High temperature, high pressure and the pressure vessel and run in the presence of hydrogen under the conditions, the corrosion of the surface of the inner wall of the reactor in order to avoid the desulfurizing reaction produce large amounts of H2S and when the reactor is stopped running, the stress caused by the of polythionic acid (H2SXO6) corrosion cracking, corrosion-resistant material in the inner wall of the reactor are usually surfacing. Molybdenum niobium as the main strengthening element of solid solution strengthening type nickel base wrought superalloy 625, having excellent corrosion resistance and oxidation resistance, from cryogenic to 980 ℃ have high strength, toughness, fatigue strength and oxidation resistance. In the atmosphere, natural water, sea water, neutral salts and alkali weak medium is essentially non-corrosive, more demanding medium, to oxidizing acid tolerant and resistant to reducing acid medium. Excellent resistance to intergranular corrosion, stress corrosion, pitting and crevice corrosion. Both require high corrosion resistance, but also meet the high temperature corrosion resistant alloy, has been widely used in the manufacture of pressure vessels.
A large area of the inner wall of the container can be used to strip cladding technology, took over the inner wall surfacing, small diameter flux cored wire the surfacing welding process (FCAW) has to adapt to the current and voltage range high deposition efficiency, productivity has improved significantly, the economy is fine; welding conditions to achieve relatively easy, easy semi-automatic and automatic welding; slag detachability good weld appearance; splash is small, excellent arc stability, high pass rate, etc. and are widely used in the production.
Based on 625 welding characteristics of nickel-based flux cored wire, a welding procedure test, to determine the effects of theWelding Fluxcored wire welding layer forming and performance welding parameters to take over the small diameter inner wall surfacing nickel-based flux-cored hardfacing scientific basis.
1 welding equipment and Welding Materials
1.1 welding equipment
This test uses ESAB LAH 500 flux cored wire welding equipment, the equipment by welding machines (including power supply wire feeder, control system) water-cooled welding torch and walking system, cooling system, air supply system. Stainless steel flux-cored gas shielded arc welding equipment level characteristics DC power by changing the wire feed speed to adjust the welding current, welding specifications more convenient adjustment. Arc length changes can cause large current changes, strong self-regulation; same time, due to the short-circuit current, the arc is relatively easy.
1.2 welding materials
Nickel-based 625-type nickel-based alloy surfacing technology requirements, according to the wire component specifications, optional WEL FCW 625 surfacing material. Wire diameter φ1.2mm, 2.25Cr-1Mo materials of 50mm, in the thickness of the nickel-based flux cored wire surfacing surfacing when strict control of the first layer of the preheating temperature, the temperature of the interlayer, and post-heat temperature, The second layer of surfacing interlayer temperature should be controlled below 100 ℃.
1.3 nickel-base alloy 625 welding characteristics
Nickel-based Alloy 625 weld metal structure as a single austenite, the fluidity of the liquid weld metal melting shades, easy to produce welding thermal cracks and pores, therefore, should be thoroughly cleaned before welding workpiece; welding use a smaller heat input quantities, so that the joint high temperature residence time is reduced, is beneficial to both the control and reduce thermal cracks, improve corrosion resistance; should select the appropriate welding speed; between the nickel base alloy welding without preheating, interpass temperature should be controlled at 100 ℃ below.
2 welding process test
Flux-cored hardfacing layer forming and performance welding parameters: welding current, welding voltage, welding speed, stem elongation, the amount of overlap.
2.1 welding current
Welding current and surfacing weld bead shape, the depth of penetration, the dilution rate, mechanical properties, has a great relationship, the welding process, the welding current is excessive spatter and large, the oxidation of the surface of the surfacing layer and prone to hot cracking; while welding current is too small prone to slag defects as well as weld forming bad. Test diameter for the φ1.2mm flux cored wire welding current is determined surfacing weld between 180 ~ 200A forming the best.
2.2 welding voltage
For the flux cored wire surfacing, the welding voltage and welding current match is very important. Under certain conditions of the welding current, if the voltage is too low, the surfacing of the weld bead is too narrow, are prone to the phenomenon of slag, and the surfacing thickness increases, causing the consumables waste; if the welding voltage is too high, surfacing weld Comparative width, so that the surfacing thickness can not meet the requirements, after several tests, φ1.2mm flux cored wire welding voltage determines the diameter between 28 ~ 32V the surfacing weld bead forming best.
2.3 welding speed
Welding speed of flux cored wire surfacing mainly two aspects: (1) surfacing weld geometry; â‘¡ surfacing layer dilution rate. Welding speed is too fast, the surfacing weld is too narrow, too thin, the next one lap welding easily create overlaps. Conversely, easy to form a the tall heap, heap width of weld, will cause nozzle clogging, could easily lead to slag φ1.2mm nickel-based flux cored wire welding speed to determine the diameter of 250 ~ 300mm/min best.
2.4 wire extension length and wire position
Wire extension length of the arc stability, penetration, arc energy and so influential, wire extension length is too long, will arc instability, erratic and big splash. Wire extension length is too short, excessive spatter easy to cause clogging of the nozzle, so that the poor gas protection, easy to produce when the stomata in the surfacing. After testing, the wire extension length should be in the range of 15 ~ 20mm. Welding, the welding gun inclination angle θ of about 40 °, preferably, if θ is too large or too small, will reduce the effect of CO2 gas protection.
The amount of overlap between the 2.5 surfacing weld
The amount of overlap between the surfacing weld (wire with the former a distance between the surfacing weld) directly affect the surfacing layer thickness and roughness, and the surfacing layer scoliosis greater performance impact, in order to solve these problems, the amount of overlap between the nickel-based flux cored wire surfacing weld series of tests, and identified for surfacing weld has good formability, excellent performance of the process parameters, i.e., before the wire with respect to an edge 0 the ~ 1mm surfacing weld forming beautiful, and good mechanical properties.
2.6 CO2 gas flow
Nickel-based flux cored wire surfacing, gas flow is 15 ~ 20L/min, if the gas flow is small, the protection gas is not enough stiffness, reducing the protective effect of gas; faster if the welding current, welding speed, wire extension longer-length, required to increase the gas flow.
2.7 optimum welding parameters
After these large welding test to determine, good formability, good performance nickel-based flux-cored hardfacing welding parameters surfacing layer. , Provides a scientific basis for the next procedure qualification, welding and product components.

3 welding procedure qualification
On an experimental basis in the process, according to the requirements of the inside the pressure vessel 625 type nickel base alloy welding technology conditions ", the welding parameters of the Table 1 the surfacing process assessment test plate, in the thickness of 50mm, 2.25Cr-1Mo material on nickel-based flux-cored hardfacing assessment surfacing strictly control the first layer welding preheat temperature, interpass temperature and post-heat temperature, the temperature control in the second layer of the surfacing layer below 100 ℃ .

4 Products to take over the surfacing
On the basis of the process test and procedure qualification, take over the inner wall surfacing, the facts show that the surfacing layer forming beautiful, nondestructive examination pass rate, the technical indicators are surfacing layer to meet the requirements.