Page 405 - Compression Machinery for Oil and Gas

Upstream Compression Applications Chapter 8 383

TABLE 8.4 Typical Characteristics for Gas Processing Plant Applications

Pressure Suction pressures typically 0.5–0.7MPa, discharge pressure
to pipeline typically 5–14MPa but potentially higher
(20–24MPa) to reduce pipe diameter or to compensate for
long piping runs between an offshore platform and the shore
Temperature 303–308K suction, discharge to pipeline typically cooled
to 303–323K
Fluids Natural gas
Compression power 3–22MW
Typical machinery Centrifugal compressors

Finally, a sales/export gas compressor is used to bring the gas from plant
pressure to pipeline pressure.
Typical operating conditions for gas processing plant compressors are
shown in Table 8.4.

Reliability and Operability in Upstream Applications

The most common upstream reliability challenges for upstream compressors
include corrosion and liquid-induced failures, and changing process conditions
can also introduce operability challenges.

Corrosion
Many gas fields produce sour gas, which is natural gas containing significant
amounts of hydrogen sulfide H 2 S (sour gas) or both H 2 S and CO 2 (acid gas).
The removal of these gases (gas sweetening) is typically performed at the
gas processing plant, so some upstream compressors in gas gathering, gas lift,
and reinjection applications operate with untreated gas. Both H 2 S and CO 2 form
corrosive acids in the presence of liquid water, which can form from the inlet or
(more commonly) discharge stream if the temperature is lowered (Hopper et al.,
2008). In addition, high levels of H 2 S can lead to sulfide stress cracking of mate-
rials in an aqueous environment.
These corrosion challenges are mitigated by judicious material selection per
NACE MR0175/ISO 15156 [9], which gives requirements and recommenda-
tions “for the selection and qualification of carbon and low-alloy steels,
corrosion-resistant alloys, and other alloys for service in equipment used in
oil and natural gas production and natural gas treatment plants in H 2 S-
containing environments, whose failure could pose a risk to the health and