Petrochemical production facilities are comprehensive industrial facilities that use petroleum and natural gas as raw materials to produce basic chemical raw materials such as ethylene, propylene, benzene and p-xylene and polymer products such as synthetic resin, synthetic rubber and synthetic fiber through a series of complex chemical reactions such as cracking, reforming, polymerization and alkylation. These processes usually involve high temperature, high pressure, hydrogen exposure and strong corrosive media, which puts extremely strict requirements on the materials of production equipment.
Advantages & Key Features
Excellent high temperature and high pressure tolerance.
The petrochemical core reaction devices, such as the radiant section tubes and high-temperature steam pipes of ethylene cracking furnace, have been operating at a high temperature above 800°C for a long time. Choosing special alloy steel with excellent high-temperature strength, creep resistance and oxidation resistance, such as HP series (25Cr-35Ni) improved heat-resistant alloy steel, is the key to ensure the long-term safe and stable operation of the plant under extreme thermal load.
Diversified anti-corrosion solutions
There are many kinds of media in petrochemical production process, and the corrosion environment is complex and changeable, including but not limited to high temperature sulfur corrosion, naphthenic acid corrosion, hydrogen corrosion, chloride stress corrosion cracking, and polythionic acid corrosion. Steel provides a complete pedigree from carbon steel, low alloy steel, stainless steel (austenite, ferrite, duplex), nickel-based alloy to special alloy through alloying, which can be tailored according to specific corrosion environment to achieve the best balance between safety and economy.
Excellent manufacturing and repairability
Petrochemical plants are mostly large-scale equipment customized in single piece or small batch. The good plasticity, weldability and mature heat treatment technology of steel make the complex structures such as cracking furnace and large tower successfully manufactured. In the long-term operation and regular maintenance of the device, the repairability of steel components (such as surfacing, repair welding and local replacement) is far superior to many other materials, which greatly prolongs the overall service life of the device.
Mature and reliable design and standard system
The petrochemical industry has mature material standards (such as ASME, ASTM, NACE, etc.) and design specifications that are universally accepted. The performance data (mechanical properties, corrosion data and welding procedure qualification) of each steel are supported by detailed databases, which provide a solid and reliable foundation for engineering design, safety assessment and risk management and control, and ensure the standardization and safety of petrochemical plant construction and operation worldwide.
Typical Applications
Ethylene cracking furnace tube: Centrifugally cast heat-resistant alloy steel tubes such as 25Cr-35Ni-Nb(HP40Nb) are widely used to withstand the wall temperature as high as 1150 C..
Adsorption tower of p-xylene (PX) plant: Stainless steel composite steel plate (SA516 Gr.70+ 304L) is often used in the tower body to resist the corrosion of aromatic medium.
Polypropylene loop reactor: made of high-strength low-alloy steel under high-pressure polymerization environment, and the inner wall is highly polished or specially treated to prevent polymer from sticking to the wall.
Pressure vessels and reactors are the core equipment in chemical and petrochemical processes, which are used for physical or chemical reactions, material storage and separation. They operate at a set pressure (usually high pressure) and temperature, and the internal medium is often flammable, explosive, toxic or strongly corrosive. Its design, manufacture and material selection are directly related to the safety and stability of the whole factory.
Advantages & Key Features
High strength and toughness ensure intrinsic safety.
As a pressure-bearing boundary, the container shell must prevent catastrophic brittle fracture and plastic explosion. By adopting high-strength low-alloy steel plates (such as SA516GR. 70 and SA537CL. 1) and ensuring that the materials (especially the weld and heat affected zone) still have sufficient impact toughness at the lowest design metal temperature, the safety margin of the equipment under abnormal working conditions is fundamentally guaranteed.
Targeted environmental cracking resistance
In wet hydrogen sulfide environment, steel plates with resistance to hydrogen-induced cracking (HIC) and sulfide stress corrosion cracking (SSC) (meeting NACE MR0175/ISO 15156 standard) should be used. The prevention of alkali stress corrosion cracking (ASCC) should be considered in the amine liquid desulfurization unit. In chloride environment, duplex stainless steel or post-weld heat treatment is needed to eliminate stress. Steel can meet these specific requirements through composition optimization and production process control.
Flexible material combination and composite technology
For highly corrosive media, it is expensive to use all advanced alloys. It is an economical and effective scheme to adopt the composite structure of "steel+corrosion resistant layer", such as surfacing stainless steel or nickel-based alloy coating on carbon steel or low alloy steel substrate, or directly using explosive composite or rolling composite steel plate. This gives full play to the strength advantages of base steel and the corrosion resistance advantages of cladding materials.
Reliable manufacturing and inspection inheritance
The smelting, rolling, heat treatment and subsequent cutting, forming, welding and nondestructive testing of steel for pressure vessels have formed a set of extremely rigorous and mature industrial systems. The internationally recognized ASME VIII, GB 150 and other specifications have made mandatory provisions on materials, design, manufacture and inspection to ensure that every ex-factory container has traceable quality assurance.
Typical Applications
Hydrogenation reactor
The typical wall thickness is huge, adopting 2.25Cr-1Mo(SA387 Gr.22) or 3Cr-1Mo steel forging welding or plate welding structure, and the inner wall is covered with TP309L+TP347 stainless steel.
Liquid ammonia spherical tank
Low alloy high strength steel (such as 07MnNiMoVDR) is commonly used to reduce the thickness of thin wall, and strict low temperature impact toughness requirements are put forward for welded joints.
Chlorine drying tower in chlor-alkali industry
Because the medium contains wet chlorine, which is extremely corrosive, carbon steel shell is usually lined with rubber or directly reinforced polypropylene (FRPP), but the key supporting structure is still steel.
Heat exchanger and condenser are the key equipment to realize heat exchange and recovery in chemical process, which are widely used in heating, cooling, condensation and evaporation of materials. Its performance directly affects the energy consumption and efficiency of the whole process. They usually face multiple challenges such as temperature difference stress, corrosion of different media on the tube/shell side, scaling and fluid-induced vibration.
Advantages & Key Features
Excellent thermal conductivity combined with strength
Although copper, aluminum and other metals have better thermal conductivity, steel has comprehensive advantages in strength, pressure resistance, temperature range and cost. Carbon steel and low alloy steel are the first choice for tubesheets and shells under many non-corrosive working conditions, such as boiler feed water heaters. For heat transfer tubes, thin-walled stainless steel tubes or low-alloy steel tubes can provide good heat transfer efficiency while ensuring pressure and temperature resistance.
Wide selection of corrosion-resistant materials
According to different corrosive media (chloride ion on cooling water side, acid media on process side, etc.), corresponding corrosion-resistant steel can be selected: 304/316L austenitic stainless steel is used in general corrosive environment; Duplex stainless steel (such as 2205 and 2507) is used to resist chloride ion stress corrosion and pitting corrosion; Titanium is used in seawater cooler, but the cost is expensive, and copper-nickel alloy is also one of the traditional choices. The steel family provides a wealth of options for this.
Good erosion resistance and vibration resistance.
In the high-velocity area such as the inlet of the tube side, the medium may cause erosion to the tube end. It is solved by selecting higher hardness materials, increasing the wall thickness of pipe ends or designing erosion-resistant baffles. The elastic modulus of steel is high, and the vibration of heat exchange tubes caused by fluid flow can be effectively suppressed and fatigue damage can be prevented through reasonable support plate layout and baffle design.
Mature manufacturing and maintenance convenience
Manufacturing processes such as tubesheet drilling, expansion or welding of heat exchange tubes, and shell coiling are very mature and reliable for steel. In case of local corrosion and leakage in operation, online maintenance can be carried out by plugging pipes, which is very important to ensure the continuity of production, and this maintainability is largely due to the processing characteristics of steel.
Typical Applications
High-pressure heat exchanger of refinery hydrogenation unit
Shell and tube are all high-pressure hydrogen medium, shell is made of 2.25Cr-1Mo steel, and tubes are made of the same material or austenitic stainless steel.
Steam surface condenser of power station or chemical plant
The shell is carbon steel, and thousands of heat transfer tubes are traditionally made of navy brass or white copper. Modern large-scale units mostly use TP304/TP316 stainless steel tubes or titanium tubes, and the tubesheet uses stainless steel composite plates.
Boiler feed water preheater of methanol synthesis unit
Usually made of carbon steel (SA179 tube, SA516 shell), with economy as the primary consideration.
Storage tanks and silos are used for static storage of raw materials, intermediate products, finished products and various auxiliary materials (such as water and chemicals). Its scale ranges from small tanks of several cubic meters to giant storage tanks of over 100,000 cubic meters. The design needs to consider the hydrostatic column pressure, material characteristics (corrosiveness, toxicity and volatility), environmental loads (wind, snow and earthquake) and foundation settlement.
Advantages & Key Features
Excellent economy and large-scale construction capacity
For atmospheric and low pressure large storage tanks, steel (mainly carbon steel) is the only material that can give consideration to strength, machinability and economy. By rolling and welding large steel plates (with a width of more than 3 meters), giant storage tanks with a diameter of more than 100 meters can be built efficiently, and the world record of single tank volume has exceeded 240,000 cubic meters, which is difficult to achieve with other materials.
Flexible design to meet different storage requirements
- Atmospheric vertical cylindrical storage tank: the tank wall adopts the method of "variable design point", and steel plates with different thicknesses are used from top to bottom to bear the increasing hydrostatic pressure economically.
- Low-pressure/internal floating roof tank: used to store volatile liquid, with special requirements for the steel of the top plate and sealing system.
- Pressure spherical tank: It is used to store liquefied gas (LPG, liquid ammonia, etc.). It is made of high-strength low-alloy steel plate (such as 07MnNiMoVDR) and then welded, so as to reduce the wall thickness and ensure safety.
- Bunker: In view of the flow and wear of powder materials, wear-resistant steel plates (such as Hardox series) can be used to make key parts.
Reliable sealing and safety protection
Ensure the tightness of the main weld of the tank through high-quality welding. For inflammable, explosive or toxic media, the steel tank can be conveniently equipped with breathing valve, flame arrester, pressure relief device, nitrogen sealing system and complete fire fighting and leakage collection facilities (fire dike) to form a complete safety protection system.
Easy to implement corrosion protection and monitoring.
According to the different storage media (crude oil, chemicals, water), corresponding anti-corrosion coating, lining (rubber, glass fiber reinforced plastic) or cathodic protection can be adopted on the inner wall of the tank. The outer wall of steel tank is protected by coating system. On-line inspection technologies such as regular ultrasonic inspection of wall thickness and magnetic flux leakage scanning of bottom plate can effectively monitor corrosion status and implement predictive maintenance.
Typical Applications
Floating roof tank of crude oil commercial storage
The volume is often 100,000 or 150,000 cubic meters, the tank wall is made of high-strength structural steel (such as SPV490Q), and the bottom plate and top are made of thin carbon steel plates.
Liquid hydrocarbon spherical tank
Used to store propylene, liquefied petroleum gas (LPG) in liquefied natural gas (LNG) receiving station, etc. The materials are mostly low-alloy high-strength steel, while the LNG storage tank is made of 9% nickel steel or full-capacity concrete outer tank.
Concentrated sulfuric acid storage tank
Usually made of carbon steel, it is protected by the principle that acid forms a dense passive film on the steel surface, and the storage concentration and moisture should be strictly controlled.
Raw material/clinker silo (steel silo) in cement industry
Carbon steel plate is welded, and the key wear areas inside are lined with wear-resistant steel plates.
The piping system of chemical and petrochemical plants is like the "vascular network" of the device, conveying various process fluids from raw materials to products. Many fluids are highly corrosive, toxic or at high temperature and high pressure. The reliability of corrosion-resistant pipeline system directly determines the continuity, safety and maintenance cost of the device.
Advantages & Key Features
Targeted alloying to resist specific corrosion
By adjusting the contents of alloying elements such as chromium (Cr), nickel (Ni), molybdenum (Mo) and nitrogen (N), the pipeline materials with specific corrosion resistance can be customized:
- Austenitic stainless steel (304/316L): General corrosion resistance, and 316L is more resistant to pitting corrosion because it contains molybdenum.
- Duplex stainless steel (2205/2507): It has the advantages of austenite and ferrite, high strength, excellent resistance to chloride stress corrosion cracking (SCC) and pitting corrosion, and high cost performance.
- Super austenitic stainless steel (254SMO, AL-6XN®): high molybdenum and nitrogen, extremely high pitting equivalent value (PREN), used in harsh environments such as seawater and strong acid.
- Nickel-based alloy (Hastelloy C-276, Inconel 625): used in the most corrosive oxidizing and reducing acid medium environment.
Complete and mature connection and installation system
Corrosion-resistant steel pipes have a complete system of fittings (elbows, tees, reducers), flanges, valves and fasteners. The connection methods are diverse, mature and reliable, including welding (butt welding, socket welding), flange connection (with corrosion-resistant gasket) and special clamp connection. This makes the prefabrication and site installation of complex pipe gallery efficient and accurate.
Good high temperature strength and thermal stability
Compared with many nonmetallic corrosion-resistant pipelines (such as plastics and FRP), metal pipelines (stainless steel and alloy steel) have unparalleled high-temperature bearing capacity. They can work stably for a long time at the process temperature of hundreds of degrees Celsius, maintaining dimensional stability and sealing, which is an inevitable choice for high-temperature process.
Predictable service behavior and online monitoring
The corrosion behavior of metal pipeline materials is thoroughly studied, and the corrosion rate data is relatively complete, which is convenient for risk-based inspection (RBI) and residual life evaluation. By regularly carrying out ultrasonic thickness measurement, eddy current detection and pulsed eddy current scanning, the corrosion thinning of pipeline system can be effectively monitored and predictive maintenance can be realized.
Typical Applications
Process piping of wet-process phosphoric acid plant
The medium contains fluosilicic acid and sulfuric acid, which is extremely corrosive. Usually, high-grade stainless steel such as 2205 duplex steel or high alloy such as Hastelloy® G-30 is selected.
High-temperature oil transfer line of atmospheric and vacuum distillation unit
Cr-Mo alloy steel (such as 1.25Cr-0.5Mo-Si, P11 steel) is used to transport high-temperature oil and gas.
Pipeline of seawater cooling system
Copper-nickel alloy (90/10 CuNi) is traditionally used, and now super duplex stainless steel (2507) or super austenitic stainless steel (254 SMO®) is increasingly used to cope with high chloride ion environment.
Ammonium carbamate solution pipeline in urea plant
The medium is ammonium carbamate solution, which is extremely corrosive under high temperature and high pressure. It is necessary to use 316L urea grade stainless steel (extremely low carbon, qualified by Huey's test) or titanium.