hi, do you have any idea regarding journal pad replacement philosophy. im a bit comfused, how do we judge to replace if we found out only 1 pad was found crack after an UT and PT check. the question is, do we need to replace all new pads altho if we found out only 1 pad crack.

additional info:
1)the next shutdown opportunities will be depend on the gas availability and operation aggreement.
2)the operation will only release the compressor if we have strong concrete proof and by condition base (increase in vibration)
3) do we want to take the risk if we run this bearing for any fews more years. how long it will last if we only replace 1 pads only?

pls let me know if you have any further queries.

Thanks

You are talking about tilting pad radial bearing? Pad was found "cracked" after UT/PT check... does that mean a debonding between babbit and base? or crack visible at pad working surface? How big in relation to the pad? Is the reason for the crack known?

If reason is not known and appears to be a developing (vs preexisting condition), that would certainly argue toward replacing all. It there has been significant wear on the existing pads, that would argue toward replacement (it might slightly change the radius of curvature related to the "preload" paramter). Otherwise, I don't know of any problems mixing old and new pads.

Part duex: no question of checking alignment.

quote:

do we need to replace all new pads altho if we found out only 1 pad crack.

The cost of one pad compared to possible production losses is negligable, as is the cost of replacing all the pads (5 or 7).

If you have 'gone into' the machine to check one pad, then there is no more effort required to replace all the pads, so why not consider changing all of them - that removes all time constraints and removes any doubt over the condition of the pads. You can then thoroughly inspect the removed pads and have them refurbished for future use

quote:

2)the operation will only release the compressor if we have strong concrete proof and by condition base (increase in vibration)

A tilting pad bearing can sustain large amounts of wear/damage before a different pattern of vibration appears. You are better off measuring gap volts (shaft centreline plots), monitoring bearing temperatures and using oil analysis to detect bearing wear metals (tin/lead)

quote:

3) do we want to take the risk if we run this bearing for any fews more years. how long it will last if we only replace 1 pads only?

This question cannot be answered sensibly

Many years ago, refinery environment, and a 10-12 week delivery on a complete new bearing, I rotated the damaged pad so that it was opposite the load zone and reassembled the gearbox. The unit ran for three more years until such time as there was another major outage.

John from PA

all,
anyway thanks for all your replies
yes im talking about tilting pad journal bearing. the crack is visible after performing the ut and pt check. we found out crack 'blood line' at the layer of babbit bearing layer. the reason of crack is still under investigation. the decision of replacing all the pad altho only pad was found crack is doubtful either replace all or not.
i also thinking better to replace all the pads as the next overhaul will be about 7 yrs time and can be by condition based (can be more than 7 yrs) for me it is quite risky and better to replace all as the spare bearing pad is available at the warehouse.
do you all know if there is any changing pad philosophy ie in journal or API that can i refer to.
another issue was happened last yr during our compressor shutdown. this compressor was running since 2004 and we open up this machine due to high vibration during start up. the service engineer insist to replace all the journal bearing pad altho we had checked the pad after underwent ut and pt test. but he still insisting to replace all as the next shutdown will be for another 6/7 yrs time. logically if we passed all the test, we still can reuse the bearing as found out the pads is still in good condition. is it political issue or other else?
anyway thanks again for all your good comments.

quote:

another issue was happened last yr during our compressor shutdown. this compressor was running since 2004 and we open up this machine due to high vibration during start up. the service engineer insist to replace all the journal bearing pad altho we had checked the pad after underwent ut and pt test. but he still insisting to replace all as the next shutdown will be for another 6/7 yrs time. logically if we passed all the test, we still can reuse the bearing as found out the pads is still in good condition. is it political issue or other else?

If the pads have been exposed to excessive vibration, there may be a concern that a portion of the fatigue life has been exhausted. Although I think most people would not replace pads on that basis alone if ut test and inspection showed no problems.

The pivots can wear as well as the pads. Have these been checked.

There has been no mention of bearing measurement. Does the bearing have the proper clearance, pre-load, and offset as designed? This is critical to proper operation.

aidil, a point to ponder - OEM's supply philosophy on bearing pads is a complete working set. and bearing(consumable item) is normally parked as stock item i.e once withdrawn, PR will be automatically generated by system. buyer will act on this and initiate the purchase order. months later you will be getting new working set (4, 5,7.. pads)

anyway, as mentioned by pete, the other pads likely had exposed to excessive vibration. and this is a good basis for you to convince related parties to perform complete pads replacement knowing the fact that nect turaround is after 7 years.

Take extra precaution when installating the pads. Ensure the fixation screw (i presume grub screw) is not overfixed and it does went into the pads fixation hole.

valve, thanks for your comment. as i mentioned earlier, all the bearing pad already underwent several test, ut and pt and passed all. for me no point to change all the pads but at that time, the service engineer insist and better toreplace as the next cycle will be for another few more years. so meaning no point to perform bearing if at the end we will replace all the pads.

my comment was merely reflecting to your original query i.e what do we comment on replacement of one bearing pad only.

back to your last respond, at any time you plan for total replacement of pads, it is a normal maintenance procedure to perform inspection (DPT etc) on the used pads unless the pads are totally damaged.

for me, if i have the spare working set, considering we are to run the unit for the next 5-7 years, i would perform total replacement. after all, the OEM is not selling the bearing pad by pad. they normally supply by working set. if i consume 1 pad only, then it is no longer denotes as spare working set. it would be painful if i reach to the time where total replacement needed.