Page 127 - Practical Machinery Management for Process Plants Major Process Equipment Maintenance and Repair

110 Major Process Equipment Maintenance and Repair

XM-19 or K 500 Monel shafting can be substituted (Table 2-4). XM-19
offers a good combination of strength, corrosion resistance and cost. If
collet-mounted impellers have proved to be unsatisfactory in a particular
service, and a change to keyed impellers is made, it may be necessary to
upgrade the shaft material to compensate for the stress raisers created by
cutting keyways and split ring grooves in the shaft. For additional infor-
mation on materials, refer also to Appendix 1A in Chapter 1 of this vol-
ume.

Graphalloy@ Bearings
Product lubricated bearings in clean liquids can be upgraded to a mate-
rial such as Graphalloy. Graphalloy is a solid carbon graphite, the pores
of which have been impregnated with molten metal in a high heat and
high pressure process. During the impregnation process the metal perme-
ates the graphite in long continuous metal filaments. It is these filaments
which give Graphalloy its ductility, high strength and good heat dissipat-
ing properties. The metal increases its strength and ductility and removes
heat generated at the bearing surface. Graphalloy contains no oil and
does not produce any toxic emission which may contaminate the pumped
product. It is extremely durable in clean products. Graphalloy bearings
operate well at temperatures from -50°F to +300"F in fresh or salt wa-
ter, gasoline, jet fuels, solvents, bleaches, caustics, dyes, liquified gases,
acids and most chemical process and transfer services. Babbitt grade
GM105.3 is generally recommended for pump bearings. However,
Graphalloy is not recommended for applications in products containing
abrasive material. In products with abrasive material, extremely hard
bearings such as tungsten carbide, boron carbide, or Tribal09 can be
utilized running on a hard journal. However, some of these materials are
extremely brittle, and cannot be externally shrink fitted.

Table 24
Typlcal Mechanical Properties of 1 in. Diameter Shaft Stock

Ultimate Yield
Tensile Strength Charpy V Notch Hardness
Strength (.2%) Wlbs (Rockwell)
XM-19 150 125 90 RC 30
Monel K-500 165 105 37 RC 30
5Pe 316 85 35 110 RB 80
Type 304 85 35 110 RB80
174PH Cond. H-1150 145 125 50 RC 33