The impeller of C02 turbine compressor was originally made of 35CrMoV low alloy steel. In the process of using, the blade inlet of stage 1 and 3 of impeller is corroded and eroded by C02 water mist, and can not be used after a short period of time. After anti-corrosion treatment, the impeller needs to be repaired for three months and replaced for one year.

Now the precision casting TC4 alloy replaces 35CrMoV low alloy steel (120 kg titanium), which has the advantages of high mechanical strength, corrosion resistance and good processing performance. The impeller was continuously operated on January 5, 1981, and it was safe and stable, and the maintenance workload was small. After 5 years of operation, the inlets of the impeller blades at all levels are inspected and the service life is expected to be more than 20 years. The original maintenance situation has been changed, and the economic benefits are very significant (see Table 2).
At present, Dalian Chemical Industry Co., Ltd. alkali plant 4 alkali-alkali method, combined with alkali method, a turbine rotor uses TC4 titanium alloy.

Table.  Comparison of economic benefits between titanium alloy and low alloy steel rotor

Project	Low alloy steel impeller(RMB)	Titanium alloy impeller(RMB)
Rotor fee	50000	60000
Service life	One year	Expected for 10 years
Equipment depreciation	50000 /year	6000 /year
Saving costs	0	44000 /year
Number of inspections per year	3	1
Cost per inspection	3000	1000
Annual maintenance fee	9000	1000
Annual cost savings	0	8000
One year downtime	3	1
One downtime	20 day	20 day
One stop loss	48000	48000
Annual downtime loss	144000	48000
Total annual savings	0	148000