Friday, November 26, 2010
SAMPLING PROCEDURES CHEMICAL TANKERS -- CAPT AJIT VADAKAYIL
SAMPLING PROCEDURES -- CAPT AJIT VADAKAYIL
Sampling is done to protect against cargo claims especially when barges are involved. How many samples are taken depends on the type of cargo.
Samples will normally be drawn prior to loading and upon completion. Similarly, at the discharge port, prior to discharge. Shore tank samples are not witnessed by ship staff , and is done by an approved surveyor.
At the start of the transfer one sample to be taken at the ships manifold on shore side with the ships manifold valve SHUT in a clear glass bottle, visually checked and retained. The Chief officer or the duty officer must witness this important sample. If the sample is milky or obvious foreign matter is present , then take another sample .The valve to the tank should be opened up only if the manifold sample is acceptable.
So it is important to know the type of pump used ashore for pumping. If a screw / gear pump or reciprocating pump is used the cargo hose will rupture. Centrifugal pump will not cause any such problems.
Compressed air used for line blowing must be dry. Shore line is usually pigged. The pig must be inspected if feasible and checked to be free of moisture , odour or cargo residues.
On the sample bottle label the ships name, voyage number, date, location, type of sample (manifold, tank etc ), product name. Retention period is one year. Prior to disposal take permission from operator.
Cargo and Fuel samples are not to brought into the accommodation.
The vessel is to keep a full set of samples for owners benefit, these are to be retained on board in sealed and marked bottles for a period of 12 months after completion of dischg, after which they can be disposed in a proper manner. Reactive samples must not be placed together
Before discharge, samples are to be taken from the ship’s side of the valve with the manifold valve closed.
In some terminals, depending on the product, the vessel may be requested to load “foot samples”. Foot sample consist of a small amount of the product being loaded to a depth sufficient to enable the cargo surveyor to take a complete representative sample from the ship’s tanks. These samples will then be delivered to the laboratory ashore for quality testing regarding contamination. When loading foot samples, ensure the loading rate is suitable as regards loading only the minimum quantity requested by the surveyor. The ullage/sounding must be constantly monitored to ensure that excessive product is not loaded.
These samples will then be delivered to the laboratory ashore for quality testing wrt contamination. When loading foot samples, ensure the loading rate is suitable. Also load only the minimum quantity required by the surveyor. The ullage must be constantly monitored to ensure that excessive product is not loaded. If first foot samples are taken a log entry should be made.
If there is an alleged claim for contaminated cargo the Master must: -
Immediately call in the local representative of the vessel’s P&I club.
Notify Operator about the alleged claim and confirm that the P&I representative is attending.
Take good care of vessel’s sealed cargo samples, i.e.
before loading sample
first foot sample
before discharge sample
--and not hand them to anyone, except in agreement with the P&I representative, and only against written receipt.
Assist the P&I representative in connection with the relevant (joint) surveys and analysis.
Sign no document related to the alleged contamination other than after consultation with the P&I representative.
Loadport:Manifold foot sample with manifold valve shut
First foot inside tank if applicable
Tank samples at completion of loading.
In case the manifold composite sample is no good take the initial contents into one tank only and record it in the remarks column of SOF.
Disport:Sample of each tank.
Manifold sample at start of discharging
Sample bottle lable must have the date , name and signature of chief officer and surveyor
Sampling is a risky process. When taking samples from pipeline drain cocks ensure the line is depressurized. The person must wear proper PPE as justified after reading the MSDS sheets.
UTI samplers can be used to do closed sampling as long as the extension tube is peforated along the entire length.
On ships with nitrogen plant this UTI tube extension ( for 30 minute static dissipation time saving ) has no value and packs huge nuisance potential, IF it is only perforated at the top , and not along entire length.
a)high mp cargoes will freeze inside and will restrict sampler from going down by gravity.
b)source of contamination.
c)ullage for foaming cargoes like veh=g oils/ molasses is not representative of tank content.
d)temperature of UTI is not representative of tank content.
e)with sediment cargoes UTI ullage is not accurate.
f) first foot sample failure can occur due to no fault of ship.
g) the wedge formula used for calculating yard provided ullage tables becomes redundant –as the formula is based on tape assuming vertical position by gravity.
h)certain cargoes like latex can never be loaded , though possible to load by COF and SS resistance tables.
i) few litres of heavier water at tank bottom will be pushed up into non perforated extension pipe by lighter inmixible cargo on top –and UTI readings will indicate full tank of water while the cargo tank actually has negligible water. Wrong bill of lading figures can cause financial disaster.
j) The slop tank water interface will not be accurate on annex 1 ships, and entries in oil record book will be wrong wrt oil and water interface quantities.
Sample bottles must be properly stowed in a dedicated sample locker. Samples must never ever be brought into the CCR or accommodation living space. The sample locker racks and cell divisions must be fully resistant to the chemical cargoes intended to be stowed. If a bottle breaks inside the sample locker it must still be contained by a SS tray, and should not seep out on deck. The locker should have high and low vents for high and low VD gases. There must be 2 lockers so that incompatible bottles are stowed together. Samples must be in glass bottles and not polythene bottles.
Certain chemicals like propylene oxide and acrylic acid samples are disposed off as soon as the cargo is discharged without claims , due to their hazardous nature.
All-levels sample: A sample obtained by submerging a stoppered beaker or bottle to a point as near as possible to the draw-off level, then opening the sampler and raising it at a rate such that it is
approximately three-fourths full as it emerges from the liquid. An all-levels sample is not necessarily a
representative sample because the tank volume may not be proportional to the depth and because the operator may not be able to raise the sampler at the variable rate required for proportional filling. The rate of filling is proportional to the square root of the depth of immersion
Bottom sample: spot sample taken from the product at or close to the bottom of a tank or container.
Clearance sample: spot sample taken at a specified distance below the bottom of the tank outlet. Composite sample (weighted): sample obtained by combining a number of spot samples in defined proportions so as to obtain a sample representative of the bulk of the product
Dead bottom sample: spot sample taken from a point on the tank bottom. Note: Such samples require the use of a device with a bottom opening, commonly used for free water samples.
Drain sample: sample obtained from the water draw-off point on a storage tank.
‘first foot’ sample: sample drawn from a vessel tank early during a cargo loading, when the depth of product in the tank(s) is approximately 300 mm, (one foot).
Note: Regulations concerning the dissipation of static charge normally require the cessation of pumping and a relaxation time of thirty minutes before ‘first foot’ samples are drawn.
Lower sample: spot sample taken at a level of five-sixths of the depth of liquid below the top surface Middle sample: spot sample taken at a level of one-half of the depth of liquid below the top surface Multi-tank composite sample: a mixture of individual samples or composites of samples that have
been obtained from several tanks or ship/barge compartments containing the same grade of material
Running sample: sample obtained with an apparatus which accumulates the sample while passing in both directions through the total liquid height, excluding any free water.Note: The apparatus passes through the liquid at such a rate that it is approximately 80% full as it emerges from the liquid.
Single tank composite sample: blend prepared from the upper, middle and lower samples from a single tank
Skim sample (surface sample): spot sample taken from the surface of the liquid.
Spot sample: sample taken at a specific location in a tank or from a pipeline.
Suction level sample (outlet sample): sample taken at the lowest level from which liquid hydrocarbon is pumped from the tank.
Tap sample: A spot sample taken via a tap, typically located on the side of the shore tank.
Top sample: spot sample obtained 150 mm (6”) below the top surface of the liquid
Upper sample: spot sample taken at a level of one-sixth of the depth of liquid below the top surface
Zone sample (core sample, flow through sample): sample taken as that part of the liquid column which is contained within the whole height of the sampler when it is sealed at a single spot location within a tank.--
CAPT AJIT VADAKAYIL ( 28 YEARS IN COMMAND )