Pressure vessels heads

In the case of pressure vessels when attaching the dished heads to the sidewall of pressure vessel head the surface of the dished head need to be machined to accommodate the thickness transition, as shown in Figure 1.54. 

Another generic problem has been the development of cracks in the control rod guide tubes of inconel which penetrate a PWR pressure vessel head. Such cracks are difficult to locate and repair because of the confined space between the tubes. After some time leaks usually develop when the cracks grow larger, ultimately requiring replacement of the vessel head. Crack formation can probably be prevented by a proper selection of material, its pretreatment and meticulous adjustment of the water chemistry. 

Soak times may be required when heating up the PCS, especially when large limiting components are involved in the heatup. Soak times are used so that heating can be carefully controlled. In this manner thermal stresses are minimized. An example of a soak time is to heat the reactor coolant to a specified temperature and to stay at that temperature for a specific time period. This allows the metal in a large component, such as the reactor pressure vessel head, to heat more evenly from the hot side to the cold side, thus limiting the thermal stress across the head. Soak time becomes very significant when the PCS is at room temperature or below and very close to its RT dt temperature limitations. 

Bijlaard, P. P., Computation of the Stresses from Local Loads in Spherical Pressure Vessels or Pressure Vessel Heads, Welding Research Council Bulletin No. 34, 1957. 

This is why most high pressure vessels do not use typical pressure vessel heads such as hemispherical or semi ellipsoidal. These heads are impractical in high pressure applications. So the economics and mechanical limits of the materials will determine the ultimate shape of the vessel. 

The lens ring is one of the most common types of joints that originated in Germany at about 1920 with ammonia synthesis. The lens ring is used primarily on piping systems with some applications for pressure vessel heads. 

The US Department of Energy s action plan on the Challenger Disaster and Davis Besse Reactor Pressure-Vessel Head Corrosion Event provides the following ... 

Columbia Space Shuttle Accident and Davis-Besse Reactor Pressure-Vessel Head Corrosion... 

In the Columbia accident The machine was talking to us, but nobody was listening. Deviations from requirements had become normal business for NASA. The Columbia Accident Investigation Board (CAIB) report referred to this as the normalization of deviations (Columbia Space Shuttle Accident and Davis-Besse Reactor Pressure-Vessel Head Corrosion Event, 2005). 

Reactor pressure vessel head vent valves. 

Following initial fuel loading, the reactor upper internals and the pressure vessel head are installed. Additional mechanical and electrical tests are performed in preparation for critical and power operations. The following conditions exist prior to initial criticahty ... 

Dimoplon, W. (1974). How to determine the geometry of pressure vessel heads. Hydrocarbon Process, Aug., 71-74. 

Shield, R, T., and D. C. Drucker, Design of Thin-Walled Torispherical and Toriconical Pressure-Vessel Heads in Pressure Vessels and Piping Design and Analysis—A Decade of Progress, American Society of Mechanical Engineers, 1972,... 

US DOE. (2005). Columbia space shuttle accident and Davis-Besse reactor pressure-vessel head corrosion event. (2005). US Department of Energy Action Plan Lessons Learned, Pubhc Domain. Retrieved from http //l.usa.gov/YOWYft... 

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