API-936 API 936 - Refractory Personnel Questions and Answers

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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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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According to API 936 and TR 980,hydraulic bonded castablesshall not be allowed toair dry for more than 1 hourbefore 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.

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.

When installation is interrupted, the partially installed refractory must becut back to the shell between anchorswhile it is still workable. This ensures a clean, rough bonding surface free from weak or partially set material. API 936 requires this method for bothhydraulic bondedandchemically bondedsystems to preserve lining integrity and avoid delamination between old and new material.

API Std 936 is very specific about the consequences of failing workability index tests:

“Plastic refractory material that fails to meet the minimum manufacturer’s workability index shall be subject to requalification testing or discarded.”

— API Std 936, Section 6.4.6​

No provision is made for adding water or extending mixing, as this would compromise material performance. Thus:

A is correct.

B and C violate the standard.

D is not a prescribed corrective action in this case.

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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.

This definition is rooted in petroleum refining terminology used in the context of fluid catalytic cracking (FCC) units:

“Reactor: The vessel in which the cracking reaction occurs or is completed and in which the product gases are separated from coke and/or catalyst particulate.”

— API Std 936, Definitions, Section 3​

Option B is the correct term describing this component. A stripper removes volatiles, a regenerator burns off coke from spent catalyst, and a standpipe is used for catalyst transport—not for the cracking reaction itself.

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The manufactureris responsible for specifying the exactdimensions, type, concentration, and metallurgical propertiesof metal fiber reinforcement in castable refractories. These fibers are often integral to the formulation and performance of the material and are introduced during manufacturing (not field mixing), with characteristics tailored to improve thermal shock resistance and crack propagation control.

API 936 defers to the manufacturer’s technical data for the design and quality control of any material component, including reinforcement. The contractor is responsible for verifying that materials match the manufacturer’s documented specification.

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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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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Creepin refractories is the slow, time-dependentdeformation of a material under constant stressand high temperature. It is critical in applications like reformers and furnaces where the refractory is under load for extended periods. The amount of deformation is typically measured over 50–100 hours in standardized tests such as ASTM C832.

Creep is not the same as thermal expansion (which is reversible), or cracking (a sudden failure).

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.

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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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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Permanent linear change (PLC)measures the irreversible dimensional change of a refractory specimen after it is subjected to a high temperature for a specified duration. It is expressed as a percentage of the original length. This property helps evaluate the stability and thermal compatibility of refractory materials during service.

This is distinct from:

Modulus of rupture (A): a strength test under bending.

Modulus of elasticity (C): a measure of stiffness.

Pyrometric cone equivalent (D): a test for melting behavior.

Flexmesh is a longitudinally hinged anchoring system used in curved refractory linings. Its flexibility allows it to conform to the contours of circular vessels such as cyclones and ducts, reducing the risk of anchor failure and refractory cracking due to thermal stress and differential movement.

According to API 936 guidance and referenced literature like API TR 980, Flexmesh is particularly suited for applications in reformers, regenerators, and vessels with complex geometries. The system improves lining integrity by allowing a more adaptable and secure attachment of the refractory lining.

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.

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.

Chemically bonded refractories, such as phosphate-bonded or acid-bonded types, develop strength through chemical reactions that requireexposure to ambient air. These materials must remainuncovered and dry during curing, as moisture or covering may inhibit the required chemical bonding or lead to improper set.

Covering chemically bonded linings (e.g., with plastic sheeting or wet burlap) — practices appropriate forhydraulic bonded(cement-based) refractories — would trap moisture and interfere with the chemical reaction process in chemical bonds.