III. Manufacturing Process & Quality Assurance
The production of the TIANYU 3” 1500LB DBB trunnion mounted ball valve adheres to the most rigorous manufacturing processes and quality control protocols in the industry, aligning with API 6D, ASME B16.34, API 607, and ISO 9001:2015 standards to ensure every valve meets or exceeds design specifications and global industry requirements. From raw material procurement to final factory testing, every step of the manufacturing process is controlled and documented, with a focus on precision, consistency, and reliability—critical for a valve designed for 1500LB high-pressure, critical-service applications.
Raw Material Procurement & Inspection
Raw materials for the valve—F22 alloy steel billets and 304 stainless steel billets—are sourced exclusively from approved, ISO 9001-certified suppliers with a proven track record of producing high-quality materials for the oil and gas and petrochemical industries. All raw materials are accompanied by a mill test certificate (MTC) that verifies chemical composition, mechanical properties, and compliance with ASTM A182 (for F22) and ASTM A240 (for 304 stainless steel). Upon receipt, the raw materials undergo rigorous incoming inspection in TIANYU’s state-of-the-art quality control laboratory, including:
- Chemical composition analysis via optical emission spectroscopy (OES) to verify compliance with ASTM standards, ensuring the F22 alloy contains the correct chromium and molybdenum content for high-temperature strength;
- Mechanical property testing (tensile strength, yield strength, elongation, hardness) via universal testing machine (UTM) and Brinell hardness tester, verifying the material’s ability to withstand 1500LB high pressure and high temperatures;
- Non-destructive testing (NDT) including ultrasonic testing (UT) and magnetic particle testing (MPT) to detect internal and surface defects, ensuring no material flaws that could compromise structural integrity;
- For 304 stainless steel, additional testing to verify corrosion resistance and compliance with NACE MR0175 standards for sour service applications.
Any raw material that fails to meet the specified requirements is rejected and returned to the supplier, ensuring only high-quality materials are used in production.
Body & Ball Fabrication
The valve body and bonnet are manufactured using a hot-forging process, where F22 alloy steel billets are heated to high temperatures (1150-1250°C) and shaped under extreme pressure using precision dies. This process enhances material density, eliminates internal defects such as porosity or inclusions, and improves mechanical properties, including tensile strength, impact resistance, and creep resistance—critical for 1500LB high-pressure, high-temperature service. After forging, the body undergoes heat treatment, including normalization and tempering, to refine its microstructure and relieve internal stresses, ensuring consistent performance across the component. The body is then machined to precise dimensions using CNC lathes and milling machines, with critical surfaces such as the ball cavity, trunnion bearing bores, stem bore, and flange faces finished to a roughness of Ra ≤ 3.2 μm to ensure proper sealing and alignment.
The 304 stainless steel ball is manufactured using a precision forging process, followed by CNC turning and milling to achieve the required spherical shape and dimensional accuracy. The ball is then lapped and polished to a surface finish of Ra ≤ 0.8 μm, ensuring optimal sealing performance with the 304 stainless steel seat assembly. After machining, the ball undergoes solution annealing heat treatment (1040-1100°C) followed by rapid quenching, which refines the microstructure and enhances corrosion resistance. The trunnions are machined from F22 alloy steel billets, ensuring compatibility with the valve’s high-pressure requirements and providing exceptional strength and rigidity.
Seat & Stem Production
The 304 stainless steel seats are fabricated from precision-machined 304 stainless steel billets, with the sealing surface lapped and polished to a roughness of Ra ≤ 0.8 μm to ensure a tight, metal-to-metal seal with the ball. The seats are fitted with high-performance stainless steel springs, which maintain constant contact between the seat and ball, compensating for thermal expansion, contraction, and wear over time. The stem is machined from F22 alloy steel billets using CNC lathes, with critical surfaces such as the sealing area and thread finished to tight tolerances to ensure compatibility with the packing system and ball connection. The stem is also machined with an anti-blowout groove, ensuring compliance with safety standards and preventing stem ejection under high pressure.
Assembly & Testing
The valve assembly process is conducted in a controlled, clean environment to prevent contamination of internal components, with skilled technicians following detailed, step-by-step assembly work instructions that align with API 6D and ISO 9001 standards. The assembly process is highly structured, with each step verified and documented to ensure quality and traceability:
- The body is mounted on a precision assembly fixture to ensure alignment of all internal components;
- The lower trunnion bearing is installed in the body bore, with a high-performance anti-friction grease applied to reduce wear;
- The two 304 stainless steel balls are lowered into the body, with the lower trunnions seated in the lower bearings;
- The pre-loaded 304 stainless steel seat assemblies (upstream and downstream for each ball) are installed into the body seat pockets, with the seat springs compressed to ensure constant contact with the balls;
- The upper trunnion bearings are installed, and the stems are inserted through the bonnet packing and connected to the balls’ upper trunnions via a square drive or keyed connection;
- The bonnet is bolted to the body using high-strength alloy steel bolts (ASTM A193 B7) torqued to the specified value using a calibrated torque wrench, ensuring uniform bolt load and a secure seal;
- The stem packing system is installed, with the packing gland torqued to the specified value to eliminate fugitive emissions;
- The gear operators are mounted to the valve, and the stems are connected to the actuator drive shafts;
- The visual position indicators are calibrated to align with the balls’ open/closed positions, and all moving parts are lubricated with a high-performance, high-temperature grease compatible with the valve’s materials;
- The bleed valve assembly is installed and connected to the central cavity between the two isolation balls, ensuring proper DBB functionality.
During assembly, critical dimensions and clearances are verified using precision measurement tools, including coordinate measuring machines (CMMs), dial indicators, and calipers, to ensure compliance with design specifications.
Factory Testing & Certification
Before leaving the factory, every TIANYU 3” 1500LB DBB trunnion mounted ball valve undergoes a comprehensive series of performance tests in accordance with API 6D, API 598, API 607, and ISO 5208 standards, with all test results documented in a factory test certificate (FTC) provided with each valve. The testing program includes:
- Shell Test: A hydrostatic pressure test conducted at 1.5 times the rated 1500LB pressure (38.79 MPa) for a minimum of 30 seconds, to verify the body’s structural integrity and no visible leakage or deformation;
- Seat Test (Hydrostatic): A hydrostatic pressure test of the seat assemblies at 1.1 times the rated pressure for both upstream and downstream flow directions, to verify compliance with ANSI/FCI Class IV leakage standards;
- Seat Test (Pneumatic): A pneumatic pressure test at 0.69 MPa (100 PSI) to verify the metal-to-metal seal’s integrity in low-pressure applications;
- DBB Function Test: A functional test to verify the double block and bleed functionality, ensuring the two isolation balls can be closed independently and the bleed valve can safely vent trapped pressure;
- Operational Test: A functional test of the gear operator to verify smooth opening and closing, accurate position indication, and positive locking;
- Fugitive Emission Test: A test of the stem packing system in accordance with ISO 15848-1, to verify emissions are below the specified limit (≤ 100 ppm for Class A);
- Fire-Safe Test: A third-party fire test in accordance with API 607 and API 6FA to verify the metal-to-metal seal maintains integrity after fire exposure;
- NACE MR0175 Compliance Test: A series of tests to verify compliance with NACE MR0175, including sulfide stress cracking (SSC) testing for sour service applications.
Only valves that pass all tests are certified and released for shipment, with the FTC including all test results, material certifications, and compliance standards for full traceability.
Quality Management System
TIANYU maintains a certified quality management system (QMS) compliant with ISO 9001:2015 and API Q1, the oil and gas industry’s premier quality standard for manufacturing facilities. The QMS covers all aspects of the manufacturing process, from raw material procurement to final delivery, with a focus on continuous improvement, customer satisfaction, and compliance with global industry standards. The QMS is supported by a team of experienced quality assurance (QA) engineers who conduct regular internal audits, process reviews, and supplier audits to ensure compliance, and a document control system that maintains all manufacturing, testing, and certification records for a minimum of 7 years—meeting the traceability requirements of the oil and gas industry.
