Thermal expansion reliefs

PR valves handling materials which are liquid or partially liquid at the valve inlet. An exception to this is made for certain thermal expansion relief valves as described below. 

Thermal Expansion Relief Valves - Routing of thermal expansion relief valve discharges was covered earlier. 

American Society of Sanitary Engineering, Performance Requirements for Thermal Expansion Relief Valve. American Society of Sanitary Engineering, Bay Village, OH, 1990. 

For a liquid thermal expansion relief device that protects only a blocked-in portion of a piping system, the set pressure shall not exceed the lesser of the system test pressure or 120% of design pressure. 

Thermal expansion on the isolation valve section (fire). Possible line fracture or flange leakage. g) Provide thermal expansion relief in the valved section. 

More Pressure 7. Isolation valve is closed in error whilst pump running. 8. Thermal expansion in the isolation valve section (fire). Lines subject to full delivery pressure. Possible line fracture or flange leakage. Covered by b). f) Perhaps worthwhile installing a pressure gauge upstream of the delivery pump. g) Provide thermal expansion relief in the valved section. 

Thermal expansion in isolation Line fracture or flange leakage. i) Provide for thermal expansion relief in... 

More Pressure 8. All of 5, 6, and/or 7. 9. Thermal expansion in isolation valve section (fire). 10. PCV fails shut or isolation valve shut in error. As for 5, 6, and 7. Line fracture or flange leakage. As for 3. Covered by b) and c). f) Install thermal expansion relief in isolation valve section. Covered by b) and c). ... 

It is very important that a melt-ont riser be installed whenever tank contents are expected to freeze on prolonged shutdown. The purpose is to provide a molten chimney through the ernst for relief of thermal expansion or cavitation if fluids are to be pumped ont or recirculated through an external exchanger. An external heat tracer, properly... 

Full liquid containers require protection from thermal expansion. Such relief valves are generally quite small. Two examples are... 

Consideration should be given to the effects of thermal expansion of liquids and pressure-relief valves installed unless ... 

Themtal. Thermal relief is needed in a vessel or piping run that is liquid-packed and can be isolated, for example pig launchers and meter provers. Liquid is subject to thermal expansion if it is heated. It is also incompressible. The thermal expansion due to heating by the sun from a nighttime temperature of 80°F to a sun-heated temperature of 120 F can be enough to rupture piping or a vessel. The required capacity of thermal relief valves is very small. 

Smaller relief valves are often used in isolated parts of the system where a check valve or directional control valve prevents pressure from being relieved through the main system relief valve or where pressures must be relieved at a specific set point lower than the main system pressure. These small relief valves are also used to relieve pressures caused by thermal expansion of fluids. 

The volumetric expansion rate Qv through the relief resulting from thermal expansion is... 

Equation 9-45 describes the fluid expansion only at the beginning of heat transfer, when the fluid is initially exposed to the external temperature Ta. The heat transfer will increase the temperature of the liquid, changing the value of T. However, it is apparent that Equation 9-45 provides the maximum thermal expansion rate, sufficient for sizing a relief device. 

Consider Problem 9-9, part a. This time use alcohol as a liquid medium with a thermal expansion coefficient of 1.12 X 10 3/°C. The heat capacity of the alcohol is 0.58 kcal/kg °C, and its density is 791 kg/m3. Determine the relief size required. 

Vessels normally have a relief device to prevent damage during thermal expansion. A stainless steel cylindrical vessel has 1/4-in thick walls and is 4 ft in diameter. It is filled with 400 gal of water, and 0.2 ft3 of air is trapped at a pressure gauge. Start at 0 psig and 50°F and then heat the vessel. At what temperature will this vessel rupture if it does not have a relief ... 

Pressure relief valves are provided to cater to two main conditions of the process -normal conditions and emergency conditions. Normal conditions relate to the designed operation of the process which emergency conditions can be caused by either (1) external fire conditions, (2) failure of reflux or cooling, (3) Failure of the power supply, (4) failure of steam supply, (5) heat exchanger failure (6) introduction of incompatible materials, (7) thermal expansion with outlets closed. 

Special consideration of thermal relief for piping exposure to sunlight (solar radiation) needs to be under taken. This is usually accomplished by painting with reflective paint or burial. Hydrocarbon containing piping is usually painted in a reflective color (i.e., aluminum) for advantages of reflection of solar radiation (heat input) to avoid thermal expansion of fluids in blocked systems. 

Results for thermal expansion coefficient of liquids are presented for major organic chemicals. The results are especially helpful in the design of relief systems for process equipment containing liquids that are subject to thermal expansion. 

Physical and thermodynamic property data, such as thermal expansion coeffici t, are important in process engineering. The following brief discussion illustrates such importance. Liquids contained in process equipment will expand with an increase in temperature. To accommodate such expansion, it is necessary to design a relief system which will relieve (or vent) the thermally expanding liquid and prevent pressure build-up from the expansion. If provisions are not made for a relief system, the pressure will increase from die diermally expanding liquid. If the pressure increase is excessive, damage to the process equipment vtdll occur. 

Furnace tubes, process piping, and heat exchangers may also have to be protected by relief valves. Incidentally, the small %- or 1-in relief valves you see on many tank field loading lines and on heat exchangers are not process relief valves. They are there for thermal-expansion protection only. This means that if you block in a liquid-filled exchanger and the liquid is heated, the liquid must expand or the exchanger will fail. That is what the thermal relief valve is there to prevent. 

---