Documentary review begins before vessel arrival. The supplier’s certificate of analysis is compared against the import purchase specification, the safety data sheet, the bill of lading, and the tank inspection report. The certificate must list test results for orthoxylene purity by gas chromatography, distillation range, color, water content, sulfur content, chloride content, and density. A certificate issued more than 60 days before loading is rejected unless the supplier provides a documentary extension under the contract’s product-release clause. The inspector verifies that the cargo quantity on the bill of lading matches the shore tank ullage report and that the product description corresponds to the correct CAS registry number 95-47-6 and UN number 1307 for xylenes, because misdeclared mixed xylene would alter flash point and density acceptance limits. The customs tariff classification and the REACH registration number for orthoxylene are checked against the European import notification. Any discrepancy between the standard designation on the certificate and the contract, particularly if ASTM D5471 is referenced but the purchase specification requires additional parameter limits, is documented and referred to the responsible receiving chemist before discharge authorization is granted.

Upon vessel berthing, the ship’s cargo tanks are inspected for evidence of water intrusion, floating roof seal condition, and previous cargo residues. The receiving surveyor requests the tank cleaning certificate and the previous three cargo declarations. A ship tank that previously carried pygas, cracked naphtha, or high-sulfur diesel is not accepted unless the tank has been gas-freed, washed, and dried and the wash water has been tested for the absence of aromatic-insoluble films. Orthoxylene dissolves hydrocarbon residues and can carry them into the shore tank, creating color bodies and fouling downstream phthalic anhydride catalyst beds. The tank is measured for free water using water paste and an ullage tape; any free water is drained before sampling. The headspace is monitored with a portable oxygen analyzer and combustible-gas indicator. Nitrogen blanketing is verified with the cargo tank pressure valve set between 3 kPa and 7 kPa gauge, and the oxygen level is maintained below 5 vol% during the entire discharge. Published data for the limiting oxygen concentration of orthoxylene vapor mixtures under marine tank conditions is limited; therefore the receiving procedure conservatively requires a maximum oxygen reading of 5 vol% before cargo transfer is authorized.

What Closed-Loop Sampling Protocol Applies to Orthoxylene Cargoes During Rainy Discharge Conditions?

Sampling during rain requires a closed-loop sampler attached to the tank’s sample point through a ball valve and stainless steel line. The sampler is purged with nitrogen at 3 L/min for 2 min before the sample bottle is opened, and the sample bottle is a 1 L borosilicate glass container with a polytetrafluoroethylene-lined screw cap. The procedure follows ASTM D3437 for sampling and handling liquid cyclic products and ASTM D4057 for manual sampling of petroleum and petroleum products. Sample ports located on the tank roof are avoided during precipitation because water ingress at the port gasket can contaminate the sample; the preferred sampling point is the tank sidewall equipped with a thief hatch or the vessel manifold with a flow-through sampling collar. The sample line is flushed with at least 3 times its internal volume into a closed waste container before collection. A composite sample is prepared from the upper, middle, and lower sections of the tank in a 2 L glass bottle, leaving 10 vol% headspace for thermal expansion. Samples for water determination are filled to the bottle shoulder without headspace and stored in a sealed metal transport can. The composite sample is labeled with the tank number, date, time, sampler identity, and ullage temperature; it is transported to the laboratory in a spark-resistant carrier and logged into the chain-of-custody system within 4 h. Retention samples are stored at 5 °C to 20 °C in a flammable-liquid cabinet for 90 days following final acceptance.

Shore tank readiness is confirmed before the vessel hose is connected. The shore tank is inspected through the manway for pitting, scale, and residual heel. A tank that previously held acetone, methanol, or a chlorinated solvent is rejected unless a documented cleaning procedure and purge gas analysis show less than 50 mg/kg residual solvent in the tank atmosphere. The shore tank lining must be an aromatic-resistant epoxy or zinc silicate system; unlined carbon steel is accepted only if the supplier provides a corrosion allowance calculation and the receiving location has a continuous water-draining program. All transfer lines are flushed with the incoming orthoxylene or with nitrogen until the purge stream shows less than 0.1 vol% oxygen and no detectable odor of the previous cargo. Line filters are opened and inspected for fiber, rust, and elastomer fragments. A conical strainer with a 0.5 mm perforated element is installed at the vessel manifold and a coalescer filter with a 5 µm absolute rating is installed at the shore tank inlet when the cargo is intended for fixed-bed phthalic anhydride oxidation. Differential pressure across the coalescer is logged; if the pressure drop exceeds 50 kPa at the normal transfer rate, the filter elements are replaced before transfer resumes.

Laboratory Gas Chromatography, Sulfur Speciation, and Distillation Range Acceptance

The shore receipt sample is analyzed by gas chromatography with flame ionization detection using an internal standardization procedure referenced in ASTM D5471. The laboratory method uses a 60 m × 0.32 mm fused silica capillary column with a polyethylene glycol stationary phase, a split ratio of 100:1, and an injection volume of 0.2 µL. A typical oven programme begins at 60 °C with a 2 min hold, ramps at 10 °C/min to 200 °C, and holds until all C9 aromatics elute. The flame ionization detector is maintained at 250 °C with hydrogen and air flows of 40 mL/min and 400 mL/min respectively. Orthoxylene elutes after meta-xylene and para-xylene separation; the critical separation is between orthoxylene and the para-isomer, requiring a resolution of at least 1.5 from the baseline. The chromatographic integration report lists benzene, toluene, ethylbenzene, para-xylene, meta-xylene, cumene, and nonaromatic hydrocarbons as individual peaks. Total orthoxylene purity is calculated by area normalization after subtracting the solvent blank and after applying relative response factors for C6 through C9 aromatics. Manual area normalization without response factors is not permitted for acceptance purposes. The method is verified using a certified orthoxylene reference material with purity 99.5 %; the measured purity must agree within 0.2 % absolute before sample data are reported. A minimum orthoxylene concentration of 95.0 wt% is commonly specified for general phthalic anhydride service; a minimum of 98.0 wt% is applied when the receiving oxidation reactor has a narrow hot-spot tolerance and uses a temperature-sensitive fixed-bed catalyst packing. Quantification of trace sulfur is carried out by ultraviolet fluorescence per ASTM D7183; the sample is injected directly without dilution, and the calibration curve is verified with sulfur standards at 0.5 mg/kg, 2.0 mg/kg, and 10.0 mg/kg. Total chloride is determined by microcoulometry per ASTM D5808 after combustion conversion of organic halides to titratable chloride. Distillation range is measured per ASTM D850 using a 200 mL boiling flask and a certified partial-immersion thermometer; results are corrected to 101.3 kPa. An initial boiling point below 143.0 °C or a dry point above 145.5 °C indicates contamination with lighter or heavier aromatic streams and requires retention of the cargo pending further investigation. The laboratory performing the acceptance tests operates under ISO/IEC 17025 accreditation for the specific methods; unaccredited laboratory data are not accepted for custody transfer.

Physical property testing in the receiving laboratory includes density, water content, chloride, sulfur, color, and flash point when the cargo is intended for safety-critical handling. Density is measured at 15 °C by a digital density meter whose cell temperature is controlled to ±0.02 °C; the instrument is validated daily with certified density reference standards at 0.800 g/cm³ and 0.900 g/cm³. The measured orthoxylene density is compared with the certificate of analysis value after conversion to the same temperature using the appropriate density correction factor; a difference greater than 0.001 g/cm³ is investigated for contamination with mixed xylenes, ethylbenzene, or nonaromatics. Water content by Karl Fischer titration per ASTM D1364 must be interpreted with caution because orthoxylene dissolves only about 0.02 wt% water at 25 °C; a value above 100 mg/kg usually indicates free water dispersed in the sample or an incompletely sealed sample container. Chloride contamination at levels above 1 mg/kg is a serious issue for downstream catalytic oxidation units because chloride species can poison vanadium pentoxide and titanium dioxide catalysts and accelerate acid corrosion in boiler feedwater systems. Sulfur values above 5 mg/kg can poison noble-metal sensors in the terminal’s vapor recovery system and may require segregation of the shore tank. Color is assessed by comparing the clear liquid against platinum-cobalt standards per ASTM D1209; an increase in color after storage suggests oxidative polymerization at the tank vapor interface, and the sample should be retested for peroxide content using a qualitative peroxide test strip before further handling.

When Off-Spec Water or Chloride Results Appear After Transit

If the shore receipt sample fails the water or chloride specification, the receiving laboratory immediately quarantines the entire tank and initiates a three-stage investigation. First, the sample integrity is checked against the retained sample and the vessel composite sample; if a sample container seal is compromised, the result is invalidated and the cargo is resampled from the tank’s lower and upper levels. Second, the shore tank heel is analyzed to determine whether the contaminant was already present before the incoming cargo; a heel chloride concentration above 2 mg/kg indicates that the shore tank, not the vessel, is the source. Third, the vessel’s pump and line configuration is reviewed to identify possible co-mingling with a previous cargo. Water contamination can often be removed by settling for 24 h to 48 h followed by bottom water withdrawal through the tank’s water draw-off connection, but the procedure is not accepted without re-analysis from the upper, middle, and lower levels. If the water content remains above 100 mg/kg, the cargo may require circulation through a drying bed charged with molecular sieves of 3A type; the drying bed must be purged with nitrogen before and after the operation to avoid creating a flammable vapor-air mixture. Chloride contamination is not removable by simple settling and typically requires source segregation. The receiving facility must obtain a new certificate of analysis or a corrective action report from the supplier before a chlorinated tank is accepted. If the chloride level is between 1 mg/kg and 5 mg/kg, the cargo may be transferred to a holding tank for slow blending with a low-chloride orthoxylene lot only if the receiving process permits blending and a stability test shows no phase separation or color shift. If the chloride level exceeds 5 mg/kg, the cargo is not blended and is returned or directed to a buyer whose process can tolerate chloride, with all decisions recorded in the non-conformance report.

Discharge transfer operations are controlled to avoid static charge generation and vapor release. Orthoxylene has a closed-cup flash point of approximately 32 °C when tested by ASTM D56; a transfer temperature above 25 °C reduces the margin against flash formation, so cargo heating is not applied unless the ship or shore tank requires flow assurance and then only to a maximum of 35 °C. The lower flammability limit is approximately 0.9 vol% and the upper flammability limit approximately 6.7 vol%; transfer areas are monitored with hydrocarbon detectors set to alarm at 10 % of the lower flammability limit. The autoignition temperature of orthoxylene is approximately 463 °C; this value is used in hazardous area classification documentation but does not reduce the need for continuous monitoring. Before starting the transfer, all metal equipment is bonded and grounded, and the piping is tested for continuity with a resistance limit of 10 Ω between flanges. The initial linear flow velocity is limited to 1 m/s until the shore tank inlet is submerged to at least 0.6 m below the liquid surface; after submersion, the velocity may be increased to 3 m/s for standard 150 mm transfer lines. Flow through the coalescer filter increases static charge density, so a relaxation chamber or a length of bare metal pipe equivalent to 30 s of residence time is provided downstream of the filter, consistent with NFPA 77 practice. The transfer pump is stopped if the shore tank pressure exceeds the vacuum/pressure vent setting or if any visible leak is observed at the hose flange. Air emissions are routed to a closed flare or a carbon adsorption bed; open vents are not permitted when the ambient temperature is above 20 °C. The receiving inspector logs line pressure, flow rate, tank level, and ambient temperature every 30 min; any deviation greater than 10 % from the planned transfer rate triggers a line inspection.

Temperature-corrected net volume, not gross observed volume, governs custody transfer.

Custody transfer uses the ship’s calibrated tank tables and the shore tank’s certified capacity table. The observed volume is read to the nearest 2 mm from the ullage tape at each tank opening, and temperatures are measured at three levels with a portable electronic thermometer calibrated to ±0.1 °C. The volume correction factor is calculated from the density at 15 °C and the observed temperature using the appropriate volume correction table for xylenes; for orthoxylene with a density of 0.884 g/cm³ at 15 °C, a temperature decrease from 30 °C to 15 °C typically reduces the observed volume by between 1 % and 1.5 %. The ship and shore quantities are compared after correction to 15 °C; a difference greater than 0.3 % of the ship’s corrected volume is investigated for line fill, heel change, or measurement error. If the shore tank contains a heel, the heel density and water content are measured before transfer and again after transfer to allow a mass balance. The final accepted quantity is based on the shore tank’s calibrated table only after the tank has been allowed to settle for at least 1 h following transfer. The imported quantity is recorded in air-equivalent mass terms using the conversion factor for orthoxylene; the factor is derived from the observed density and the standard air density of 1.2 kg/m³. Any dispute is handled under the contract’s quantity clause, and the retention sample remains sealed until the fiscal quantity is accepted.

After the transfer is complete, the shore tank is sealed and a post-discharge sample is drawn from the upper level for confirmatory testing. The ship’s lines are blown with nitrogen at 50 kPa gauge to recover liquid heel, and the hose is disconnected only after the pressure is reduced to atmospheric and the flange is blinded. The used sample bottles, filter elements, and waste purge solvent are collected as flammable hazardous waste under the site’s waste permit. The retention sample is stored in a locked flammable cabinet at 5 °C to 20 °C for 90 days or as required by the purchase contract. The inspection report is assembled with the certificate of analysis, vessel ullage report, shore tank report, laboratory test results, filter pressure logs, and any non-conformance records. If the cargo is accepted, the report is forwarded to the terminal’s quality manager and the customs broker. If the cargo is rejected, the retention sample remains sealed for independent analysis under a mutually agreed referee laboratory, and the receiving facility is not required to discharge the cargo further until the referee result is received.