(2) Flux material selection Flux plays the role of isolating air, protecting weld metal from air immersion and participating in the metallurgical reaction of molten pool metal in the welding process. When the welding wire is determined, the matching flux becomes the key material, which directly affects the mechanical properties (especially plasticity and low-temperature toughness), crack resistance, occurrence rate of welding defects and welding productivity of the weld metal.

2.1 Product design
The overall design of non-metallic contraction joints shall be carried out according to many factors such as the application position of contraction joints, medium composition (corrosion and scouring conditions), application temperature and pressure, and device requirements (device length, connection mode, size restrictions, etc.). After selecting the structure, design the internal structure (relative position of each component, assembly method, etc.) according to the request of compensation amount; If anti-corrosion is required, establish the anti-corrosion plan for the contraction joint, and stop the design of each part of the contraction joint, that is, the selection and size of the non-metallic compensator, the material and size of the metal components, and the construction and material selection of the dust and heat insulation layer under different temperature levels.
In terms of structural design, considering the wear resistance, the compensator adopts double straight edge draft tube to avoid the erosion of the draft tube caused by gas due to changes in the position of the compensator.
2.2 Non metal expansion joint
2.2.1 Selection of expansion joint base material
According to the working conditions, the non-metallic expansion joints of the non-metallic compensator in the hot and cold air ducts are made of silicone rubber tape, and the non-metallic expansion joints in the flue are made of fluorine rubber tape.