Free Practice Questions for API API-936 Exam

Phosphate-bonded plastic refractories develop their final bonding during high-temperature exposure. As described in TR 980:

“Phosphate-bonded plastics require temperatures between 500°F and 700°F (260°C and 370°C) to form a permanent ceramic bond.”

— API TR 980, Section 5.2.3​

According to API Std 936, when applying refractory via pneumatic gunning, the angle below the horizontal must be controlled to avoid rebound and poor bonding.

“For downward gunning, the maximum angle below the horizontal shall be 30°.”

— API Std 936, Section 6.6.2.1​

This restriction ensures proper adherence and consolidation of refractory materials.

Shelf life is defined as the maximum period during which a material may be stored under specified conditions and still remain in a usable condition. API 936 emphasizes that materials such as monolithic refractories, when stored properly, should be used within their specified shelf lives to ensure they retain the required properties for performance.

The term "rebound" is officially defined in API Std 936 as follows:

“Rebound: That portion of a refractory that does not adhere to the surface and falls away when a material is applied by gunning.”

— API Std 936, Section 3, Definitions​

This makes "rebound" the precise and correct term describing the material that fails to adhere during gunning. The other options, such as “slurry,” refer to different material states or applications, and “trimmings” or “overspray” are not used with this specific meaning in the standard.

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Hydrationrefers to the chemical reaction between water and cement components in refractory concretes (hydraulic bonded castables), resulting in the formation ofcalcium-aluminate hydrates, which are responsible for initial strength—known asgreen strength. This strength enables the lining to be demolded and eventually dried without mechanical failure.

Hydration is not related to final heat resistance or dryout; those come later during the firing or heat-up stages. It is distinct from setting in air-setting refractories or sintering in ceramic-bonded types.

According to API TR 980, a form must be able to support its own weight and the pressure from the refractory material:

“Formwork shall be self-supporting and capable of withstanding the static and dynamic loads imposed during installation.”

— API TR 980, Section 4.2.1, Form Requirements​

Transparency and chemical resistance are not required characteristics for refractory formwork in installation.

PerAPI Std 936, friable materials are defined as:

“Friable: A term applied to a material that is easily reduced to a powdery or granular state by crushing or rubbing.”

—API Std 936, Section 3: Definitions​

This is a key property considered in refractory evaluation because friability can indicate material weakness after installation.

Therefore:

A (friable materials)is the correct and technically defined term.

The other terms refer to distinct classes of materials not defined this way.

API 936 requires thata minimum of two test specimens be cast for each material, per mixing crew, per shiftduring casting applications. This ensures quality assurance through redundancy, enabling confirmation of critical physical properties like density and compressive strength. The testing must reflect real field conditions and each active crew’s installation consistency.

API TR 977 defines refractory abrasion in the context of erosion resistance testing:

“Abrasion is the wearing away of the surface by the mechanical scouring action of solids moving across the surface.”

— API TR 977, Section 2​

This distinguishes abrasion from gas or chemical attack and aligns with ASTM C704 test context.

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