What are the installation process requirements for the external coils of carbon steel external coil storage tanks?

The installation process for the external coils of carbon steel external coil storage tanks must strictly adhere to pressure vessel manufacturing standards to ensure structural safety and heat transfer efficiency. Before installation, the coil materials must undergo incoming inspection, including material certification, ultrasonic testing, and dimensional tolerance measurement. The bending radius should not be less than three times the pipe diameter to avoid localized stress concentration. Three-dimensional layout technology is used for coil positioning to ensure uniform pipe spacing (typically 1.5-2 times the pipe diameter), and the gap with the tank wall is controlled at 5-10mm to balance thermal expansion space and heat transfer efficiency. The welding process requires argon arc welding for the root pass followed by manual arc welding for the fill pass. Low-hydrogen E5015 electrodes or matching special welding materials are used. Welding current and voltage parameters must be determined through process qualification. Each weld must undergo 99.99% penetrant testing (PT) and 20% radiographic testing (RT) sampling inspection. The acceptance standard complies with the Class II requirements of NB/T 47013.

The coil support structure design must consider thermal displacement compensation, using elastic supports or sliding supports, with a fixed point spacing not exceeding 2 meters to prevent vibration fatigue. The flange connection surfaces at the pipe ends must be machined to a roughness of Ra3.2 or lower, using metal spiral wound gaskets and tightening with a torque wrench in a cross-shaped sequence. After installation, a hydrostatic test at 1.5 times the design pressure is required, with a pressure holding time of no less than 30 minutes, while simultaneously checking the sealing of all welds and connections. For the airtightness test, nitrogen is pressurized to the working pressure, and micro-leakage is detected using soapy water. Corrosion protection construction is carried out simultaneously with the tank construction; the outer surface of the coil must be sandblasted to Sa2.5 level and then coated with a high-temperature resistant epoxy coating with a dry film thickness ≥200μm. Afterwards, a heat transfer medium circulation test is conducted to verify the uniformity of flow distribution and the system's pressure-bearing capacity.