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I. API610 is a internationally renowned standard for centrifugal pumps. Currently, there are three most authoritative pump standardization organizations in the world: the B73 standard under the American National Standards Institute (ANSI)； TC-115 standards under the International Standards Organization ISO ； Standard 610 issued by the American Petrochemical Institute API. Among the three renowned standards, API610 is a standard for centrifugal pumps specifically developed for the oil and chemical industries. It was formulated by comprehensively summarizing the accidents and lessons learned from pump design or manufacturing in refineries and chemical plants. As a result, many experts consider API610 to be the culmination of experience and wisdom, making it the most authoritative standard for centrifugal pumps used in the oil, chemical, and gas industries. The API 610 standard sets very strict requirements for the design and manufacturing quality of pumps. Therefore, pumps manufactured in accordance with API standards are more expensive, as the cost associated with maintaining such quality levels increases. II. Introduction to the API610 Standard The eighth edition of the API610 standard was published in August 1995. This standard specifies in detail the general provisions such as scope, terminology, and related standards ； Basic design elements such as the pressure pump casing, the forces acting on the pipe ends, the rotor, shaft seals, bearings, and materials ； Auxiliary machines and accessories such as motors, couplings, bases, and instruments ； Inspection, testing, and shipment ； Sections such as various specific types of pumps and seller information. There are 6 differences between the eighth edition and the seventh edition: (1) The number of chapters has increased from 5 to 6, with an additional chapter on \"Specialized Pumps\" ； (2) There is also a change in the name; it has been changed from “Centrifugal pumps for general refinery use” to “Centrifugal pumps for the petroleum, heavy chemical, and natural gas industries” ； (3) In terms of units of measurement, the eighth edition uses the SI international system as the primary units, with US imperial units serving as auxiliary units, along with reference conversion values provided ； (4) The eighth edition provides a comparison table of the standards applicable in various countries ； (5) The eighth edition also provides a comparison table of material standards across various countries ； ； (6) The eighth edition adds new content on dynamics, shaft vibration, and particularly machine seals ； The eighth edition covers the 6 basic types of cantilever pumps, namely: OH1 – foot-mounted pump ； OH2- centerline mounted pump ； OH3-Vertical pipeline pump with independent bearing housing ； OH4- Rigid coupling driven vertical pipeline pump ； The OH5 is a vertical pipeline pump with a coaxial drive, while the OH6 is a vertical pump integrated with a high-speed gearbox. The first two are horizontal centrifugal pumps, while the latter four are vertical centrifugal pumps. It also covers the 5 basic types of double-ended supported pumps, all of which are multi-stage centrifugal pumps. In addition, this standard also covers 7 types of vertical suspended centrifugal pumps. The eighth edition of API610 states in its “Preface” the purpose of this standard: to provide a purchasing specification to facilitate the manufacturing and procurement of centrifugal pumps for use in the oil, chemical, and gas industries. The content of this standard is mainly to establish minimum requirements for mechanical issues. This standard requires the buyer (user) to provide certain detailed specifications and characteristics to ensure the quality of the pump. This standard recommends using methods such as improvement, deletion, and expansion of content to update it, rather than rewriting it or incorporating its chapters into other standards. At the time of publication, this standard states that API assumes no obligation or liability for any loss or damage resulting from the use of this standard, nor for any conflicts that may arise between this standard and certain laws. III. API610 requirements for high-speed pumps: Thanks to the efforts of American Pump Company Sundyne, high-speed pumps have been included in the 8th edition of API610 under the basic pump type “OH6”. Here, the unique requirements of API610 for high-speed pumps are highlighted; some general requirements such as raw materials, drive methods, piping, and processes will not be covered. 1. API610’s requirements for the drive method of high-speed pumps: API610 defines high-speed pumps as pumps driven by an integral gearbox; it requires that there be a speed-increasing gearbox that is integrated with the pump. The impeller is directly mounted on the output shaft of the gearbox. There is no coupling between the pump and the gearbox ； However, the gearbox and the drive motor are connected by a flexible coupling. Pumps can be vertical or horizontal. 2. Requirements of API610 for the impeller design of high-speed pumps: API610 specifies that the impellers of high-speed pumps can be of open, semi-open, or fully enclosed type. The impeller should be made as a single cast piece or welded assembly. Welded impellers require the buyer’s special approval. Since high-speed pumps are often used under conditions of low specific speed, open impellers offer the best efficiency, as they reduce the disc friction losses of the impeller. 3. Requirements of API610 regarding the dynamics of high-speed pumps: API610 requires that high-speed pumps undergo a transverse critical speed analysis to ensure that the vibration amplitude remains at an acceptable level across the entire expected operating speed range. This standard states that high-speed pumps are typically subject to thorough research during development, and their typical rotor dynamics analysis is effective and applicable. Transverse analysis should only be required for pumps that are unique, new, or operate under hazardous conditions. The critical speed is the rotational speed corresponding to the lateral natural frequency (natural vibration frequency) of the rotor. The so-called dry critical speed refers to the natural vibration frequency of the rotor, calculated under the assumption that the rotor is supported only by bearings and that these bearings have infinite stiffness. The so-called wet critical speed refers to the natural vibration frequency of the rotor, which is calculated by taking into account the additional supporting and damping effects exerted by the liquid being pumped under operating conditions within the clearance spaces around the rotor, as well as the flexibility and damping properties of the bearings. For conventional rigid rotors, API 610 requires that their first critical speed be higher than the pump’s maximum permissible continuous speed by a certain safety percentage: for rotors designed for wet operation only, this percentage is 20% ； The rotor designed to operate dry must be 30% higher. 4. Requirements of API610 for high-speed pump bearings: Version 8 of API610 specifies that the applicable condition for rolling bearings is that their dm•n value must not exceed 500,000 mm•r/min ； Under rated conditions, continuous operation should be at least 25,000 hours ； At the maximum radial and axial loads and at the rated speed, it should be at least 16,000 hours ； The energy intensity of the pump (the product of rated power in kW and rated speed in r/min) does not exceed 4 million. If the above conditions are exceeded, that is, if the dm•n value is greater than 500,000 mm•r/min, the operating life is less than 25,000 hours or 16,000 hours, and the energy intensity is greater than 4 million, then hydrodynamic radial bearings and thrust bearings should be selected, with the hydrodynamic radial bearings having to be of the monolithic type. Compared to API 610 Seventh Edition, the Eighth Edition has set higher and stricter requirements for bearings. In the seventh edition, the dm•n value for rolling bearings is 300,000 mm•r/min, and the energy intensity is 2 million. There is no change in terms of lifespan; both have a rating of 25,000 hours or 16,000 hours. 5. Requirements of API610 for the dynamic balancing of rotating components in high-speed pumps. API610 sets the following requirements regarding dynamic balancing: a. Dynamic balancing is required when the operating speed of the components is ≥ 3800 r/min. b. The weight of the spindle used for dynamic balancing should not exceed the weight of the component being balanced. c. When the ratio of the outer diameter to the width of the component to be balanced is 6 or greater, it is permissible to perform dynamic balancing on only one plane. Otherwise, dynamic balancing should be performed on both planes. d. Rotors operating at speeds below 3800 r/min shall be balanced according to the G2.5 balance quality grade specified in ISO standard 1940. Rotors with a speed of over 3800 r/min must be balanced to the G1.0 balance quality level according to ISO standard 1940. e. When balancing the rotor (rotating components), rotating parts such as shaft sleeves and mechanical seals are not included; however, any missing single keyways must be filled with half a key. f. Rotors with high flexibility (whose flexibility coefficient L4/D2 ≤ 1.9X109 mm2), when used at speeds above 3800 r/min, require special attention in terms of design, manufacturing, and maintenance in order to achieve and maintain a G1.0 balance level. Here, L is the bearing span, and D is the shaft diameter at the impeller. 6. Main structural requirements for mechanical seals per API610: a. Mechanical seals shall have a modular structure to facilitate testing and installation. b. A standard single-face mechanical seal should be an internally balanced seal. c. The standard non-pressure double mechanical seal (formerly known as a tandem mechanical seal) should also be a balanced seal, capable of withstanding a pressure of 275 kPa from the buffer fluid. d. The standard pressurized double mechanical seal (previously known as a double-face mechanical seal) should also be a balanced seal. This seal must be designed to withstand reverse pressure differences without causing the sealing surfaces to open. e. The specified sealing interfaces and those on the pump shall be marked with durable symbols on the components and in the drawings. f. Whether the mechanical seal requires cooling (or heating) flushing should be determined through mutual agreement among the buyer, the seller, and the seal manufacturer. g. For mechanical seal auxiliary devices, refer to Appendix D of API610; various options are available. 7. Requirements of API610 for pump testing and pump performance: a. The buyer has the right to attend the seller’s pump testing, and the items to be tested must be agreed upon in advance. The seller shall provide complete information and facilitate on-site inspections. b. The seller shall provide test data on head, flow rate, power, and vibration at at least 4 points (high-speed pumps cannot be tested at the shut-off point). These 4 points are the minimum continuous stable flow rate point, the midpoint between the minimum flow rate and the rated flow rate, the rated flow rate point, and the maximum allowable flow rate point (the point of highest efficiency at least at 120%). c. A 3% decrease in head should be considered a sign of pump performance failure. Cavitation tests should be conducted on all the above 4 points. The NPSHr at the rated point shall not exceed the value specified in the contract. Here is a brief introduction to pump cavitation, net positive suction head (NPSH), available net positive suction head (system NPSHa), and required net positive suction head (NPSHr). Centrifugal pumps must operate at a certain speed, flow rate, temperature, and suction head pressure. When one or more of these conditions change, the pressure of the liquid inside the pump – usually at the inlet of the impeller – can become equal to or lower than the vaporization pressure of that liquid. As a result, the liquid being pumped vaporizes, the pump’s performance deteriorates, and it may even fail to deliver liquid; in addition, vibration increases. This phenomenon is known as cavitation in the pump. The so-called net positive suction head is the total absolute suction head at the pump inlet, measured in meters, starting from the base level, minus the vapor pressure of that liquid (an absolute pressure value, also in meters). For vertical pumps, the base plane refers to the centerline of the pump inlet ； For horizontal pumps, the base plane refers to the centerline of the pump shaft. The so-called effective net positive suction head available (NPSHa of the pump unit) is the net positive suction head determined by the buyer (user), based on the pump unit (under conditions of rated flow rate and normal pumping temperature), and is expressed in meters. The so-called required NPSHr is the NPSH determined by the seller based on water usage tests (in meters). The required net positive suction head is measured at the suction flange and corrected (converted) to the reference level. The required NPSHr at the rated flow rate and other flow rates is equal to the NPSH at which a 3% decrease in head occurs due to cavitation inside the pump. 8. Requirements of API610 for the minimum flow rate of pumps: 1. Minimum continuous stable flow rate: The lowest flow rate at which the pump can operate without exceeding the specified vibration limits. Unless the user specifies otherwise, the minimum flow rate of the pump is always as defined here. 2. Minimum continuous thermal limited flow rate: The minimum flow rate at which the pump can operate without its performance being impaired by the temperature rise of the liquid being pumped. 3. Determine the minimum flow rate based on the vibration data from pump testing: a) The relationship curve between flow rate and vibration; b) The pattern of change in pump vibration as the flow rate changes. API610 states that the vibration of a centrifugal pump varies with the flow rate, being at its lowest value around the point of optimal efficiency, and increasing as the flow rate increases or decreases. The variation of vibration with flow rate starting from the optimal efficiency point depends on the pump’s specific energy, specific speed, and cavitation specific speed. Generally, the variation in vibration increases with increasing energy density, higher specific speed, and higher cavitation specific speed. c. Division of the pump flow rate operating area: Based on the characteristics of vibration variation with flow rate as described above, API610 divides the operating flow rate range of centrifugal pumps into two zones; one of these is called the “preferred operating zone,” in which the pump exhibits low vibration levels. The other is called the “allowable operating area”; this area is defined by flow rates at which the vibration of the pump reaches higher levels, but remains at an “acceptable” level. The figure above illustrates this concept. It should also be noted that several factors other than vibration, such as the increase in temperature rise as flow rate decreases, or the increase in required net positive suction head NPSHr as flow rate increases, may cause the \"allowable operating range\" to become narrower. d. Vibration reference values for dividing flow rate operation zones: For vertical high-speed pumps, the API610 standard specifies that the vibration reference value at each flow rate point in the preferred operation zone is the root mean square value (RMS) of the unfiltered vibration velocity, Vu55 m3/h, for impeller diameters D2 > 150 mm ； b. Pumps with a rotational speed n > 3600 rpm. 2) Dynamic balance accuracy requirement: Pumps operating under condition a above shall meet a standard of not lower than G6.3 per ISO1940 ； Pumps operating under condition b as mentioned above should meet at least G2.5 grade per ISO1940. 3) Requirements for vibration velocity per GB3215: When the pump is operating without cavitation, the root-mean-square vibration velocity VRMS measured on the bearing housing shall be ≤ 4.5 mm/s. 4. Requirements of GB3215 for bearing selection 5. Requirements of GB3215 for the accuracy of pump performance testing. GB3215 stipulates that tests and measurements shall be carried out in accordance with GB3216 and GB3214. When the pump’s head is less than or equal to 300 m, Class C standards apply; when the pump’s head is greater than 300 m, Class B standards apply. The accuracy grades B and C specified in GB3216 are shown in the table below. Since the principles regarding terminology, prime movers, pressure testing, materials, sealing auxiliary systems, and packaging delivery are all the same as those in API610, this section will not be covered.