Maintenance Strategy Based on Reliability Analysis and FMEA: A Case Study for Hydraulic Cylinders of Traditional Excavators with ERRS

Table 3

Suggested ranking system for the severity of failure modes [37].

Rank ()	Failure effect	Failure criterion	Illustration (e.g.)
10	Inconsistent with the safety legislation or the regulations	Hazardous without warning	Failure of a braking system
		Potential safety, health, or environmental issue
9		Failure will occur with warning	Leakage of a braking system
		Potential safety, health, or environmental issue
8	Disruption or decline to facility function	The machine runs malfunctioning	Uncoordinated boom, arm, and bucket movements
7		The machine runs properly but moderate disruption to facility function	Travel slower than the speed limit
6	Disruption or decline to secondary function	Some portion of secondary function is lost	Failure of a position feedback of the GPS
5		Moderate disruption to secondary function	Shock absorber of the seat is damaged
		Some portion of process is delayed
4	Appearance of noise and other functions are poor	Most users (>75%) are likely to complain	Abnormal engine noises
3	Poor	More than half (>50%) of the users are likely to complain	Distortion of the hood
2		A few users (>25%) are likely to complain	Excessive clearances on the surfaces
1	No discernible effect on safety, environment, or mission