breaks, reactor coolant pump suction line breaks, and reactor coolant pump seal breaks. 

ISSUE TITLE Pipe cracks and feedwater nozzle cracking in BWRs (Cl 8)... 

The issues on pipe cracks and feedwater nozzle cracking were resolved with the issuance of NUREG-0313 and NUREG-0619, respectively. 

NUREG-0619, "BWR feedwater nozzle and control rod drive return line nozzle cracking", November 1980. 

NUREG-06I9 Rev.I, BWR feedwater nozzle and control rod drive return line nozzle cracking Resolution of generic technical activity A-IO (Technical Report). R. Snaider. US NRC, (Nov. 1980). 

Other forms of carbon-carbon composites have been or are being developed for space shutde leading edges, nuclear fuel containers for sateUites, aircraft engine adjustable exhaust nozzles, and the main stmcture for the proposed National Aerospace plane (34). For reusable appHcations, a siHcon carbide [409-21 -2] based coating is added to retard oxidation (35,36), with a boron [7440-42-8] h Lsed sublayer to seal any cracks that may form in the coating. 

For environmental reasons, burning should be smokeless. Long-chain and unsaturated hydrocarbons crack in the flame producing soot. Steam injection helps to produce clean burning by eliminating carbon through the water gas reaction. The quantity of steam required can be as high as 0.05—0.3 kg steam per kg of gas burned. A multijet flare can also be used in which the gas bums from a number of small nozzles parallel to radiant refractory rods which provide a hot surface catalytic effect to aid combustion. 

Larger tubular, or single-can, units usually have more than one nozzle. In many cases a ring of nozzles is placed in the primary zone area. The radial and circumferential distribution of the temperature to the turbine nozzles is not as even as in tubo-annular combustors. In some cases, high stresses are exerted on the turbine casing leading to casing cracks. 

Variable nozzles produce a series of jets of gas entering the rotor, and these impulses add up to form a frequency equal to the blade-passing frequency the number of revolutions per second multiplied by the number of nozzle vanes, which is of the order of thousands of cycles per second. Frequently the rotor will resonate at this frequency, and if it does, it will be fatigued and crack and break up thus these frequencies must be avoided, and the manufac turer should be asked to supply information to the customer on this subject. 

Ceramic, plastic and other non-metal tower shells are used quite often (Figures 9-3, 4, and 5). It is important to consider in ceramic construction that the main inlet or outlet nozzles or any other large connections should be oriented 90° to each other to reduce the possibility of cracking the walls, as most cracks go one-half diameter. Preferably there should only be one nozzle at any one horizontal plane. The nozzles should never carry any piping or other stress load. 

A principle of application relative to internals is to obtain as many 180° or (second preference) 90° turns of the gas flow after it enters the drum as reasonably possible. Plat plate pieces, baffles, etc., welded to the side or nozzles are not recommended, because the vibration forces tend to fatigue and crack the welds. Baffle plates have been known to break loose on one face and ratde around in the drum. This can be potentially dangerous. The vessel itself should be designed for rugged service. 

An efficient feed injection system produces extremely small droplets that vaporize quickly. Rapid vaporization minimizes the amount of non-vaporized hydrocarbons that block the active sites. An effective feed nozzle system must instantaneously vaporize and crack asphaltenes and polynuclear aromatics to lower boiling entities. 

F. Feed/effluent exchanger nozzle-to-shell weld, cracks in welds and in exchanger tubes. 

A 960 516 331 2.28 26 1.5 NPS Schedule 80 nozzle was broken off a catalytic reformer outlet line during a shut down. Metallography indicated surface decarburization and intergranular cracking with bubbles. Cr content was 1.09 percent. 

The choice and properties of the aeration gas are important factors for maintaining stable standpipe operation. The condensate source for steam aeration can cause several problems. If the steam is not kept dry, the condensate can lead to stress cracking of the tap piping, plugging of the tap nozzle with mud, erratic aeration rates, orifice erosion, and potentially catalyst attrition. Similar problems can occur with wet fuel gas as an aeration source. When possible, dry air and/or nitrogen are preferred rather than steam as aeration media for standpipes. However, in actual... 

Figure 17.15. A fired heater as a high temperature reactor, (a) Arrangement of tubes and burners (1) radiant tubes (2) radiant panel burners (3) stack (4) convection chamber tubes (Sukhanov, Petroleum Processing, Mir, Moscow, 1982). (b) Radiant (surface-combustion) panel burner (1) housing (2) ceramic perforated prism (3) tube (4) injector (5) fuel gas nozzle (6) air throttle Sukhanov, Petroleum Processing, Mir, Moscow, 1982). (c) Fired tubular cracking furnace for the preparation of ethylene from naphtha.

Buyan, Frank M., and Ross, Mark S. Fluid catalytic cracking reactor multi-feed nozzle system, USP 4650566 (1987) Campbell, H. W., and Hurn, E. J. Circulating Fluidized Bed Combustion on Stream at California Portland Cement Company, Coal Technology (Houston), 8th (3-4), p. 19 (1985). 

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