1 General
1.1 The results of these tests will allow the master, through confirmation with the
attached checklist, to establish if the backload is acceptable for carriage on board the
vessel. Acceptance is based on the reported analytical data and the measured physical
properties, the known nature of the chemical composition and the previous cargo carried
in the vessel's tanks. A generic risk assessment should be available on board the vessel
and updated when new information and circumstances become apparent. Offshore
installation crew should be aware that in certain circumstances the master of the vessel
may require advice from the vessel's onshore technical advisers and that a response from
onshore may take time to receive.
1.2 Recognizing the relatively complex nature of the cargo, the material intended for
backloading should be subject to a series of test to provide an indicative overview of
the constituent composition and reactive properties of the material.
1.3 The tests carried out prior to backloading should reflect the conditions in the
vessels tanks, that is to say there will be no agitation and no forced ventilation
unless specifically required or requested.
1.4 If there is any doubt regarding the result of the test, the test should be repeated
and reviewed.
2 Testing prior to backloading
2.1 Flashpoint
The minimum acceptable flashpoint of 60°C (Pensky-Martens closed cup method or
equivalent) is applicable to wet bulk waste. Sampling should be set up to detect the
worst case situation, particularly where there is potential for crude oil or condensate
contamination where the oil will rise to the surface of the tank. Base oils typically
have flashpoints in the range of 70 to 100°C. If the only oil component in a bulk waste
is base oil then the flashpoint cannot be lower than that of the base oil itself. If the
flashpoint is relatively low (60 to 70°C) an explanation should be provided before the
analysis form is presented to the vessel's master. Prior to sampling, the material
should be left without agitation for at least 30 min and then surface sampled.
2.2 Lower Explosive Limit (LEL)
The LEL gas detector will confirm potential flashpoint issues. The noxious gas test is
modified to simulate the unvented vessel's tanks. The sample is placed in a closed
container with a sampling port on top and left to equilibrate for 30 min. A tube is then
connected from the port to the gas analyser and the sample is analysed. The flashpoint
and LEL results should be consistent with each other. LEL gas meters are normally set so
that the alarm goes off in the range of 10 to 20% LEL methane equivalent. Any number
above 25% would be considered high. Other gases potentially present can have a different
LEL range than methane.
2.3 Hydrogen sulphide (H2S)
2.3.1 H2S most commonly arises from the activity of sulphate reducing
bacteria (SRB). SRB will become active provided there is a "food" source and low oxygen
conditions. This would be typical of stagnant oil-contaminated fluid stored for a long
time. H2S is an extremely poisonous gas which is heavier than air. The
maximum exposure limit is 10 ppm over an 8 hour period. Offshore sensors and routine
offshore analysis methods will detect if H2S is a potential problem in
backloads. In the event of a positive test another sample should be collected to confirm
the result. If this second result is positive further work may be required to determine
the source of the H2S. The sample should be taken from below the surface of
the unagitated tank. Most oil will be in the top layer and will give a worst case oil
content.
2.3.2 As a precaution, treatment of the material may be required. The SRB organisms
thrive in a pH range of 5.5 to 8.0. The lower the pH the greater the breakout of
H2S. The backload can be treated on the installation to prevent breakout
of H2S in the vessel tanks. Biocides kill the bacteria but do not remove
dissolved H2S. H2S scavengers will remove dissolved H2S
but do not stop biological activity. Caustic soda will raise the pH and prevent
H2S gas breakout. In the event that H2S is detected, tests should be
carried out offshore to determine the best treatment prior to backloading. After
treatment a final H2S test should be carried out to confirm zero
H2S and noted on the analysis form before the hose is connected to the
vessel for backloading.
2.4 pH
The pH of seawater is typically 8.3. Oil mud is alkaline and could raise the pH
slightly. Cement contaminant is highly alkaline. In general alkaline pH (above 7)
protects from corrosion. Highly alkaline materials can be caustic and require care in
handling. Cement and sodium silicate can lead to high pH value. Low pH (less than 4) is
highly acidic and an explanation should be provided on the analysis form. Acids such as
citric acid or acidic chemicals such as hydrochloric acid can lead to low pH. It should
be noted that pH less than 9 means that H2S will already have broken out as a
gas.
2.5 Retort analysis (solids, water, oil volume %)
This should match the estimated composition (volume %) on the analysis form. It should
be noted that it may be difficult to get representative samples if the liquid tends to
separate. Some divergence is expected, for example if oil is noted as 5%, the range
could be 3 to 10%. If separation is likely a range is preferred, for example 5 to 10%.
The solids component can form a residue in the vessel tank and be a potential location
for SRB activity and H2S.
2.6 Specific gravity (SG)
The specific gravity of common water-based fluids cover the range of 1.03 (seawater),
sodium chloride (1.2), and calcium chloride (1.33). Rarely used brines such as caesium
formate can reach an SG of 2.2. Oil mud is typically 1.1 to 1.5, but can exceed 2.0.
Mixtures will have intermediate values, most tending towards 1.03 as seawater is the
major component. It should be noted that if mixtures separate the top half can have a
different density than the bottom half.
EXAMPLE OF THE ANALYSIS FORMfootnote
TO BE
COMPLETED AND PROVIDED TO OSV MASTER PRIOR TO
BACKLOADING
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Sample description
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Sample reference
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Vessel
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Date
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Offshore asset
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Producer
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Well name & number
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Waste company
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Total number of barrels
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Waste note number
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WASTE
COMPONENTS
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Component name
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Concentration
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Units
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MSDS
available
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% Volume
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% Volume
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% Volume
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% Volume
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% Volume
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% Volume
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% Volume
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% Volume
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LABORATORY ANALYSIS
RESULTS
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Test
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Method
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Units
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Results
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Range of results / Guidance
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Salinity (Chloride)
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Titration
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mg / l
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Flashpoint
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Closed cup flashpoint
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ºC
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Should be >60ºC to backload
If flashpoint is low (<70ºC) then explanation
should be provided
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Gas test (H2S)
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Gas meter
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ppm
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Should be zero Indication of bacterial
activity
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Gas test (LEL)
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%
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<25%, ideally zero. Meter alarm
typically set to 10-20% LEL. Should be consistent with flashpoint
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Gas test (Oxygen)
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%
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pH
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pH meter
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4-11 is acceptable range for OSV tank coatings.
SHOULD be 9.5-10.5 to keep any H2S in solution
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Water
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Retort
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% Volume
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Oil content
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Retort
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% Volume
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Confirm retort report agrees with appendix 10 – F,
Section 4 components and waste consignment note
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Solids
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Retort
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% Volume
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Confirm retort report agrees with appendix 10 – F,
Section 4 components and waste consignment note
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Bulk specific gravity
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SG
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<2.5 If >2.5 seek further guidance on
vessel capability
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Appearance
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Odour
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Date and time of analysis
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CONCLUSIONS
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Analysis to be
conducted by person competent to do so
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Comments (Yes / No / Details)
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This liquid has been
analysed as per GOMO appendix 10 – F and it is my opinion that it is safe
for carriage in a standard clean OSV bulk tank.
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This liquid has been
analysed as per GOMO appendix 10 – F and will be loaded into a tank with
residues / existing cargo. Compatibility has been risk assessed and found to
be safe for carriage.
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H2S
Avoidance
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Details of mandatory wet
bulk waste treatment with biocide (chemical / quantity)
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Details of wet bulk waste
treatment in order to produce pH of between 9.5 and 10.5 (chemical /
quantity)
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Has waste handling
facility been informed of volume and ETA onshore? (Yes / No)
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Does the waste handling
facility have the capability to take off the waste at the first port call?
(Yes / No)
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Name
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Signature
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Date
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Analyst
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Operations Representative
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