API MPMS Chapter 12, Section 1, Part 1 - Calculation of Static Petroleum Quantities Application From The Independent Inspector’s Perspective

Introduction:
The purpose of this technical bulletin is to provide information and commentary to IFIA Member Companies
and their clients.
In August, 1996 the American Petroleum Institute published Chapter 12,
Section 1, Part 1 of its Manual of
Petroleum Measurement Standards.
This document is titled, “Calculation
of Static Petroleum Quantities - Upright Cylindrical Tanks and Marine
Vessels”. While static calculations
have been sited in other prior API
MPMS documents, this is the first
time that they have been compiled
into one stand-alone document.
It might be assumed that as there has
been little significant change in static
petroleum measurement for many
years, this document would not have
much impact on the industry in general. However, this is not the case.
By the introduction of a new correction for the effect of temperature on
the steel shell of a tank [CTSh], this
standard has introduced a significant
change in how shore tank quantities
are calculated. While not the only
change required by this new standard,
it is the only one that involves a significant departure from previous
methods of calculation.
The New Correction
Upright cylindrical tanks have capacity tables based upon a specific tank
shell temperature. In the U.S.A. this
is usually 60°F. If the actual tank shell
temperature differs from the capacity table tank shell temperature, the
volumes extracted from that table will
need to be corrected, accordingly.
There are three items to be considered in making this correction; calculate the temperature of the tank
shell, determine the correction and
apply the correction.
Note: The new correction is only
applicable to upright cylindrical tanks. It does not apply to spherical, horizontal
cylindrical, square or rectangular tanks.
Calculate the Temperature of
the Tank Shell:
On a non-insulated tank this is done
by adding 7/8 [0.875] of the product
temperature to 1/8 [0.125] of the ambient air temperature.
For example, what is the tank shell
temperature if the temperature of the
product in the tank is 135°F and the
ambient air temperature is 88°F?
135 x 0.875 = 118.13
88 x 0.125 = 11.00
Tk Shell Temp = 129.13
Rounding to the nearest degree, the
tank shell temperature is recorded as
129°F.
The new standard does not provide
any instruction or advice on how or
where to take the ambient air temperature. IFIA Member Companies
recommend if the terminal has a
weather station, it should be used. Alternatively, leave a cup-case thermometer in a shady area for at least
fifteen minutes or use a portable electronic thermometer that has stabilized
to the surrounding air. Ambient air
temperatures should not be taken in
direct sunlight or enclosed areas.
On insulated tanks, the temperature
of the tank shell is considered to be
the same temperature as the product
in the tank.
Determine the Correction:
For mild steel tanks that were calculated using a tank shell temperature
of 60°F, this can be easily achieved
by entering the table in Appendix
“B1” of the new standard with the
temperature of the tank shell. The
factor can be read directly from the
table. In our example, the correction
for a tank shell temperature of 129°F
is 1.00086.
The “Appendix B” table of correction factors will apply in most situations; however, tanks that contain
heated products often have capacity
tables that were calculated using a
tank shell temperature other than
60°F. Alternately, tanks containing
specialty products such as corrosive
chemicals may be constructed from
something other than mild steel, such
as stainless steel. In this case it will
be necessary to use the formula found
in section 9.1.3 of the new standard,to calculate the correction factor. This
formula is:
CTSh = 1 + 2α∆T + α
2
∆T2
Where:
α = Linear coefficient of expansion
of the tank shell material [see
note 4]
∆T = Tank Shell Temperature (TSh)
minus Base Temperature (T
B
(
The Base Temperature (T
B
) is the
tank shell temperature for which the
capacity table volumes were calculated to. In the US, this is usually
60°F. The base temperature is usually stated on the capacity table. If
this is not the case, contact the company that generated the table. Some
capacity tables make reference to an
operating product temperature; this
should not be confused with the base
temperature, which is a tank shell
temperature. If the tank capacity
tables only reference a product operating temperature, it will be necessary to obtain the actual base tank
shell temperature that was used to
compute the capacity table volumes.
If the tank is insulated, it can be assumed that the base tank shell temperature is the same as the product
operating temperature. If the tank is
not insulated, the user should contact
the company that generated the capacity table to determine what base
tank shell temperature was used.
Some capacity tables state both the
operating product temperature and
the ambient air temperature. In this
case it is possible to calculate the tank
shell temperature; however, caution
must be exercised. Prior to the publication of API MPMS Chapter 2.2A,
in February 1995, the 7/8ths product
and 1/8th ambient temperature rule
for calculating tank shell temperatures did not apply. In earlier documents, tank shell temperature was
calculated by averaging (50/50) the
product temperature and the ambient
air temperature. If this sounds confusing, it is because it is confusing;
and, for this reason we recommend
contacting the company that produced the capacity table, just to be
on the safe side.
When calculating ∆T it is important
to maintain the arithmetic sign as this
value can be positive or negative and
must be applied as such in the CTSh
formula. Table B2 in Appendix B
lists linear expansion coefficients of
various metals.
How to apply the factor
The correction must be applied to the
table volume after it has been corrected for free
water; and, before any correction is made
for the floating
roof, if applicable. The
floating roof
correction is a
function of the
weight of the
roof and the
observed density [API Gravity] of the liquid it floats in;
therefore, it is
essential that
the CTSh is applied before
the floating
roof correction. This gives
the gross observed volume
[GOV] which
is corrected to
gross standard
volume [GSV] in the usual manner,
by applying the VCF.
TABLE VOLUME
GROSS
OBSERVED
VOLUME
GROSS
STANDARD
VOLUME
Volume Correct ion
Factor
[Multiply]
Minus Free
Water
Multiply by CTSh
Plus or Minus
Floating Roof Adjustment
History
As previously mentioned, API
MPMS Chapter 12, Section 1, Part 1
was published in August 1996 and
became effective when it was published. The introduction of the new
correction factor caused both confusion and consternation within the industry and its implementation by oil
companies and terminals has been
extremely varied. Some facilities
implemented it as soon as they could
reprogram their computers while others have yet to implement it.
The position of IFIA Member Companies to this new API standard was
the same as that of any API standard,
which is to implement it fully, unless
another procedure is agreed to by all
parties. It must be borne in mind,
however, that the U.S. Customs may
be one of those parties. When conducting an inspection that falls under the jurisdiction of the U.S. Customs [this includes all imports and
both foreign and domestic merchandise entering and exiting foreign trade
zones, bonded warehouses and
bonded tank farms] independent inspection companies are required to
carry out their inspection activities
according to the latest API standards,
as specified in 19CFR151.13(g)(2).
According to “Houston Service Port
Trade Bulletin 97-15” issued by the
U.S. Customs Service on April 8th,
1997, the Customs will begin man dating the requirements of API
MPMS Chapter 12.1.1 on June 1st,
1997.
No sooner had the industry gotten
used to the idea of a new calculation
standard, than it was discovered that
there were a number of errors in it.
Most of these were typographical in
nature or situations where a formula
had been modified but the associated
IFIA NAC - Technical Bulletin 97-1Page 3
text had not. However, the equation
that was used to calculate the tank
shell correction was taken from API
MPMS Chapter 2.2A and this was
subsequently found to be incorrect.
This also impacted most of the data
in “Appendix B” including Table B1.
On April 24th, 1997 an errata to API
MPMS Chapter 12.1.1 was issued.
Any references made herein to the
standard include any changes incorporated in the errata.
When working cargoes that are not
subject to Customs jurisdiction, the
application of this standard is a commercial issue and may be used or not,
subject to the agreement of the parties concerned.
Other Requirements
There are additional changes that this
standard imposes, which while not as
significant as the tank shell temperature correction, are nevertheless important.
One of the aims of API MPMS Chapter 12.1.1 was to produce a strict performance standard whereby different
individuals with the same base data
would arrive at exactly the same
number. While coming most of the
way to achieving this aim, it falls a
little short in the area of Volume Correction Factors [VCF], also referred
to as the Correction for the Temperature of the Liquid [CTL].
Table 1of API MPMS Chapter
12.1.1, which details the number of
significant digits (i.e. decimal places)
to use with various measurement
units, shows four decimal places for
the volume correction factor or CTL.
There is also a notation attached
which states that the standard for producing volume correction factors is
the computer subroutine implemenIFIA NAC - Technical Bulletin 97-1
tation procedures of API MPMS
Chapter 11.1, Volume X; which,
when fully implemented generates a
factor of five significant places. The
use of the printed table is acknowledged as a matter of practical necessity but the notation goes on to staate
that this only produces volume correction factors with four decimal
places, in addition to limiting table
entry discrimination levels. It further
states that in the event of a dispute,
the computer generated volume correction factor should take preference.
The procedure for calculating Net
Standard Volume [NSV] from Gross
Standard Volume [GSV] requires the
sediment and water percentage
[S&W] to be converted into a correction factor which is applied to the
GSV. If the volumetric value of the
S&W is required, the NSV is subtracted from the GSV.
There are many other requirements
of API MPMS Chapter 12.1.1 which
are not referenced in this technical
bulletin and it is in no way intended
for this to be a substitute for the standard. The Manual of Petroleum Measurement Standards, of which Chapter 12.1.1 is a part, is published by
the American Petroleum Institute,
1220 L Street Northwest, Washington D.C. 20005-4070. Copies of the
standard are available from API Publications and Distribution (202) 682-
8000, Order No. H12011.

TEST OBSERVATION AT THIRD PARTY LABORATORIES (Previously “Witnessing of Analysis”)

IFIA Guidelines recommend that Member Companies carry out testing in their own laboratories. An IFIA
member company that draws samples and conducts its own laboratory analysis can be certain of the
provenance of the samples tested and can vouch for the analysis results. When engaged only to do Test
Observation, however, an inspection company:
• Cannot guarantee the origin of samples they did not participate in drawing,
• Cannot guarantee that when samples are split to allow multiple tests to be conducted on subsamples at different testing stations, such samples are tested without alteration,
• Cannot observe multiple tests being conducted at multiple test stations at the same time,
• Cannot vouch for the accuracy, calibration and maintenance of testing equipment that it does not
own and operate, and
• May not, at every location, ordinarily engage an observer with qualifications sufficient to judge
whether the laboratory techniques employed for specific tests are appropriate and properly
executed.
Where Members are contracted to observe tests carried out by designated third party laboratories this is
on the basis that the Member bears no responsibility for the accuracy of the results but simply that a
suitable representative (an inspector or laboratory technician) will attend during the testing and ascertain
by observation that in his/her opinion the tests were carried out on the correct sample.
Recent discussions have been held with client organisations in order to reinforce the above position,
particularly with regard to responsibility. The position has not changed but the following outline scope of
work has been suggested to form the basis of a service that will provide some additional value for the
client while at the same time avoiding unreasonable responsibilities for the Member.
• Check the test slate.
•
•
•
Enquire whether the designated laboratory can perform the required tests. If not, advise the client,
possibly suggesting that some tests are performed at the Member’s laboratory.

Prepare a Check List for the agreed test slate.
This should be a simple sheet listing the tests to be carried out with results to be noted for each
test.
If agreed, draw samples, deliver to the laboratory and observe compositing
Where samples are from an auto-sampler available performance data should be noted in
accordance with normal procedures. Where samples are ‘supplied’ this should be clearly noted.
Confirm that the correct sample is used for each test.
Alternatively state that this cannot be confirmed, eg not present, missing seal, etc.
Obtain copies of result print outs where available.

Report/record whether results are within or outside the agreed specification, if available.
Countersign the Test Report issued by the designated laboratory adding a suitable disclaimer, eg
‘Observed Only and without Responsibility for Results’. A similar disclaimer should be included on the
Check List.
Attach the Observation Report and completed Check List to the designated laboratory’s Test Report.
Results are to be issued only on the designated laboratory paperwork and NOT transcribed on to
Member Company letterhead. The Member Company should never represent as its own, results from
tests conducted by others or tests carried out on samples of unknown or uncertain provenance.
This bulletin is for information and guidance and addresses the limitations upon the process of Test
Observation and the risks inherent in relying upon it. IFIA strongly recommends that attention is given to
comments regarding responsibility for analyses and disclaimers and, particularly recommends that third
party results, whether observed or not, should be reported only on the document prepared by the
designated laboratory and must NOT be transcribed.
Parties to Letter of Credit transactions where an independent Certificate of Analysis is required ordinarily
should not expect to receive such a certificate based solely upon Test Observation. Attention is drawn to
the IFIA Technical Bulletin relating to Letters of Credit, TB 06-02.
If an IFIA Member is contracted to observe testing in a third-party (e.g. terminal) laboratory, which is operated
by that same IFIA Member, the IFIA Member Company will advise the Principal immediately of the situation.
Note: 'Test Report' in this bulletin refers to any document issued by a third party laboratory containing test results. Such documents may also be referred to as Laboratory Reports, Certificates of Quality, Certificates of Analysis etc., depending on the location.