Why Do Loading Arms Leak?
Leakage in loading arms can be attributed to multiple causes, categorized into internal defects and external influences:
1. Internal Causes from the Loading Arm Itself
Material Deficiencies:
Using substandard materials (e.g., non-corrosion-resistant steel for acidic media) leads to material degradation and perforation.
Inadequate PTFE lining thickness (below 3mm) in corrosive environments causes early wear-through.
Manufacturing Imperfections:
Low machining precision of swivel joint sealing surfaces (surface roughness >Ra1.6μm) results in sealing failure.
Improper welding (e.g., incomplete penetration) in pipelines creates leakage paths.
Operational Misuse:
Exceeding the allowable working pressure (e.g., operating at 1.5× design pressure) causes pipeline expansion and gasket failure.
Forcing the arm beyond its rotation limits (e.g., exceeding 180° lateral rotation) damages joint seals.
Inadequate Maintenance:
Neglecting seal replacement (beyond the 1-year service life) leads to aging PTFE seals losing elasticity.
Failure to calibrate the dry-type valve spring (force below 0.5MPa) results in incomplete sealing.
2. External Factors Contributing to Leakage
Mechanical Damage:
Collision from tank trucks (impact force >500N) deforms the outer arm, cracking welded joints.
Improper lifting (using crane hooks without protective padding) scratches PTFE linings.
Environmental Corrosion:
High-temperature oxidation (above 200°C) causes stainless steel surfaces to scale, compromising seal compatibility.
Chemical corrosion from atmospheric pollutants (e.g., SO₂) accelerating gasket degradation in outdoor installations.
Climatic Influences:
Freezing of water in joints at subzero temperatures (below -20°C) expands and cracks cast iron components.
Thermal cycling (temperature fluctuations >50°C) leading to loosened flange bolts (torque loss >30%).
3. Preventive Measures Against Leakage
Material and Design Improvements:
Specify corrosion-resistant materials (e.g., 316L stainless steel for seawater environments) and verify with NACE MR0175 certification.
Increase welding inspection rates (to 100% UT/RT) for critical joints.
Operational Discipline:
Enforce pressure limits (display real-time pressure on control panels) and prohibit overloading.
Implement torque wrenches for flange connections (tightening to specified values, e.g., 40-45N·m for DN50 flanges).
Proactive Maintenance:
Conduct quarterly ultrasonic thickness measurements on pipelines (thickness loss >20% requires replacement).
Perform annual soap bubble tests on all joints (test pressure 1.1× working pressure, no bubbles within 5 minutes).
Environmental Protection:
Install impact barriers (energy absorption capacity ≥1000J) around loading arms to prevent vehicle collisions.
Apply anti-corrosion coatings (e.g., zinc-rich primer) to outdoor components, with recoating every 2 years.
Key Prevention Indicators
Material Compliance Rate: 100% (verified by material test reports).
Maintenance Completion Rate: ≥95% (monitored via CMMS systems).
Leak Detection Efficiency: ≤1 hour (using infrared gas detectors).
By addressing both internal vulnerabilities and external risks, the probability of loading arm leakage can be reduced by over 90%, ensuring safe and reliable operations.
