AN OVERVIEW OF API SPEC 6A, APPENDIX F

API Spec 6A has undergone extensive revisions to become a more widely accepted specification worldwide. API 6A is no longer a dimensional specification. The 15th Edition of API 6A, which was effective 4/86, dealt in detail with quality levels of the iron used to manufacture API 6A components. The 16th Edition, which was effective 4/89, dealt in detail with quality and performance of API 6A metallic components, seals and sealing materials. The new API 6A will now make it possible for a user to spec in the cleanliness of the steel and the performance requirements of the seal required to meet the actual intended service conditions which include pressure (oil or gas), produced well fluids, actual well temperature and production variables such as inhibitors, acidizers, etc.

Performance testing for valves currently identified in API Spec 6A was developed by surveying users of API equipment A task team, consisted of 56 members, both users and manufacturers, was set up to analyze this data. These team members were mostly technical in background. After two years of technical discussions analyzing data and test programs, the team agreed to the performance testing shown in Appendix F of API 6A. The testing outlined for valves represents what the average product would endure in its field life. The three pressure temperature cycles outlined for wellhead seals, hangers, etc. represent a tortuous path that, if endured by a seal, it would continue to perform for its expected life.

DRIVING FORCES BEHIND ENDURANCE TESTING

Prior to the 15th Edition of API Spec 6A, many users of 6A products worldwide had identified weaknesses in Spec 6A. North Sea users were requiring equipment which basically met PSL 3 as now defined in Spec 6A. The MMS required SPPE surface safety valves be used on all wells drilled in Outer Continental Shelf waters. The requirements for this equipment exceeded PSL 2 and PR 1 as now defined in Spec 6A. Several major worldwide users of 6A equipment had developed internal specifications which outlined requirements for equipment which exceeded PSL4 and PR2 as now defined in Spec 6A.

API Spec 6A has undergone extensive revisions to become a more widely accepted specification worldwide. API 6A is no longer a dimensional specification. The 15th Edition of API 6A, which was effective 4/86, dealt in detail with quality levels of the iron used to manufacture API 6A components. The 16th Edition, which was effective 4/89, dealt in detail with quality and performance of API 6A metallic components, seals and sealing materials. The new API 6A will now make it possible for a user to spec in the cleanliness of the steel and the performance requirements of the seal required to meet the actual intended service conditions which include pressure (oil or gas), produced well fluids, actual well temperature and production variables such as inhibitors, acidizers, etc.

Performance testing for valves currently identified in API Spec 6A was developed by surveying users of API equipment A task team, consisted of 56 members, both users and manufacturers, was set up to analyze this data. These team members were mostly technical in background. After two years of technical discussions analyzing data and test programs, the team agreed to the performance testing shown in Appendix F of API 6A. The testing outlined for valves represents what the average product would endure in its field life. The three pressure temperature cycles outlined for wellhead seals, hangers, etc. represent a tortuous path that, if endured by a seal, it would continue to perform for its expected life.

Prior to the 15th Edition of API Spec 6A, many users of 6A products worldwide had identified weaknesses in Spec 6A. North Sea users were requiring equipment which basically met PSL 3 as now defined in Spec 6A. The MMS required SPPE surface safety valves be used on all wells drilled in Outer Continental Shelf waters. The requirements for this equipment exceeded PSL 2 and PR 1 as now defined in Spec 6A. Several major worldwide users of 6A equipment had developed internal specifications which outlined requirements for equipment which exceeded PSL4 and PR2 as now defined in Spec 6A.

It become obvious that users wanted to protect their investment in these products and limit their liability. Also, some equipment was used/installed in remote areas/subsea, etc. where access to the equipment was very limited which made it expensive to replace/rework equipment which did not have a long life. In summary, the performance testing in API 6A, Appendix F, has improved the reliability of the equipment for the user and has decreased the warranty claims for the manufacturer.

OBJECTIVE:

Perform 10,000 hydrostatic blowdowns (emptying or depressurizing of a material from a vessel) on a VG-300 gate valve that had previously completed an API Spec 6A Appendix F PR2 test

PR2 TEST:

  • Production model valve built with API 6A 16th Edition PSL3 components.

  • Test valve assembled fully lubricated with Vetco Gray GMS Y002 grease.

  • Dry Nitrogen gas was the pressure medium throughout the test with temperature ranging from -20° to +350°F.

ENDURANCE TEST PROCEDURE:

  • Valve was opened and closed the entire stroke by hydraulic motor.

  • Each time valve closed, 15,000 psi was applied using a hydrostatic pump. When pressure reached 15,000 psi, hydraulic motor opened valve causing a full hydrostatic blowdown.

  • 500 blowdowns were performed every 8 hours.

  • Valve was greased at onset of test and at the end of every 1000 cycles.

  • A 1-hour 15,000 psi hydrostatic hold was performed at the end of every 500 cycles. Hold time started at the point of valve pressure stabilization.

  • Strip chart recorder was used to record pressure and torque for entire endurance test.

  • No detectable drop in pressure during any 1 -hour pressure hold.

POST-ENDURANCE TESTS:

  • After completing 10,000 blowdowns, valve pressure source was converted to Nitrogen.

  • Valve pressurized to 15,000 psi; pressure stabilized; held for 2 hours; recorded on a chart recorder.

  • Downstream end of valve blinded and submerged in water with bubble monitor line attached.

  • Pressure reduced to 800 psi; held for 2 hours; no bubbles were observed; and chart recorder drew a straight line.

  • Valve was torque tested in blowdown condition and in running condition.

  • Valve disassembled, cleaned, reassembled with light motor oil.

  • 15,000 psi and 800 psi gas tests run for 1 hour each.

  • No bubbles were observed; chart recorder drew a straight line; post-endurance testing successfully completed.

PHYSICAL EXAMINATION:

  • Stem Packing:

    • I.D. of seal lips, bumps worn to seal's major I.D.

    • O.D. of seal lips, no measurable sign of wear or deformation.

  • Seat/Gate Seal Surface:

    • Gate – excellent shape, reusable.

    • Seat – almost unmarked, reusable.

    • Upstream Gate Face and Seat Face – no damage.

  • Stem in Packing Area, no detectable wear.

  • Bearings, extremely good condition. No difference in wear between the top and bottom sets, looked acceptable for further use.

  • Stem/Drive Bushing Threads, worn but in extremely good condition.

CONCLUSION:

Stock 2-1/16″ 15,000 psi VG-300 gate valve successfully passed an API Spec 6A, Appendix F PR2 test, then successfully completed a 10,000 cycle blowdown endurance test. Valve was still capable of sealing 15,000 psi and 800 psi Nitrogen gas for 2 hours without one bubble of leakage. Valve was still in excellent shape and could have endured much more testing.

The above API test program plus the ABB Vetco Gray Endurance Test program identifies a properly designed product which when subjected to worst case load/pressure conditions while being properly serviced will exceed many times the life expectancy of API 6A products. This improved reliability of a product reduces risk and increases safety for the end user. This opens up the application of this product into areas such as subsea or remote areas where access to the equipment is limited and expensive. This improved reliability also allows the application of this product by the end user into areas that are extremely environmentally sensitive.

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