API 623 Standard Summary

The API 623 standard covers the requirements for globe valves used in the downstream refinery industry for oil and gas. Specifically, the standard specifies a thicker walled construction and mandates low emission performance unless otherwise specified when compared against ASME B16.34 valves. The standard outlines the design feature requirements, testing requirements, material requirements of these valves, along with additional documentation, packaging, and information requirements.

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Standard Basic Information

Title: Steel Globe Valves – Flanged and Butt-welding Ends, Bolted Bonnets | Edition: First Edition | Date of Publish: January

Status: ACTIVE | Next revision to be published Late /Early

Organization: American Petroleum Institute

Work Group: Committee on Refinery Equipment (CRE) & Subcommittee on Piping and Valves (SCOPV)

Sections

1. Scope
2. Normative References
3. Terms and Definitions
4. Pressure/Temperature Ratings
5. Design
6. Materials
7. Testing, Inspection and Examination
8. Marking
9. Preparation for Shipment
10. Annex A: Information to be Specified by the Purchaser
11. Annex B: Identification of Valve Terms
12. Annex C: Valve Material Combinations
13. Bibliography

Standard Overview

Scope

• Globe valve
• Size: 1 NPS to 24 NPS (25 DN to DN)
• Class : 150 to 2,500
• Steel

Design

• Wall thickness is thicker than ASME B16.34, most sizes are more than 3mm greater than ASME B16.34.
• End designs to ASME B16.5, ASME B16.47, or ASME B16.25
• Face-to-face dimension to ASME B16.10 (ISO)
• Tabulated minimum seat internal diameter
• Bonnet shall be one-piece construction and have backseat and secured packing gland boltings.
• Bonnet-to-bonnet joint shall be connected with a gasket
• Disc shall require guiding in certain sizes and pressure.
• Tabulated minimum stem diameter (and permitted under tolerance). Larger than BS minimum.
• Many details in regards to the designs of the drivetrain, in response to operational issues.
• Tabulated nominal packing sizes
• Valve shall be qualified by testing to API 624
• Feature requirements on stop-check globe valves

Materials

• Acceptable valve materials are listed in ASME B16.34. Groups 1 and 2 are considered listed and acceptable materials.
• The standard specifies material requirements for trims and other listed parts.
• Trim is defined to be:
  • Stem
  • Body seating surface
  • Disc seating surface
  • Bushing/weld for the backseat
  • Small internal parts that normally contact the service fluid
• Other listed parts:
  • Body and bonnet
  • Disc
  • Separated yoke
  • Body bonnet bolting
  • Bonnet gasket
  • Gland and yoke bolting
  • Seat ring
  • Gland flange
  • Gland
  • Packing
  • Lantern ring, spacer ring
  • Stem nut
  • Handwheel
  • Handwheel nut
  • Pipe plugs
  • Bypass piping and valves
  • Identification Plate
• Tabulated Trim Table, identical to API 600.

Testing, Inspection and Examination

• Valve shall be tested to API 598
• Valve design shall be qualified to API 624

Important Notes

API 623 is written for after the industry repeatedly specifies an API 600 globe valve. The standard models after API 600 and maintains the same section as API 600. Any notes regarding special service, specification, and custom modification that may make a valve not meet API 623 may require the manufacturer to strike out API 623 in the nameplate to maintain compliance with their API monogram program.

For access to the API standard, please check IHS | Techstreet |

For information on additional valve standards, please see Standards Summaries.

Other Standards

How we found the problem

Opportunities, it is said, often arise from a problem. Recently, my colleagues were part of a task force designing and building a new crude unit at a major US refinery site. The owner expected a significant tax credit if the unit could be started before the end of the year, and commissioning of the unit was underway. During the week before Christmas, we started receiving reports from the site that the bypasses around control valves were leaking from the stem and packing area, leading to flash fires.

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Since the unit wasn't completely mechanically complete, some control valves were not yet in place or were still being configured, so the unit was “running on bypass,” with operations personnel manually adjusting the bypass globe valves as the unit was being brought up to full operations. As this was part of a major expansion, many of the operators were newly hired. The process temperatures were already high enough to be above flash point, so any leakage immediately erupted into small fires, prompting the operators to close the valves and back away, putting the startup in serious jeopardy.

When new valves have a problem, the first course of action is generally to assume the product is defective. In this case, the valves were provided by an approved manufacturer with a very high-quality reputation, reinforced by the fact that no other valves from this manufacturer were reported to be leaking. We started to suspect another issue as we realized that all these valves were in locations where flashing (a sudden release of vapor from a hydrocarbon liquid when the pressure drops) was expected.

We theorized that the flashing was occurring inside the valve, and the vibrations and pressure fluctuations were causing the leakage. The operators indicated that they were only opening the valves about one or two turns when they saw and heard the leakage and, in some cases, saw fire. This small partial opening was causing a large pressure drop and instigating flashing.

Because we were pressed for time to bring the unit completely online, we decided to cut into the bypass line at each of the affected control stations and add a second globe valve, in order to split the pressure drop across two valves. This solution worked, allowing us to successfully complete the startup, and the client was satisfied. We verified with several of our major clients, and most agreed that they had experienced similar problems but didn't have much insight into the reasons beyond “a lot of globe valves do that.”

A number of operators stated that it was common to hear globe valves making those vibrating noises, but most didn't have a clear understanding of what caused it. One major refining company had studied the problem and issued a practice limiting the allowable pressure drop across globe valves.

The normal practice in our office and many others was to arbitrarily size the bypass line in a control station as the next line size down from the pipe size in and out of the control station. We even published a chart demonstrating this sizing method. For example, if the line in and out of the control station was NPS 6 (DN 150), the bypass line was typically selected as NPS 4 (DN 100).

This mirrored control valve sizing in broad terms, in that a control valve with a port size of NPS 4 was usually selected based on having a specific minimum Cv based on the desired pressure drop and flowrate. It's important to note that port size only broadly corresponds with the specified control valve Cv.

This sizing method often resulted in the globe bypass valve having significantly more Cv than the control valve, making it challenging to throttle the globe bypass valve to a desired flowrate, especially during startup situations. This led us to develop a corporate practice underscoring the necessity of reviewing control station design in lines with flashing service. Essentially, it calls for the globe valve bypass to have a flow coefficient Cv at least equal to that specified for the actual control valve.

In practice, this means if the process line is NPS 6, the globe bypass valve would often be sized at NPS 3 or 2 (DN 80 or 50). A year or two after the initial startup problems, we applied this practice to a similar crude unit being built at another refiner’s largest refinery with a similar number of flashing services, successfully bringing the unit online without valve fires and without undue control valve bypass issues.

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