Page 65 - Machinery Component Maintenance

50 Machinery Component Maintenance and Repair

labor came to well over $1 ,OOO,OOO. The cause of the wreck was eventu-
ally traced to the buildup of deposits on a brass piston in the hydraulic
shutdown system which was in a hot dead-ended oil circuit. The heat
caused the oil to decompose over a long period of time, in turn causing
the piston to stick. As a result, the plant now checks trip circuits more
frequently. They have also installed backup trip devices on many trains,
and are developing new design and operating practices.

Spare Parts

The time to check spare parts is not in the middle of the night following
an emergency phone call from the operating department manager. Most
large companies have some degree of computer control on the warehous-
ing and reordering of spare parts. But how many times have you been
lied to by a computer? There is no substitute for a hands-on check of
parts by a knowledgeable individual. Part numbers must be checked be-
cause the item on the shelf is not necessarily the one you expected to find.
Many major plants allocate special boxes to major machinery spare
parts storage. The boxes have individual compartments for labyrinths,
seals, bearings, etc. A list on the lid details all parts inside, their location
in the box, the manufacturer’s part number and the company’s stock
number. Once filled, the box is sealed and stored in the usual manner.
During an overhaul, the box is taken to the field and some or all of the
parts consumed. The box is then returned to the warehouse with a list of
consumed parts to be replaced. A call-file system should be used to keep
tabs on rotors that are out of the plant for repairs and delivery of other
critical spare parts.
When checking spare parts, it is important to recognize that not only
must the part be the right size, it also must be in good condition. Han-
dling and improper storage, as well as deterioration with time, arc a few
of the hazards associated with a warehousing operation. A nicked O-ring
or a carbon seal face out of flatness could require a second shutdown to
correct the problem. The use of an optical flat, a set of micrometers, and
a knowledgeable pair of eyes can be invaluable in detecting a defective
part.
Also, remember that just because the part came from the factory,
doesn’t necessarily mean it is the right one for your machine. While
equipment manufacturers have various quality control procedures, they
too rely on human beings, and errors do occur. In addition, some parts
have a finite shelf life (case split line sealant is an example) and must be
fresh when the time comes to use them.
This is also the time to check on the availability of special (custom fab-
ricated) tools. These should be kept in a separate box, inventoried at reg-