Project Background
This offshore platform undertakes crude oil separation and processing, generating approximately 1,200 cubic meters of oily produced water per day. In accordance with environmental protection and formation preservation requirements, this water must be treated through oil removal and filtration before being reinjected into the formation to maintain reservoir pressure. The original single-bag filter, made of 304 stainless steel, suffered pitting corrosion in the associated gas environment with high chloride content. Additionally, its design pressure of only 6 bar could not match the discharge pressure of the newly replaced injection pump, leading to frequent flange face leaks that seriously compromised platform operational safety.
Equipment Selection Basis
The platform operator places extremely high demands on safety and weather resistance. After load calculations and material justification, the JYMF-12P-316L multi‑bag filter was ultimately selected, with a single unit capable of meeting the peak instantaneous processing flow of 55–60 m³/h during high‑load periods. The key selection considerations are as follows:
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All‑316L construction and grit‑blasting finish: In the platform’s high‑salt, high‑humidity environment, 316L stainless steel effectively resists seawater splash and stress corrosion from H₂S and chlorides in associated gas. The external surface is grit‑blasted instead of conventional pickling and passivation, forming a more stable passive film in the marine atmosphere while also reducing glare from sunlight reflection on the deck, in compliance with the platform’s visual safety management regulations.
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Bottom inlet/outlet and high‑pressure sealing: The bottom‑in‑bottom‑out configuration (10‑inch, Class 150, ASME B 16.5 flanges) facilitates automatic backflow of oily water in the filter chamber to the upstream buffer tank during shutdown, thereby preventing splashing of contaminated liquid when changing filter bags. The design pressure of 10 bar perfectly matches the injection pump discharge pressure. The flange sealing faces passed an on‑site hydrostatic test (at 1.5 times the design pressure) with no pressure drop over 30 minutes.
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Offshore maintenance‑friendly design: Space on the platform is limited and lifting equipment is constrained. The hydraulic rocker arm enables easy opening and closing of the cover (which weighs several tens of kilograms) and allows it to be stopped at any angle. The detachable forklift base (carbon steel crossbeam painted with the same colour) allows the equipment to be unloaded by marine forklift upon arrival and moved to the installation foundation; the crossbeam is removed after positioning to prevent long‑term salt‑fog exposure that could become a corrosion source.
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Key interface configurations: The 2‑inch NPT drain port and vent port are each equipped with a shut‑off valve. The drain port is used regularly to discharge settled oil sludge and mechanical impurities at the bottom; the vent port is used for air release during initial system startup and after maintenance, preventing uneven pressure distribution across filter bags due to air binding. A 1/4‑inch shock‑resistant pressure gauge (dial graduated in bar) is installed at both the inlet and outlet, enabling operators to accurately read differential pressure on the moving platform.
Filter Basket Structural Optimisation
To address fine formation sand particles and corrosion products in the reinjection water, the filter basket is designed with 2 mm thickness, 10 mm diameter perforations, 6 mm spacing, and a 60° triangular staggered arrangement. This perforation design provides ample flow area while maintaining basket strength; the measured clean‑bed pressure drop is only 0.15 bar. Combined with high‑precision polypropylene filter bags (nominal rating 50 µm), it effectively traps suspended solids and protects the downstream injection well formation from clogging.
Seal Material Selection
EPDM is chosen for the sealing rings. Given the platform’s water injection temperature of 50–65°C and the presence of small amounts of alcohol‑based antifreeze in the water, EPDM demonstrates excellent performance in temperature resistance, polar solvent resistance, and compression set resistance. No hardening or tearing leakage of the O‑rings has occurred since commissioning.
Actual Operational Performance
After six months of continuous operation, a cover inspection revealed that the inner wall’s grit‑blasted surface remained as smooth as new, with no rust spots or pitting. The filter basket remained structurally intact with no deformation or collapse. The average bag replacement interval was 45 days, approximately 20% longer than comparable onshore operating conditions. The sludge regularly discharged from the drain valve had low water content, facilitating subsequent treatment of oily solid waste on the platform.
Post time: Jun-30-2026