API 5L X42 Steel Line Pipe is generally used for the conveyance of oil and gas in transmission lines,distribution main lines,and offshore pipeline systems.Zhonghai supplies welded and seamless API 5L grades through X 70 for high pressure applications,All of the API 5L X42 Steel Line Pipe products we are supplying can reach the international standard API 5L,.Our company’s production is carried out in accordance with API 5L,CE,UKAS,PED and ISO9001 Integrated Management(quality) Systems.

Place of Origin: China
Application: Be widely used for conveyance of oil and gas in transmission lines,distribution main lines,and offshore pipeline systems
Steel Line Pipe Standard: API 5L X42
Outside Diameter: 21.3mm-914mm
Wall Thickness: 2mm-50mm
Length: Random 6m-12m or fixed 6m,12m
Bevel pipe ends and black anti-rusting paint is available if you need.
Also can process as per clients’ order.
Steel Line Pipe Packing: In bundles or bulk.
One 20’or 40′ container can load maximum 26 tons.

API 5L Steel Line Pipe Physical Properties

The condenser is important auxiliary equipment in the thermal generator set. The condenser is generally composed of neck, casing, water chamber, tube bundle, tube plate, support rod, steam baffle, air cooling area, hot well and other parts, which is the key equipment to determine and affect the load and thermal efficiency of a steam turbine. The heat exchange tube, as the main heat transfer component of the condenser, is the key component of the condenser. With the increase of suspended solids, chloride ions and sulfur ions in the cooling circulating water, there is a higher requirement for a condenser cooling pipe.

Condenser heat exchanger pipe should have excellent heat transfer performance, good corrosion resistance, erosion resistance and wear resistance, but also should have good strength and stiffness, as well as economic and good processing performance. The materials of condenser heat exchange pipe are mainly copper alloy pipe, Austenitic stainless steel pipe, Ferrite stainless steel pipe, Duplex stainless steel pipe, titanium and titanium alloy pipe. The copper alloy pipe mainly includes military brass pipe (C26800), tin-brass pipe, aluminum-brass pipe, nickel-copper pipe, etc. Stainless steel grades mainly include Austenitic stainless steel tube TP304, TP316L, TP317L and Ferrite stainless steel grades TP439, TP439L, and duplex stainless steel tube 2205, 2507, titanium and titanium alloy tube mainly includes GR1, GR2, GR5, etc..

Different materials of the heat exchange pipe because of its own characteristics and cost factors, its application scope and working conditions are not the same. The corrosion in the Condenser is always an important problem in boiler accidents in power plants. The condensers of power plants in offshore areas generally use Cu-Zn tubes and Cu-Ni alloy tubes. The corrosion resistance of the latter is better than that of the former, because the thermodynamic stability of Ni is close to that of Cu, and the nanoscale compact and stable surface film will be generated on the surface in water or air. Therefore, the Cu-Ni tube in high saltwater (or seawater) and dilute acid, alkali medium is not easy to corrosion. But once there is an attachment on the surface of the copper tube, pitting will occur. Pitting corrosion is autocatalytic and latent, which will bring great damage. The condenser tube blockage and leakage frequently occur in the offshore area due to seawater backfilling, corrosion, dirt and other reasons. Yongxiang operates the generator set. Why is the brass condenser tube so easy to corrode? It depends on the type of corrosion. The corrosion of copper alloy condenser tube is affected by many factors, and the corrosion types are various, mainly including the following items:

Selective corrosion

Because the condenser copper tube is mostly composed of copper zinc alloy, zinc potential is lower than copper, so zinc is easy to become the anode of corroding battery, so that zinc selectively dissolved to corrode the copper tube. The theory and practice show that the corrosion process of copper tube is closely related to the performance of the protective film on the surface of copper tube. If the initial dense protective film is not formed, the corrosion of copper tube is more likely to occur. If there is no initial coating treatment of FeSO4 on the condenser copper tube, it is also easy to lead to local dezincification corrosion.

Electrocouple corrosion

Coupling corrosion may occur when two different metal materials come into direct contact in a corrosive medium. In the condenser, the copper alloy condenser tube material is different from the carbon steel tube sheet material in the cooling water potential, there is the possibility of galvanic corrosion between them. The potential of the condenser copper tube is higher than that of the tube plate, which will accelerate the corrosion of the tube plate. But because the thickness of the carbon steel tube plate is larger, generally 25~40mm, the galvanic corrosion won’t affect the safe use in clean freshwater, but in the environment with a high salt concentration of water galvanic corrosion is more likely to occur.

Pitting corrosion

This corrosion is prone to occur on the surface of the copper tube protective film rupture. Because the cooling water contains Cl and Cu oxidation generated by Cu+ to generate unstable CuCl, can be hydrolyzed into stable Cu2O, and make the solution local acidification thermal equipment corrosion. If the condenser copper tube is not cleaned on schedule, the uneven surface deposits promote corrosion and eventually lead to punctate corrosion perforation. In the operation of the condenser copper pipe in frequent start-stop, load change is bigger, the impact of the high-speed turbine exhaust steam, the role of copper tube by alternating stress, easy to make the brass surface membrane rupture, produce local corrosion, pitting corrosion pit formation, reduce material fatigue limit, and because the stress concentration at the corrosion, pitting bottom is easy to crack, Under the erosion of NH3, O2 and CO2 in water, the fracture is gradually expanded.

Erosion corrosion

This type of corrosion can occur on both the waterside and the steam side, mainly in the waterside. Suspended solids, sand and other solid granular hard objects in circulating cooling water impact and friction on the copper tube at the inlet end of the condenser. After a long time of operation, the inner wall of the front section of the copper tube at the inlet end is rough. Although there is no obvious corrosion pit, the surface is rough, the brass matrix is exposed and the copper tube wall becomes thin. The anodic process of erosion and corrosion can be said to be the dissolution of copper, and the cathodic process is the reduction of O2. The high flow rate will hinder the formation of stable protective film, is also the cause of erosion-corrosion, the general flow rate is not more than 2m/s.

NH3 corrosion

Excess NH3 enters the condenser with steam and concentrates locally in the condenser. If O2 is present at the same time, NH3 erosion will occur on the steam side of the copper tube in this area. Its characteristic is uniform thinning of the tube wall, and NH3 erosion is easy to occur when ammonia content in water reaches 300mg/L. The condensate at the baffle hole is too cold and the dissolved ammonia concentration is increased, which will also cause the annular strip ammonia erosion in the copper tube.

Stress corrosion cracking

When the condenser copper tube is not installed properly, vibration and alternating stress will occur in the operation of the copper tube surface to destroy the protective film and corrosion, finally, produce transverse crack to break the copper tube. This is mainly due to the relative displacement of grains inside the copper tube under the action of alternating stress, and the formation of anodic dissolution in the corrosive medium, mostly occurring in the middle of the copper tube.

Microbial corrosion

Microorganisms can change the medium environment in local areas of the condenser wall and cause local corrosion. The electrochemical corrosion process of metal in cooling water is promoted by the biological activity of microorganisms, which generally occurs on the carbon steel tube plate at the inlet side of the condenser. Cooling water often contains bacteria that thrive on Fe2+ and O2, called iron bacteria, which form brown slime. The anoxic conditions at the bottom of the slime provided a suitable environment for the survival of anaerobic sulfate-reducing bacteria. The combined action of iron bacteria and sulfate-reducing bacteria promotes metal corrosion. Operating temperature on the high side, the corrosion scale inhibitor and water quality and operating temperature are not appropriate, inadequate dosage or concentration fluctuations in the scale, will cause the condenser tube wall local Cl – easy through scale layer, caused the corrosion of the metal matrix, and the corrosion of metal ion hydrolysis, leading to higher medium H + concentration of algae and microbial activities also cause increased acidity of medium, The passivation film on the metal surface is destroyed and the metal matrix is further corroded.

Caustic Cracking, also known as caustic embrittlement, is the metals cracking in alkaline solutions due to the combined action of tensile stress and corrosive media, is a type of SCC. The cause cracking of pressure boiler mainly occurs in the parts where steam is repeatedly evaporated and condensed or in contact with caustic soda, which may be carbon steel, low alloy steel, ferrite steel and austenitic stainless steel equipment. Cause cracking explosion accidents often occur in boilers system, also caused by Na+ concentration may also occur in autoclaps, waste heat recovery systems and Al2O3 evaporators of electrolytic aluminum enterprises in chlor-alkali chemical plants, paper mills and nuclear power industries.

When sodium hydroxide concentration is more than 5%, carbon steel and low alloy steel steam pipelines are almost likely to produce caustic crackings, alkali stress corrosion generally occurs at more than 50~80℃, especially near the boiling point of high temperature area, alkali concentration of 40% ~ 50%. According to the theory, when the mass fraction of local NaOH is greater than 10%, the protective oxide film of the metal will be dissolved, and the matrix metal will react with the alkali further to form loose and porous magnetic corrosive oxides, and the aqueous solution is alkaline. As long as 10~20mg·L-1 NaOH is contained in the water of boiler or heat exchanger, local repeated evaporation can lead to the concentration of alkali under the sediment or in the crevices, causing local alkali corrosion.

The factors affecting the sensitivity of caustic cracking

Caustic cracking is easy to occur in the concentrated parts of alkali containing liquid with high residual stress, such as welding joint parts, this type of SCC is usually developing intergranular and the fractures are filled with oxides.

The alkali-brittle cracks in the carbon steel steam pipeline appear as fine intergranular cracks with oxides. There are several main factors that determine the brittleness of alkali: alkali concentration, metal temperature and tensile stress. Experiments show that some caustic cracking occurs within a few days, while most occur when exposed to more than 1 year. Increasing the alkali concentration and temperature can improve the cracking rate.

Medium 

Caustic cracking is the corrosion that occurs at high temperatures in concentrated lye. When the mass fraction of NaOH is lower than 5%, there won’t cause caustic cracking. This concentrated lye can be the working medium or can be gathered during. The higher the concentration of caustic soda, the greater the sensitivity of caustic cracking, which is not only related to the concentration of the alkali but also depends on the temperature of the solution.

The temperature

The cracking fracture time of low carbon steam pipeline steels increases with the decrease of stress. It is found that the metal in the heat-affected zone with the largest residual plastic deformation, that is, the metal heated to 500~850℃ in the welding process, has the largest SCC tendency. It was found in the maintenance of alkali equipment that the metals heated at temperatures over 550℃ and slightly lower than the recrystallization zone during welding had the greatest cracking tendency in alkaline solution, where the welding residual stress and microstructure stress are the largest.

Metal elements

Because the caustic cracking and nitrate brittleness of low carbon steel is fractured along the grain, it is theorized that the sensitivity of such brittleness is caused by the segregation of C, N and other elements at the grain boundary. The chemical elements that cause the caustic cracking of low carbon steam pipeline steel are as follows:

▪ C and N segregation at grain boundaries increases the caustic cracking sensitivity;

▪ The effect of trace elements, due to the segregation of S, P, As and other impurities at grain boundaries increase alkali embrittlement sensitivity. However, a small amount of La, Al, Ti and V may be due to reducing the segregation of harmful impurities in the grain boundary reducing the alkali embrittlement sensitivity.

▪ The caustic cracking increases as grain size increase,;

▪ Heat treatment. The caustic cracking sensitivity of the steel after spheroidizing is greater than that of the normalized state, which may be due to the increase of grain boundary segregation during the spheroidizing of carbides.

Potential 

The sensitive potential of caustic cracking of low carbon steam pipeline steel in boiling 35%~40% NaOH solution is -1150~800mV (SCE), and the potential of caustic cracking occurs in the range of -700mV (SCE) at boiling point (120℃). At the critical potential, the section shrinkage of the sample decreases greatly. The X-ray structure analysis shows that the Fe3O4 protective film is formed on the surface of the sample.