I. Case Background: Foshan’s Blue-License Dongfeng D6 Sewage Treatment Vehicle Procurement Requirement In 2023, a municipal sanitation department in Foshan City, Guangdong Province, launched a new round of sewage treatment equipment upgrade program. Due to the region’s prolonged rainy season and year-round relative humidity exceeding 80%, coupled with peak sewage treatment demands during summer heavy rainfall periods, the vehicle was required to operate continuously for 8–10 hours per day under extreme conditions—including resistance to sludge-water corrosion and frequent start-stop cycles. Through public tendering, the department ultimately selected the blue-license Dongfeng D6 chassis-based sewage treatment vehicle supplied by Chengli Special Purpose Vehicle Co., Ltd., with the project budget capped at approximately RMB 398,000 (per publicly available tender information), and an average unit price of around RMB 320,000. Consistent with local procurement practices, this tender prioritized evaluation of the vehicle’s anti-corrosion coating process, sealing component durability under hot-humid conditions, and high-load performance under rain-season operational frequency. Leveraging its mature expertise in sanitation equipment, Chengli delivered the CLW5070GSSD6 model—compliant with China VI emission standards—which has now operated stably at local sewage treatment sites for over one year. II. Equipment Fatigue Management Under High-Load Conditions: Real-World Challenges Encountered by the Dongfeng D6 in Foshan In the Foshan case, the sewage treatment upper-structure mounted on the Dongfeng D6 chassis must withstand the following three major fatigue risks: 1. Sludge-Water Corrosion and Rusting: Sewage contains acidic and alkaline substances; prolonged contact with the chassis, tank, and piping causes conventional coatings to peel off easily. Chengli adopted a multi-layer anti-rust coating system (epoxy primer + polyurethane topcoat), validated via salt-spray testing to ensure rust-free performance for at least five years under hot-humid conditions. 2. Sealing Component Aging and Failure: During rainy-season operations, hydraulic systems and discharge valves’ sealing components endure frequent actuation and sludge-water scouring. Chengli selected oil- and water-resistant silicone rubber seals and added protective covers, extending service life to 1.5 times that of standard products. 3. Powertrain Overload: Continuous operation increases thermal load on the engine and cooling system. The Dongfeng D6 chassis features a reinforced radiator and low-RPM high-torque characteristics; combined with Chengli’s optimized hydraulic pump matching, it maintains coolant temperature below 90°C during operation. According to Chengli’s after-sales feedback, this batch of vehicles successfully endured two full rainy seasons in Foshan (June 2023 – September 2024) without any downtime or maintenance incidents caused by corrosion or seal failure—validating the reliability of its heavy-duty design. III. Chengli’s Core Heavy-Duty Design Enhancements: Anti-Corrosion Coating & Sealing Component Durability To address the unique environmental challenges faced by the Foshan Dongfeng D6 sewage treatment vehicle, Chengli incorporated the following key improvements into its design: 1. Upgraded Anti-Corrosion Coating System Based on the official announcement parameters for the CLW5070GSSD6 model, Chengli applied a ‘three-coat, two-bake’ process to the tank and piping: a zinc-rich epoxy primer (zinc content ≥70%), an intermediate epoxy micaceous iron oxide coat, and a high-solids polyurethane topcoat. This coating system achieved over 1,000 hours of salt-spray resistance in laboratory hot-humid testing (40°C, 95% RH)—significantly surpassing the industry standard of 720 hours. 2. Sealing Component Selection and Protection At critical locations—including sewage pumps and discharge valves—Chengli specified imported fluorocarbon rubber O-rings, paired with stainle