In the petrochemical industry, flanges serve as critical connection and sealing components, playing a vital role across the entire industrial chain—including crude oil extraction, refining and processing, oil and gas transportation, and chemical reactions. Their application scenarios are highly tailored to the industry's unique demands: "high temperature, high pressure, strong corrosion resistance, and handling highly flammable or explosive media." These applications can be further explored through the following key scenarios:

1. Oil and Gas Extraction & Gathering System: Ensuring Safe Connections Between Wellheads and Pipeline Networks

In the upstream segment of the petrochemical industry (oil and gas extraction), flanges are primarily used to connect wellhead equipment, gathering and transportation pipelines, and related devices. Their core function is to withstand high-pressure oil and gas surges while effectively preventing medium leakage.

Wellhead Equipment (Christmas Tree): As the core device for wellhead control, the Christmas tree relies on high-pressure flanges—such as weld-neck flanges or integral flanges—to securely connect its valve body, four-way connections, and casing head. These flanges must withstand pressures ranging from several megapascals (MPa) up to tens of MPa at the wellhead, while also enduring corrosive media like hydrogen sulfide (H₂S) and carbon dioxide (CO₂) present in crude oil. For this reason, materials such as sulfur-resistant carbon steel (e.g., 35CrMo) or corrosion-resistant alloys are commonly used, ensuring that flange seals remain intact and preventing potential oil and gas leaks caused by corrosion-related failures.

Pipeline connections for gathering and transportation: The oil and gas pipelines running from wellheads to gathering stations must be connected in sections using flanges, enabling convenient access for future inspection and maintenance. Additionally, these pipelines are equipped with attachments such as filters, flow meters, and pressure gauges. Given that these installations are typically located in open, outdoor environments characterized by extreme temperature fluctuations and frequent sandstorms, the flange sealing systems must balance both "temperature resistance" and "dust-proof performance." To ensure reliable sealing even under harsh conditions, flexible graphite gaskets or metal-wound gaskets are commonly used.

II. Oil Refining and Petrochemical Equipment: Designed for High-Temperature, High-Pressure, and Multi-Media Corrosion Resistance

Petroleum refining and petrochemical processing—such as distillation, catalytic cracking, and hydrotreating—are the most complex application scenarios for flanges, as operating conditions vary significantly across different units, placing extremely high demands on the flanges' ability to withstand temperature, pressure, and corrosion.

Atmospheric and Vacuum Distillation Unit: In this unit, flanges are primarily used to connect the outlet piping of the heater, the initial distillation column, the atmospheric column, and heat exchangers. Operating conditions require the flanges to withstand high temperatures ranging from 350°C to 450°C and pressures between 1 and 3 MPa. Additionally, the process media contain highly volatile light components of crude oil, making butt-welded flanges (typically made of 15CrMoG) or integral flanges the preferred choice. These options not only ensure the ability to handle extreme temperature and pressure conditions but also significantly reduce the risk of medium leakage.

The connections between the regenerator, settler, and cyclone separator in the catalytic cracking unit—and the alignment of the catalyst transfer pipelines—are all secured using flanges. These operating conditions are particularly demanding, requiring flanges capable of withstanding high temperatures ranging from 600 to 700°C and pressures between 2 and 4 MPa. Additionally, the process media contain catalyst particles, which can easily erode the sealing surfaces of the flanges. To address these challenges, necked butt-weld flanges (typically made from P91 heat-resistant steel) and tongue-and-groove flanges are commonly employed. The tongue-and-groove design not only enhances sealing performance but also minimizes direct erosion of the sealing surfaces by catalyst particles.

Hydrotreating Unit: The connections between the hydrogen reactor's inlet and outlet, as well as the high-pressure heat exchanger, are critical application points for flanges. In this scenario, flanges must withstand high temperatures ranging from 300 to 400°C and pressures as high as 8–15 MPa. Additionally, the presence of highly corrosive hydrogen sulfide in the process medium further demands robust flange materials. As a result, integral flanges (made from materials such as 2205 duplex steel or Inconel alloy) or high-pressure self-tightening flanges are commonly selected. The latter not only reduces the number of bolts required but also enhances sealing reliability, making them ideally suited for the demanding conditions of high-pressure, highly corrosive environments.

Delayed coking unit: Flanges are required to connect the coke drum to the heater and to join the bottom piping of the fractionation column. Operating conditions demand resistance to high temperatures ranging from 400–500°C and pressures between 3–5 MPa. Additionally, the process medium contains highly coking-prone coke particles. For these reasons, weld-neck flanges (typically made of Cr5Mo alloy) and raised-face or grooved-face flanges are commonly used. The raised-face or grooved-face design facilitates easier cleaning of coking deposits from the sealing surfaces later on, ensuring long-term stability and reliability of the seal.

3. Chemical Production Systems: Meeting the Needs for Multi-Media and Precision Sealing

In downstream petrochemical processes—such as ammonia synthesis, methanol production, ethylene manufacturing, and synthetic fiber production—flanges must withstand corrosion from a variety of chemical media (including acids, bases, and organic solvents), while also ensuring the "gas-tightness" of the reaction system (since some reactions require isolation from air).

Connection of Reactors: The connections between the reactor vessel and its lid, as well as between the vessel and the feed/discharge pipelines in chemical reactors, must all be designed as detachable, sealed joints using flanges. For instance, in polymerization reactors used to produce ethylene—where the medium is highly flammable and explosive—flanges should feature a "tongue-and-groove face + metal-jacketed gasket" assembly. This combination ensures precise alignment via the tongue-and-groove design and leverages the exceptional sealing performance of the metal-jacketed gasket, effectively preventing ethylene monomer leakage and mitigating the risk of safety incidents. Meanwhile, for reaction equipment used in sulfuric acid production—where the medium exhibits strong corrosive properties—flanges must be made from 316L stainless steel, a material specifically resistant to sulfuric acid corrosion. This choice safeguards the flange body from perforation due to corrosion, ensuring the reliable operation of the entire system.

Utility systems—such as steam, cooling water, and compressed air pipelines used in chemical plants—require flanged connections for valves, pumps, heat exchangers, and other equipment. Although these systems operate at relatively low pressures (1–2 MPa) and temperatures (≤200°C), the process media may contain chloride ions (e.g., in cooling water). Chloride ions are known to induce stress corrosion cracking in flanges, so it’s crucial to select 304 stainless steel or plastic-lined flanges. These materials’ inherent properties help resist chloride-induced corrosion, ensuring the long-term stability and reliability of pipeline connections.

4. Storage Tanks and Loading/Unloading Systems: Ensuring Safe Storage and Transportation of Media

Raw materials in the petrochemical industry—such as crude oil and methanol—and finished products like gasoline and diesel must be stored in tanks. During loading and unloading, these processes often involve connecting to tank trucks or transport pipelines. In this context, flanges primarily serve the critical need for "large-diameter, low-pressure, and easily removable" connections.

Tank inlet and outlet: For large storage tanks—such as the 10,000 m³ crude oil tank—the bottom inlets/outlets and top breather valve connections must utilize large-diameter flanges (typically ranging from DN500 to DN1200). Since the operating conditions are at ambient temperature and pressure, and the medium is non-corrosive, Q235B carbon steel is commonly selected for its cost-effectiveness. The sealing surfaces are either flat or raised, paired with either asbestos-rubber gaskets or nitrile rubber gaskets, ensuring reliable sealing performance while maintaining budget-friendly design considerations.

Cargo arm connection: When loading or unloading oil and gas from tank trucks, the connection between the cargo arm and the truck’s interface must be made using a quick-flange system, such as a CAMLOCK quick-connect flange. These flanges enable rapid plug-and-play operations, significantly reducing handling time and minimizing volatile losses of easily evaporating media like gasoline and ethanol during the loading and unloading process. Additionally, they offer moderate impact resistance, allowing them to accommodate minor misalignments when coupling with the tank truck—thereby enhancing both the safety and efficiency of the loading and unloading operations.

V. Core Technical Requirements for Flanges in the Petrochemical Industry

The unique characteristics of the petrochemical industry dictate that flange applications must meet stringent standards—far beyond those required for general-purpose industrial flanges.

Material Compliance: Materials must meet specialized petrochemical standards such as API 5L (pipeline steel) and ASTM A182 (forged steel flanges). For example, sulfur-resistant flanges must comply with the NACE MR0175 standard. By ensuring strict material compliance, we prevent issues like sulfide stress corrosion, thereby safeguarding the flange's structural integrity and corrosion resistance.

Sealing Reliability: The gasket type must be precisely selected based on the medium's properties—use metal gaskets (such as metal ring joints) for high-pressure, high-temperature applications; employ PTFE gaskets in highly corrosive environments; and opt for flexible graphite gaskets in flammable or explosive scenarios. By carefully matching "flanges with gaskets," manufacturers can prevent "leakage, emission, and dripping" (a critical requirement in the petrochemical industry, where zero leakage is paramount), ensuring safe production processes.

Structural Adaptability: For high-pressure applications, integral flanges or weld-neck flanges are preferred to prevent welding stress concentrations through optimized structural design. For low-pressure, large-diameter applications, slip-on flanges are chosen to meet operational requirements while keeping costs down. Additionally, for connecting vibration-prone equipment such as pumps, loose-type flanges are used—leveraging their flexible design to absorb vibrational movements during operation, thereby minimizing the impact of vibrations on sealing performance.

In summary, the application of flanges in the petrochemical industry essentially involves "selecting the appropriate flange type, material, and sealing configuration based on the pressure, temperature, and corrosive properties of the process media under different operating conditions." Their performance directly determines the safety, stability, and operational efficiency of petrochemical equipment, making them a critical component for ensuring continuous production throughout the industrial chain.