Steam pressure vessels, inspection

The original steam generators were simple pressure vessels that were prone to caiasirophic failures and loss of life. Due to better boiler design, tube-fired boilers, and boiler inspections, the incidence of catastrophic failure is now to a rare event (about once every 100,000 vessel-years). In Great Britain in 1866, there were 74 steam boiler explosions causing 77 deaths. This was reduced to 17 explo.sions and 8 deaths in 1900 as a result of inspections performed by the Manchester Steam User Association. In the United States, the American Society of Mechanical Engineers established the ASME Pressure Ves.sel Codes with comparable reductions. 

In 1854, the Manchester Steam Users Association was formed to help with the prevention of explosions in steam boilers and to find efficient methods in their use. To achieve this, the Association employed the first boiler inspectors, whose services were then made available to the Association s members. Within a short space of time, the members became convinced that insurance to cover the high cost of repair or replacement of damaged boilers was desirable, and this resulted in the first boiler insurance company (The Steam Boiler Assurance Company) being formed in 1858. The scope of the services for inspection and insurance later extended to include pressure vessels, steam engines, cranes, lifts and electrical plant, the insurance protection in each case being supported by an inspection service carried out by qualified engineer surveyors. 

In almost all countries today, safety codes and regulations exist for the construction, operation, and inspection of all boilers and associated pressure vessels and boiler systems. Both HW and steam-raising plants are provided with several vital boiler appurtenances (appliances or fittings) and various subsystems containing auxiliaries (accessories) that must be maintained, monitored, and controlled. However, for small HW and LP steam boiler plants the inspection process may be rather cursory with regard to the pressure vessel internals and tends to concentrate primarily on ensuring the proper operation of the various appurtenances that provide for boiler safety. 

At the age of 32, he joined the Travelers Insurance Company at Hartford, Connecticut where (except for the period of active duty during World War I) he served until his retirement in 1956 at age 74. In 1925, he was promoted to assistant superintendent of the Engineering and Inspection Division. Heinrich conducted safety courses for students at New York University for more than 20 years, beginning in 1938. In 1942, he was appointed chairman of the War Advisory Board, Safety Section, providing assistance to the U.S. Army safety effort. In 1956, he was appointed chairman and president of the Uniform Boiler and Pressure Vessels Laws Society, an organization promoting the uniformity of laws governing the safety of steam boilers and pressure vessels in the United States and Canada. Heinrich died in 1962. 

Pressure vessels, boilers and steam lines, fuel and gas lines, electrical equipments, and plant layout are inspected by Factory Inspectors from safety point of view. 

Statutory inspection of some key equipments has become due, and it is necessary to stop the plant, overhaul and repair (wherever necessary) and present to authorities for annual inspection as per the law, e.g. steam-generating boilers, pressure vessels, electrical installations, and safety devices. 

Steam is one of the most common options for heating. However, a steam pressure of 10 kg/cm and more will be required for achieving 150 °C and higher temperatures. This needs specially designed and fabricated vessels (heating jackets and coils), steam pipelines, and valves, with the approval of Pressure Vessel and Steam Boiler Inspection Authorities in the country. This is not necessary when heat transfer oils are used for heating even up to 270 °C as the system can operate at atmospheric pressure. 

A particularly dangerous breach in a pressure vessel happened in a steam generator where a crack (about 70 per cent of the circumference with a depth equal to a significant fraction of the thickness) was discovered on a circumferential weld. At some points the crack was through wall . It was discovered during a visual inspection thanks to the humidity patch on the external insulation layer of the component. 

The reactor pressure vessel, pressurizer, primary side of the steam generator and associated piping, pumps, valves, bolting and component supports are subjected to inspection. 

Reactor and steam generator are connected by a coaxial duct which is enclosed in a pressure shell. Cold helium under high pressure flows In the outer annulus, so the pressure vessel is never subjected to any Impermissible temperature loads. The "two vessel side-by-side" arrangement has advantages with regard to accessibility, adaptability, repairability, easy maintenance and low radiation dose during routine operation inspection and replacement of components, which is easily achievable. 

Very rare events include failure of pressure vessels (e.g. pressurizer and steam generator shell), failure of structural supports and turbine break-up. Pressure vessel and structural failures are precluded in the design by use ol)for example, the appropriate level of design and manufacturing codes and standards, quality assurance and in-service inspection. Again, safety analysis is not required. 

Other vessels located in the containment, such as the pressurizer and the steam generators, might also potentially damage various barriers at the same time, but this probability is intrinsically lower than that of the reactor vessel as they are more distant from the core (it can be lowered by provisions concerning the strength of the structures and because they are not exposed to neutron damage and can more easily be inspected during service). 

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