WHEN TO TAKE ADDITIONAL SAMPLES
- Manifold: if nominated shore tank has changed.
- Manifold: resuming cargo operations following a suspension.
- If there is a question of the cargo being off-spec.
The manifold sample is the most critical, representing the cargo condition as it passes from shore to ship. It must be taken immediately at the start of loading, ideally with the manifold valve closed. Without it, the vessel may be held liable if first foot samples are off spec. Sample points must be cleaned or flushed to avoid contamination. Manifold samples must be retained, and a visual check ensures the correct cargo is received.
If cargo is suspected to be off-spec, additional samples must be taken from various levels, dead bottom, lower, middle, upper as well as running samples from each affected tank. It is standard practice to suspend loading after receiving the first foot of cargo for sampling and analysis.
Even if the terminal does not require it, the vessel must take first foot samples when innages reach one foot to verify that ship lines and tanks are clean, particularly for high-spec or sensitive cargoes. Pump stack samples may also be taken on chemical tankers to confirm line cleanliness before cargo enters tanks. If samples pass, loading resumes; if not, ship’s management and a P&I representative should be contacted immediately.
Before discharge, samples must be taken from all tanks, especially for high-spec cargoes that require analysis approval before discharge. A pre-discharge manifold sample is crucial to demonstrate the cargo was on-spec when it left the vessel.
If cargo condition is contested, these samples are compared with post-loading samples to detect any onboard contamination. In contamination cases, the full sample chain, from shore tanks and lines to ship’s tanks and lines, is analysed to identify the contamination point. Drip samples, though often taken at the manifold as a form of running sample, are less reliable due to fluctuating loading rates.
VISUAL ANALYSIS
A visual analysis must be carried on all samples throughout the loading and discharge operations to ensure continued quality of the cargo.
SAMPLING METHODS
There are three main sampling methods. Namely, closed, open and restricted. To prevent the risk of spoiling the cargo it is imperative that the right method is used.
Closed sampling is the preferred method for most cargoes. There are two ways to carry out closed sampling. The first
is using a dedicated sampling/ullage point. Portable equipment is used with a vapour lock system to ensure it remains a closed system. Secondly, a fixed inline system can be used. These are common on vessels which deal with high specification or sensitive cargoes.
Closed sampling must be used for any cargo which the following applies:
- Requires inerting or - A nitrogen blanket - Toxic or very toxic cargoes - Corrosive cargoes - UV sensitive cargoes - Hygroscopic cargoes - Oxygen sensitive cargoes
Open sampling is when the cargo hatch is opened and the sampler is lowered into the tank with the cargo in sight. If open sampling is being carried out the tank opening should only be uncovered long enough to complete the sampling. This kind of sampling can be acceptable for vegetable oils.
There is a risk of combustion if open sampling is carried out on a cargo that requires inerting. Carrying out open sampling on cargoes that require a nitrogen displaces the nitrogen blanket exposing the cargo to UV light and moisture which risks turning the cargo off-spec.
THE REPORT | SEP 2025 | ISSUE 113 | 75
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