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.
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.
By early 2024, the operator recorded escalating wellhead-related failures across the field:
The operator evaluated proposals from three API 6A-licensed manufacturers. Puyang Zhongshi Group was selected based on the following technical and commercial criteria:
| Evaluation Criterion | Requirement | Zhongshi Response |
|---|---|---|
| API 6A Monogram License | Mandatory - PSL 2 minimum | PSL 3G capability, license valid since 2002 |
| H2S/CO2 Material Compliance | NACE MR0175/ISO 15156 | Material classes AA through FF, full NACE compliance |
| Pressure Rating | 3,000-5,000 PSI working pressure | 2,000-20,000 PSI range, all verified by hydrostatic testing |
| Forging Source Traceability | Full mill certificates required | Heat lot traceability from forging to final assembly |
| Delivery Lead Time | 8-12 weeks from PO | Delivered in 6 weeks including custom material qualification |
| Engineering Support | On-site installation supervision | Provided commissioning engineer for first 3 wells |
| Aftermarket Commitment | Spare parts availability - 5 years minimum | Established consignment stock at operator's warehouse in Muscat |
| Item | Specification | Quantity |
|---|---|---|
| API 6A Christmas Tree Assembly | 5,000 PSI WP, 2-9/16" nominal bore, dual-wing configuration, material class DD (sour service), PR2 tested | 8 sets |
| Tubing Head Spool | 7-1/16" x 2-9/16", bottom flanged connection, with dual lockdown screws and secondary seal injection ports | 8 units |
| Casing Head Housing | 9" top connection, slip-on weld bottom, with dual casing hanger landing shoulder | 4 units |
| Gate Valve (Manual) | 2-9/16" 5K, metal-seated, rising stem, with grease injection fitting and backseat test port | 16 units |
| Adjustable Choke | 2-9/16" 5K inlet, 2" outlet, with calibrated bean and needle tip, tungsten carbide trim | 8 units |
| Ring Gaskets & Seal Kits | Type BX-153/BX-154, Inconel 825, with elastomeric backup seals | 8 complete sets |
Based on this successful deployment, Puyang Zhongshi recommends the following complementary equipment for operators seeking integrated wellhead-to-downhole solutions:
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.
| Model Range | Pressure Rating | Bore Size | Material Class Options |
|---|---|---|---|
| ZS-CT-2K | 2,000 PSI (13.8 MPa) | 2-9/16"~7-1/16" | AA, BB, CC |
| ZS-CT-3K | 3,000 PSI (20.7 MPa) | 2-9/16"~7-1/16" | AA, BB, CC, DD |
| ZS-CT-5K | 5,000 PSI (34.5 MPa) | 2-9/16"~7-1/16" | AA, BB, CC, DD, EE |
| ZS-CT-10K | 10,000 PSI (69.0 MPa) | 2-9/16"~7-1/16" | AA, BB, CC, DD, EE, FF |
| ZS-CT-15K | 15,000 PSI (103.5 MPa) | 2-9/16"~7-1/16" | AA, BB, CC, DD, EE, FF |
| ZS-CT-20K | 20,000 PSI (138.0 MPa) | 2-9/16"~7-1/16" | AA, BB, CC, DD, EE, FF |
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.
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.
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".
| Certification | Standard | Valid Since |
|---|---|---|
| API 6A | Wellhead and Christmas Tree Equipment | 2002 |
| API 5CT | Casing and Tubing | 2003 |
| API 10D | Bow-Spring Casing Centralizers | 2010 |
| API 11AX | Subsurface Sucker Rod Pumps | 2002 |
| API 11E | Pumping Units | 2002 |
| ISO 9001 | Quality Management System | 1998 |
| ISO 14001 | Environmental Management System | 2012 |
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.
| KPI | Before Retrofit | After Retrofit | Improvement |
|---|---|---|---|
| Unscheduled wellhead downtime (hrs/quarter) | 380 | 152 | 60% reduction |
| Average well intervention cost per event | $42,000 | $18,500 | 56% reduction |
| Annual wellhead maintenance spend | $680,000 | $295,000 | 57% reduction |
| Gate valve replacement frequency | 18-24 months | No replacements in 14 months | In progress |
| Number of active suppliers for wellhead components | 5 | 1 | 80% reduction |
| Mean time between wellhead-related interventions | 11 weeks | 35 weeks | 3.2x improvement |
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."
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:
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.
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.
