Hydrocarbon Processing - October 2021 - GP-32

TURBOMACHINERY
Turboexpander evaluations and repairs. Troubleshooting
over the phone or with the help of an onsite field service
technician can solve many customer issues. However, in some
instances, shop repair may be required. The damaged MCS
and/or IGV assembly will need to be shipped to a qualified
repair shop with specific experience in turboexpanders.
Repair times vary depending on the severity of the damage.
Most turboexpanders are designed for a specific plant's
process. Although OEMs have standardized some components,
most critical parts are unique to a specific machine,
and one OEM's standardization does not correlate to another
OEM's standardization initiatives. Rarely does any turboexpander
OEM stock parts, even when duplicate units have
some standardized parts. Most parts are manufactured to order
for each repair. This should be an incentive to operators
and maintenance teams to maintain a healthy spares package
for turboexpanders.
With the time it takes to inspect and make a proposal, issue
a purchase order, repair and manufacture the machine,
and assemble and ship the machine, major repairs can take 4
mos-6 mos for oil-bearing machines, and potentially significantly
longer for a magnetic-bearing machine.
Upon arrival to the shop for evaluation, the machine will
go through a number of general steps before a detailed disposition
report can be issued to the customer for consideration:
* Checking for rotor rotation (is the rotor stuck?)
and key clearances, such as rotor end play, etc.
* Disassembly and photographic record
* Inventory of parts received
* Visual inspection and recording condition of parts,
noting findings of wear, rubs, cracking, corrosion,
discoloration, etc.
* Cleaning of parts and photographic record
* Non-destructive examination (NDE) of
the wheels and other key components
* Runout inspections on shaft (mechanical and electrical)
* Dimensional record of key components
(wheel fits, seal areas and bearings).
Spare parts inventory recommendations. Components
are rarely stocked at the OEM. Requested parts are ordered
by the OEM from suppliers, or are manufactured to order,
usually with long lead times. The following spares are recommended
for each turboexpander:
* Major spares include:
° MCS assembly
° IGV assembly
* Repair kits and systems spares from vendors include:
° Accumulator repair kit
° Lube oil repair kit
° Regulator differential repair kits
° Temperature control valve repair kits
° Pressure transmitter gauge
° Pressure differential indication transmitter
° Speed pickup
° Speed transmitter
° Resistance temperature detector
° Vibration probes
° Vibration transmitters
32 SEPTEMBER/OCTOBER 2021 | GasProcessingNews.com
° Programmable logic controller (PLC) relay
° Fuses
* Consumables from vendors include:
° Filters
■ Lube oil
■ Seal gas
° Seals
■ O-rings
■ Cup seals (used for low-temperature applications)
■ Gaskets.
A final and important note should be made as to how to
store spare parts. For a spare MCS, the wheels should be
bubble-wrapped, the ports plugged and the section should be
placed in a wooden crate. If an expander has been sitting unprotected
for an extended period, as a precautionary measure,
it may need to be inspected in a repair shop before the next
outage (planned or unplanned). Any corrosion across the
expander shaft hub and bearings is a cause for concern, as it
could amount to a bearing failure.
The most common method of storage is vacuum packing.
After manufacture or repair, the MCS should be placed in a
vacuum bag with desiccant, sealed and placed in a wooden
crate for long-term storage. This system can provide corrosion
protection for approximately 10 yr. After this time, the spare
MCS should be inspected by the OEM and resealed.
A costlier, but very effective method of storage is a nitrogen
purge container. The container is more robust and is equipped
with indicators to show if the purge has been compromised. If
the purge is maintained, then there is no end to the shelf life.
IGV assemblies should be crated and placed in a sealed
bag with desiccant. Seals, O-rings and gaskets should be kept
away from contaminates and in the original packing. The life
of Teflon seals and O-rings is usually limited to a 10-yr shelf
life from the manufacturer.
Conclusion. Turboexpanders are critical equipment for many
applications, and their longevity and sustained performance
are often key to the profitability of a business. This article provides
an overview of the major elements involved in the work
of maintaining turboexpanders. The discussion traces issues
related to the design of the machine, field operation and shop
repairs. Users will find valuable insights and suggestions by
practitioners with an OEM and aftermarket perspective. GP
LITERATURE CITED
1
Avetian, T. and L Rodríguez, " Fundamentals of turboexpander design and operation, "
Gas Processing & LNG, May/June 2020.
LUIS E. RODRÍGUEZ is a Design Engineer at L.A. Turbine, a
Chart Industries Company, responsible for the mechanical
design of turboexpanders. Prior to L.A. Turbine, he worked for
10 yr at Sulzer Turbo Services in La Porte, Texas. Mr. Rodríguez
is a Texas-registered professional engineer with a BS degree
from Universidad Simón Bolívar in Venezuela and an MS degree
from Texas A&M University.
RUSTY HOCH is Regional Sales Manager at L.A. Turbine,
a Chart Industries Company, responsible for fostering new
customer relationships, managing current customer
partnerships and providing turboexpander aftermarket
services and solutions. Mr. Hoch is an Air Force veteran who
holds a BBA degree from Texas A&M University and an MBA
degree from Webster University.
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