Case Study: Middle East Operator Cuts Wellhead Downtime 60% with Puyang Zhongshi API 6A Christmas Tree Retrofit

About Puyang Zhongshi Group

Puyang Zhongshi Group Co., Ltd. was restructured from the Central Plains Oilfield Branch of SINOPEC in 1997. With over 25 years of manufacturing experience in petroleum machinery, the company operates 9 specialized factories with more than 500 employees, including 160+ technical and administrative professionals. Annual output value exceeds 200 million yuan.

The company holds API monogram licenses for 5CT, 6A, 10D, 11AX, and 11E, as well as ISO 9001, ISO 14001 certifications. Products have been exported to more than 30 countries including the United States, Canada, Russia, Venezuela, Colombia, Thailand, Indonesia, UAE, Saudi Arabia, and Kazakhstan. Core product lines include sucker rod pumps, pumping units, wellhead equipment and Christmas Trees, pressure vessels, drilling solids control systems, and cementing accessories.

Customer Background

A mid-sized independent operator in the Sultanate of Oman manages a mature onshore oilfield in the Ghaba Salt Basin. The field produces 28-32° API crude from the Barik sandstone formation at well depths ranging from 2,400 to 3,100 meters. Reservoir pressure varies between 1,800 and 2,600 PSI, with H2S concentrations measured at 1.2-2.8% by volume and CO2 content averaging 3.5%. Bottom-hole static temperature reaches 98°C under flowing conditions.

The operator runs 47 active production wells, of which 31 are naturally flowing and 16 require gas lift assistance. Daily gross production averages 18,500 barrels of fluid with an average water cut of 64%. The field has been on production since 2004, and the original wellhead equipment was approaching the end of its design service life.

Initial Problems

By early 2024, the operator recorded escalating wellhead-related failures across the field:

• Gate valve seat leakage: 12 wells experienced internal leakage past gate valve seats, requiring frequent injection of valve sealant as a temporary measure. Two wells had progressed to full valve body washout.
• Flange ring groove corrosion: RTJ flange ring grooves on 5 wells showed pitting depths exceeding 1.5 mm, compromising pressure integrity during well intervention operations.
• Tubing hanger neck seal degradation: Elastomeric seals in 8 tubing hangers had hardened and lost elasticity, producing measurable gas migration to the secondary seal area at casing head outlets.
• Operational impact: Unscheduled downtime reached 380 hours per quarter across the field. Well intervention costs averaged $42,000 per event. The operator spent approximately $680,000 annually on emergency wellhead repairs, sealant injection campaigns, and replacement components from multiple suppliers.
• Procurement fragmentation: Sourcing replacement parts from 5 different suppliers created inventory complexity and inconsistent material traceability across the field.

Why Customer Chose Puyang Zhongshi

The operator evaluated proposals from three API 6A-licensed manufacturers. Puyang Zhongshi Group was selected based on the following technical and commercial criteria:

Products Purchased

Recommended Products for Your Operations

Based on this successful deployment, Puyang Zhongshi recommends the following complementary equipment for operators seeking integrated wellhead-to-downhole solutions:

1. API 6A Wellhead Christmas Tree Assembly

Available in pressure ratings from 2,000 to 20,000 PSI with nominal bore sizes from 2-9/16" to 7-1/16". Configurable as single-wing or dual-wing with optional pneumatic or hydraulic safety valves. Material classes AA through FF to suit any well fluid composition. All assemblies undergo hydrostatic body testing at 1.5x rated working pressure and gas testing at rated pressure with full NDT documentation.

2. API 11E Beam Pumping Unit

For wells transitioning from natural flow to artificial lift, Zhongshi's API 11E pumping units provide reliable mechanical lifting with stroke lengths up to 200 inches and peak torque ratings to 912,000 in-lbs. Available in conventional, Mark II, and air-balanced configurations with API structural ratings from 6.4 to 912.

3. API 11AX Subsurface Sucker Rod Pump

Insert and tubing pumps in sizes from 1-1/16" to 4-3/4" with barrel options including chrome-plated, nickel-carbide coated, and carbon steel. Available in RHAC, RHBC, RWHC, and RWBC configurations. All pumps are individually dyno-tested before shipment.

4. Cementing Accessories

Complete range of float collars, float shoes, centralizers (bow-spring and rigid), cement baskets, and stage cementing tools. Fully compatible with standard API casing and tubing sizes from 4-1/2" to 20".

Quality Assurance & Certifications

Technical Solution

Material Selection Process: The operator's corrosion engineering team provided produced fluid analysis data. Zhongshi recommended Class DD material per API 6A — a 75K minimum yield strength low-alloy steel with controlled hardness (HRC 22 max) per NACE MR0175 for H2S service. All pressure-containing forgings underwent 100% ultrasonic testing (UT) to ASTM A388 and magnetic particle inspection (MPI) to ASTM E709 prior to machining.

Valve Design Upgrade: A key departure from the previous equipment was the specification of metal-seated gate valves with Stellite 6 hard-facing on both gate and seat sealing surfaces. The previous supplier had used elastomer-insert seats that degraded within 18-24 months under combined H2S and thermal cycling. The metal-seat design eliminated this failure mode entirely.

Corrosion Protection: All exposed carbon steel surfaces received a three-coat offshore-grade paint system: zinc-rich epoxy primer, high-build epoxy intermediate coat, and polyurethane topcoat. Internal wetted surfaces were left uncoated to avoid coating delamination risk in sour service.

Quality Inspection: Each Christmas Tree assembly underwent hydrostatic body testing at 1.5x rated working pressure (7,500 PSI) with a 15-minute hold period, followed by gas testing at rated working pressure with nitrogen at 5,000 PSI. Test certificates and UT/MPI reports were compiled into a data book delivered with each assembly.

Packaging & Export: Each assembly was skid-mounted on steel frames with bolted tie-down points, wrapped in VCI (Volatile Corrosion Inhibitor) film, and enclosed in plywood crates with desiccant packs. All flange faces received protective covers with bolted retainers. Shipment departed Shanghai by container vessel with 24-day transit to Port of Sohar, Oman.

Project Results

The operator's production superintendent reported: "The Zhongshi Christmas Trees have been running without a single valve leak or seal issue since commissioning. Our intervention team can now focus on artificial lift optimization instead of emergency wellhead repairs."

Why This Project Matters

Procurement Insight: This project demonstrates that material specification — not just pressure rating — is the critical differentiator when selecting wellhead equipment for sour service. The operator's previous supplier satisfied the API 6A mechanical requirements but used materials unsuitable for the corrosive environment, resulting in chronic failures.

Selection Tips for Operators:

• Always request complete material class certification per API 6A Annex F before issuing a purchase order
• Insist on UT and MPI reports for all pressure-containing forgings — not just certificates of conformity
• Consider consignment stock agreements to reduce inventory carrying costs and ensure spare parts availability
• Evaluate Total Cost of Ownership including intervention costs, not just unit price at PO stage

For Artificial Lift Engineers: Wellhead integrity directly impacts artificial lift system performance. Gas migration past tubing hanger seals can artificially depress casing pressure readings, leading to inaccurate gas lift valve set-point calculations. Stable wellhead conditions are a prerequisite for reliable artificial lift optimization.

Frequently Asked Questions

Q: How do you determine the correct API 6A material class for sour service?
A: Material class selection depends on H2S partial pressure, chloride concentration, pH, and temperature. For H2S concentrations above 0.05 psi partial pressure, NACE MR0175 applies. Class DD and EE materials are commonly specified for Middle East sour fields. Always provide your corrosion engineer with complete produced fluid analysis data.

Q: What is the typical lead time for API 6A Christmas Tree assemblies?
A: Standard lead time is 8-12 weeks from receipt of an approved order. Custom material grades or non-standard bore sizes may add 2-4 weeks. Expedited delivery can reduce lead time to 6 weeks for standard configurations.

Q: Can existing tubing heads be reused when upgrading Christmas Trees?
A: It depends on the condition of the tubing head flange face, ring groove, and lock screw threads. We recommend a dimensional inspection and NDT of the existing tubing head before committing to reuse. If ring groove pitting exceeds 0.8 mm or thread engagement is below 75%, replacement is recommended.

Q: What testing is performed before shipment?
A: Every assembly undergoes hydrostatic body test at 1.5x rated working pressure, gas test at rated working pressure, and function test of all gate valves (open/close cycles). Test reports, material certificates, and NDT records are compiled into a deliverable data book.

Q: How do metal-seated gate valves compare to elastomer-seated valves in sour gas service?
A: Metal-seated valves with Stellite hard-facing provide superior resistance to H2S embrittlement and thermal degradation compared to elastomer seals. While metal seats require higher operating torque and may not achieve zero-bubble-tight shutoff, their service life in sour environments is typically 3-5x longer than elastomer alternatives.

Q: What after-sales support is available for remote locations?
A: Remote technical support is available via video call within 24 hours. On-site engineering support can be arranged with 7-10 days notice. Consignment spare parts programs are available for operators with fleets of 10+ wells.

Q: Is OEM interchangeability supported for existing wellhead configurations?
A: Yes. Replacements can be manufactured to match existing OEM flange dimensions, bolt patterns, and ring groove profiles. Detailed dimensional data from the existing equipment is required for accurate interchangeability engineering.