API API-936 - API 936 - Refractory Personnel

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.

According to API 936, ceramic fiber batten strips are used in fiber lining applications to secure joints or protect against gas penetration. The specification sets a strict requirement on their length:

“Ceramic fiber batten strips shall be a maximum length of 3 ft (0.9 m).”

— API Std 936, Section 5.3.2.3​

Other anchoring methods such as lock studs or staples may apply in different contexts or materials, but they are not prescribed for ceramic fiber batten strips per this specific requirement.

The term “production run” is defined by API 936 as follows:

“Production Run: The quantity of material manufactured using the same formulation in an uninterrupted manufacturing operation.”

— API Std 936, Section 3: Terms and Definitions​

This distinguishes it from a test sample (a subset), a pallet (a packaging unit), or a bag (a smaller containment unit). The production run forms the batch basis for qualification and traceability.

API Std 936 defines crack length acceptance as follows:

“Surface cracks in dense firebrick shall not exceed 1/2 in. (13 mm) in length and shall not extend through the thickness of the brick.”

— API Std 936, Section 8.3.3​

Therefore, Option C is the correct maximum allowable length for a visible crack on firebrick.

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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 936 clearly states that applicators/installers must be qualified to demonstrate the ability to install refractory linings in accordance with the specified project quality standards. This includes using the correct methods, achieving proper material density, and avoiding defects like voids and laminations.

API TR 980 explicitly defines the minimum temperature requirements for castable installation:

“Installation should not proceed if the ambient temperature, substrate temperature, or material temperature is below 50°F (10°C). The material and substrate must be maintained at or above this temperature throughout the placement and curing process.”

— TR 980, Section 4.5.1 Cold Weather Installation​

Therefore:

Option D is correct as it meets the standard.

Option A is partially correct but does not include the shell or ambient temperature.

Option B is incorrect—work should not start if temperature cannot be maintained.

Option C is incorrect and contradicts API guidance.

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According to API Std 936, responsibilities are clearly defined when it comes to conflicts in documents or drawings:

"Where conflicts exist in documents and/or drawings, resolution shall be by the owner."

— API Std 936, Section 4.2.1 Responsibilities​

Therefore, Option B is correct. Inspectors may report or note discrepancies, but only the owner has the authority to officially resolve such conflicts.

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The standard specimen size for conducting tests on Permanent Linear Change (PLC) of refractories is2 in. x 2 in. x 9 in. (50 mm x 50 mm x 230 mm). This dimension is consistent with ASTM C113, which is referenced in API 936 for evaluating the dimensional stability of refractory materials after heat treatment.

Permanent Linear Change testing is essential to determine the expansion or shrinkage behavior of refractories when exposed to high temperatures, a critical property for ensuring dimensional compatibility in service.

Mock-up installations serve as a qualification tool to verify that the installation procedures, personnel, and equipment can consistently meet quality standards. API 936 stipulates that refractory samples cast during the mock-up must becured for a minimum of 24 hoursbefore demolding or further processing. This curing period ensures full initial set and adequate strength development of the castable.

Failure to meet this curing requirement can result in incomplete hydration, premature cracking, or misleading performance test results. The 24-hour period allows for optimal moisture retention and chemical reaction completion in hydraulic-bonded castables.