There have been many pump codes and standards that apply to different pumping applications. American National Standards Institute (ANSI) pumps or manufacturer’s standard pumps have been used in services such as utilities and chemical applications.
However, for nearly all oil, gas and petroleum services in upstream, midstream and downstream—such as crude oils, petroleum liquids, refinery products and others—American Petroleum Institute (API) pumps should be specified and used. API pumps have been recommended for critical applications such as main services in oil, petroleum, petrochemical and chemical services.
API pumps have some advanced features over ANSI pumps, manufacturer’s standard pumps and other types in these harsh applications. For example, API pumps have the capability to withstand relatively high allowable nozzle loads, provisions for larger and better mechanical seals, better bearings and components. All of these result in higher performance and reliability. It is generally easier to align, commission, operate and maintain API pumps as well.
API covers a wide range of horizontal and vertical pumps. Horizontal-type API pumps have been more popular, and they have been commonly specified and used in many oil, gas and nonprocess petroleum services. Although vertical API pumps have their own preferred services, a valid question is, “can others be used in utility or so-called nonprocess services in oil, gas or petroleum plants?”
The answer to this question is yes—under certain conditions. In fact, API pumps have not been popular for many ordinary or utility services in a wide range of noncritical applications because of high costs and complexities.
ANSI pumps or manufacturer’s standard pumps are often limited to the following service limits and, above these, robust pump codes (such as API) are recommended:
- Discharge pressure not exceeding 19 bar gauge (barg).
- Temperature of the pumped liquid is not less than -30 C (-22 F) and not exceeding 130 C (266 F).
- The driver power rating does not exceed 250 kilowatts (kW); although for some applications this limit might be higher, even 500 kW or more.
Many non-API pumps produced by reputable manufacturers have been used beyond the above-mentioned limits. ANSI pumps have usually been employed for temperatures below 130 C and pressures below 18 barg. ANSI pumps and OEM standard pumps are used for many utility or noncritical pumps. Standard pumps from reputable manufacturers, with successful operating references in similar service and sizes, can safely be used in many services.
With an ANSI pump, manufacturer’s standard pump or a non-API pump, pay attention to shaft deflection, which should not be excessive. In between-bearing pumps, excessive deflections can result in internal contacts and operational issues. In overhung pumps, excessive deflections can lead to serious problems, such as catastrophic contacting.
Another area of concern is dimensional limitations in some non-API pumps, which may not accommodate proper and modern mechanical seals or other components. Weak baseplates have been used in some non-API pumps, whereas API has recommended strong and heavy-duty baseplates. Two other concerns are insufficient net positive suction head (NPSH) margins and bearing selection.
Variable speed pump operation has been considered for many oil, gas and petroleum pumping applications. Variable speed drives (VSDs) have been widely used in large- and medium-size pumps in these services. However, the trend is to use them in small applications where energy savings and operational flexibility can outweigh the VSD costs. For many critical pumps in oil and gas, both the variable speed and control valve (installed at downstream) are used for the control of flow rate/pressure. Variable speed steam turbine drivers have often been used in medium and large pumps in refineries and petrochemical services.
VSD electric motors are becoming more popular. In some key services, there are two pumps, one in operation and another at standby. One pump is steam turbine driven (with variable speed capability) and another is VSD electric motor driven.
The selection and bidding stages are critical for expensive and sophisticated pumps in oil and gas facilities. In the bidding process, pay attention to:
- high reliability
- focus on efficiency
- manufacturer’s experience and successful operating reference list
- details of each service and operational considerations
Usually, the selected pump for each service can handle the assigned task. However, it is not always the best available pump. A critical issue is the selection of the best pump considering the lowest total cost of ownership. The selected pump should usually offer the highest efficiency at best efficiency point (BEP) with operating range as close as possible to BEP.
For special oil and gas services, the manufacturer’s experiences and the pump’s model reference check should be examined. Reliability, high-quality manufacturing and trouble-free operation depend on practical capabilities, manufacturing/quality-control systems, and successful operating references, in addition to engineering/sales capabilities.
Many pumps are purchased as isolated equipment without learning from experiences gained from operations in similar services. Examine previous failures in similar services to investigate potential weak points and improvements.
To obtain a high-quality pump, a proper specification should be written and all required details should be specified. Requirements should be discussed and confirmed in a proper format to make sure each item is considered and all associated costs are included in the proposal. Good pieces of information that should be evaluated in a pump bidding process include:
- the pump shaft diameter
- the pump shaft length and bearing details
- the shaft slenderness ratio (shaft length/shaft diameter)
Performance, operation, reliability and life of pumps are related to mechanical designs and manufacturing. These are also related to the pump materials’ ability to resist corrosion, erosion and wear that influence the parts and components. The need to maximize reliability and extend the pump’s life makes the selection of appropriate materials crucial.
The selection of materials that are cost effective and technically suitable for an application requires knowledge of the pump design, manufacturing processes, and the engineering properties of the materials. Particularly, knowledge is needed of the materials’ corrosion, erosion and wear resistance properties when subjected to the conditions in each service. The material selection is linked directly to the pump liquid, its compositions and its temperature. For instance, sour oils or corrosive services need suitable materials resistant to their adverse effects.
There have been different locations and configurations for the installation of pumps in oil and gas plants. A common configuration used in oil and gas plants, refineries, petrochemical plants, etc., is the installation of pumps near suction sources to keep suction piping as short as possible.
In downstream oil and gas plants, there are usually large, multilevel pipe-racks in each unit (or area). Pumps that are mainly API horizontal pumps may be installed under the pipe-rack, often close to the suction source.
A variation of this configuration has been to install pumps partially under the pipe-rack with the casing set outside the pipe-rack column line. In this case, the discharge of piping of pumps can rise into the vertical slot (that is usually provided) and the piping line can easily be routed to the pipe-rack.
Check if a pump is under air coolers or near similar equipment with the potential of liquid spill. Potential spills to the electric motor driver (or other driver types) would be a major risk.