API-936 API 936 - Refractory Personnel Questions and Answers

Abrasion resistance testing of refractories, especially under ASTM C704 as referenced by API 936, evaluates material durability by measuring the loss of volume after a defined wear process using silicon carbide grit. This test simulates erosion environments (e.g., FCCU risers) and outputs the result in cm³ or in³ of volume loss .

Loss of mass or density may also occur, but volume is the defined reporting metric.

The API 936 terminology section defines "green refractory" as:

“Green Refractory: A monolithic refractory that has been placed but has not yet been exposed to curing or dryout temperatures.”

— API Std 936, Section 3: Definitions​

Thus, “green refractory” is the technically correct term for the unheated, freshly installed condition.

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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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The ASTM C704 standard requires the use of two specimens per sample for testing abrasion resistance:

“The abrasion resistance shall be determined using two 4½ in. × 4½ in. × 1 in. (114 mm × 114 mm × 25 mm) specimens per test sample.”

— API Std 936, Section 6.4.4, Abrasion Resistance​

This ensures accurate and reproducible results for quality control in refractory installations.

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According to API 936, the installation contractor must secure prior written approval or agreement from the owner regarding 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.

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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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.

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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According to API Std 936, the quality control program includes several essential elements to ensure compliance with material specifications and installation procedures. These elements include:

"Key quality control activities include, but are not limited to: material qualification testing, initial inspection, installation monitoring, and as-installed testing."

— API Std 936, Section 4.1, Quality Control Program​

Although documentation is essential, report writing is not listed as a core quality control element within this section. Therefore, A, B, and C are the correct answers.

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API 936 clearly stipulates that the selection, installation, inspection, and testing of anchors must comply with the project'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 Std 936 – Refractory Installation Quality Control, the roles and responsibilities of each party are clearly defined. Specifically, it states:

“The contractor shall be responsible for… the preparation of the surface prior to lining, and the quality of the workmanship, including the welding of anchors and any required preheat or post-weld heat treatment.”

— API Std 936, Section 5.3.1, Contractor Responsibilities​

Therefore, surface preparation and welding activities, including anchor welding, fall under the Contractor's scope of work. The inspector's role is to verify compliance, not to execute procedures.

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Removable back panels in gunning test panels are required to allow inspection for internal defects , particularly voids, laminations, and rebound pockets that are not visible from the surface. These panels are taken off after gunning so that the interface between layers or the entire cross-section can be visually examined.

This approach ensures that the test section is representative of actual field performance and that the gunning technique (angle, nozzle distance, rebound control) is achieving full compaction without defects.

The curing of newly installed refractory linings must adhere strictly to manufacturer guidelines to ensure integrity and performance:

“Forms shall not be stripped until the lining has cured per the manufacturer’s recommendation.”

— API Std 936, Section 5.4.2.1​

The manufacturer's recommendations ensure that the product reaches sufficient strength before demolding.

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Apparent porosity is 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 a percentage . 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.

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.

mixing time

mix water levels

installation procedures

According to API Std 936 and supporting guidance from TR 980, cast sample mock-ups are used during pre-installation trials to ensure the suitability and repeatability of installation variables such as mixing procedures and water content. These mock-ups are critical to confirm that the material can be properly installed under anticipated field conditions.

From API 936:

“Mock-up cast sample trials shall be used to demonstrate the adequacy of the mixing time, water addition (mix water levels), and installation procedures prior to production installation.”

— API Std 936, Section 6.3.2​

This ensures that full-scale application performance is achievable using the approved methods and materials. However:

The “quality of the inspection equipment” and

“fabricator of the mock-up”

are not part of the qualification objectives defined for cast sample testing.

Correct selections:

mixing time

mix water levels

installation procedures

Applicator qualification testing is a term used in API 936 to describe the testing required to evaluate whether installation equipment and personnel can achieve the required physical properties (e.g., density, strength) in the final refractory. This testing often involves a mock-up or practice panel where variables like rebound, compaction, and finish are assessed.

The objective is to ensure:

Installation consistency across shifts or crews

Operator competence with specific materials

Adequate equipment settings (nozzles, air pressure, etc.)

Applicator qualification must be completed before production installation begins and is separate from material qualification or final as-installed testing.

When the owner does not provide explicit temperature criteria for mixing and placement, the refractory manufacturer’s instructions prevail:

“If not specified by the owner, the refractory manufacturer’s published recommendations shall be followed for temperature limits of both material and mixing water.”

— API TR 980, Section 4.5.2​

Thus, Option B is correct.

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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API 936 requires that a minimum of two test specimens be cast for each material, per mixing crew, per shift during 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.

According to API 936 and TR 980, hydraulic bonded castables shall not be allowed to air dry for more than 1 hour before the application of a curing compound. Prolonged exposure to air allows surface moisture to evaporate, leading to potential surface cracking and weak zones. Early application of curing compounds preserves internal hydration processes, which are essential for strength development.

Hydraulic bonded castables, such as those using calcium aluminate cement, cure through a hydration reaction that requires the presence of water. Premature drying due to wind, sun, or heat can halt the hydration process, weaken the structure, and cause surface cracking. API 936 mandates that no part of the exposed surface of the castable shall be allowed to dry more than 3 hours before a membrane curing compound is applied.

This statement ensures:

Retention of sufficient surface moisture for ongoing hydration.

Prevention of microcracking, which can later act as stress risers during service.

Uniform strength development across the lining.

The curing compound forms a film that limits evaporation, allowing for continued hydration over the next 24–48 hours.