Hydrocarbon Processing - August 2021 - GP-32

EQUIPMENT
TABLE 2. Comparison of API 618 with API 11P/ISO 13631
Subject
API 618 (2007)
Application
Driver speed, rpm
Piston speed,
lubricated, m/sec
Piston speed,
non-lubricated, m/sec
Stroke
Expected valve life,
Theoretical
Driver, gas engine
Oil-free cylinder
Critical service
Service life
Uninterrupted
operation
Cylinder liner
Cylinder jacket
Startup unloading
Capacity control
Distance piece
Size
Cost
Low/moderate
200 rpm-799 rpm
2.8-4.5
2.3-3.8
Long
229 mm (9 in.)-508 mm (20 in.)
3 yr
No
Yes, and lubricated
Yes
Minimum 20 yr
Minimum 3 yr
Yes
Yes
Automatic valve unloader
Automatic valve unloader
Type A used for non-flammable
service
Medium to large
Higher than API 11P
TABLE 3. Main wear mechanisms
in RGC cylinders
Wear category Mechanism
Mechanical
Chemical
Abrasive/sliding
Particle impingement/erosion
Adhesion/scuffing
Corrosion
refining, gas and petrochemical industry
applications, even though the gas involved
may not be corrosive, toxic, lowtemperature
or high-pressure. Some end
users insist on liners in their compressors
based on maintenance lessons learned.
Liners are a key subject during the RGC
engineering and procurement stages, and
they may increase the CAPEX of RGCs;
however, liners have a significant positive
impact on OPEX, especially for large or
multistage cylinders and where service is
critical or special, without any standby.
Another benefit of a liner is to reduce the
cylinder bore size to meet certain operating
capacity conditions. By installing
liners with different bore sizes, the same
32 JULY/AUGUST 2021 | GasProcessingNews.com
ISO 13631 (2002)/API 11P (1989)
Packaged high speed, separable
High
800 rpm-1,200 rpm
4.6-6.1
Not available
Short
76 mm (3 in.)-203 mm (8 in.)
2 yr
Yes
No, only lubricated
No
No, gas engines need routine maintenance
(sometimes at least once per year)
Generally no
No
Bypass
Speed and bypass
Type 1 are used in many sweet gas
applications
Small to medium
Lower than API 618
cylinder can be used to accommodate
a range of capacity and pressure conditions.
This is useful when renting a compressor,
as opposed to buying one.5
API 618, API 11P and ISO 1363 do
not define low-, medium- and high-speed
compressors in terms of the piston and
rotating speed. Normally, they are defined
in the client's specifications. The main
differences between API 618 (5th edition)
and API 11P (ISO 1363) are summarized
in TABLE 2.
Definition of wear. Wear may be defined
as material or mass removal from
the surface of any part due to contact
with another surface. Wear can also result
due to mechanical or chemical behavior
of the material. Cylinders experience
wear at the point of contact with the piston
rings. In horizontal arrangements,
cylinder wear is greatest at the bottom
because of piston weight. In compressor
cylinders, different types of wear can occur,
as outlined in TABLE 3.
Sliding wear. Surface-to-surface interactions
happen whenever one surface
In similar applications
In similar applications
slides relative to another over a distance.
Friction between two parts is the main
cause of this kind of wear. In RGCs, sliding
wear generally happens between parts
such as cylinders with piston rings. Also,
hard particles may form inside cylinders,
which may cause abrasive wear in the
cylinder. Cylinders in RGCs are at risk of
abrasive or sliding wear due to reciprocating
motion and the risk of contacting the
piston with the cylinder wall due to wear
band ring failure (FIG. 2).
Particle impingement/erosion. This
type of wear may be due to different causes:
* Solid particles enter the cylinders
with gas and impinge on the
cylinder from an external source
(FIG. 3)
* Solid particles from broken parts,
such as a broken valve due to fatigue
(i.e., high vibration over a period of
time), which is common.
API 618 requires valves and cylinders
to be designed so that neither the valve
guard nor the assembly bolting can fall
into the cylinder, even if the valve assembly
bolting breaks or unfastens (Clause
Critical service is not defined in API 618
Remarks
Low to moderate speed, integral
Speed ranges are author's experience
and are not addressed in API
Speed ranges are author's experience
and are not addressed in API
Speed ranges are author's experience
and are not addressed in API
Stroke ranges are author's experience
and are not addressed in API
Author's experience, similar valve
at similar services
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