Pumps for Asphalt, Bitumen and Pitch: Technical Guide to Heated Transfer

1. Three distinct families: asphalt, bitumen and pitch

Asphalt, bitumen and pitch are often treated as synonyms in the market, but from a pumping standpoint they are three very different products. Asphalt, in the Brazilian technical sense, refers to CAP — Cimento Asfáltico de Petróleo — classified by penetration (30/45, 50/70, 85/100) per ANP specification. It is a refined, clean product with Newtonian behavior between 150 °C and 180 °C, used primarily in road paving.

Bitumen is the generic international term for any heavy hydrocarbon and includes both CAP and blown (oxidized) bitumen, which undergoes controlled oxidation that increases viscosity three to five times and slightly alters rheological behavior.

Pitch is a totally distinct product: residue from the distillation of coal tar or, to a lesser extent, wood tar. It is solid at ambient temperature, with softening point between 40 °C and 120 °C depending on grade, highly thixotropic, contains particulates and is abrasive. It is frequently confused with asphalt on the shop floor, but operationally it is far more demanding: it requires robust heating, abrasion-resistant materials, enlarged clearances and strict start-up procedures.

The practical difference between the three products directly determines selection: CAP is predictable and clean; blown bitumen requires higher torque and slightly enlarged clearances; pitch requires practically a dedicated pump.

2. Viscosity by temperature: the central problem

All asphalt pumping revolves around viscosity at operating temperature. CAP viscosity approximately follows the exponential law described in ASTM D2493, and a practical rule derived from that law is crucial: a 20 °C drop typically doubles viscosity, doubling the torque required at the pump shaft.

A motor sized to run CAP 50/70 at 165 °C (320 cSt) and actually running at 145 °C (where 50/70 viscosity exceeds 550 cSt) enters mechanical overload and trips the motor thermal — one of the most common failure modes in poorly instrumented asphalt plants.

3. Pump heating: steam jacket, thermal oil or electrical tracing

An asphalt pump without integrated heating fails sooner or later. The heat from product passing through the casing is not sufficient to keep the pump's entire metallic mass above the critical pumping temperature — especially at the mechanical seal, bearings and end covers, which lose heat to the environment more rapidly. There are three technical approaches to this requirement: saturated steam jacket, thermal oil jacket or electrical tracing.

Each has specific conditions in which it is the correct choice.

The saturated steam jacket at 6-10 bar (150-180 °C) is the classic asphalt industry standard and remains the preferred option for conventional plants with steam generation already available. Heating is uniform, response is rapid, and there are no cold spots. Thermal oil jacket replaces steam when the plant already operates a thermal fluid circuit — typical in refineries producing CAP and waterproofing factories. The advantage is more stable temperature, absence of condensate and lower auxiliary-system maintenance.

Both the FB Bombas FBE and FBEI lines offer steam or thermal oil jacket options, factory-specified. Electrical tracing is acceptable only for small pumps (DN50 or smaller) or auxiliary lines, because it cannot deliver uniform heating on the lower casing and fails repeatedly on cold starts. It should not be used on the main transfer pump.

4. Cold start: the number-one error in asphalt pumps

Every cold start is a slow-motion destructive test. Most asphalt pump failures in Brazilian plants do not arise in continuous regime but in start-up attempts without sufficient warm-up. The minimum practical temperature to start an FBE pump with CAP 50/70 is 130 °C measured at the pump casing itself — not the tank, not the line, not the steam jacket outlet.

Below this temperature, CAP 50/70 viscosity exceeds 1,500 cSt and start torque breaks keys, deforms gear teeth, damages the coupling or trips the motor breaker.

A mature start-up procedure in a well-managed asphalt plant follows four steps. First, heat the pump jacket for 45 to 60 minutes before energizing the motor, confirming via local thermocouple on the casing that temperature has reached the specified minimum. Second, confirm the discharge valve is open — starting a positive displacement pump against a closed valve is a guaranteed catastrophic failure. Third, energize the motor and run at minimum flow for two to three minutes before loading the system.

Fourth, monitor vibration and bearing temperature during the first five minutes, when most mechanical start-up problems manifest. Typical damage from a forced cold start includes key shearing, gear tooth deformation, shaft rupture, immediate seal failure from thermal misalignment and bushing leak from differential expansion.

5. Why gear pumps dominate: centrifugals do not work

There is a clear transition point in selecting between centrifugal and positive displacement pumps: above 150 cSt, a centrifugal rapidly loses efficiency; above 300 cSt, it becomes unfeasible — efficiency drops exponentially, required NPSH spikes and the pump enters dry cavitation.

CAP 85/100 at 180 °C has about 110 cSt, the lower edge of the range; CAP 50/70 at 180 °C is at 170 cSt; and all other operational asphalts are clearly above those values. This means, in practice, that all Brazilian asphalt operates within the zone where the correct technology is gear pump.

Gear pumps deliver flow proportional to rotation, independent of fluid viscosity, with typical volumetric efficiency of 85% to 95%. The FBE line (external gear) covers the vast majority of general asphalt transfer applications at 150-180 °C.

The FBEI line (internal gear) comes in when sustained viscosity exceeds roughly 1,000 cSt, or when other requirements enter the picture: the need for low pulsation to feed filters or metering nozzles, low shear to preserve polymers in modified CAP (SBS, AMP), batch accuracy in inline blending, or silent operation. Between the two, they cover 99% of applications in Brazilian asphalt plants.

6. Typical pumping points in an asphalt plant

A conventional asphalt plant for road paving has between six and ten distinct pumping points, each with a specific operational profile. The table below lists the typical points with operating temperature, expected viscosity range, and the recommended FB Bombas series.

Note that the burner feed pump (when the plant uses asphalt itself as tank heater fuel) and the polymer-modified SBS CAP lines are the points that most often justify choosing the FBEI line over the standard FBE.

7. Materials: when cast iron is enough and when stainless is actually needed

A recurring market belief is that asphalt is corrosive and requires stainless steel. This is false in the vast majority of cases. Hot CAP at 150 °C to 180 °C is chemically inert over cast iron and carbon steel — and the default choice for FBE pumps in conventional CAP transfer is cast iron casing and hardened carbon steel gears.

This configuration has field lifetimes of eight to twelve years under well-managed operation. Specifying stainless for this application is a waste of capital, costing three to five times more without measurable technical gain.

There are, however, two important exceptions where stainless is actually required. The first is asphalt emulsion (CAE) transfer — an asphalt-in-water dispersion with acidic emulsifiers, pH between 2 and 4, which effectively attacks any ferrous component. For this application, the FBEI pump casing and rotor must be AISI 316 stainless.

The second exception is polyphosphoric acid (PPA) modified CAP, a technique used in high-performance road asphalts: PPA at 180 °C is aggressive to iron, requiring 316 stainless casing and alloy steel gears. Outside these two specific applications, cast iron and carbon steel are the technically correct and economically sensible choice for asphalt, blown bitumen and pitch.

8. Myths and truths about asphalt pumping

The Brazilian asphalt sector has accumulated, over decades, a set of operational beliefs that mix technical truths with incorrect assumptions. Three of these beliefs appear repeatedly in specification conversations and deserve explicit correction.

• Myth 1: "An asphalt pump needs no maintenance, it just transfers." Truth: internal clearances grow from cyclic thermal wear, and volumetric efficiency drops approximately 20% in 18 months without inspection. A semi-annual inspection plan is the minimum to keep the pump operating within curve.
• Myth 2: "Any gear pump works for CAP." Truth: commercial hydraulic pumps have no heating jacket, internal clearances are designed for oil at 60 °C, and seals do not withstand 180 °C. Those pumps fail in weeks when wrongly applied to CAP — require a gear pump designed specifically for asphalt, with jacket, correct clearances and appropriate mechanical seal or graphite packing.
• Myth 3: "Asphalt is corrosive, it needs stainless." Truth: hot CAP is chemically inert over cast iron and carbon steel; stainless is a technical requirement only for asphalt emulsions (acidic pH) and for PPA-modified CAP. For pure CAP, stainless is a waste of capital.