Page 314 - Reciprocating Compressors Operation Maintenance

Overhaul and Repair of Reciprocating Compressors 299

WELD REPAIR

Crankshaft journals, mains as well as throws, can be repaired by weld-
ing and grinding back to standard. However, weld repairs are feasible
only with steel shafts. This technique requires real weld repair expertise.
Because of the carbon content of these shafts, the material is difficult
to weld without inducing surface embrittlement and cracking. These
cracks may be microscopic and usually cannot be detected except by
magnetic particle inspection or metal etch testing. If cracks are induced
through welding and the shaft is returned to service, it will eventually
fatigue and break.

WELD REPAIR PROCEDURE

It is important that the proper weld procedures be followed when mak-
ing weld repairs on crankshafts. An approved procedure will go a long
way towards maintaining the integrity of the crankshaft.

1. Cracks in the crankshaft shall be removed by grinding.
2. Crankshaft shall be inspected with magnetic particle method to
ensure that the cracks are removed.
3. Crankshaft shall be preheated to a temperature between 350°F and
800°F. This preheat temperature shall also be the minimum inter-
pass temperature.
4. If weld repair of crankshaft is necessary, weld depth shall not
exceed a 0.250".
5. Stress relief shall be performed immediately after welding at a tem-
perature between 1000°F and 1200°F. The minimal stress-relief time
shall be one hour per inch of shaft diameter.
6. Non-destructive testing (NDT) inspection.

Journals can be ground undersize and special bearings used. There is a
limit on the amount of undersize a shaft may be ground. Journal grinding
is often feasible in-place, with portable equipment.
Journals may be trued up, prepared for plating, and chrome plated
back to size. However, chrome plating is not always accepted by insur-
ance companies.