Centrifugal Pump Protection Policy

1. Purpose

This procedure describes Inflection Point Engineering’s centrifugal pump protection policy. Also described are Inflection Point Engineering’s practices regarding piping and instrumentation used at start-up or for pump protection.

2. General

The attachments to this procedure present several Piping & Instrument Diagram (P&ID) representations of pump systems. These drawings are presented only for the purpose of providing a general understanding and are not intended to supersede the standard P&ID pictures that are available from P&ID Drafting. When in doubt, consult P&ID Drafting or the Process Specialist for the specific process involved.

Reference Procedure for information on the role spillbacks play in pump protection.

3. Warm-Up Systems

3.1 Warm-up Lines (Spare Off-Line Pumps)

Pumps require warm-up lines if they have an elevated temperature prior to start-up. If this is the case, warm the spare off-line pump to within 50F (28C) of the normal operating temperature. This ensures that there is no rotor rubbing or seal failure due to rapid and non-uniform heating.

Project specifications do not indicate requirements for warm-up lines. However, P&IDs show the warm-up line as a 3/4 inch line with a globe valve piped around the discharge check valve and block valve. This allows a small stream of hot process fluid to flow backwards through the pump operating off line. The P&IDs also show a flow arrow for back flow coming from the operating pump discharge through the pump that needs to be warmed. Reference Sketch A in Attachment 1 for a P&ID representation of warm-up lines.

With some processes, e.g., Sorbex, the requirement for warm-up lines is waived for process reasons. However, other than this exception, apply the following rules:

a. Single Stage and Two-stage Pumps

A warm-up line is required on all single stage overhung (process type pumps), Sundyne pumps, double suction, double bearing type pumps, and two-stage pumps if the normal operating temperature is equal to or greater than 300F (149C).

b. Multistage Pumps

Warm-up lines are required on any pump with more than two stages if the operating temperature is equal to or greater than 200F (93C).

3.2 Additional Warm-up Systems on Multistage Pumps for Unit Start-up

Multi-stage pumps require additional warm-up systems for initial cold start-up. Warm all parts of the casing to within 50F (28C) of each other and the operating temperature. The maximum heat up rate is 100 F (55C) per hour.

Skin thermocouples mounted on the pump casing shall be specified to monitor the casing temperature during the warm-up procedure.

To slowly warm the pump casing, it is necessary to provide a blend of discharge liquid and liquid from an outside source. However, the method of introducing this liquid varies depending on whether the pump discharge pressure is above or below 1000 psig. Sketches B and C in Attachment 1 show this as a P&ID representation. The P&ID shows a local TI for checking the temperature of the mixture and thermocouples (TXI) on the pump casing.

In special circumstances it may be impractical to provide a warm-up stream. In this case, add a note to the pump specification. This forces the vendor to design the pump for start-up from ambient to operating temperature.

4. Pump Casing Vents

4.1 When to Show Vents on P&IDs

Pump casings are vented for the following reasons:

• Priming of pumps (removal of air) for initial startup or after maintenance
• De-inventoring of light hydrocarbon pumps prior to maintenance

All conventional pumps require venting and liquid filling prior to commissioning. Air must be displaced from the casing. Otherwise the pump will not move liquid forward.

Most single stage API 610 Process Pumps by virtue of their nozzle configuration are self-venting. The discharge nozzle is the of the casing and there is no space for air pockets to form.

Pumps in vacuum service are an exception. The vent must be shown routed to a low pressure source on the P & ID. If the vent is not routed to a low pressure source the liquid in the suction vessel under vacuum will not displace the air in the pump. The air pressure inside the pump must be lower than the liquid pressure in the suction vessel.

Show vents with specific locations (other than relief header) on the P & ID for only the following services:

• Pumps in vacuum service require a vent line routed to the suction source.

• Pumps handling light hydrocarbons for recovery. When to recover light hydrocarbons is an economic decision. Consider pumps which handle large amounts of propane and lighter materials.

Show pumps vents to the relief header and drains to a closed drain system for services requiring closed vent and drain systems per Standard Procedure . This includes the following:

• 0.5 wt% Bz minimum
• 1 wt ppm H2S minimum
• 25 wt% C6-C9 aromatics minimum
• C3 and lighter hydrocarbons

• All other services are expected to have temporary piping erected for venting and draining to oily water sewer.

4.2 How to show Vents and Drains on P & ID’s

Most single stage process pump casings have a self venting design and are not provided with a vent connection on the casing. The vents for these pumps come off the discharge check valve. For 100% flashing hydrocarbon venting to the relief header reference Standard Drawing 8-136, “Pump Vent System for High Vapor Pressure Liquids”, for 100% non-flashing hydrocarbon reference Standard Drawing 8-137, “Pump Drain System”, for all other hydrocarbons venting to the relief system reference Standard Drawing 8-135, “Pump Vent and Drain System”

For vacuum services or light hydrocarbon recovery show the specific location for the vent on the P & ID. Identify the low pressure source for the vacuum service vent and the hydrocarbon recovery destination for the light hydrocarbon vent.

The design of the following types of pumps allow for an air pocket to form inside the casing; Sundyne, Two Stage, Multi-stage. Therefore all Sundyne, two stage and multi stage pumps are typically provided with vent connections on the casing to remove this air pocket.

Since Standard Drawings 8-135, 8-136, 8-137 address the casing vents for non-self venting pumps (notes 5 or 6), use the same P&ID depiction for both self-venting and non-self-venting pumps.

5. Pump Suction Strainer Pressure Differential Indicator

A pressure differential indicator (PDI) is required across the pump suction strainer in applications where operating a pump with a restricted inlet (plugged strainer) may result in serious damage or hazardous operation in a short time. When applying the following guidelines, consider the complexity, cost, power level, and cleanliness of the pump service. Sketches B and C in Attachment 1 show a P&ID representation of a PDI on a suction strainer.

5.1 Two-stage Pumps

A PDI is only required across the suction strainer on pumps that develop a differential head greater than 1500 feet (460 meters).

5.2 Multistage Pumps

A PDI is required across the suction strainer of all multistage pumps with more than two stages. Note that a multistage hydraulic power recovery turbine does not require a PDI.

5.3 Sundyne Pumps

PDIs are required across the suction strainer only for higher flow rate, head, and power applications. Provide a PDI on a Sundyne pump if all the following criteria are met:

6.0 Automatic Shutdowns

6.1 Low Level Shutdown

Because of its sensitivity to dry running operation, a multistage pump with a differential pressure of 500 psi (35 kg/cm2) or greater, or a horsepower of 300 (225 kW) or greater, requires an automatic driver shutdown (2 out of 3 voting type) that is initiated by low upstream liquid level.

Low Flow Shutdown

Multistage pumps with a differential pressure of 500 psi (35 kg/cm2) or greater, or a horsepower of 300 (225 kW) or greater, require a spillback system AND an automatic low flow shutdown of the driver. See Procedure IPE-TM-500-05, “Centrifugal Pump Spillback Policy”.

Attachment 1 Warm-up Systems

A. Single Stage and Two-stage Pumps

B. Multistage Pumps Below 1000 psig Discharge Pressure

C. Multistage Pumps Above 1000 psig Discharge Pressure