Oil & Gas Innovation Summer 2020 Digital | Page 50
for example, and will be more
comparable to measurements taken by
other instruments.
In addition, the calibration gas
used by OGE is a representative
multicomponent gas essentially similar
to pipeline natural gas. As a result,
the calibration is made using gas that
behaves essentially similar to the way
pipeline gas behaves, by slowly building
up a layer of condensation. It is this
condensation behavior that makes
it possible to establish the 5mg/m3
threshold. This is opposed to a single
component calibration gas, such as
propane, which is often used to calibrate
this type of instrument. Propane has a
very different condensation behavior
that results in so much condensate
forming at once that it is not possible
to limit the condensation to 5mg/m3.
Because of this, it is not possible to
discern the beginning of condensation.
In other words, calibrating to 5mg/m3
ensures that the analyzer is set to the
level of “best” evidence for registering
the start of condensation. It is worth
noting that ONLY Vympel instruments
are sensitive enough to actually resolve
5mg/m3. Competitor devices can only discern
a film that corresponds to 40mg/m3 or more,
depending on the instrument. This lack of
sensitivity represents a level of uncertainty
that will not ensure the required degree of
measurement accuracy. For these devices, the
GERG calibration requires the incorporation
of a correction factor, adding to measurement
uncertainty. Vympel instruments are not subject
to this uncertainty!
The calibration for the water dew point
measurement channel is also not as
straightforward as one might expect. Water
vapor in a hydrocarbon matrix, such as
natural gas, does not behave in quite the same
way that it does in regular air.
In 1995, the GERG group carried out a
project for developing a mathematical
correlation between the water content and
water dew point in natural gas in order to
more accurately define the behavior of water
Dr. Markus Wolf, Head of the Gas Quality Department at OGE delivering a presentation
about calibration of dew point analyzers according to the GERG* project 1.64.
* Groupe Européen de Recherches Gazières (European Gas Research Group).
Vympel engineer using computer-based diagnostics as part of
VympelCare service for a Hygrovision BL portable dew point analyzer.
condensation in hydrocarbon gas mixtures.
GERG also realized that it was necessary to
build a comprehensive and accurate database
relating measured water content to water dew
point values for a variety of representative
natural gases. It was shown that there was a
need to improve the existing correlation values.
As a result, a more accurate, compositiondependent
correlation was developed on the
basis of GERG’s database. This research is the
basis for the current ISO standard 18453:2004
“Natural gas — Correlation between water
content and water dew point” which also
incorporates. And it is this standard that OGE
uses when calibrating the water dew point
channel for VympelCare units.
After calibration VympelCare analyzers are
returned to the Vympel facility in Düsseldorf
for a final check before being returned to
their owners. The whole procedure usually
is completed within seven to ten days, and
the analyzer that is returned to service can
be relied upon to operate well for another 12
months at least.
From the beginning VympelCare was
developed in response to three basic needs:
to provide timely prevent maintenance to
Vympel analyzers; to provide those analyzers
with the best calibration; and to make it
easy and economical for owners to take
advantage of these services. The ultimate
goal of VympelCare is to ensure that Vympel
instruments in the field provide accurate
quality control information for the entire
service life of the instrument. •
If you would like to know more about the
solutions discussed in this article please
contact:
SPA Vympel
+49 211 21077391
[email protected]