HDPE single & double‑wall composite pipe with electrofusion fittings is produced by multi‑layer co‑extrusion process, designed for underground fuel transportation, suction and vapor recovery pipelines of gas stations. Single‑wall composite pipes adopt integrated multi‑layer wall structure, which can be equipped with conductive inner layer and EVOH barrier layer according to practical demands, focusing on anti‑permeation and static‑dissipation performance. Double‑wall composite pipes adopt pipe‑in‑pipe structure, the inner pipe undertakes fuel delivery task while outer pipe provides secondary containment function. The interlayer space can cooperate with leakage monitoring devices. Once inner pipe appears damaged, leaked fuel will be confined inside the interlayer instead of seeping into soil and groundwater, realizing early‑warning protection against underground leakage. Matching electrofusion fittings include couplings, elbows, tees, reducers and end caps, forming a complete buried piping connection system together with composite pipes.
Traditional metal pipelines have obvious limitations in long‑term buried application. Metal materials are susceptible to electrochemical corrosion caused by soil moisture, salt‑alkali components and stray current. Corrosion defects will continuously expand, which may finally cause underground leakage and pollute surrounding environment. Field installation mainly relies on thread connection or arc welding, human operation errors easily produce hidden leakage risks at joints. Ordinary single‑layer plastic pipes without composite modification lack barrier and static‑conductive capacity, fuel vapor permeation loss is obvious, and static charges accumulated by high‑speed fuel flow cannot be released normally, bringing potential safety hazards. Unmatched non‑standard connecting parts will lead to poor sealing performance of the whole pipeline network, and the failure probability of joint positions is greatly increased.
HDPE composite material features excellent chemical resistance, resisting erosion from gasoline, diesel, alcohol‑blended fuels and various soil chemical components, and keeps stable mechanical properties under long‑term underground burial. The adhesive tie‑layer between each functional layer ensures firm bonding, avoiding inter‑layer separation under temperature change, ground stress and medium immersion. Continuous coil‑type supply effectively reduces the number of field joints compared with rigid pipelines. Supporting electrofusion fittings are made of matched composite raw materials. In‑site connection relies on electro‑fusion welding principle. After electrification and heating, the contact surface of pipe and fitting melts sufficiently to realize molecular fusion, forming integral, high‑strength and high‑sealing joints. The welding quality is less affected by manual skills, greatly lowering the failure probability of connecting positions.
Good flexibility enables pipes and fittings to adapt to slight ground displacement and foundation settlement, preventing crack fracture caused by external extrusion force. Complex pipeline layout can be completed without a large number of special shaped pieces, reducing trench excavation workload and shortening construction period. In the engineering design phase, working pressure, burial depth, soil condition, fuel type and station layout should be comprehensively considered. Reasonably select pipe specification and supporting electrofusion fittings according to actual flow demand. Backfill materials shall not contain sharp hard impurities to prevent scratching pipe outer wall. After construction, pressure test and tightness test shall be carried out for single‑wall pipeline, as well as inner pipe and interlayer of double‑wall pipeline, to check the integrity of pipe body and welding joints. Scientific type‑selection, standardized welding construction and regular inspection work guarantee stable and safe operation of the whole buried fuel piping system, meeting safety and environmental protection requirements of gas station oil storage and transportation facilities.