Technical requirements for dry-type breather valves in concentrated sulfuric acid storage tanks

I. Performance parameters (pressure regulation/volume of ventilation/operating conditions)

II. Material requirements (resistance to concentrated sulfuric acid corrosion/oxidation resistance) 1. For the main body material (corrosion resistance requirement), Hastelloy C-276 is the preferred choice (for valve bodies, valve discs, and valve seats); it can resist corrosion from 100% concentrated sulfuric acid at all temperatures, and its oxidation resistance is more than 10 times that of 316L stainless steel； Alternative: Carbon steel/316L stainless steel lined with PTFE, with a PTFE thickness of ≥3 mm, to completely prevent contact between concentrated sulfuric acid and the metal substrate. 2. Seal material for valve seats/valve discs: Polytetrafluoroethylene (PTFE)/expanded polytetrafluoroethylene (ePTFE); resistant to strong oxidation by 100% concentrated sulfuric acid, does not become brittle at low temperatures nor soften at high temperatures; surface roughness of the seal surface ≤ 0.04μm (mirror finish) ； Connection flange seal: Fluororubber (FKM/Viton), suitable for use with concentrated sulfuric acid; temperature range of -20°C to 200°C, with no swelling or aging ； 3. Material of the drying unit: desiccant composed of molecular sieve (4A/5A) and silica gel; it offers high moisture absorption efficiency, is reusable, and prevents the desiccant from being corroded by concentrated sulfuric acid vapor ； Drying chamber housing: Same material as the valve body (Hastelloy/PTFE-lined) to prevent the desiccant from absorbing moisture and forming dilute sulfuric acid that could corrode the housing. 4. Other components – springs: 316L stainless steel (to resist atmospheric corrosion) ； Fasteners: Hastelloy C-276 (to prevent pitting and intergranular corrosion).

III. Structural design parameters 1. Structure type: Independent dual-valve disk design with pressure and negative pressure functions; the drying unit is integrated at the inhalation end, while a flame arrestor/moisture prevention device is installed at the exhalation end. The inhalation and exhalation channels are separated to prevent failure of the drying unit； 2. Drying unit: Removable and washable/replaceable, equipped with a moisture absorption indicator window to facilitate online monitoring of the desiccant’s condition; replacement cycle ≥ 6 months (under normal temperature conditions) ； 3. Moisture prevention design: The intake side is equipped with a one-way check valve and a drying chamber as a dual protection mechanism, while the exhaust side features a gas-liquid separation plate to prevent concentrated sulfuric acid vapor from flowing back into the drying unit and causing it to fail ； 4. Valve disc type: Airfoil-shaped high-sensitivity valve disc, with an full-open pressure of ≤1.1 times the set pressure, which reduces the frequency of opening and closing and lowers the probability of water vapor ingress ； 5. Connection method: Flange connection, PN1.0MPa; flange standard HG/T 20592-2009 (standard issued by the Ministry of Chemical Industry), suitable for the flange specifications on the tops of sulfuric acid storage tanks ； 6. Waste discharge/venting: A waste discharge port (DN20) is provided at the bottom to facilitate the removal of condensate from the drying unit as well as small amounts of dilute sulfuric acid, thereby preventing corrosion caused by accumulated liquid.

IV. Installation and Related Parameters 1. Installation location: The highest point at the center of the tank roof, at a distance of ≥0.8m from the roof surface; avoid openings such as manholes and cleaning ports to prevent local pressure variations； 2. Installation angle: Install vertically with an inclination angle of ≤5° to prevent the valve disc from getting stuck and the desiccant from accumulating and becoming ineffective ； 3. Piping requirements: There should be no diameter changes or elbows at the inlet and outlet of the breather valve (it should be connected directly to the tank top) to prevent water vapor condensation caused by airflow disturbances ； 4. Supplementary accessories: • Install sun and rain shields to prevent direct sunlight from causing the desiccant to become ineffective, as well as to stop rainwater from entering the drying chamber ； • The desiccant replacement port is equipped with a quick-install flange, facilitating on-site maintenance without the need to remove the breather valve entirely. V. Manufacturing and Inspection Standards 1. Main body manufacturing: SY/T 0511-2010 \"Breather Valves for Oil Storage Tanks\", API 2000 \"Ventilation and Breathing of Atmospheric Storage Tanks\" ； 2. Corrosion testing: The valve body material was tested for intergranular corrosion and pitting corrosion, and meets the requirements of GB/T 4334-2022 ； 3. Drying performance test: After the air is dried, its dew point should be ≤-40°C to ensure that no moisture enters the tank.

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