Hydrocarbon Processing - August 2021 - GP-31

EQUIPMENT
Are cylinder liners necessary for high-speed
reciprocating gas compressors?
S. ZARDYNEZHAD, TurboTech Consulting Corp., Calgary, Alberta, Canada
Wear is common in reciprocating gas
compressors (RGCs) due to sliding and
rotational motion of parts. In the design of
RGCs, wear study and calculation by empirical
formulas are conducted to estimate
and forecast the life of the parts. However,
wear during real working conditions is different
from theoretical estimations and,
sometimes, catastrophic failure is experienced
during operation due to considerable
mechanical or chemical wear.
Wear in the cylinder wall due to reciprocating
motion of the piston is a good example
of such circumstance and the main
subject of this article. Low- and moderate-speed
RGCs are normally furnished
with a cylinder liner; however, high-speed
RGCs may or may not be furnished with
a cylinder liner. In this article, the main
differences between low-, medium- and
high-speed RGCs are discussed; the wear
mechanism in the cylinder is explained;
the importance of cylinder liners to RGCs
is addressed; and the author's recommendations
for decision-making when considering
liners are explained.
Standards for RGC operation. The
American Petroleum Institute (API) produced
API Standard 618 (1964)1
Standard 11P (1976).2
and API
These standards
are frequently used for the design and
manufacture of RGCs. API 618 (Edition
1) was published in 1964 based on the operating
experience of 1950s compressor
models. During that time, manufacturing
and materials technology were not advanced
and the speed was limited to 100
rpm, which is why the 1st edition of API
618 covers only low-speed compressors.
Manufacturers encouraged coupling
RGCs to gas and diesel engines with
speeds of 800 rpm and higher, which increased
their size and cost. This led to the
publication of API 11P in February 1976,
TABLE 1. Comparison of rotational speed range of RGCs
Speed, rpm
Low
API
Author's experience
Some manufactures
Not specified
100-350
100-600
approximately 12 yr after the publication
of the first revision of API 618. Moderatespeed
units were derived from high-speed
units and added to API 618 in 1995.
RGCs are classified into three types
in terms of rotational speed, as shown
in TABLE 1. High-speed, packaged RGCs
for oil and gas service are covered under
API 11P, which has been withdrawn by
API and replaced by ISO 13631 (2002),
" Petroleum and natural gas industries-
Packaged reciprocating compressors. " 3
The driver can be either an engine or an
electric motor. Sometimes they are coupled
via a gearbox. Their operating speed
is typically 800 rpm-1,800 rpm, based
on the author's experience, with engine
drivers above 1,000 rpm and motor drivers
of 800 rpm-1,000 rpm.
High-speed RGCs are skid-mounted
and packaged. They are easy to install,
easily transportable to different sites due
to their modularized and compact design,
and have a relatively small CAPEX. Highspeed
RGCs have higher maintenance
costs than low- and medium-speed compressors.
Low- and medium-speed compressors
run at speeds of 100 rpm-799
rpm. These compressors have lower speed,
higher stroke and higher efficiency over a
wide range of operating conditions and
require less maintenance than the highspeed
units because of their lower speed.
However, low- and medium-speed compressors
usually must be field-erected and
require heavy foundations. They have high
degrees of vibration and pulsation suppresMedium
Not
specified
350-799
600-1,200
High
Not specified
800-1,800
1,200-1,800
FIG. 1. API 618 compressor cylinders are
frequently supplied with centrifugally cast,
removable liners to reduce reconditioning costs.
sion compared to low- and medium-speed
compressors. Large low-speed compressors
are shipped to the site as loose items
(e.g., throws, frame, driver, etc.).4
API 618 compressor cylinders are frequently
supplied with liners (FIG. 1) to
reduce reconditioning costs. RGC cylinder
liners are removable in case of accidental
scoring or wear over a long period
of service. In general, liners are not used
in high-speed machines (API 11P/ISO
13631) where the rotating speed is higher
than 800 rpm. Liners are almost always
used in API 618 compressors, especially
in critical services where the gas being
handled is corrosive, toxic, low-temperature
or high-pressure, and in special designs
like free-floating piston.
However, API 618 does not define
the meaning of " critical services. " Liners
have become a standard design for many
Gas Processing & LNG | JULY/AUGUST 2021 31
Hydrocarbon Processing - August 2021

Table of Contents for the Digital Edition of Hydrocarbon Processing - August 2021
