API-936 API 936 - Refractory Personnel Free Practice Exam Questions (2025 Updated)

API 936 establishes quality assurance testing frequencies based on usage, service condition, and criticality of application. Forerosion service refractory, which is subject to high-velocity particle impingement (e.g., in FCCU units), the standard testing frequency isone sample per 2 tons or less. This ensures that each significant quantity used in fabrication is represented by a test sample to verify compressive strength, density, and abrasion resistance.

Failure to meet this frequency may risk undetected variability in raw material batches or mixing inconsistencies.

According to TR 980, direct open flame torches are not recommended for dryout because of their uneven heating and local overheating risk:

“Initial heating may be performed using portable burners, electrical heating elements, or process heating devices. Use of open torches is not recommended due to potential for localized overheating and damage.”

— API TR 980, Section 5.3.3​

Therefore:

A (electrical heating elements): Acceptable

B (open torches): Not acceptable

C (portable burners): Acceptable

D (process heating devices): Acceptable

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According to API 936, thecontractoris responsible for submitting adetailed dryout procedure. This procedure must be reviewed and approved by the owner or the owner’s representative. While manufacturers may provide guidance, the contractor is accountable for ensuring the procedure aligns with project specifications, material requirements, and environmental conditions.

Cold wall refractory systems are typically backed by steel shells, which are poor at withstanding the thermal stresses that come from reverse heating. API 936 and API TR 980 clearly emphasize thatthe heat-up or dryout process for cold-wall linings must always begin from the hot face— that is, the process-exposed surface.

Heating from thehot faceallows for controlled migration of moisture toward the cold face and eventual venting to the atmosphere. Conversely, heating from the cold face or steel shell side traps moisture between the hot impermeable material and the outer surface, leading to:

Steam buildup

Explosive spalling

Cracks in the material or at the interface with the steel

For these reasons,only the hot facemethod is specified unless the design and dryout plan justify a different method under special engineering review.

When qualifying materials and personnel for gunning applications, the standard test panel orientation is:

“The gunned panels shall be prepared on steel plate forms inclined at 45° to the horizontal.”

— API Std 936, Section 6.5.1, Gunning Test Panels​

This standardized angle helps evaluate rebound and build-up in conditions that simulate typical applications.

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Metal fiber reinforcement isnot a universal requirementfor all castables; it isused only when explicitly specifiedby theowneror 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 isclearly indicated in the job specifications, it is not assumed or automatically added.

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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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.

According toAPI TR 980, Section 4.4.2, mock-ups are required prior to actual installation for vibration-cast materials to verify theadequacy of equipment, the method of vibration, and vibrator attachment. These mock-ups are not intended to assess the craft skill in form construction.

"Mock-up vibration-casting trials are used to demonstrate the adequacy of the equipment, the means of vibrator attachment, and the method of vibration for the particular installation geometry and refractory type."

—TR 980, Section 4.4.2​

Therefore:

B (equipment)is correct.

C (means of vibrator attachment)is correct.

D (vibration method)is correct.

A (craftsman’s ability to construct the forms)is not the intent of this mock-up and thus not correct.

API 936 mandates specific AQL values during pre-shipment testing:

“Physical property test results shall meet the specified requirements with a minimum AQL of 5.0 percent.”

— API Std 936, Section 5.2.4​

Hence, the correct AQL for physical property verification of pre-shipment brick testing is 5%.

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As per the testing procedures outlined in API 936:

"All specimens used in ASTM C704 and ASTM C133 tests shall be dried and fired to 1500°F (815°C) prior to testing."

— API Std 936, Section 6.3.1​

Firing to 1500°F ensures proper evaluation of the refractory's behavior under service conditions.

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.

API 936 clearly stipulates that the selection, installation, inspection, and testing of anchors must comply with theproject's drawings and specifications. These documents define anchor spacing, type, material, orientation, and welding requirements, which must be followed during construction and QA processes.

API 936 does not defer this responsibility to external documents like API RP 577 or welding codes unless explicitly referenced in the project specifications. QA/QC departments may oversee adherence, but do not define the criteria themselves.

According to API 936, duringapplicator qualification testing, the equipment used must beidentical to the equipment that will be used in the actual installation. This ensures that all conditions (air pressure, nozzles, mixers, vibration tools, etc.) accurately reflect field performance and allow for a true demonstration of the applicator’s ability to meet the project’s quality requirements.

This rule eliminates discrepancies between mock-up performance and production work, which might otherwise compromise the quality of the installed refractory. Testing with alternative or idealized equipment does not represent real installation challenges.

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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The correct ASTM designation for testingcold crushing strength (CCS)of refractory materials isASTM C133. This test determines the load at which a sample fails under compressive stress and is essential for assessing the structural integrity of castable and formed refractories.

ASTM C113 relates to permanent linear change.

ASTM C704 is for abrasion resistance.

ASTM C417 is not related to CCS in this context.

According to API 936, theinstallation contractor must secure prior written approval or agreement from the ownerregarding all details of the installation. This includes procedures for curing, dryout, anchoring, repairs, and quality control. The owner or their authorized representative is the ultimate authority for project specification conformance.

Apparent porosityis a measure of the volume of open pores (voids that can absorb water) within a refractory sample, relative to the total volume. It is always expressed as apercentage. Testing is done using standards such as ASTM C20, which API 936 references. This metric is crucial for understanding a material’s permeability, thermal shock resistance, and mechanical integrity.

Per API Std 936 Section 6.3.2.1, qualification trials for castable refractories require strict control over water content. The variation must be within ±1.0% of the manufacturer’s recommended water addition to ensure consistency and reliability in performance.

"Acceptance of the test results from the cast sample trial shall be contingent on the mix water being within ±1.0 % of that recommended by the manufacturer."

— API Std 936, Section 6.3.2.1​

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