High-strength steel is mainly used in marine engineering, lifting equipment, construction machinery, containers and storage tanks and other important steel structures with harsh working conditions and hope to reduce their own weight. The application of high-strength steel, in addition to reducing material costs, transportation costs, and production costs;It can also save welding consumables consumption, welding man-hours, and reduce post-welding stressReduce the welding preheating temperature, reduce the post-welding heat treatment requirements, etc.
Since the Q235 was printed in the GB T 700 in 1956, the QXXX family has continued to flourish for more than three decades. In the past 30 years, the QXXX family has never stopped their pace of becoming higher and stronger, all the way from general strength steel to high-strength steel and ultra-high-strength steel. Become an important steel partner for the development of human society.
A common member of the QXXX family in China.
Carbon Structural Steel》GB T 700-2006, strength level Q195 Q235 Q275;
Low-alloy high-strength steel》 GB T1591-2008, strength level Q345 Q690.
Quenched and tempered steel for high-strength structure》 GB T16270-2009, strength levels Q460 Q690 and Q800 Q960.
Internationally, the QXXX family has more names, such as Q690 is known as S690 or P690 in Europe.
With the continuous progress of steel materials, welding materials manufacturing and welding technology, the strength level of structural steel continues to increase, and the steel grades above 1000MPa are common, and the overall demand for high-strength steel is increasing year by year.
In construction steel structures, pressure vessels, bridges, shipbuilding, marine engineering and other industries, high-strength steels for structures are commonly used Q345, Q390, Q420, Q460, Q620, Q690, etc. Offshore cranes, marine tanks, jack-up offshore platform pile legs, coal mine hydraulic supports, etc., more use of Q690 high-strength steel;In automobiles, containers, construction machinery pump trucks, cranes, etc., the so-called ultra-high strength steels Q800, Q890, Q960, and even higher strength Q1100, Q1300, Q1600, etc. are used.
For the offshore field, 690MPa grade high-strength steel has become a watchdog steel grade. Although high-strength steels such as Q800 and Q960 have also been tried to be used, there are still very few successful applications of higher-strength steels due to the constraints of material welding.
Commonly used 690MPa high-strength steel
The commonly used 690MPa high-strength steels are: A514 grade B of ASTM A514 "Welded High Yield Strength Quenched and Tempered Tempered Steel", A517 grade Q of A517 "Quenched and tempered high-strength alloy steel plate for pressure vessels".S690 of EN10025-6 "Welded High Yield Strength Quenched and Tempered Steel", P690 of EN10028-6 "High Strength Quenched and Tempered Steel for Pressure Vessels".Q690 of GB T16270-2009 "Quenched and tempered steel for high-strength structures". Domestic such as Baosteel, Anshan Iron and Steel, Wuhan Iron and Steel, Wugang, Nanjing Iron and Steel, Xingang, Xiangshan Iron and Steel, etc. have the ability to produce.
Note: The national standard requires a reference to NB 006；The European standard requires NB 006，cu≤0.06，zr≤0.15。
The heat treatment of high-strength steels is commonly used by n nl normalizing;q ql, q +t quenching and tempering;M ML TMCP THERMOMECHANICAL CONTROLLED ROLLING, AND PH PRECIPITATION STRENGTHENING. The commonly used quenching and tempering treatment of 690MPa high-strength steel is generally Q + T quenching + tempering treatment. After quenching (450 650), the hardness is reduced, the toughness is improved, and the strength is slightly reducedThe strength can be adjusted by changing the tempering temperature.
Another characteristic of 690MPa high-strength steel is its fine grain, which can be refined by Al, Ti, Nb and other elements (grain size 30 m), which can obtain high yield and tensile strength, ductile fracture, high fracture toughness, and excellent weldability.
Application of 690MPa high-strength steel in offshore products
LPG Marine Fluid Tank.
LPG ship is short for Liquefied Petroleum Gas (LPG) ship. LPG ships mainly transport petroleum hydrocarbons or a mixture of the two with propane and butane as the main components, as well as some chemical products. LPG ships have special requirements in all aspects due to their special use, and their technical difficulties represent the level of shipbuilding technology in today's world. The tank is the most important structure of the LPG ship, and the quality of the tank determines the service life and safety of the ship.
The marine full-pressure tank is made of high-strength steel with a strength level of up to 690MPa, which can greatly reduce the weight of the tank and thus reduce the transportation cost. In recent years, affected by the increasing demand for energy, the manufacturing technology of domestic LPG carrier storage tanks has developed rapidly, and has basically realized localization. By the end of 2018, there were 329 pressure-type LPG vessels (over 3,000 cubic meters for non-Chinese flags) worldwide, including six new vessels delivered in 2018 (with a total capacity of 36,500 cubic meters).
2 offshore drilling platforms.
China's annual offshore oil and gas production exceeds 100 million tons, helping China to become the world's largest offshore oil producer, and offshore drilling platforms will also be developed. In order to ensure the economy of offshore oil platform construction and the safety of service period, platform steel should have higher strength, better low-temperature toughness and weldability, and the application of high-strength steel in drilling platforms will be more extensive. At present, the highest strength grade of high-strength steel for offshore platforms certified by classification societies is FH690, and A517Q and A514Q in the ASTM standard are commonly used for high-specification rack steels for offshore platforms in the world. China builds 50-60 offshore drilling platforms every year, and the market capacity of high-strength steel is nearly 40 billion yuan per year.
3. Offshore lifting equipment.
Another important type of offshore products is offshore lifting equipment, mainly including marine deck cranes, offshore platform cranes, offshore heavy cranes, etc., in which Q690 high-strength steel is used in the stressed parts such as booms, booms and pedestal turntables.
4. Welding of 690MPa high-strength steel for offshore products.
In the early nineties, domestic shipyards were involved in liquid tank products, and now they have basically mastered the full set of construction technology of LPG leg LNG liquid tanks, but they are mainly manual welding, the welding method is monotonous, and the welding efficiency is low. In the manufacture of high-strength steel tanks, the main high-efficiency welding methods currently used include semi-automatic gas shielded welding, simple automatic welding;Automatic gas shielded welding and special submerged arc automatic welding.
Application status and development trend at home and abroad
S690 high-strength steel has been applied to offshore platforms in Europe, and Norway's Ekofisk offshore drilling rig is the first offshore platform in Europe to use S690Q steel plates with improved toughness. In Russia, S690 high-strength steel is becoming more and more widely used, such as the Arktickeskaya jack-up drilling platform. Japan has been an early adopter of steel for offshore platforms, and Nippon Steel has developed the HTUFF technology to produce wel-ten series high-strength steel plates using the precipitation process of microalloying elements. Nowadays, in order to reduce the thickness of steel plates, ultra-high strength steels with yield strength of more than 1100 MPa are being produced abroad through quenching and tempering processes, but the difficulty of welding and corrosion cracking problems hinder its development.
At present, China's shipbuilding and marine engineering steel has been able to meet most of the needs of the domestic market, but some high-grade special steel still relies on imports, mainly large thickness of steel plates with high strength, lamellar tear resistance, large heat input welding, ultra-low temperature toughness, high crack resistance and other properties, the production process is very strict, the equipment requirements are high, and the development is difficult. To this end, it is urgent to develop a series of high-quality marine engineering steels to further promote the development of China's marine engineering industry.
As a key structural material for offshore engineering equipment, steel is widely used in drilling platforms, production platforms and submarine pipelines. Due to the long service time, to resist the harsh wind and wave conditions for a long time, the cost of underwater repair and maintenance is extremely high, and the steel plate used in it is gradually developing in the direction of high strength, high toughness, easy weldability, good corrosion resistance, large thickness and large standardization.
With the increase of material strength, the difficulty and risk of welding also increase, and new requirements are put forward for the welding process. Different from thin plates and general strength steel, the production problems of high-strength steel structures are mainly reflected in weldability, workability, and the prevention of welding defects such as cracks.
The next Dao brother will focus on the welding process characteristics of 690MPa high-strength steel.