Stainless Steel Oil Storage Tank Processing Flow

The processing flow of stainless steel oil storage tanks involves multiple steps, from design to finished product delivery. It is necessary to ensure structural strength, sealing performance, and corrosion resistance to meet the safety and durability requirements of the petroleum industry. The following is a detailed processing flow, explained by stage:

1. Design and Planning

• Requirement Analysis: Determine the capacity, dimensions, pressure rating, and environmental conditions (such as temperature and corrosiveness) based on the intended use of the oil storage tank (e.g., storing crude oil, refined oil, or chemical liquids).
• Material Selection: Select suitable stainless steel materials, commonly 316L, 304, or duplex stainless steel, considering corrosion resistance and cost. Must comply with standards such as API 650 (Welded Tanks for Oil Storage).
• Drawing Design: Use CAD or 3D modeling software (such as SolidWorks) to create detailed drawings of the oil storage tank, including the tank body, inlets and outlets, supports, manholes, vent valves, and other components.
• Stress Analysis: Simulate the stress distribution of the tank body under full load, pressure, or seismic conditions through finite element analysis (FEA) to ensure structural safety.

2. Material Preparation

• Plate Procurement: Purchase stainless steel plates according to design requirements (thickness is usually 4-20mm, depending on the tank size and pressure).
• Surface Treatment: Clean the plates to remove oil stains and oxides to ensure welding quality.
• Cutting and Blanking: Use CNC plasma cutting machines, laser cutting machines, or waterjet cutting to cut stainless steel plates to make the tank body, bottom plate, top plate, and accessories (such as flanges and manhole covers).
• Edge Treatment: Grind or chamfer the cut edges to reduce welding defects.

3. Tank Body Forming

• Plate Rolling: Feed the stainless steel plate into a plate rolling machine to roll it into a cylindrical tank body wall. Large oil storage tanks may be rolled in sections and then spliced.
• Bottom Plate and Top Plate Processing:
  • The bottom plate is usually flat or conical, using spliced plates and ensuring flatness.
  • The top plate can be a fixed roof or a floating roof (suitable for volatile liquids), cut and formed according to the design.
• Accessory Pre-fabrication: Process manholes, inlet and outlet nozzles, level gauge interfaces, vent valves, and other components, usually using lathes or CNC machining centers.

4. Assembly and Welding

• Assembly: Temporarily fix the bottom plate, wall plate, top plate, and accessories on the assembly platform, using fixtures to ensure alignment.
• Welding:
  • Use argon arc welding (TIG) or plasma welding to ensure smooth and corrosion-resistant welds.
  • Key welds (such as the connection between the bottom plate and the wall plate) need to be double-sided welded or fully penetrated welded.
  • Control heat input during welding to avoid intergranular corrosion caused by overheating of stainless steel.
• Weld Inspection: Use non-destructive testing (NDT) methods, such as X-ray (RT), ultrasonic (UT), or penetration testing (PT), to check the weld quality and ensure there are no cracks, pores, or other defects.

5. Surface Treatment

• Polishing: Mechanically or electrochemically polish the inner and outer surfaces of the tank to achieve a surface roughness of Ra0.4-0.8μm, reducing oil adhesion and corrosion risk.
• Pickling and Passivation: Use pickling solution (such as nitric acid + hydrofluoric acid) to remove the welding oxide layer and form a passivation film to improve corrosion resistance.
• Sandblasting (Optional): Sandblast the external surface to enhance aesthetics and coating adhesion.

6. Accessory Installation

• Install manholes, inlet and outlet pipes, valves, level gauges, temperature sensors, and other accessories.
• Ensure all connections are well sealed, usually using stainless steel flanges and oil-resistant gaskets.
• For pressure storage tanks, install safety valves and pressure gauges.

7. Inspection and Testing

• Dimensional Inspection: Measure the tank dimensions, wall thickness, roundness, etc., to ensure they meet the design drawings.
• Pressure Test:
  • Perform hydrostatic or pneumatic pressure tests (such as 1.5 times the design pressure) on pressure storage tanks to check the tanks strength and sealing performance.
  • For atmospheric storage tanks, the focus of the test is on sealing performance to prevent leakage.
• Corrosion Resistance Test: Test the corrosion resistance of stainless steel in a simulated oil environment.
• Visual Inspection: Ensure the surface is free of scratches and dents, and the welds are smooth.

8. Corrosion Protection and Coating (Optional)

• Although stainless steel itself is corrosion-resistant, the exterior may be coated with epoxy resin or polyurethane coating to enhance UV resistance and environmental corrosion resistance.
• Sandblasting is required before coating to ensure coating adhesion.

9. Packaging and Transportation

• Protective Packaging: Cover the tank surface with a protective film to prevent scratches during transportation.
• Transportation Method: Small storage tanks are transported as a whole, while large storage tanks may be transported in sections and assembled on-site.
• Fixing and Protection: Use brackets or wooden boxes to fix the tank to ensure transportation safety.

10. On-site Installation and Commissioning

• On-site Assembly (If applicable): Large oil storage tanks complete wall plate splicing, top plate installation, and final welding on-site.
• Foundation Construction: Ensure the storage tank is installed on a flat concrete foundation or steel structure support, in accordance with API 650 standards.
• Commissioning: Connect the piping system, test the functions of level gauges, valves, etc., and perform trial operation.

Precautions

• Safety Standards: The processing process must comply with OSHA or Chinese GB standards (such as GB 50128) to ensure the safety of welding, lifting, and other operations.
• Quality Control: Each process must have strict quality inspection records, in compliance with ISO 9001 or relevant certifications in the petroleum industry.
• Environmental Adaptability: For the petroleum industry, storage tanks need to consider special environments such as high temperature and sulfur-containing oil, and select appropriate materials and processes.
• Customized Requirements: According to customer requirements, linings (such as polytetrafluoroethylene) or insulation layers (such as rock wool) may be added.

Typical Materials and Process Parameters

• Materials: 316L stainless steel (containing 2-3% molybdenum, resistant to chloride ion corrosion) or 304 stainless steel (lower cost).
• Wall Thickness: 4-20mm, depending on the tank diameter and pressure.
• Welding Current: TIG welding is usually 100-200A, adjusted according to the plate thickness.
• Polishing Grade: Inner surface Ra≤0.8μm, meeting petroleum storage hygiene requirements.