Importance and Load Bearing Analysis of Boiler Safety Valves

Importance and Load Bearing Analysis of Boiler Safety Valves


A safety valve or a globe valve is one of the main safety accessories of steam boilers. As a valve with important protection functions, safety valves are widely used in various pressure vessels and piping systems of steam boilers. When the pressure vessel reaches the upper limit of the specified pressure tolerance value, the valve can be automatically opened by auto-induction, and discharge the excess medium out of the pressure vessel. Then, it can be automatically closed after the discharge is completed, thereby ensuring that the pressure vessel can be operated safely and reliably within the allowable range of pressure to avoid major safety accidents in the steam boiler.
 
The normal operation of safety valves of steam boilers is not only related to the normal and safe use of pressure vessels, for example steam boilers, but also directly related to people's lives and property. Therefore, we must seriously focus on common failures of safety valve springs of steam boilers and eliminate them in time. The reasons for failures of safety valve springs of steam boilers are analyzed and discussed in the following.
 
When the safety valve spring of steam boilers is assembled, it is subjected to normal downward pressure of 430MPa. When the valve is fully opened, it will be subjected to pressure of 480MPa. The steam temperature in the pipeline changes at a degree of around 350℃, because the spring is closed and installed on the upper part of the valve body, resulting in its temperature being slightly low. The factors that affect the failures of safety valve springs of steam boilers include relaxation failures, temperature difference failures and the material of the spring itself. The main factor is the corrosion of safety valve springs of steam boilers, which is affected by non-central loads and impact loads.
 
Load bearing analysis of safety valve springs of steam boilers
1. Axial or radial loads
The safety valve springs used on steam boilers are mostly cylindrical. According to calculations, when the safety valve spring is subjected to axial or radial loads by the axial spring, the deformation and shear stress are inversely proportional to the diameter of the spring wire; when the spring is corroded in use, the diameter of the spring wire becomes smaller. The amount of deformation and shear stress increases, resulting in spring failures.
 
2. Being affected by non-central loads
During the operation of the steam boiler, the overpressure steam must be periodically discharged for safety valves. After the steam is exhausted, the valve stem is easy to deviate, causing safety valves to leak and springs to be eccentric under non-central loads, which reduces the safety stress value of the circular spring. The safety stress is inversely proportional to the load eccentricity distance, which makes the safety valve spring ineffective and shortens the service life.
 
3. Being affected by impact loads
During the operation of the steam boiler, the safety valve is in a state of a frequent bounce, which produces a great impact velocity when exhausting. At this time, the first three rings of the spring first bear the impact load and absorb more impact energy. Because the impact load can not be quickly and effectively transmitted to the spring ring behind, result in plastic deformation and failures of the first three spring rings.