PUMPS FOR HYDROCARBON & NON HYDROCARBON SERVICE

Centrifugal Pumps
Unless restricted by capacity, pressure or Net Pressure Suction Head (Available) (NPSH(A)) have limitations, as a rule centrifugal pumps used for hydrocarbon service for fire water and jockey pumps shall be designed to API 610. Centrifugal pumps used for non-hydrocarbon service shall be designed to ASME B73.1 and B73.2 or ISO 5199.
All large capacity multistage centrifugal pumps shall be provided with a minimum flow by pass to ensure adequate flow through the pump during shut off or restricted flow operation.
Large centrifugal pumps shall be provided with Motor Operated Valves (MOV) on suction and discharge and these MOV’s shall be incorporated into pump control system to ensure pump motor starts with discharge valve closed.
Pumps with suction specific speed greater than 11000 (when computed in gpm, ft and rpm units) shall not be used, to minimize potential vibrations associated seal and bearing problems.
Use of inducers to improve NPSH in Centrifugal pumps shall not be permitted.
The required NPSH(R) shall be at least 3 ft less than NPSH(A), when the Centrifugal Pump is operating at it’s maximum capacity.
Pumps handling flashing hydrocarbons shall be provided with cartridge type double mechanical seals to API 682 with flushing arrangement to API Plan 11 and Plan 52/53 for cooling and lubrication of the seals. Materials for mechanical seal components shall be selected based on operating pressure, temperature & fluid properties.
All Pumps shall be provided with spacer type flexible disc coupling for ease of maintenance and spacer shall be positively constrained from flying out in the event of flexible disc failure.
While centrifugal pumps are generally preferred, pump selection will be based up on desired duty. Other types of pump such as screw, reciprocating, diaphragm, progressive cavity pumps may be selected for difficult pumping condition such as multiphase pumping, low available NPSH, viscous fluids etc.
Hydraulic energy by letting down of high pressure liquid flow stream to low pressures will be recovered through a Hydraulic Power Recovery Turbine (HPRT) if the economic analysis of power saving versus added equipment cost justifies provision of HPRT. The HPRT shall be designed as per API 610 and used to assist another drive running the driven equipment. An over running clutch that transmits torque in one direction and free wheels in the other direction shall be used between HPRT and the Train to allow driver train to operate independently.
 

Positive Displacement Pumps
Reciprocating pumps shall be designated to API 674 and Control Volume Pumps shall be designed to API 675.  Single acting plunger pumps of horizontal construction shall be considered for moderate capacity and high differential pressure.
Unless specified otherwise, the capacity regulation on small capacity pump shall be by online stroke adjustment for chemical injection service etc. Capacity regulation of large reciprocating pump for process duties shall by variable speed drive or by bypass control to suit process requirements.
Pump suction line shall be as short as possible and sized to no more than 3 ft/sec fluid velocity with minimum bends & fittings.
The total of acceleration head and the required NPSH shall be less than available NPSH, by at least 3 psi. Pulsation dampers shall be provided on the suction and discharge sides of pumps operating at speeds over 150 rpm. Rotary Pumps shall be designed to API 676. Positive displacement rotary pumps of gear or screw type rotating elements shall be employed for viscous liquids where centrifugal pumps are considered not suitable or higher viscosity service (usually above 50 to 100 Cp) when the efficiency of centrifugal drops off.
For delivery of small precisely controlled amounts of liquids for chemical injection duty, diaphragm pumps shall be preferred because of their controlled metering capability, in wide range of materials, and their inherent leak proof design.

UNFIRED PRESSURE VESSEL AND STORAGE TANK DESIGN CRITERIA

All unfired pressure vessels, shall be designed, fabricated and tested in accordance with ASME Section VIII Boiler and Pressure Vessel Code Div.1, API 650 Welded Steel Tanks for oil storage, ASME VIII Div 1/ API 2510 Design and Construction of LPG Installations, Uniform Building Code and refer to Pressure Vessel/ Storage Tank/ Spherical Tank specification and their relevant datasheets.

Allowable stress of pressure parts shall be in accordance with the applicable code. Allowable stress for vessels and tanks material which not covered by any code shall be prohibited.

Process conditions shall dictate the materials used for vessel construction, taking into account the corrosive nature of fluids, maximum/minimum and design operating pressure and temperature requirements.

Manholes (18" nominal diameter minimum) with davits or inspection openings (8” nominal diameter minimum) shall be provided for removal of vessel internals and internal inspections unless otherwise specified.

Piping arrangements around vessels or tanks shall allow for maintenance, testing, service of the vessels or tanks and their associated instrumentation with a minimum dismantling of piping. Vessel internals and tanks (if any) shall be bolted for ease of removal.

Filters/ filter separators/ coalescers up to 24” diameter, which require replacement of filter elements, shall be provided with full size, quick-opening end closures, complete with davits.  Vessels greater than 24” diameter may be provided with a full size bolted flange assembly complete with davit and cover lifting features.

Surface preparation for protective coating shall be accomplished by blast cleaning method. However for small and inaccessible areas, or areas where equipment may be damaged by blasting, hand tool or power cleaning tool methods may be utilized.

In case the equipments applied for hot temperature services (70oC or more), they should be furnished with hot insulation and or personal protection. Unless otherwise stated on the individual vessel data sheets and/or drawings, the corrosion allowance shall be 3 mm minimum on the shells, heads and nozzles.