Sampling Methods and Locations

• Sampling is essential for maintaining high product quality by meeting specifications set by both the plant and its customers.
• Samples are collected at various points throughout the process system.
• Materials at each stage of production have specific requirements to ensure the final product is acceptable.
• Verifying the waste products complies with environmental and governmental regulations.

Sampling Points

• Usually a smaller diameter pipe branching from the main pipe.
• Sampling locations are strategically placed to detect problems early.
• Early problem detection to prevent waste generation.
• In a typical multi-stage process, raw material is combined in a mixer, pumped to a reactor to undergo further processing.
• Sampling is done to check quality of raw materials, intermediate products, and final products.

Sampling Location

• Sampling is performed at different process units.
• Location of sampling includes feedstock, intermediates, finished goods, process streams, auxiliary systems, utilities like steam and cooling water, and environmental outputs.
• Environmental sampling includes testing outfall and scrubber gas.

Sampling container

• Containers should be washed with distilled water and dried to prevent contamination.
• Container selection depends on the sample's volume, nature (solid, liquid, gas), temperature, container material, and chemical properties (light sensitivity).
• Clear bottles are good for general oil products.
• Brown glass bottles are suited to light-sensitive products.
• Tin or Cans work well for high-density products like bitumen or oil residue.
• Sampling bombs are used for volatile, high vapor pressure liquids or gases like butane, propane, and LPG.

Sample Tags

• Sample tags ensure traceability and integrity.
• A tag should include the process plant name, sample date and time, sample identification, batch number, required tests, and any special handling requirements.

Procedure Steps for Liquid Sampling

• Inspect the container for cracks.
• Flushing the sampling line removes any dead legs.
• Note that flushed liquid is disposed of according to plant procedure
• Dead leg is previous material that remains in the sampling line.
• Rinse with process fluid before taking the sample.
• Collect approximately 80% of the sample container's volume.
• Use a pipette to transfer liquid drums liquids into the sample container.
• Label the sample and conduct a visual inspection, recollecting the sample if abnormalities exist.

Sampling Gases

• Gas bombs are used to sample gases.
• This is applicable above atmospheric pressure.
• Vacuum pumps are used to draw the gas when the sampling is at or below atmospheric pressure.
• Nitrogen is uses to push gas when sampling gases such as Hydrogen Sulfide.

Procedure Steps for Sampling Gases (Above Atmospheric Pressure)

• Gas bombs should be rinsed and dried.
• Gas bombs can also be be flushed with nitrogen gas to prevent contamination.
• Connect the sampling bomb to the sampling point.
• Open both valves to allow the container to purge.
• Open inlet valve to purge with process gas.
• Reduce the sampling point flow rate after purging.
• Close the outlet valve, then the inlet valve, then sampling point.
• Attach a sample label.

Procedure Steps for Sampling Gases (At or Below Atmospheric Pressure)

• Connect the sampling point to the sampling bomb using tubing.
• Connect the outlet valve of the sampling bomb to a vacuum pump.
• Start the vacuum pump.
• Open both valves on the sampling bomb.
• Close both valves after collecting the sample.

Sampling Tools for Liquid

• Liquid Sampling Tools are suited to taking sample at different depths in large containers.
• A liquid sampling thief, or pipette assists with this task.
• Dipping vessels designed to open at certain depth. -Vessels have marks on the cord wire to indicate correct depth.

Sampling Tools for Solid

• Solid raw materials have varying particle sizes.
• Finer solids separate from coarser solids during storage and transportation.
• A representative sample contains a mixture of different solids.
• Solid sampling tools include augers, splitters, and sampling thieves.

Auger

• Auger bore down into solid samples, obtaining a representative sample of solid materials.

Sample Splitter

• Solids flow down by gravity.
• Solids are separated into two equal portions
• One portion is re introduced into the hopper, until the required quantity is achieved.

Solid Sampling Thief

• A sampling thief is a tube within a tube.
• Handle controlled openings along the length of both tubes for sampling.
• Adjust the handle to close the opening and push the thief down into the material, then adjust the handle to align openings and collect the sample.

Number of Samples

• The number of samples impacts sample representation.
• Samples taken after an upset is not representative.
• The type of sample include spot, running, and composite samples.

Spot Sample

• Spot samples are collected at a designated level of the tank at a regular interval ie every 4 hours.
• Spot samples are collected from the top, middle and bottom of the tank.

Running sample

• Running samples are used for testing API gravity in petroleum products, which tend to phase over time.
• These use a bottle sampler with an open stopper.
• Samples are taken evenly from all levels of the tank.
• Sampling is done by slowly lowering and raising the bottle through the tank.

Composite Sample

• Equal quantities are blended into one container.
• Procedure involves weighing equal quantities of smaller samples using either a measuring cylinder for liquids.
• Weight balance for solids and mixing in a new container by swirling or rotating.

Safety Precautions for Sampling

• Technicians must understand sampling conditions to conduct activities safely.
• Assess conditions before sampling, including location, weather, sample nature, and personnel load limits.
• Escape routes must be accessible.
• Adequate lighting is needed in low-lit areas.
• Wear an air purifying or air-supplied respirator in areas with insufficient oxygen.
• Air purifying equipment is recommend at tank roof of a gas blanketed storage tank.
• Gas detector is used to check sampling areas are de pressurized.
• No sampling of volatile products during rain and thunderstorms.
• Sampling is performed in an upwind position.
• Ground all tapes, cables, or rods attached to sample containers, if using a sampling tool the causes static electricity
• Perform inspection to check for ignition source.
• Use proper Housekeeping to prevent fire hazards.
• Use suitable carrier i.e. sampling basket to carry samples.
• Secure glass containers during transportation.