Basic specification requirements:
(1), when installing steel structure at negative temperature, attention should be paid to the deviation of the overall dimensions of steel structure caused by temperature change. If the steel structure is built at normal temperature and installed at negative temperature, measures should be taken to adjust the deviation.
(2) For steel started at negative temperature, Q235 steel, 16Mn, 15MnV, 16Mnq and 15MnVq steel shall be accepted. Steel should ensure impact toughness. Q235 steel should have-20° D, others should have-40° Qualified guarantee.
(3) covered electrode and welding wire for welding negative temperature steel structure should be selected. On the premise of meeting the predetermined strength requirements, low hydrogen covered electrode with low yield strength and good impact toughness should be selected. Important structures can accept high toughness and ultra-low hydrogen covered electrode.
(4) Alkaline covered electrode must be baked in accordance with the provisions of the factory certificate before use. After passing the baking, store it at 80 ~100° D It's in the oven. Take it out and put it in a thermos when you use it. Take it with you. Covered electrode exposed to negative temperature for more than 2 hours should be baked again. Covered electrode baking times should not exceed three times.
(5) The flux must be baked according to the provisions of the factory certificate before use, and its water content shall not be greater than 0.65438 0%. During negative temperature welding, the interval of flux reuse shall not exceed 2h, otherwise it must be re-baked.
(6) The purity of carbon dioxide for gas shielded welding shall not be less than 99.5% (by volume) and the moisture content shall not exceed 0.005% (by weight). When using bottled gas, stop using it when the pressure in the bottle is lower than 1N/mm2. When using at negative temperature, check whether the bottle mouth is frozen.
(7) High-strength bolts and ordinary bolts shall have product certificates. The torque coefficient and axial force of high-strength bolts should be rechecked at negative temperature, and they can be used only after they meet the requirements.
(8) Coatings for steel structures shall meet the functional requirements of negative temperature coating, and water-based coatings are prohibited.
Extended data:
Low temperature welding construction technology;
Because the welding operation is carried out in a low temperature environment, in order to better complete the welding task, welding materials with low hydrogen content should be selected as far as possible, and necessary baking and heat preservation measures should be taken for the welding materials. In order to reduce the heat loss as much as possible, the corresponding protective room can be built where the welding operation is carried out, thus forming a relatively closed space.
If the conditions do not allow the construction of protective houses, other measures can be taken to protect the heat loss. In some gas shielded welding operations, necessary heat preservation measures should also be taken for gas cylinders. Preheating and interlayer temperature. Compared with the preheating of normal temperature welding, the preheating temperature of low temperature welding is slightly higher, and the area needing preheating is larger, which is usually more than or equal to twice the thickness of steel around the welding point, and this range is not less than100 mm.
The temperature of the welding layer is usually higher than the preheating temperature, or not lower than the minimum temperature of 20℃ specified in the corresponding regulations, whichever is higher; Adopt reasonable welding method. Try to use narrow pendulum, multi-layer and multi-pass welding, and strictly control the interlayer temperature; Heating and heat preservation after welding. After welding, the welded joint shall be treated with post-heat preservation in time. It is beneficial to the escape of diffused hydrogen, preventing cold cracks caused by too fast cooling speed, and at the same time, proper afterheating temperature can also reduce the preheating temperature appropriately.