December 2022

Digital Feature

Highlights of API 685 3rd Edition, Sealless Pumps—Part 2

Part 2 of the article on API 685 has highlighted most of the “other changes of interest to the reader” and provides insights into the various other points of discussion the API 685 task force addressed, along with the rationale behind changes found in the July 2022 published 3rd Ed. of the standard.

Korkowski, F., Applied K3nowledge Consulting; Hess, T., The Equity Engineering Group, Inc.; Cooper, J., Bechtel Inc.; van den Heuvel, M., BP

Authors: Korkowski, Applied K3nowledge Consulting, Brea, California; T. Hess, E²G | The Equity Engineering Group, Inc., Philadelphia, Pennsylvania; J. Cooper, Bechtel Energy Inc., Houston, Texas; and M. V. D. Heuvel, bp, Randstad, Netherlands

API 685, “Sealless Centrifugal Pumps for Petroleum, Petrochemical and Gas Industry Process Service,” has been updated to the 3rd Ed. and was published in July 2022. It addresses both magnetic drive pumps (MDPs) and canned motor pumps (CMPs).

Due to the nature of the extensive work done to compose the 3rd Ed., there are three parts to this article. Part 1, published in November 2022, addressed the significant changes in API 685 3rd Ed. This work (Part 2) will cover the other changes of interest to the reader in understanding revisions from the previous API editions, including the influences and reasons behind each. Part 3 will focus exclusively on secondary containment/secondary control, along with associated instrumentation requirements. The contents of this article were first published at the Turbomachinery and Pump Symposium held in Houston, Texas (U.S.) in September 2022.


The following items represent changes and additions which may be of interest to those who use the API 685 3rd Ed. document regularly to ensure compliance:

  1. Annexes
  2. Performance test points; hydrotesting
  3. Normative references
  4. Pipe gussets
  5. Auxiliary connections
  6. Wear rings
  7. Vibration and balancing
  8. Bearings and bearing housings
  9. Preparation for shipment
  10. Specifics for MDP
  11. Specifics for CMP
  12. Disassembly after testing
  13. Updated paragraph numbers and tables.

Annexes. Some re-lettering of the annexes in API 685 3rd Ed. was done to be consistent with the API 610 12th Ed. annexes. Old and new annex lettering is shown in TABLE 1.

TABLE 1. A comparison of annexes in API 685 2nd Ed. and API 685 3rd Ed., as to re-labeling and changes

The following are highlights:

  • Annex J, “Residual Unbalance,” was completely re-written to reflect the latest balancing technical details and images.
  • Annex Q, “Multistage Overhung Sealless Pumps,” informative annex was added
  • Annex H, “Material Columns,” had material columns I-1, I-2, S-1 and S-3 removed.
  • Annex N, “Data Sheets,” now provides columns for the purchaser to specify two additional operating conditions. Columns for “Normal” and “Rated” conditions remain, but the “Maximum” and Minimum” columns have been removed, and columns for four additional “Alternate” operating conditions are included in the “Operating Conditions” section of the data sheets.
  • Annex D, “Magnet Materials for Magnetic Couplings,” informative annex was modified as described in the “Materials” section of Part 1 of this article.
  • Annex G, “Materials Class Selection Guidance,” informative annex has been updated to reflect API 610 12th details and includes material columns used specifically for sealless pumps, as described previously in the “Materials” section of Part 1 of this article.
  • Annex P, “Hazard-Based Specification of Control/Containment Guidelines,” informative annex has been updated to state that the vapor pressure information the purchaser is to provide the vendor must include the range between 15°C (25°F) above rated temperature and ambient. This ensures vendors address the worst-case vapor margin conditions to prevent flashing conditions within the pump rotor chamber.

Performance test points; hydrotesting. Performance test points indicated in API 685 3rd Ed. are basically the same as that from the 2nd Ed. other than adding “or 10% of BEP (best efficiency point)” instead of the shutoff point on the performance curve. The reason for this was to provide additional protection to CMP and MDP thrust bearings to prevent higher thrust loads at low flow conditions below 10% BEP. This allowance protects the bearings from any potential damage because of performance testing at extremely low flows. TABLE 2 shows a comparison of the test points for API 610 pumps and API 685 pumps. The difference is due to traditional API 610 pumps typically ranging from low to high flows, where taking additional performance test points are advantageous to show the curve shape more accurately. Most API 685 pumps are low to medium flows and, as such, the extra test points are not necessary.

TABLE 2. Comparison of performance test points between API 610 12th Ed. and API 685 2nd and 3rd Eds. For very low-flow pumps with a BEP less than 11.4 m3/hr (50 gpm), points 3 and 5 are not required.

The underfilling of impellers is an adjustment vendors perform on a regular basis to slightly increase the total developed head and does not require prior approval by the purchaser. However, in many customer overlay specifications, vendor overfilling and/or V-notch of impellers does require prior approval by the purchaser. For this reason, an “if specified” statement has been added in both API 610 12th Ed. and API 685 3rd Ed. for these two types of impeller rework.

Three new testing items have been added. These include the following:

  • All preliminary running tests and machine checks should be completed by the vendor prior to the purchaser’s final inspection.
  • For pumps running in parallel, the minimum 10% rise-to-shutoff head requirement is to be verified during performance testing and included in the final test report.
  • Testing at shutoff may not be feasible for high-energy pumps due to temperature rise which can quickly damage a pump.

An important change regarding hydrostatic testing has been made, as well. In API 685 2nd Ed., use of a wetting agent to reduce the surface tension of the hydrotest water was an “if specified” item. API 685 3rd Ed. now makes it mandatory to use a wetting agent when any of the following conditions exist:

  • Pump liquid having specific gravity of < 0.7
  • Pump liquid temperature > 260°C (500°F)
  • Casing made from a new or altered pattern
  • Materials known for poor castability.

Normative references. Since the use of cast iron has been removed from the API 685 3rd Ed. (as explained in the Materials section of Part 1), various ISO or ANSI/ASME standards for this material have also been removed. Certain ISO specifications addressing other materials have remained, since there are no ANSI, ASME or U.S. equivalent specifications.

The following new references have been added:

  • API: 614 and 682
  • API RP: 686 and 691
  • ABMA Standard 9 (R2008)
  • ANSI/AWS D1.1
  • ANSI/HI 9.6.7
  • ASME B 18.18.2M and B31.3.

Pipe gussets. API 685 3rd Ed. now mandates that except for flushing connections, all auxiliary connection piping NPS 1 and smaller should be gusseted. This had changed from the API 685 2nd Ed. requirement for piping gussets “if specified.” This is consistent with API 610 12th Ed. The gusseting reinforces the key casing pressure boundary connections and adds strength to the joints.

API 610 11th Ed. introduced the subject of gusseting auxiliary piping connections to the pump casing. Details were provided for gusset design, and because it was a bulleted paragraph, gusseting was required only when a customer imposed the requirement. However, with API 610 12th Ed., gusseting is now mandatory for piping sizes NPS 1 and smaller, and it is no longer a bulleted requirement.

Auxiliary connections. Like API 610 12th Ed., API 685 3rd Ed. now has a subsection for auxiliary connections. The subsection defines which connections are included: vents, drains and external connections which are designated for external cooling (when needed), and the associated lubrication plans. This section now combines details from API 685 2nd Ed. (“pressure casing connections”) with API 610 12th Ed. (“auxiliary connections”) to address all requirements for these casing connections.

Secondary casing connections for MDP and CMP are generally threaded. Also, these connections may end in a flange; however, it is best for the customer and vendor to review these items and confirm whether any of these joints must be upgraded to socket welds for higher integrity connections.

As previously mentioned, gusseting of small diameter auxiliary connection piping is now mandatory to be consistent with API 610 12th Ed.

Wear rings. API 685 3rd Ed. added the requirement that the locking holes drilled to secure wear rings be positioned in the center of width of the ring. The paragraph specifying the method of securing wear rings had previously required that the diameter of the holes for the locking pins or screws be no more than one-third the width of the wear ring but did not include detail of the hole’s location. Positioning the holes for the locking pins or screws in the center of the ring width is a good practice to ensure the ring has equal material on the sides of the holes to help prevent potential cracks in the ring. The locking hole location in the center of the wear ring width was required in a few end users’ overlay specifications.

Vibration and balancing. Vibration measurements at the specified physical locations on horizontal and inline overhung pumps are now required to be taken in both horizontal and vertical planes at the rated point.

Measurements at all other hydraulic operating points are taken in the same plane as the highest reading obtained at the rated point. This differs from the previous edition where the vibration was taken in both planes at all operating points. 

A carry-over item from API 610 12th Ed. is the mandatory requirement to provide a plotted spectrum for vibration. In earlier editions of both API 610 and API 685, this was a bulleted paragraph and was required to be done only when specified by the purchaser.

A new item added in API 685 3rd Ed. is to perform a residual unbalance test per Annex J when a rotor is balanced as an assembly.

Bearings and bearing housings. A reminder has been added to API 685 3rd Ed. about the importance of providing proper cooling and lubrication of product-lubricated bearings when the pump liquid is of low viscosity [typically below 0.2 centipoise (cP)], since these liquids provide very little lubricity to the bearings and flashing is a concern.

New to API 685 3rd Ed. is the requirement that steel material be used for:

  • Bearing housings
  • Load carrying covers and brackets between the casings (or heads) and the bearing housings
  • Driver supports for vertical inline pumps which have thrust bearings in the driver.

This is now consistent with API 610, which for several editions has prohibited using cast iron (typical past practice) because it runs the risk of cracking when applying cold water to a unit when putting out a fire in a facility.

Preparation for shipment. Many new paragraphs have been added that are aligned with API 610 12th Ed. requirements for shipment preparation, including:

  • If specified, for MDPs, perform a physical alignment between the pump’s shaft and driver.
  • The alignment report is to be included as part of the final documentation package.
  • The smallest measured radial clearance between each hold-down bolt and its respective hole is to be measured to ensure no bolt-bound conditions exist after shop alignment is performed.
  • If specified, the alignment check is to be witnessed.
  • Coat the bearing housing and carbon steel components in the oil system with an oil-soluble rust preventative.
  • Protect against moisture and dirt entry.
  • Attach bags (containing vapor-phase inhibitors) to flanged covers and identify the bags with corrosion-resistant tags.

Specifics for MDPs. There are several new items and changes to API 685 3rd Ed. addressing MDPs. Details are in the MDP section of the API 685 and are in addition to the basic design requirements for all sealless pumps. Nearly all were adopted from API 610 12th Ed.  The new items include the following:

  • The pump’s centerline height should be minimized to ensure compliance with API nozzle load requirements.
  • Sufficient clearance between the pump drain and the baseplate should be provided to facilitate easy interface with the purchaser’s connecting piping.
  • Enough cross-members under the pump and driver supports should be provided in the pump baseplate. These members must be shaped to aid in locking into the grout.
  • The vendor is to advise whether any equipment must be removed prior to baseplate grouting.
  • The primer applied to the underneath of the baseplate is to be compatible with epoxy grout; and the vendor is to advise the purchaser of the specific primer used.
  • The baseplate lifting lugs must be attached by continuous welds that are 100% non-destructive tested (NDT), per the appropriate code.

The two changes to the MDP section are:

  • API 685 3rd now states that decoupling of the magnets is to be avoided at any specified operating condition instead of just the rated condition point, as was stated in API 685 2nd Ed.
  • Consistent with API 610 12th, transverse and axial alignment positioning jackscrews are now always required to position equipment on the mounting pads. API 685 2nd Ed. required jackscrews only when a component weighed more than 250 kg (500 lb).

Specifics for CMPs. While a limited number of changes were made to the API 685 3rd Ed. specification section addressing CMPs, some are fundamental to safety and design. The following items were modified:

  • The CMP’s stator housing should be designed to the equivalent maximum allowable working pressure as the pressure casing. This requirement was not changed, but a reference was added to direct readers to the specific design criteria covered under the generic pressure casing design section.
  • The motor connection box sizing was previously specified to be one size larger than IEC’s (NEMA’s) minimum size. The new requirement is to use standard IEC (NEMA) sizing which is generally large enough.
  • The maximum number of starts per hour was a set value and now must be specified by the pump manufacturer. A note was added to clarify that the maximum number of starts might not be limited by the motor design but by application limits, such as the vaporization of liquids in the motor compartment.
  • The isolation class H (180°C) remained as minimum design case, but a note was added to clarify that other insulation classes can be used for higher temperature services.
  • For specific services (e.g., toxic fluids), a decontamination purge may be specified on the stator assembly to ensure safe disassembly of the CMP after failure of the stator liner. This would be necessary, as the stator area is now contaminated by the pumped fluid. Unfortunately, flush or drain connections are often not allowed on the motor assembly as this may void the motor explosion-proof certification.

The following items were added to the API 685 3rd Ed. specification:

  • It is an industry best practice to have a thermal protection cutout device on the motor. This requirement was added to the specification with guidance that individual winding temperature sensing elements per phase can be requested for monitoring. Monitoring of the winding temperatures is especially relevant to variable frequency drive applications.
  • An inherent disadvantage of the canned motor design is the inability to see the direction of rotation. Correct direction of rotation can be established by comparing the pump design operating parameter vs. the field data. Simpler and more effective than comparing data is the use of instruments that detect pump rotation direction or avoid running the pump in the wrong direction. Such an instrument is now prescribed.

Note: Vibration analysis using casing measurements to detect bearing wear is difficult with fluid lubricated sleeve bearings. There are many different technical solutions available to trend or indicate bearing wear based on the shaft position. It is an option to add such a bearing wear detector to the scope of delivery.

Disassembly after testing. For sealless pumps, additional text has been added to explain that it may not be possible to drain all the water after testing, though it is important to do so. The optional approach of disassembling the pump may be invasive to a point of impacting its mechanical integrity.

Updated paragraph numbers and tables. For the most part, API 685 3rd Ed. follows the same format established for the 2nd Ed. regarding the table of contents, a generic section for sealless pumps and specific pump sections for CMP and MDP requirements.

The one major change was moving the proposal and contract data requirements under vendor data Annex L in the 3rd Ed. This was done primarily because it is outside the realm of specification requirements and considered commercial in nature.

There are numerous edits made throughout the document to improve the wording of requirements for easier reading. This included moving some paragraphs into different locations. Since there are many abbreviated terms used throughout the document (e.g., ASTM, BEP, Cf, MT, PWHT), a listing of abbreviated terms was added to the beginning of the standard. Many of the wording changes were incorporated from API 610 12th Ed. for consistency, as was the re-labeling of most of the annexes, which was addressed previously in this article.

Takeaways. Part 2 of the article on API 685 has highlighted most of the “other changes of interest to the reader” and provides insights into the various other points of discussion the API 685 task force addressed, along with the rationale behind changes found in the July 2022 published 3rd Ed. of the standard.

Where do we go from here? Does industry keep API 685 as a standalone document or perhaps make it part of API 610? Does industry expand API 685 to include overhung multi-stage sealless pump designs within the main body of the future standard? What new technologies must be explored and applied to API 685?

The authors welcome all comments and suggestions for topics—within and beyond what has been addressed in this article—for additional consideration.


Part 1 of this article covering the “significant changes in API 685” was published in Hydrocarbon Publishing in November 2022. Part 3—which addresses exclusively secondary control and secondary containment, along with associated instrumentation requirements—is planned to be published soon.

For a full list of acknowledgments and references, see Part 1 of this article.


Frank Korkowski ( is the Director of Engineered Training at Applied K3nowledge Consulting. He is a consultant recently retired from Flowserve and previously was the Marketing Manager for the API 1- and 2-stage process pumps. He spent 45 yr in various pump roles with Ingersoll Rand, Ingersoll-Dresser Pumps and Flowserve. Korkowski earned a BS degree in industrial engineering from the New Jersey Institute of Technology, with post-graduate studies in mechanical engineering and business administration at Lafayette College and Fairleigh Dickinson University. For the last 25 yr, he has served on API task forces API 610, API 685, API RP-691, and currently on API 682 and API 674.

Tom Hess ( is the Principal Rotating Engineer for The Equity Engineering Group, Inc. Prior to joining Equity, Hess worked as a Rotating Reliability Engineer in an oil refinery. He has been fascinated with sealless pumps for nearly 30 yr. He earned his BSME degree from Villanova University, is a member of ASME and is a registered professional engineer in the Commonwealth of Pennsylvania. Hess is a member of the API 685, 610, 682 and 613 Task Forces.

Jeremy Cooper ( is a Principal Rotating Equipment Specialist for Bechtel Energy Inc. in Houston, Texas (U.S.). Since 2001, he has worked as a Project Manager and Project Engineer with suppliers such as Flowserve and IFS. Prior to joining Bechtel, he was a Rotating Equipment Engineer at Fluor. Cooper currently serves as the Chairman of the API SOME, is the task force chairman of API 610 and API 685 and participates in several other task forces. He has worked startup and commissioning assignments in both international and domestic projects and is currently the Functional Lead for Rotating Equipment at Bechtel.

Martein van den Heuvel ( is a Senior Rotating Systems Engineer working for the central innovation and engineering team of bp. This year, he celebrated 30 yr of rotating equipment related experience in various operational, maintenance and engineering roles in the chemical and oil and gas industry. Heuvel received a BS degree in Mechanical Engineering from the Technische Hogeschool Rotterdam and a MS degree (honors) in maintenance management from the Caledonian University in Glasgow. He is a member of the API 685 taskforce. 

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