Per API 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.

The inspector’s responsibilities , as defined in API 936, include visual and mechanical inspection of installed linings. Hammer testing is one such non-destructive method used to detect delamination, voids, and rebound areas by listening for variations in sound. It is a practical method during and after installation.

Other tasks like providing compliance documentation or water testing are typically done by the contractor or laboratory personnel.

For linings intended for erosive service, API 936 requires testing that includes specimens that experience real service wear simulation:

“For erosive service, bulk density shall be determined using the abrasion resistance test specimens and the linear change specimens.”

— API Std 936, Section 6.4.3​

Thus, both abrasion plates and linear change bars are used to evaluate density in erosion-sensitive applications.

The cure period before initiating the dryout process is a critical phase of installation:

“Newly installed air-setting, hydraulic, and chemically bonded materials shall be allowed to cure for a minimum of 24 hours at 60 °F (16 °C) or above prior to initial heating.”

— API TR 980, Section 6.2.1​

This condition ensures chemical bonding processes are complete before exposure to thermal stress.

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Hydration refers to the chemical reaction between water and cement components in refractory concretes (hydraulic bonded castables), resulting in the formation of calcium-aluminate hydrates , which are responsible for initial strength—known as green 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.

ASTM C704 specifies silicon carbide as the standard abrasive media used in the abrasion resistance test for refractories. This test simulates service wear caused by mechanical erosion (e.g., in FCC units). Silicon carbide is used because of its consistent hardness, angularity, and wear characteristics that represent severe operational conditions.

Metal fiber reinforcement is not a universal requirement for all castables; it is used only when explicitly specified by the owner or design engineer based on the thermal and mechanical service conditions. Fibers are typically added to enhance resistance to thermal shock, spalling, or dynamic loads, particularly in cyclic or erosive environments like FCCU risers.

API 936 requires adherence to project specifications, and unless the use of fiber reinforcement is clearly indicated in the job specifications , it is not assumed or automatically added.