Process Measures for Repairing Surface Cracks on Blast Furnace Hot Blast Stove Shell

1. Assessment of the location, length, and depth of welds on the hot blast stove shell:

First, use ultrasonic testing to accurately determine the location, length, and depth of each weld crack. Then, drill approximately 10-mm-diameter relief holes at both ends of the crack, 10–20 mm away from the crack tips. If the crack is particularly long, it can be treated in segmented sections.

2. Perform repair operations using the hot blast stove's shutdown period:

The specific construction schedule will be coordinated with the hot blast stove operation unit at the blast furnace company, making full use of the furnace shutdown periods to expedite the work and ensure that every weld is properly executed.

3. Use carbon arc gouging to remove the root in sections:

Cracks must be thoroughly treated—during cleaning, if you notice even tiny cracks extending into the material’s thickness, first use the weld rod’s penetration depth to melt the microcracks before proceeding with root preparation. Otherwise, even if no cracks are visible during welding, they could still continue to grow over time.

4. Use carbon arc gouging to clean grooves on the bevel surface:

Clean the end of the crack-arrest hole, ensuring a smooth transition at the bevel without any noticeable grooves. Then, use a polishing machine to refine the surface, followed by either coloration or ultrasonic testing to inspect for cracks or defects. Only after confirming the absence of such flaws can the process proceed to the next step.

5. Treatment for cracks extending to the base metal root:

Considering that welding can only be performed on the outer side of the hot blast stove, the base material at the weld area can be cleaned down to the root using carbon arc gouging or gas welding tools. Before welding, a 3mm-thick welding backing plate or a round steel bar with a diameter of 12mm should be added at the root (both materials must match the base metal). This setup facilitates the welding process and ensures high-quality weld seams.

6. Preheat the furnace shell welds before welding:

Welding begins with preheating using gas welding, at a preheat temperature ranging from 100 to 150°C.

7. Welding electrode drying treatment:

Before use, bake at 350°C to 400°C for 1 to 2 hours, then maintain the temperature at 100°C to 150°C. When welding, use the insulated cylinder—simply take it out as needed.

8. Welding Process for Cracks in the Hot Blast Stove Shell:

The first three layers are to be welded using manual arc welding, with requirements for narrow weld beads, thin weld layers, minimal bead width, and a maximum weld layer thickness of no more than 5 mm. For the remaining layers, carbon dioxide gas-shielded welding is permitted, employing a multi-pass, multi-layer welding process.

9. Precautions when welding cracks in the hot blast stove shell:

(1) Surround the area with cloth strips during welding to ensure welding quality.

(2) Except for the root weld, each layer of weld must be stress-relieved by hammering before proceeding to the next layer.

(3) Throughout the welding process, the interpass temperature must not fall below the preheating temperature, nor exceed 400°C.

10. Surface Heat Treatment of Hot Blast Stove Welds:

After the weld surface has passed color or ultrasonic testing, proceed with localized flame heat treatment using a two-plate cutting method to apply the localized flame. The recommended temperature range is 600–640°C, followed by insulation with thermal blankets for 2 hours, allowing the weld to cool gradually afterward. Once the localized heat treatment is complete, perform an ultrasonic inspection of the weld, ensuring it meets the GB11345-89 Grade I acceptance criteria. Finally, conduct a 100% visual color inspection of the weld surface, verifying that no cracks are present. The entire heat treatment process must be completed within 12 hours.