The main structure of the casting crane is easy to be damaged and destroyed at the welding seam or the base metal at the abrupt change of the section at the stress concentration nearest to the moving load.
There are two key factors, namely, the dynamic impact part of the moving load and the stress concentration part of the structure itself. One type of moving load application point is the traveling main trolley wheel, and the other type is the traveling cart wheel. The stress concentration parts include the arc transition area of the section, the abrupt change of the section, the cruciform weld, the door opening, the main beam fillet weld, and the butt cross weld. The identification of different types of damage and destruction is shown in the table.
| Type | Position | Risk | Timeliness |
| Cracking of butt weld in pressure area | Butt weld between T-shaped steel and main web | Easily found, repairable, slow crack growth | It often occurs in the middle of fatigue life |
| Box beam opening, edge weld cracking | Main beam auxiliary web door hole weld | Easy to find, repairable, fast crack growth | It often occurs in the middle or early stage of fatigue life |
| Cracking of fillet weld in pressure area | Fillet weld between upper cover plate of main beam and main web | Easily found, repairable, slow crack growth | It often occurs in the middle of fatigue life |
| Cracking of butt cross weld in pressure area | Butt weld between T-shaped steel of main beam | Easily found, repairable, slow crack growth | It often occurs in the middle of fatigue life |
| Cracking of weld at the tip of section change of tensile zone | Base metal or weld at the end of main beam | Difficult to find, difficult to repair, high possibility of re cracking | It often occurs in the late fatigue life |
| Cracking of stiffening plate at the change of right angle of section in tensile zone | Base metal at the end of auxiliary main beam | Difficult to find, repairable, slow crack growth | It often occurs in the middle of fatigue life |
| Cracking of cross weld | Welds at the connection between end beam and wheel seat; Cross weld of auxiliary web | Dangerous crack, fast crack growth | It often occurs in the late fatigue life |
| Weld cracking in variable section stress concentration zone | Arc transition zone weld of bridge end beam | Dangerous crack, fast crack growth | It often occurs in the middle of fatigue life and continues to the late stage |
The damage of the butt weld between the T-shaped steel and the main web often occurs in the middle of the equipment life cycle, which is the main weld closest to the moving load of the main trolley wheel, and is affected by the reciprocating alternating action of wheel pressure. When the deviation between the trolley track center line and the main web center line exceeds the standard, or the trolley track joint gap and height difference exceed the standard, such weld cracking is easy to occur.
The damage of the door opening weld of the main beam auxiliary web often occurs in the middle or early stage of the equipment life cycle. The high residual stress of the arc welding of the door opening and the high stress concentration factor at the hole edge are the reasons for the cracking of such welds. Local reinforcement is required for repair here.
The damage of the fillet weld between the upper cover plate and the main web of the main beam often occurs in the middle of the equipment life cycle. Such weld cracks often occur in some box girders that do not use T-shaped steel, but this form is rarely used in the design of the main girder of the casting crane at present.
The damage of the butt weld between the T-shaped steel of the main beam often occurs in the middle of the equipment life cycle. This is the cross weld closest to the moving load of the wheel of the main trolley. The welding process requirements are strict, and local reinforcement is required for repair here. The damage of the base metal or weld at the end of the main beam often occurs in the late period of the equipment life cycle, where it is affected by the running impact of the cart wheels, so it is difficult to repair, and the possibility of cracking again is high, so it is a dangerous crack.
The damage of the base metal at the end of the auxiliary main beam often occurs in the middle of the equipment life cycle, where the crack propagation is slow, but it is difficult to find it in daily spot inspection.
The damage of the weld at the connection between the bridge end beam and the wheel seat often occurs in the late life cycle of the equipment. This is the fillet weld closest to the moving load of the crane wheel seat. It is a dangerous crack due to the influence of the current situation of the crane track. The damage of the welding seam in the arc transition area of the bridge end beam often occurs in the middle to late period of the equipment life cycle. This is the variable cross-section welding seam closest to the moving load of the cart wheel. Such damage often cracks in the same shape area in several directions of the bridge successively. The possibility of cracking again after repair is high, and it is a dangerous crack.
When the bridge main beam is hinged to the end beam, the axle sleeve of the connecting shaft is prone to wear and shake after several years of use, which will lead to the wear of the connecting shaft. If the shaft and axle sleeve are not replaced in time, the connection weld of the wheel seat will be more vulnerable to horizontal impact. Such damage often occurs in the middle of the equipment life cycle.
The practical engineering experience in recent years shows that the structural damage in the late life cycle of equipment is often the regular and paired cracking failure of multiple areas or parts of the same form. When the failure of this group of parts is repaired and strengthened, a new group of stress concentration areas will have regular and paired cracking failure. The recurrence of damage and failure is an important feature of late fatigue life.