Root Cause Analysis (RCA) related to Bucket elevators chains lives too short and teeth wear too rapid – both perennial.
Article Type: | Root Cause Analysis (RCA) |
Category: | Mechanical |
Equipment Type: | Pipelines and Miscellaneous Problems |
Author: | S. Raghava Chari |
Note: This root cause analysis (RCA) is from real-time scenarios that happened in industries during the tenure of two or three decades ago. These articles will help you to improve your troubleshooting skills and knowledge.
NPK Fertilizers, Urea, and Sand handling Bucket Elevators; < 6 months’ chain lives against the former >3½ years and 10-12 months Shaft & Twin Sprocket Assembly’s’ (STSA) sprocket segments (SS):
The sprocket assembly came with Sprocket Segments bolted to the body (fig 1), to replace worn teeth segments with new ones during the fortnightly plant cleaning ½ shift shutdowns (SDs).
Crew could not unbolt the rust and corrosion frozen fasteners; hence, they replaced the teeth worn STSA with bought out STSA and reconditioned the removed from service STSA.
Hence, the manufacturer furnished ones let us call them Warehouse Sprocket Segment (WSS) remained unused.
The plant lived with the STSA replacement 2-days shutdown totaling to several days because of 12 elevators population.
The author on becoming maintenance manager root cause analyzed the first paragraph given problems.
The crew leader answer to Root Cause Analysis Query (RQ) when the problem started was 2 years after commissioning, i.e., after shop- reconditioned SSA use and perhaps the locally bought chains use worsens the situation.
The author assigned inspection engineer (IE) certified the local chain material hardness and fit up as good as the short few imported links held in the warehouse i.e., its MOC and workmanship confirm to standards.
Responding to that, the crew leader offered he and the (IE) reviewing the reconditioning procedure and carefully witness each task and get back.
Two days later they reported they could not find any flaw with the reconditioning; perhaps the author should witness a job in progress; he may find what they missed.
The author found, the technician checking a finish ground tooth with a single tooth template (STP fig 1). This didn’t seem right, but the author couldn’t pinpoint the flaw then.
Few hours later it flashed! STP check ensured correct each tooth profile, but not the teeth pitch; in addition, it missed skew – angular offset between absence between LSA and right RSA.
He asked them to find ways to avoid these errors. He also thought whenever time available and got a method.
After a week he found the crew leader had not got a method.
The author’s method is: make a template to mark all TEETH PROFILEs at correct TEETH PITCH on LSA and RSA skew free.
He named it All correct teeth skew prevent template (ACTSPT, fig 1). Make it thus:
Correct the reconditioned STSA as under:
The author guided the crew as follows:
Crews rebuilt all STSA’s worn teeth as above.
Benefits from ACTSPT are:
However, the continued 2 days plant shutdown (SD) to change the rotable STSA bothered the author. Hence, he asked the crew to find out a way of segments replacing as the manufacturer intended to eliminate the rotable changes two days outages.
Pondering over the problem, the author arrived at the below given method to achieve the above objectives:
Recondition worn TSs thus:
Author: S. Raghava Chari
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