Page 169 - Reciprocating Compressors Operation Maintenance

Operation and Maintenance of Reciprocating Compressors 1 55

Environmental Effects

Listed here are combined influences on valve life and performance
derived from the gas itself. These are:

1. Corrosive Elements
Substantial amount of corrosive contaminants in a gas will usual-
ly show up on the valve. Even small amounts, though they will not
rust away the valve, can cause stress corrosion and lead to such
damage as breakage of the sealing element (seat and plate). Certain
compounds become corrosive only if moisture is present in the sys-
tem or develops after shutdown. This moisture, in combination with
the contaminants in the gas, can corrode valves.
Coping with corrosiveness may require metallurgical upgrading
of valve plate, strip, or channel, or, in severe cases, the materials of
all valve components. Since this involves a major expenditure, be
sure to investigate which measures are called for.
Although hydrogen is not corrosive by itself, it can, under certain
conditions, cause embrittlement due to molecular penetration of the
metal (hydrogen embrittlement) of at least the top layer. The ensu-
ing cracks lead to deterioration and subsequent fracture. Hydrogen
embrittlement can be prevented by changing materials.
2. Foreign Materials and Impurities
Despite proper filters or scrubbers, foreign particles can get
wedged in the valve and prevent its proper operation, causing dam-
age. Examine the seat lands and impact surfaces of the valve plates
for traces of debris. Minor indentations and imprints of particles
may show up between the plate and seat. Make certain filters, sepa-
rators, knockout pots, and drains are working properly and are sized
to handle any impurities from upstream.
3. Liquid Carryover
Liquid slugs can have a devastating effect on valves. The plate or
strips will be subjected to extreme destructive forces and will
crack. Slugs occur when entrapments get carried through. They are
formed when saturated gas contacts the cylinder walls. Prevention
involves raising the cooling water temperature 10 to 15° above the
incoming gas temperature. If liquids are coming from the upstream
feed line, separators can be checked and much of those liquids