manual sampling temp measure

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Chapter 3: Manual Sampling and Manual Temperature Measurement Part 2, Volume 1

Revision 14 BP Measurement Standards18/05/98 ii Issue 1

Contents

Introductory Notes........................................................................................................................iii

3.1. Equipment.............................................................................................................................. 1

3.2. Sampling ................................................................................................................................ 5

3.3. Sampling procedures - vertical cylindrical tanks................................................................ 6

3.4. Sampling procedures - horizontal cylindrical tanks............................................................ 8

3.5. Manual temperature measurement - vertical cylindrical tanks........................................... 9

3.6. Manual temperature measurement - horizontal cylindrical tanks .................................... 10

3.7. Recording of results and labelling of samples.................................................................. 11


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Part 2, Volume 1 Chapter 3: Manual Sampling and Manual Temperature Measurement

BP Measurement Standards Revision 14Issue 1 iii 18/05/98

Introductory notesThis chapter recommends procedures for manual sampling and temperature measurement ofstatic bulk products in vertical and horizontal cylindrical tanks.

Bulk product measurement is not simple and poor sampling procedures will contribute to theoverall error. It is therefore important that sampling procedures should follow internationallyrecognised methods.

Homogeneity of SamplesProduct storage tanks do not generally have mixers. Consequently homogeneity of productcontained in a tank, which would improve the reliability of sampling and temperaturemeasurements, can only be approached during times of turbulence created during a receipt.Sampling and temperature measurement are therefore at their most accurate immediately after areceipt and wherever possible these operations should be carried out as soon as safetyprecautions permit. However, problems may still be encountered since layering can be causedby:

the density difference between the product contained in the tank prior to receiptand the product to be received.

the quantity of oil being received into the tank in relation to the tank contents priorto receipt.

a low rate of product receipt.

Furthermore, sampling and temperature measurements will frequently have to be carried out ontanks whose contents have remained static for some time, thereby increasing the likelihood oflayering.

To minimise the effect of any layering, samples for analysis shall be taken from various levels

within the tank.The most careful work in oil measurement may be rendered useless if samples are taken withinsufficient care.

Manual Temperature MeasurementThe importance of accurately determining the temperature of a volume of oil cannot be over-emphasised. Errors introduced into quantity calculations resulting from incorrect temperaturesare generally greater than those introduced by other causes.

Approximately, each 1C error causes a volumetric error (at 15) of 0.1%.

In order to assess actual losses, it is necessary to maintain stock accounting records at standardtemperatures. Subsequent differences will then represent real (e.g. evaporation) and or apparent(measurement/calculation errors) losses.

Calibrated portable electronic temperature instruments are recommended for use in determiningproduct temperatures. However, in heated fuel oil tanks, the device, pictured inFigure 3.3, mustbe thoroughly cleaned before it is rewound onto the drum, otherwise oil may clog the equipmentand prevent re-use.

An alternative to the equipment picture inFigure 3.3 for use in heated fuel oil tanks is shown inFigure 3.4 , this equipment consists of a temperature probe attached to a cable reel, the cablebeing marked at 1 metre intervals.

Installations holding both black and white oils, may find it more practicable to hold both types ofportable temperature monitoring equipment.


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Revision 14 BP Measurement Standards18/05/98 iv Issue 1

Depths for Sampling and Temperature MeasurementThe number of samples required is governed by the depth of oil in the tank.

It is generally assumed that, if only on sample can be obtained from a volume of oil, the bestsample will be taken from the mid-point. This assumption is the basis for determining the levelsfrom which further samples should be taken. The tank is regarded as being divided into the same

number of layers as samples required. A sample is then taken from the mid-point of each layer.Normally three samples are taken from the mid-point level of the upper, middle and lower thirds ofthe tank contents. The depths corresponding to each sample are thus one sixth, one half andfive sixths (1/6, 1/2 and 5/6) of the total oil depth. These three samples are known as Upper,

Middle and Lower samples respectively (Figure 3. 1).

The average quality of the tank contents is taken to be the arithmetic average of the resultsobtained on Upper, Middle and Lower samples as shown in the following example:

Sample Density (kg/l at 15C)

Upper 0.8568

Middle 0.8570

Lower 0.8569

Arithmetic average 0.8569

The example shows the agreement that may be obtained when the tank contents arehomogeneous. By analysing each of the samples separately, possible layering can be detectedand the necessity of further sampling and/or mixing (if fitted) if time permits, can be determined.For this reason, running and all level samples shall not be taken in shore tanks for oilmeasurement purposes (see 3.3.1).

The number of samples required for smaller oil quantities and the levels at which they should betaken, are set out in3.3.1. The procedure outlined follows IP Recommendations, Sampling forQuantitative Purposes, PMM, Part VI, Section 1, Manual Methods. See also API Manual ofPetroleum Measurement Standards (MPMS) Chapter 8, Section 1 - Manual Sampling ofPetroleum and Petroleum Products.


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BP Measurement Standards Revision 14Issue 1 v 18/05/98

Figure 3. 1- Sample Layers

If layering has occurred, it is recommended that manual temperature measurements should be

determined at five depths. For vertical cylindrical tanks, it is easy to extend the theory given forthree level sampling to five level sampling and the corresponding depths are 1/10, 3/10, 5/10,7/10 and 9/10 of oil depth.

Five layer temperature determinations are only required if the product depth is greater than 3.5meters and the mid-point tank temperature differs from the mean of the other measurements by0.5C in unheated tankage and 1.0C in heated tankage.

In nearly all cases, the mean quality (e.g. temperature/density) shall be the arithmetic average ofthe measurements. The main exception is the accurate determination of temperature inhorizontal cylindrical tanks (3.6.2)

In horizontal tanks which are full or nearly full, dispute/referee measurements should be taken at

levels corresponding to 1/6, 1/2 and 5/6s of the oil depth.However, if the horizontal tanks are partially filled, dispute/referee measurements shall be takenat levels corresponding to 1/6, 1/2 and 5/6s of the total oil volume in the tank. These levels arefound by reference to the tank capacity table.

When the oil depth in horizontal tanks is less than 2m, only one sample need be taken at a levelcorresponding to half the total oil volume.

Sample ContainersThe choice of sample containers depends upon a number of considerations:

Size of sample: the container should be large enough to hold sufficient sample for adensity determination, preferably 1 litre size. There should be sufficient ullage (10 -15%) to allow for expansion and insertion of a homogeniser shaft (if applicable).

Sample integrity: sample transfer from one container to another on the tank top,should not be carried out as this may result in serious measurement errors andsignificant loss of representativity of sample transferred. Light ends may be lost duringtransfer and water may remain in the container used to take the sample. Samples fordensity determination must be sealed with a tightly fitting screw cap to prevent loss oflight ends prior to testing.

Insertion of homogeniser head (if applicable): samples for water determination byKarl Fischer and distillation must be homogenised before testing (Chapter 4). Thecontainer shall have a sufficiently wide neck to accommodate the homogeniser shaft
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Revision 14 BP Measurement Standards18/05/98 vi Issue 1

and head. The ullage space shall be sufficient to allow insertion and homogenisationwithout the sample overflowing.

The sample container should preferably be a wide necked glass bottle, with a capacity of1 litre (to allow for ullage space), which can be firmly sealed with a screw cap.

If a suitable container meeting all these requirements is not available, it may be necessaryto take two samples from each level. One litre screw cap bottles are ideal for density and16 oz bottles capped with plastic tops are suitable for water content samples. Corks shall

not be used.

Once the container has been selected, it may be necessary to construct a suitable samplecage (3.1.2).

SamplingSamples for quality shall be taken by lowering the container in the oil to the required level,opening it and allowing it to fill before raising it to the surface. The position from which thesample is taken (sample/still well) should preferably be at least 0.5 metres from the tank wall.Samples shall not be taken through pipes connected to the tank wall at various heights, since thistechnique violates the principles of sampling and may seriously affect the sample representativity.

Extreme accuracy in measuring the depth to which the sample container should be lowered is notnecessary. A simple and effective technique using a short length of knotted rope to lower thesample cage in metre steps is described in3.3.2. Operators should be encouraged to adopt thistechnique, since it is fast and certainly more accurate than guesswork. Once fitted, a gauge ropemay be left in position and used over a considerable period. When taking samples for qualitydetermination, the procedure described requires a small amount (10-15%) of oil to be pouredback into the tank immediately the sample has been taken. This allows an ullage space for oilexpansion and also permits the homogeniser shaft and head to be inserted without the sampleoverflowing.

It takes approximately 30 minutes to draw three samples and to measure the temperature at fivelevels, using a portable electronic temperature tape.


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BP Measurement Standards Revision 14Issue 1 1/11 18/05/98

3.1. EquipmentThe general reference for sampling equipment is the IP PMM, Part VI Section 1.

3.1.1 Sample Containers

The container in which the sample is taken shall be the container in which thesample is transferred to the laboratory.

The containers shall satisfy the following requirements:

Size: large enough to contain the required sample size with sufficientullage to allow for expansion. For samples requiring homogenisation(Chapter 4), the neck shall be large enough and the ullage sufficient (10-15%) to allow insertion of the homogeniser shaft and head without loss ofsample by overflowing or splashing during homogenisation.

Sealing: samples for density shall be sealed with tight fitting screw

caps vapour tight). The cap inserts shall be clean, dry and free from oilproduct contamination. If samples are for water content alone, vapour tightseals are desirable but not essential. Corks shall not be used.

Material: glass bottles are preferred but metal containers may be used.

3.1.2 Sampling Cage

The type of equipment required for lowering a sample container into a tank is wellknown in the oil industry (example shown in Figure 3. 2). If required, furtherinformation can be found in IP PMM Part VI (Section 1) or API MPMS Chapter 8.1.

For safety reasons the sampling cage shall be made of brass and the suspendingrope shall be made of natural fibres.

The sampling cage may have to be made locally to fit the container selected(3.1.1).

3.1.3 Portable Electronic Temperature Instruments

Calibrated portable electronic temperature instruments shall be used to manuallymeasure tank temperatures.

The instrument shall be earthed whilst in use.


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Revision 14 BP Measurement Standards18/05/98 2/11 Issue 1

Figure 3. 2- Sampling Cage and Bottle

3.1.3.1 Calibration

Portable electronic temperature instruments, e.g.Figure 3. 3 andFigure 3. 4shall be calibrated over their working range in a controlled temperaturebath(s) at 10C intervals, against traceable laboratory standardthermometers calibrated to an accuracy of at least 0.1C.

They shall be calibrated before use, after repair/maintenance and at leastonce every six months thereafter. Records of these calibrations should bereadily available for inspection. Temperature corrections shall be applied tomeasurements made.


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3.1.3.2 Calibration Checks (Weekly/Monthly)

If the instrument is in daily use it shall be checked weekly. If used lessfrequently, a monthly check will suffice. A check will also be carried outwhen the batteries are changed.

The checking procedure shall consist of comparing the instrument readingagainst a calibrated thermometer at two temperatures within the devicesnormal working range. These temperatures should be close to the extremesof the working range. If a controlled temperature bath(s) is unavailable, athermos flask filled initially with crushed ice/cold tap water and then filledwith warm/hot tap water is recommended.

If the instruments reading, after applying any appropriate correctionsrecorded during the six monthly calibration (3.1.3.1), is within 0.2C of theactual temperature at each check temperature, then the devices calibrationis satisfactory. However, if the instrument reading at one of the check

temperatures differs from the actual temperature by >0.2C, re calibrationbefore further use is required.

Figure 3. 3 Portable Electronic Temperature Tape


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Figure 3. 4 Portable Cable Electronic Temperature Instrument

3.1.4 Laboratory Thermometers

Only laboratory mercury-in-glass thermometers which have been calibrated within

the last year by an approved standardisation laboratory shall be used forcalibrating/ checking portable electronic temperature instruments. The followingthermometers are recommended:

IP39C for the temperature range -1C to +38C.

IP64C outside the above temperature range.

Calibration corrections shall be applied to all observed readings.


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3.2. Sampling

3.2.1 Sample Containers

Sample containers (3.1.1) shall be visually inspected to ensure that they are clean

and dry.

3.2.2 General Precautions To Be Observed

3.2.2.1. Sampling for density shall be carried out immediately after water, level andtemperature gauging.

3.2.2.2. The depth of free water should be ascertained before samplingcommences. This enables the Upper, Middle and Lower sampling levels tobe calculated correctly.

3.2.2.3. The sampling apparatus shall be dry and free from any substances that

may cause contamination.

3.2.2.4. Samples which are required from various levels in a tank or bulk containershall be drawn from the top downwards, so that each sample is obtainedbefore the liquid at that level is disturbed.

3.2.2.5. The product, once sampled, shall be protected as far as possible from theeffects of the weather.

3.2.2.6. After removal from the tank, samples shall be tested in the laboratory assoon as is practically possible.


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3.3. Sampling procedures - vertical cylindrical tanks

3.3.1 Sampling Level And Number Of Samples Required

The number of samples required is governed by the depth of oil above any freewater in the tank.

The following table shows the number of samples to be taken and applies to allproducts.

DEPTH OF OIL NUMBER OFSAMPLES

POSITION

Less than 2metres

1 Mid-Point, (M)

2 to 3.5 metres 2 & of oil

depth (U), (L)

Greater than 3.5metres

3 1/6, & 5/6s ofoil depth

Table 3. 1 - Tank Samples

Running and/or all level samples shall not be taken for oil measurement

purposes.

3.3.2 Sampling Procedure3.3.2.1. Samples shall be taken as soon as safety considerations permit.

3.3.2.2. The sample container shall be lowered in the cage unit the required depthis reached. The stopper shall then be jerked out of the container. Thecontainer shall remain at the required level for sufficient time to enable thecontainer to be completely filled. Whereupon the cage and container shallbe hauled to the top of the tank. A small quantity (10 to 15%) of thesample shall then be poured back into the tank to create ullage space inthe container. The container shall then be securely sealed immediatelyand removed from the cage.

Samples shall not be poured from one container to another.

3.3.2.3. To minimise loss of light ends when transporting volatile products to thelaboratory, the containers shall be inverted in the carrying crate.

3.3.2.4. Samples shall be labelled as recommended in 3.7.

3.3.2.5. The following procedure is recommended for lowering the sample cage tothe correct depth:

Tie a short length of rope (gauge rope) to the sampling pipe.

Tie a knot in the gauge rope so that it is one metre from the pipe when therope is held taut.


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Lower the container in its cage to the product surface and hold steady.

Place both taut ropes together and hold the sample cage rope at the exactpoint where the knot in the gauge rope has been tied.

Lower the sample cage until your hand reaches the sample pipe (cage

lowered 1 metre). Then hold steady and return hand to start position (in linewith knot on gauge rope).

Repeat the lowering procedure a metre at a time until the required depth isreached. The last fraction of a metre, if applicable, must be estimated.


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3.4. Sampling procedures - horizontal cylindrical tanksFor routine sampling, a mid-level sample can be taken to be representative of the tank contents.However, in cases of dispute or for referee measurements, samples shall be taken at levelsequivalent to 1/6, 1/2 and 5/6s (Upper, Middle and Lower) of the oil depth when the tank is full or

nearly full or 1/6, 1/2 and 5/6s of the total oil volume when the tank is partially filled. When theoil depth is less than 2 metres, only one sample need be taken at a level corresponding to half

the total oil volume.

3.4.1 Routine Samples - Fixed Tanks

3.4.1.1. Where possible3.2.2 shall be followed.

3.4.1.2. A single sample taken from the mid-point using a procedure similar to3.3.2shall be followed.

3.4.1.3. Samples shall be labelled as recommended in3.7.

3.4.2 Routine Samples - Road/Rail Wagons3.4.2.1. Single compartment wagons.

A sample, if required, shall be taken at the mid-level according to3.3.2. Atrailer shall be treated as a separate wagon.

3.4.2.2. Multi-compartment wagons.

If the wagon is carrying a single grade, a sample (if required) shall be takenat the mid-level from one compartment, according to3.3.2.

If the wagon is carrying more than a single grade, a sample (if required) of

each grade shall be taken from the mid-level of one respective compartment.The procedure laid down in3.3.2shall be followed when taking samples.

A trailer shall be treated as a separate wagon.

3.4.2.3. Samples shall be labelled according to3.7.


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3.5. Manual temperature measurement - vertical cylindricaltanks

Calibrated portable electronic temperature instruments (3.1.3) shall be used for all manual tanktemperature determinations.

When the mid-point tank temperature differs from the mean of the other two measurements(Upper and Lower) by more than 0.5C in unheated tankage and by more than 1.0C in heatedtankage, then readings shall be taken at five levels. However, even if a discrepancy of thismagnitude is not recorded, measurements at five levels are recommended. This procedureinvolves measurement at 1/10, 3/10, 1/2, 7/10 and 9/10s of oil depth, corresponding to the mid-points of each layer if the tank contents are divided into five equal layers. This is a simpleextension of the theory on three layer tank sampling given in the Introductory Notes to thisChapter and will ensure greater accuracy. When oil depths of less that 3.5 metres areencountered, temperature measurements shall be taken as detailed in Table 3.1 - TankSamples.

If severe thermal layering is encountered, it is recommended that measurements be taken

throughout the total oil depth at 1 metre intervals, commencing 0.5 metres below the productsurface and not finishing within 0.5 metres of the tank bottom.

3.5.1. The instrument shall be earthed and the probe lowered by unwinding the tape orcable until the first (closest to the surface) level required for temperaturemeasurement is reached.

3.5.2. The probe shall be moved up and down 30 cm for a time, whilst observing thetemperature reading. Record the temperature in a note book or suitable logsheet once the reading has remained stable for approximately 20 to 30 seconds.

3.5.3. The probe shall then be lowered to the next level and the process repeated until

measurements have been made at all the required oil depths.3.5.4. Ensure that any relevant calibration corrections (3.1.3.1) are applied to the

temperatures recorded by the instrument, before calculating an average tanktemperature.


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3.6. Manual temperature measurement - horizontal cylindricaltanks

3.6.1 Fixed Tanks - Routine Procedure

3.6.1.1. The number of measurements shall be that specified in3.4.3.6.1.2. The procedure shall be similar to that specified in3.5.

3.6.2 Fixed Tanks - Referee Temperature Method

The following procedure is recommended by the Institute of Petroleum and shallonly be used in cases of dispute for full or nearly full tanks.

3.6.2.1. Temperatures shall be determined at the Upper, Middle and Lower levelsspecified for horizontal tanks in3.4.

3.6.2.2. Procedures similar to those specified in3.5shall be followed.

3.6.2.3. The mean temperature shall be taken to be one tenth the sum of threetimes the Upper, four time the Middle and three times the Lower.

NB: If the dip in a horizontal cylindrical tank is less than 2 metres, onlyone temperature measurement is necessary. This should be taken at themid-point of the oil volume.

3.6.3 Road/Rail Wagons

Road/rail wagons are generally loaded via a meter. In these circumstances in-linetemperature measurements are generally accepted as being representative of theproduct transferred.

If wagons temperatures are required, a mid-level temperature will be sufficient. Incases where vehicles have multi-compartments, one measurement shall be madeat the mid-level of each and the arithmetic average calculated.


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BP Measurement Standards Revision 14I / 8/0 /98

3.7. Recording of results and labelling of samplesAll temperature readings and sample identities shall be recorded immediately the reading orsample is taken. A label shall be attached to the sample container giving the relevantinformation. The writing on the label shall be indelible and non-running. The minimuminformation shall be:

Sample Identification:

Date:

Time:

Tank Identification

Product Type:

Sample Level: (Upper, Middle or Lower)

Sampling data should also be recorded in the gaugers notebook together with temperature dataas follows:

Electronic Temperature Instruments Serial Number:Probe Observed CorrectedDepth Temperature Temperature

A

B

C

D

E

Arithmetic Corrected Average =

Dips or ullages shall be measured at the time of temperature measurement and sampling andshall be recorded in the gaugers notebook as specified in1.2. (If the tank is being sampled aswell as gauged, then the sampling shall be carried out last.)

It is imperative that the refinery/terminal retains test data of all samples taken.

manual sampling temp measure

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