Hydrocarbon Processing - July 2022 - 10

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es, and has set that tolerance band to ensure the finished part will
consistently fall within specification and perform as expected.
Now consider the replica part's material of construction.
Despite their near identical appearance,
non-OEM components are still likely to
underperform, resulting in significant costs in
terms of downtime, equipment damage and
personnel hazards.
In contrast, the replicator has a single, and typically used, part
that they measure to determine the target dimension. They then
use that dimension as their new target and will fabricate parts in
a tolerance around that measured value. The replicator does not
know the OEM target dimension or the allowable tolerance, so
the resulting parts will often fall outside OEM specifications, as
shown on the right of FIG. 3. This can create significant performance
issues when the component is placed into service.
The x-ray fluorescence analyzer in the PMI gun can identify
the chemical composition and grade of the part,
but that is only a small piece of a much broader
specification. Every OEM part has detailed
specifications for external coating materials and
thickness, heat treatment, hardness and surface
finish (TABLE 1).
These processes are carefully chosen to extend
part life, minimize friction, manage specific stresses
expected in normal operation, and perform as
expected. The non-OEM part manufacturer has
no way to determine any of this information from
a PMI gun reading, so they finish the part until it " looks right, "
and then box it up for shipment to a hapless customer.
The difference in part performance can be significant. Hardness
and surface finish impact the friction of the component as it
moves, which can cause control valves to hunt around setpoint.
The non-OEM parts also tend to gall and wear earlier, as well
as leak and fail prematurely in cavitation or flashing conditions.
Additional value from OEM parts. The dimensions and material
of construction obviously have a significant impact on the
performance and service life of a valve component. However,
another significant benefit is associated with OEM parts: the
knowledge and expertise of the manufacturer itself.
A host of professional standards organizations are dedicated
to maintaining the safety and reliability of process control
valves, while ensuring the metallurgical fabrication techniques
are the best available. Nearly every OEM control valve supplier
has active representation on many of these standards committees,
offering valuable knowledge and staying current on the latest
industry developments.
That knowledge is translated into continuous improvements
in the materials of construction and manufacturing techniques
that are used to fabricate valve parts. Just as every product has a
FIG. 2. While a PMI gun can reveal some details regarding materials of
construction, it does not provide a complete picture. Source: Emerson.
TABLE 1. A PMI gun reading can indicate the specifi c material
of construction, but it cannot determine the host of other
material specifi cations, post-treatment and testing a typical
valve part requires
FIG. 3. The OEM part (left) is fabricated to a design dimension and
falls within an allowable tolerance band. The non-OEM part (right)
is based on a single dimension taken from a used part. The resulting
dimensions will often fall outside the allowable OEM tolerance band.
Source: Emerson.
10 JULY 2022 | HydrocarbonProcessing.com
Replication vs. OEM design: Materials
ASTM A494 Fisher ASTM A494
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Raw material control
Chemistry control
Heat qualifi cation bend test
Liquid penetrant (LP) examination
Heat treat temperature control
Heat treat time control
Quench method control
PWHT major repairs
Weld fi ller control
Interpass temperature control
LP examination weld repairs
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