PetroStreet

1)Always provide Flat on top (FOT) eccentric reducer in pump suction line :-

Concentric or Eccentric Reducers do not "cause" cavitation. Cavitation occurs naturally in all pump suction lines. The suction of a pump is the lowering of the pressure in the suction line to the pump. The lowering of the pressure of the line fluid lowers the vapor pressure in the line. The lowering of the vapor pressure allows the fluid to "Boil" at a lower temperature. When a fluid boils it starts to form bubbles. As the bubbles form they will join and become larger. These large bubbles create "cavities" in the suction fluid. When these cavities come in contact with the pump impeller they cause cavitation erosion.

We cannot prevent the formation of these tiny cavitation bubbles. What We can do is reduce the potential for the build-up of larger bubbles and therefore reduce the impact of cavitation erosion. A reducer installed in the line does not cause or prevent the formation of the tiny bubbles or cavitation. What it can do, if improperly installed is to provide a place where the tiny bubbles can collect, build bigger bubbles and then be sucked into the pump.

An Eccentric Reducer properly installed, with the Flat-On-Top (FOT) in a pump suction line does not provide a place where these bubbles can collect. They are swept right through the pump while they are small and insignificant. On the other hand a Concentric Reducer or an Eccentric Reducer installed improperly (Flat-On-Bottom) in a pump suction line will provide a place for the tiny bubbles to collect and build. Then We have a higher effect of cavitation erosion.

Kindly share in this thread your experiences regarding "Good piping layout guidelines(techniques)" so that all members can be benefited.

Good initiative.

Placement of valves within a piping system should be carefully handled as inappropriate placement can be detrimental to system function. The valve may malfunction in waterhammer and can lead to failure. Some brief considerations have been provided:

Control Valves
Control valves shall be installed with the valve stem in the upright position and a minimum of 3 diameters of straight pipe shall be provided both on the upstream and downstream of the valve in order to reduce the turbulence of the fluid entering and leaving the valve.

Butterfly Valves
Butterfly valves shall be provided with minimum of 5 diameters of straight pipe on the upstream of the valve.

Check Valves
In case of check valves, it has been experienced that chattering occurs due to turbulence on the upstream of the valve due to branches and elbows so the designer must consider the guideline provided by the valve manufacturer and provide a straight length of piping on the upstream side. The preferred position of check valves is in the horizontal run of the piping but swing check valves also operate normally in vertical runs of the pipe also with the flow UP. However, the velocity and the rate of flow must be enough to lift the valve disk from the seat.

Safety Valves
Safety relief valves shall be installed in an upright position always with fittings on the top of the horizontal run of the pipe (pressure source) and shall at least be placed one nominal diameter of header from any butt weld.

3) Underground Piping Installation Practices

Underground piping installation shall be made very carefully especially where electrical cables are nearby so that any leakage from piping during operation may not affect electrical cables network. Sand barriers and brick arrangement shall be provided around the electrical cables. It should also be noted that electrical cables must follow the path that should be above the underground piping. For both underground electrical cables and piping, sand bed of at least 300 mm must be provided which would prevent any damage to the piping while any excavation. Supports / anchors at bends on underground piping shall be properly installed especially when non-metallic piping is being laid. Much of the load comes to the anchors / supports which if not transferred properly may cause any piping joint to leak.

4) Reciprocating Compressor Suction & Discharge Piping
1. Normally, suction of compressor is provided on the top of the cylinder and discharge on the bottom
2. Branch connections to the suction header of compressor are given from the top of the header.
3. Suction & discharge piping shall be kept as straight as possible between the compressors and the headers.
4. The piping should have minimum overhanging weight, bracing structure should be provided as needed to reduce vibrations produced by compressor.
5. For piping, high strength butt weld fittings must be considered and socket weld fittings to be avoided.
6. Most likely failure which can take place in compressor piping is fatigue due to cyclic loading. Adequate supports must be provided and follow point 4.

The basic philosophy behind designing of General piping is to provide access for maintenance & operability. All the manual valves should be in easy access. No dead lugs should happen to avaoid liquid or vapor containments. Drain and vent are provided at lowest and highest points. Expasion loops should provided as per temperature and size requirements to avoid abnormal expansion. Flange joints should be minimum but should be provided where maintenance is necessary. Where two different fluid & pressure streams mixing is required NRV should be provided to avoid backflow and contamination. Hot insulation along with steam tracing should be provided where there is chance of liquid freezing. Hot insulation shall also be used where there is chance to hot exposure to the operators. Generally Butt welding is provided for 2" above piping and socketweld joints are preffered for 2" and below pipes. When above ground piping is connected to underground piping insulations kits are provided for electrical isolation as UG piping is connected to CP system. Where there is class break proper provisions should be facilitated. All field welds and golden joints shall be RT tested if they are above 2". Smaller piping shall be atleast DPT tested. Piping route should be simple and striaght as far as possible. Rolling may provided when necessary.

Keep going Usman.

Insulation Shoes & Cradles

1. Locate Insulation shoes anywhere a line crosses a support for hot insulated piping when the piping is 3 inch and over in carbon and alloy steel material with design temperatures over 650 degrees F.

2. Large diameter stainless steel lines (20 inches and over) where galvanic corrosion may exist, lines with wall thickness less than standard weight, and vacuum lines should be analyzed to determine if shoes or wear plates are needed.

3. Provide cradles at supports for insulated lines in cold service and for acoustical applications.

Positioning of Pipes on Pipe Racks

1. Place the large diameter pipes (greater than 12") close to the columns of supporting steel / civil structure to reduce the stresses on the support beams.
2. Utilities piping (cooling water, steam, nitrogen, instrument air etc.) should be provided with a blind at the end of the piping in order to facilitate flushing or purging of lines when required.
3. Steam and other high temperature lines requiring expansion loops shall also be placed in a way that the expansion loop must come inside the pipe rack area (towards the inside)
4. Under the pipe rack after each 30 m the area must be left free / unoccupied from piping in order to facilitate maintenance activities.
5. When change of elevation or direction is required on the pipe racks, just for economic reasons, use 2 - 90 deg elbows for piping equal or less than 4" and one 45 deg elbow and one 90 elbow should be considered.