Tank interior abrasive blasting: how do you get it right?

Blasting a tank interior successfully takes five conditions: confined space entry under permit, ventilation that removes dust and keeps the atmosphere safe, strong lighting suited to the area classification, dehumidified air that keeps the steel above the dew point until priming, and complete abrasive recovery. Inspection of cleanliness, profile, dust and soluble salts always comes before the lining.

A tank interior is one of the most demanding blasting jobs: access through a manway, a closed volume, dense dust and an immersion lining that tolerates no preparation defect. This guide is written for maintenance managers and project managers in Quebec and Ontario. It complements our article on preparing a mobile blasting site and our guide to industrial tank lining selection.

Why is a tank interior a confined space?

Because it has limited openings, is not designed for occupancy and its atmosphere can become hazardous: oxygen deficiency, residual vapours from the stored product, blasting dust, then solvent vapours during coating. Entry therefore follows the site confined space program.

In Quebec, the Regulation respecting occupational health and safety governs confined space work; in Ontario, it is Ontario Regulation 632/05. CSA Z1006 describes how to manage this work. In practice:

• Tank isolation. Draining, cleaning, blanking or removing piping, lockout of agitators and pumps.
• Atmosphere testing. Oxygen, flammable gases and contaminants measured before entry and continuously.
• Entry permit. List of entrants, attendant outside, means of communication.
• Rescue plan. Equipment and procedure ready before the first entry.

How do you ventilate a tank during blasting?

You ventilate by mechanical extraction: dirty air and dust are drawn to a dust collector, and fresh air, preferably dehumidified, enters through another opening. The airflow must sweep the whole volume, with no dead zone at the bottom or under the roof.

Ventilation does three jobs. It keeps a breathable atmosphere around the operators, who work under supplied-air helmets. It removes dust, which improves visibility and work quality. During coating, it keeps solvent vapours below the lower explosive limit set by the safety plan. Airflow is sized for the tank volume, openings and method; it is set in the work plan.

The position of the openings matters as much as the airflow. Extraction is usually placed low, where heavy dust and solvent vapours settle, and fresh air enters high on the opposite side. A tank with a single manway needs a ducted supply that reaches the far end, otherwise air short-circuits at the opening. Ventilation keeps running during breaks and between shifts, and the atmosphere is tested again before every re-entry.

What lighting does a tank need?

It needs strong, even lighting that lets the operator see into the profile and the inspector judge cleanliness. Fixtures and cables must suit the area classification and withstand abrasive impact.

• During blasting. Protected floodlights, aimed to limit shadows on welds and corners.
• During inspection. Additional low-angle lighting to reveal rust shadows and traces of old coating.
• During coating. Fixtures rated for solvent vapours, according to the classification set by the safety plan.

Poor lighting hides preparation defects that later become corrosion sites under the lining.

Why dehumidify during blasting?

Because blast-cleaned steel oxidizes quickly in humid air, and the surface must stay clean until the primer goes on. A dehumidifier keeps the air dry inside the enclosure, which keeps the steel temperature above the dew point with the margin set by the specification and ISO 8502-4.

Dehumidification also lets you "hold the blast": a large area is blasted over several shifts without flash rust, then given a brush-up blast before priming. Heating is added in winter to meet the minimum product temperature. Our article on dehumidification and heating for coating jobs covers equipment selection.

How is abrasive recovered from a tank?

Spent abrasive is vacuumed out through the manway with an industrial vacuum system, as work progresses and at the end of blasting. No grit may remain on the floor, in corners, on stiffeners or in nozzles, because it would be trapped under the lining.

Depending on the job, abrasive can be recycled on site, which cuts waste volume, or removed for disposal. The choice depends on the metal, the required profile and any contaminants; our guide to choosing a blasting abrasive compares the options. If the old coating contains heavy metals, the waste follows an appropriate disposal route.

What must be inspected before lining the interior?

Before any coating, you check cleanliness, profile, dust, soluble salts and ambient conditions, and record each reading. An immersion lining applied over poor preparation blisters or disbonds in service.

• Welds and edges. Preparation to NACE SP0178 or ISO 8501-3: spatter removed, sharp edges rounded, welds ground to the required grade.
• Cleanliness. Grade per the specification, often SSPC-SP 5 or SP 10 (ISO 8501-1 Sa 3 or Sa 2½). See our NACE 2 / SSPC-SP 10 surface preparation guide.
• Profile. Measured to ASTM D4417 and compared with the data sheet range; see surface profile.
• Dust. Tape test to ISO 8502-3.
• Soluble salts. Sampling to ISO 8502-6 and measurement to ISO 8502-9, with washing and re-blasting if the specification limit is exceeded.

After coating come thickness, holiday testing and adhesion, described in our article on coating inspection.

How do you plan tank blasting during a shutdown?

You plan blasting together with coating, because they form one time-bound sequence: isolation, cleaning, scaffolding, blasting, inspection, primer, further coats, cure and return to service. The duration of each step is set at the quote stage based on volume, condition and method.

Our article on tank lining shutdown planning shows how to fit this sequence. Our tank lining page presents immersion systems, and our tank and water tower painting service covers interiors and exteriors.

How do you get a quote for interior blasting?

Send the tank dimensions, the number and size of manways, the stored product, the condition of the existing lining, the target protective coatings system and the shutdown window. Our crews and qualified subcontractors then propose the right method, ventilation and equipment.

Our abrasive blasting page describes our methods. We work from LaSalle, including in Becancour and across Quebec and Ontario. Submit a request for a quote: pricing on consultation, reply within 24 business hours.

Frequently asked questions

Can a tank interior be blasted without a dehumidifier?

It is possible in dry weather if small areas are coated quickly, but the risk of flash rust and condensation is high. For an immersion lining, dehumidification is generally required.

Does all the old lining have to be removed?

For an immersion lining, full removal to the specified grade is usually the target. A local repair is only an option if the old system is well bonded and compatible.

How do you know whether soluble salts are a problem?

You measure them. Saltwater, chemical and process tanks often accumulate them. If the specification limit is exceeded, the surface is washed and blasted again before priming.

Who supplies the confined space attendant?

It depends on the site program. Some sites require their own attendant, others accept the contractor's. The split is set in the work plan.