Asphalt tanks serve as critical storage equipment for base asphalt, modified asphalt, and other asphalt products in road construction, chemical engineering, and municipal engineering fields. During long-term use, asphalt residues (hardened asphalt deposits), weld corrosion, and anti-corrosion coating degradation can occur—these issues not only reduce the effective storage volume (residues can occupy 5%-15% of the tank volume) but also compromise structural integrity (corroded welds may lead to tank leakage, and degraded coatings accelerate metal oxidation). According to industry data, proper cleaning and maintenance can extend an asphalt tank’s service life from 8-10 years to 15-20 years, while reducing maintenance costs by 30% annually. This manual focuses on three core maintenance tasks—tank residue removal, weld inspection, and anti-corrosion coating renovation—providing detailed operational guidelines, safety requirements, and quality control standards to ensure the long-term stable operation of asphalt tanks.

1. Tank Residue Removal: Eliminate Hardened Deposits, Restore Effective Storage Volume

Asphalt residues primarily consist of hardened asphalt (resulting from long-term static storage and temperature fluctuations), aging modifiers (in modified asphalt tanks), and impurities (such as sand and gravel mixed during asphalt transportation). These residues adhere to the tank bottom, inner walls, and heating tubes, not only reducing storage capacity but also blocking heating tubes (lowering heat transfer efficiency by 20%-40%) and contaminating new asphalt. Residue removal must follow a "safe pre-treatment → targeted cleaning → post-cleaning inspection" workflow to avoid tank damage and safety hazards.

1.1 Pre-Cleaning Preparation: Ensure Safety and Operational Readiness

Before residue removal, thorough preparation is required to address risks such as toxic gas accumulation, confined space operations, and asphalt ignition:

Tank Emptying and Ventilation:

Fully drain the asphalt in the tank (use a heat-preserving pump for viscous asphalt, preheating the pump and pipeline to 120-150℃ to prevent asphalt solidification). After emptying, open all manholes (top and bottom manholes) and install axial flow fans (air volume ≥ 500m³/h) for forced ventilation, lasting at least 48 hours.

Test the concentration of toxic and harmful gases in the tank (e.g., benzene, toluene, and hydrogen sulfide) using a gas detector—ensure concentrations are below the national occupational exposure limits (benzene ≤ 1mg/m³, toluene ≤ 60mg/m³). 同时检测氧含量（需保持在 19.5%-23.5%），避免缺氧作业。

Safety Protection Configuration:

Implement confined space operation management: Assign a dedicated supervisor outside the tank, and equip operators with self-contained breathing apparatus (SCBA, working time ≥ 45 minutes), anti-high-temperature gloves (heat resistance ≥ 200℃), and anti-slip safety shoes (to prevent slipping on residual asphalt).

Install safety barriers around the tank, post warning signs ("Confined Space Operation, No Unauthorized Entry"), and prepare emergency rescue equipment (e.g., rescue ropes, stretchers) at the site.

Tool and Material Preparation:

Cleaning tools: High-temperature steam cleaners (steam pressure 0.8-1.2MPa, temperature 180-200℃), pneumatic chisels (air pressure 0.6-0.8MPa, for thick residues), and nylon scrapers (avoiding metal scrapers that scratch the tank’s inner anti-corrosion coating).

Auxiliary materials: Asphalt softeners (e.g., diesel-oil mixture in a 1:3 ratio, for softening hardened residues), absorbent pads (for collecting liquid residues), and waste residue containers (sealed to prevent asphalt volatilization).

1.2 Residue Removal Methods: Classified Treatment Based on Residue Thickness and Location

Residue removal methods vary by residue thickness (thin:<5mm; medium:="" thick:="">15mm) and location (tank bottom, inner walls, heating tubes). The goal is to completely remove residues without damaging the tank structure or inner coating.

（1）Tank Bottom and Inner Wall Residue Removal

Thin Residues (<5mm): High-Temperature Steam Cleaning

Operate the high-temperature steam cleaner (nozzle distance from the residue surface 15-20cm) to spray steam evenly on the inner wall and bottom. The high-temperature steam softens the asphalt residue (asphalt softening point is typically 45-100℃), allowing it to flow into the tank bottom’s drainage outlet.

After cleaning, use absorbent pads to wipe the inner surface, ensuring no residual asphalt film remains (check with a white cloth—no asphalt stains on the cloth indicate thorough cleaning).

Advantages: No mechanical damage to the tank, suitable for tanks with intact anti-corrosion coatings.

Medium Residues (5-15mm): Steam Softening + Pneumatic Chiseling

First, spray the residue with high-temperature steam for 30-60 minutes (depending on thickness) to soften it, then use a pneumatic chisel (equipped with a flat chisel head) to remove residues. The chisel angle should be 30-45° to the tank surface to avoid direct impact on the metal plate or coating.

For residues in corner areas (e.g., tank bottom and wall joints), use a small-diameter pneumatic chisel (head diameter ≤ 10mm) to prevent missing residues. After chiseling, clean the surface with steam to remove loose particles.

Thick Residues (>15mm): Mechanical Crushing + Steam Cleaning

For extremely thick residues (e.g., hardened asphalt layers at the tank bottom), use a small hydraulic crusher (weight ≤ 50kg, to avoid damaging the tank bottom) to crush the residue into small pieces (<10cm), then remove the crushed residues manually (using shovels and buckets).

After crushing, spray the remaining fine residues with high-temperature steam, and clean them thoroughly with absorbent pads. For residues adhering to welds, use a nylon brush to scrub gently (avoiding weld scratches).

（2）Heating Tube Residue Removal

Heating tubes (common in asphalt tanks for maintaining asphalt fluidity) are prone to residue blockage, which reduces heat transfer efficiency. Residue removal requires targeted operations based on tube type (straight tubes or coil tubes):

Straight Heating Tubes: Use a Flexible Steam Lance

Insert a flexible steam lance (diameter 15-20mm, length matching the tube length) into the heating tube, and inject high-pressure steam (1.0-1.2MPa) while moving the lance back and forth. The steam flushes out residues from the tube, which are collected through the tube’s outlet.

After cleaning, test the tube’s flow rate: Inject water into the tube at a pressure of 0.5MPa, and measure the flow rate—ensure it reaches 90% or more of the design flow rate (e.g., a 50mm diameter tube should have a flow rate ≥ 15m³/h).

Coil Heating Tubes: Use Chemical Cleaning + Steam Flushing

For coil tubes with narrow inner diameters (≤ 30mm) that are difficult to access with a lance, first inject a chemical cleaning agent (e.g., a mixture of diesel and surfactant in a 10:1 ratio) into the tubes, and let it soak for 24 hours to dissolve residues.

After soaking, flush the tubes with high-pressure steam (0.8-1.0MPa) to remove dissolved residues. Repeat the process 2-3 times if necessary, and test the flow rate to confirm no blockages remain.

1.3 Post-Cleaning Inspection and Disposal

Residue Removal Quality Inspection:

Visually inspect the tank inner surface: Ensure no visible residues, and the metal surface (or anti-corrosion coating) is exposed. For key areas (e.g., tank bottom drainage outlets, heating tube inlets), use a borescope (for hard-to-reach areas) to check for hidden residues.

Measure the effective storage volume: Fill the tank with water to 80% of the design volume, and record the water level—compare it with the volume before cleaning to confirm that residues have been completely removed (the volume should increase by 5%-15%, consistent with the estimated residue volume).

Waste Residue Disposal:

Collect all asphalt residues in sealed steel drums (labeled "Waste Asphalt Residues, Non-Hazardous Waste"), and transport them to a qualified waste treatment facility for recycling (e.g., mixing with new asphalt for low-grade road base construction) or harmless disposal. Do not discard residues arbitrarily to avoid environmental pollution.

2. Weld Inspection: Detect Defects Early, Prevent Structural Leakage

Welds are the weakest parts of asphalt tanks—they connect the tank body, manholes, inlet/outlet pipes, and other components, and are prone to defects such as cracks, pores, and incomplete fusion due to thermal stress (from asphalt heating/cooling cycles), corrosion (from asphalt and moisture), and mechanical vibration. Weld inspection must be conducted systematically to identify hidden defects and repair them promptly, preventing tank leakage (which can cause asphalt loss and environmental contamination) and structural failure.

2.1 Inspection Scope and Frequency

Inspection Scope: Cover all welds in the asphalt tank, with a focus on high-stress and high-corrosion areas:

Tank body welds: Vertical welds (connecting tank wall plates), horizontal welds (connecting adjacent tank wall rings), and bottom welds (connecting the tank bottom and wall).

Component welds: Welds for manholes, inlet/outlet pipes, heating tubes, and liquid level gauge nozzles (these areas are prone to stress concentration).

Seam welds: Welds for anti-corrosion coating joints (if the tank has an inner coating, check for coating peeling at welds).

Inspection Frequency:

Routine inspection: Conduct visual inspection every 6 months (during regular maintenance) to check for obvious defects (e.g., weld rust, cracks, or asphalt leakage).

Comprehensive inspection: Conduct non-destructive testing (NDT) every 3 years (for carbon steel tanks) or 5 years (for stainless steel tanks) to detect internal defects. For tanks storing modified asphalt (which has stronger corrosiveness), shorten the comprehensive inspection interval to 2 years.