Technical requirements of nodular cast iron in Cylinder Casting

Nodular cast iron intake cylinder is one of the important parts in the front end of heavy duty gas turbine unit. Its main function is to introduce air evenly into the compressor. It is a large pressure bearing component. The outer contour of the intake cylinder casting is bell shaped (see Fig. 1). The whole set of cylinder casting is divided into one upper half and one lower half. The upper and lower half are produced together and processed and assembled in the subsequent cylinder assembly. The rough machining blank weight of the upper and lower half castings is 12500 kg and 13500 kg respectively, the outline size is Φ 4250 mm (diameter) × 1500 mm (height), the maximum wall thickness is 400 mm, the minimum wall thickness is 60 mm.

The casting material is nodular cast iron, which is the only nodular iron casting among the four sets of large cylinders of the unit. The material grade is fcd450. The mechanical property technical requirements have higher requirements on tensile properties and mechanical property index requirements.

After rough machining of inlet cylinder castings, nondestructive testing shall be carried out according to relevant non-destructive inspection standards

Magnetic particle testing (MT): 100% of all surfaces.

Ultrasonic testing (UT): important and critical areas. The Red areas in Figure 2 are high-level areas for ultrasonic testing.

Dye penetrant testing (PT): the position where MT can not be performed mainly includes the dead corner where some wall thickness intersects, and the cross position where the inner cavity space is narrow.