Views: 4 Author: Site Editor Publish Time: 2016-09-22 Origin: Site
9 Ni steel is w (Ni) is 8.5% ~ 9.5% of low carbon martensite is a cryogenic steel size, is a kind of excellent material used in the manufacture of LNG storage tank.9 ni steel welding, appropriate USES string cable energy, multilayer multipass welding, without preheating before welding, but need to control interlayer temperature below 100 ℃.Specific process is:
1, the welding methods
At present, the 9 ni steel can be adopted method of welding is mainly: electrode arc welding (SMAW), submerged arc welding (SAW).
2, welding material,
In order to obtain the superior performance of welded joint, to guarantee the weld has adapted to 9 Ni steel low-temperature toughness, the welding must use appropriate welding material in the production, according to the mass fraction of the Ni can be divided into: 1) more than 60% of Ni base type (Ni - Cr, Mo alloy);2) 40% Fe - Ni base type (Fe - Ni - Cr alloy).These two types of welding materials is the most suitable choice of 9 ni steel welding.
3, welding current,
In order to avoid magnetic blow, had better use ac square wave welding power source, and cooperate with the ac welding of nickel base alloy electrode.
4, before cleaning and welding groove processing
Before welding, use organic solvent cleaning or polishing method, was carried out on the welding groove surface cleaning, ensure the groove surface and its nearby area without scale, grease, moisture and impurities such as organic matter.
Groove processing: usually USES the X and Y groove.Due to the large LNG storage tank 9 ni steel wall thickness of steel plate is 10 ~ 36 mm, the thickness of the span is large, therefore, bevel cutting, thin steel plate adopts the single V (Y) groove, thick steel plate by X-ray groove.
5, preheating temperature, interpass temperature and welding heat input
The preheating temperature, interpass temperature and welding heat input will directly affect the cooling speed of steel after welding.The slower cooling rate, grain growth, the more significant, resulting in a decline in the low temperature toughness, therefore, 9 ni steel generally do not need to preheat before welding, and should be controlled between the layers under 100 ℃ temperature, weld heat input should be controlled between 7 ~ 35 kJ/cm.
Of thickness more than 8 mm 9 ni steel, as far as possible when welding using multilayer multipass welding, to avoid single pass welding.Studies have shown that string cable energy (15 kJ/cm) single channel thermal cycle of CGHAZ low temperature (196 ℃) impact energy is lower, after 800 ℃ or 900 ℃ after secondary thermal cycle, obviously improve the low temperature impact energy, three thermal cycle can further improve the low temperature toughness of CGHAZ.In practice, but also seriously do a good job in interlayer cleaning to ensure that no impurities such as slag, and then on to the next layer of welding.
6, the welding test
9 ni steel welding method is commonly used nondestructive testing.Nondestructive testing including radiographic testing, ultrasonic testing and penetration testing.The interior of the weld defects mainly by radiographic testing and ultrasonic testing, the surface of the weld defect is mainly by penetrant testing.