Piping and Valves SS

PIPINGS/VALVES and PRESSURE VESSELS

Piping StandardSchedule number

Pipes were originally classified on the basis of wall thickness as standard (extra strong, and double extra strong).Because of modern industrial demands for more exact spec, pipes are now specified according to wall thickness by a standard formula for schedule number designated by the American Standards Association.Schedule number is defined by ASS as: = 1000 Ps/Ss where Ps = safe working pressure Ss = safe working fiber stress


Ten schedule numbers are in use at present.These are 10, 20, 40, 60, 80, 100, 120, 140, 160For pipe diameters up to 10 in, schedule 40 corresponds to the former standard pipe and schedule 80 corresponds to the former extra strong pipe.

Piping StandardSchedule numberHow they came up with the formula?Bursting pressure of a thin walled cylinder may be estimated from the following equation: Pb = 2STtm/Dm where: Pb = bursting pressure ST = tensile strength tm = minimum wall thickeness Dm = mean diameter


A safe working pressure Ps can be evaluated from equation if the tensile strength is replaced by a safe working fiber stress Ss

Ps = 2Sstm/Dm

Piping StandardNominal pipe diameter

Pipe sizes are based on the approximate diameter and arereported as nominal pipe sizes. This permits the use of standard fittings and treading tools on pipes of different schedule numbers. It is neither I.D or O.D of pipe.

Piping StandardTubing

Copper tubing, brass tubing are used extensively in Industrial operations. Other metals, such as nicklel and stainless steel, are also available in the form of tubing.Although pipe specifications are based on standard nominal sizes, tubing specs are based on the actual outside diameter with a designated wall thickness.Conventional system, such as the Birmingham wire gauge (BWG) are used to indicate the wall thickness.

Piping StandardFitting and other piping auxiliaries

Fittings, flanges, valves, flow meters, steam traps and many other auxiliaries are often rated on the basis of the safe operating pressure as: 25 psi low pressure 125 psi standard 250 psi extra heavy 300 to 10,000 - hydraulic

Piping: Code and Standards The American National Standards Institute (ANSI) and the American Petroleum Institute (API) have established dimensional standards for most widely used piping componentsANSI B31 - List of standards in the ANSI B31 code section - Section also lists specifications for pipe and fitting materials and testing methods of the American Society for Testing and Materials (ASTM) - American Welding Society (AWS) specification - Standard of the manufacturers Standardization Society of the Valve and Fitting Industry (MSS)

Piping: Code and Standards The design of piping system applied to this project is listed asASME B31.3

ASME stands for American Society of Mechanical EngineerASME 31.3 is actually a section of ANSI B31 ASME (ANSI) 31.3 is a Standard Number and designation is Chemical Plant and Petroleum Refinery PipingASME (ANSI) 31.1 scope and application: For all piping within the property limits of the facilities engaged in the processing or handling of chemical, petroleum or related product unless specifically excluded by the codeInformation on latest issue can be obtain for ASME. 345 East 47th st. New York NY 10017

ValvesGate Valves used to minimize pressure drop in the open position and to stop flow rather than to regulate it.

Valves2. Globe Valves - offer ease in throttling

ValveDiaphragm valves limited to 50psi, excellent for fluid containing suspended solids3. Diaphragm valves

Valves Plug valve for throttling service, little likelihood of leakage when closed.

Valve5. Ball valves

Valves6. Butterfly valve

Valves7. Needle Valves offer flow adjustment on small lines

Valves

Check ValvesUsed to prevent reversal of flow1. Swing check valve - Normal design is for use only in horizontal lines2. Lift check valves - Vertical lift check valve for installation in vertical line, where the flow is normally upward - Globe check valve for use in horizontal lines - Angle check valve used for installation where a vertical line with upward flow turn horizontal3. Tilting disk check valve - May be installed both horizontally and vertically. Less pressure drop at low velocity but greater at high velocity. Arrests slamming.

Pressure-Relieving DevicesThe possibilities for development of excess pressure exist in nearly every process plant.Excess pressure can develop from: 1. explosion 2. chemical reaction 3. reciprocating pumps or compressors 4. process upsets 5. external fire around equipmentIn addition to the possible injury to personnel, the loss of equipment can be serious and an economic setbackMost countries have laws specifying the minimum attention required in the applications of pressure-relieving equipment in process and steam power plants.

Types of Pressure Relieving DevicesRelief valvesSafety valvesSafety-relief valveConventional and balance valvesFrangible disk (rupture disk)

Relief ValveA relief valve is an automatic pressure-relieving device actuated by the static pressure upstream of the valve, and which opens further with increase in pressure over the set pressureUsed primarily for liquid servicesRated capacity is usually attained at 25 percent over pressure

Relief Valve

Safety ValveA safety valve is an automatic pressure-relieving device actuated by the static pressure upstream of the valve and characterized by full opening or pop action upon openingUsed for steam, gas or vapor serviceRated capacity is reached at 3, 10 or 20 percent overpressure, depending upon applicable code.

Safety Relief Valve

Conventional and Balance Safety ValveConventional safety valves operate satisfactorily only when there is relatively constant back pressure. Changes in back pressure can seriously affect its operational pressure and flow capacityBalance valves operate satisfactorily under varying back pressure as this has little influence on performance

Frangible Disk (Rupture Disk)A rupture disk is a thin diaphragm (metal, plastic, non metallic) held between flanges and designed to burst at a predetermined pressure.Each bursting requires the installation of a new diskUsed in corrosive service, and for required bursting pressure not easily accommodated by the conventional valve.Applicable to steam, gas vapor and liquid system

Definition of Pressure Relief TermsSet pressureIs the inlet pressure at which the safety or relief valve is adjusted to openThis pressure is set regardless of any back pressure on the discharge of the valve

2. OverpressurePressure increase over the set pressure of the primary relieving device is over pressureIt is the same as accumulation when the relieving device is set at the maximum allowable working pressure of the vessel

Definition of Pressure Relief Terms3. AccumulationPressure increase over the maximum allowable working pressure of the vessel during discharge through the safety or relief valve, expressed as a percent of that pressure.4. Maximum allowable working pressureThe maximum allowable working pressure of an unfired pressure vessel is that pressure determined by code requirements, the metal material of construction and its operating temperature, above which the vessel may not be operatedFor a given metal temperature, this pressure is the highest pressure at which the safety device may be set to open.

Definition of Pressure Relief Terms5. Operating pressurePressure (gage), to which the vessel is subjected in serviceA processing vessel is usually designed for a maximum allowable working pressure, which will provide a suitable margin above the operating pressure to prevent undesirable operation of the relief deviceMargin is approximately 10 % higher, or 25 psi which ever is higher.

Definition of Pressure Relief Terms6. BlowdownThe reduction in flowing pressure below the set point required for a device to close Is the difference between the set pressure and the reseating pressure of a safety or relief valveExpressed as percent of the set pressure or psi7.Back pressurePressure developed on the discharge side of safety valves is back pressureThis pressure may be generated by the flowing fluid as it passes through the relief discharge piping, or it may be an established pressure as a part of a discharge vent system into which the valve is dischargingIt may be combination of these two.

Vacuum Breaker

Electric Solenoid

Emergency Relief Vent

Thermal Valve

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Piping and Valves SS