The bimetallic wear-resistant pipe is composed of an outer carbon steel matrix and an inner high-chromium wear-resistant alloy layer. It is widely used in material transportation scenarios such as power plant ash discharge and mine tailings. Pipeline welding is a key step in on-site installation. If the operation is improper, it is very likely to cause weld cracks, inner lining cracking, and even the detachment of the wear-resistant layer, directly shortening the service life of the pipe. The material properties of the pipe's inner and outer layers are significantly different. The high-chromium alloy layer on the inner layer is relatively brittle, and improper control of the welding heat input can result in significant thermal stress. Before construction, the construction personnel need to fully understand the structure of the pipe, distinguish the material characteristics of the outer carbon steel and the inner wear-resistant alloy layer, and strictly prohibit direct fusion welding of the inner wear-resistant alloy layer. Before welding, the bevels need to be cleaned, removing oil, rust, and dust in the bevel area. At the same time, check if there are any damage to the inner lining， and damaged pipe pieces need to be dealt with in advance to avoid further expansion of defects after the welds receive heat.
The process control during on-site welding is the core for preventing cracks and inner lining detachment. It is necessary to strictly control preheating， welding parameters， and interlayer temperatures. Before welding， the welding area should be preheated to reduce the welding temperature difference and minimize the generation of thermal stress. The preheating temperature should be set reasonably based on the pipe specifications and environmental temperature. Only the outer carbon steel matrix is welded， and the welding rod should be selected to match the carbon steel base material. Control the welding current and speed to reduce the heat input and avoid excessive heat transfer to the inner wear-resistant alloy layer. Use a segmented， multi-layer， and multi-pass welding method. Do not make the single weld seam too long to prevent excessive local temperature. After welding， do not quickly cool with water， but take a slow cooling measure to release the residual stress gradually. Also， avoid randomly starting arcs or knocking on the inner wear-resistant layer surface. Arc burns can cause micro-cracks in the inner layer alloy， which will gradually expand under the action of material erosion and temperature changes， eventually leading to the detachment and failure of the inner lining.
After welding， the inspection and subsequent protection are also crucial. A complete acceptance process can promptly identify welding hazards. After the weld cools， perform an appearance inspection to check for defects such as pores， slag inclusions， and surface cracks. Focus on observing the inner lining area near the weld seam to check for signs of cracking or peeling. After the pipeline welding is completed， try to avoid performing heavy impacts or forced corrections at the weld seam location. During the project construction phase， the manufacturer can provide corresponding welding operation guidelines， and on-site technicians can brief the welders， clearly defining the welding禁区. Strictly follow the specifications to conduct welding operations， which can effectively reduce the risk of weld failure and ensure the stable operation of the bimetallic wear-resistant pipe under long-term material transportation conditions， reducing the cost of subsequent maintenance and replacement.
Appendix： Frequently Asked Questions about Purchasing
Q： Can the high-chromium wear-resistant layer of the bimetallic wear-resistant pipe be directly welded?
A： It is not recommended to fuse weld the inner high-chromium wear-resistant alloy layer directly. This material is brittle and direct welding is very likely to cause cracks. The welding is only performed on the outer carbon steel matrix.
Q： Why is preheating and slow cooling necessary during the welding of the bimetallic wear-resistant pipe?
A： Preheating can reduce the welding temperature difference and lower thermal stress； post-welding slow cooling can reduce residual stress and avoid cracking and peeling of the inner wear-resistant alloy layer due to thermal shock.
Q： What consequences will be brought about if an arc is randomly initiated on the inner wear-resistant layer?
A： Arc burns will cause micro-cracks in the inner layer alloy. Under the action of continuous material erosion and temperature changes， the cracks will continue to expand， eventually causing the inner lining to detach and fail.