Hydraulic testing of ethylene spheres

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All details regarding the hydrostatic testing of ethylene spheres have been published on the official WeChat account: Petrochemical Engineering Notes. Ethylene spheres are large in size; in current new ethylene tank farm projects, these spheres are usually transported to the site in sheet form for installation there. Spherical tanks constructed on-site are subject to certain stresses, and various defects may also exist during installation. Hydrostatic testing can be used to detect these defects, while overload testing can be employed to eliminate some or all of the assembly stresses and welding stresses. The overload test can cause local yielding, and by adjusting the peak value of the residual stress in the vicinity of the joint, the stress is softened, which in turn leads to an improvement in angular deformation and ovality. Water is incompressible; even if it ruptures during the test, its energy release is less than that of gases. Gases have high compressibility, allowing them to store large amounts of energy; once they rupture, the danger increases even further. So hydrotesting is safer, but pneumatic testing is sometimes used as well, though under stricter conditions. Taking a 3000 m³ ethylene sphere tank in a certain project as an example, plate 09MnNiDR is used for on-site construction and installation. Its design pressure is 2.16 MPa, and the hydrostatic test pressure is 2.71 MPa, which is 1.25 times the design pressure. Under normal operation, with a loading factor of 0.9, the amount of material to be loaded is approximately 1,200 tons ； During the hydrostatic test, the total mass of water filled in is approximately 3,000 tons, which is 2.5 times that of the material used during normal operation. The weight of the spherical tank shell itself is approximately 530 tons; during the hydrostatic test, the total weight including accessories such as ladders attached to the tank is about 3700 tons. 1. Reasons for hydrostatic testing 1.1. Verifying structural strength and integrity; detecting potential defects: By applying a load higher than the design pressure (usually 1.25 times the design pressure), hydrostatic testing can reveal defects that may exist during manufacturing or installation, such as weld cracks, weak points in the material, or leaks at connections. l Plastic deformation test: Through pressure testing, it can be confirmed that the spherical tank will not suffer permanent deformation or rupture under extreme pressures, ensuring a safety margin during actual operation. 1.2. Checking sealing performance – Leak inspection: During the pressure retention phase, the sealing integrity of the spherical tank is verified by observing whether the pressure gauge remains stable and by checking for any leaks at joints such as welds and flanges. Ethylene is a flammable and explosive gas, and even minor leaks can lead to serious accidents; therefore, tight sealing is essential. 1.3. Simulation of actual operating conditions and verification of adaptability: Load testing – The hydrostatic test simulated the static pressure condition of the spherical tank when filled with liquid, in order to verify the tank’s capacity to withstand pressure under full-liquid conditions as well as the stability of foundation settlement. 1.4. Basis for quality acceptance: The results of the hydrostatic test are important documents for project acceptance, providing a technical basis for subsequent operation permits. 2. Preparations before hydrostatic testing