The fundamental purpose of a pressure test is to verify the mechanical integrity and leak-tightness of pressure-retaining welds. To perform this verification effectively, the welds must be fully accessible for visual inspection during the test to identify any potential leaks, weeping, or deformation under pressure. Applying a refractory lining over these welds would conceal them, making a proper inspection impossible and potentially masking a critical defect. Therefore, standard industry practice, as codified by API, requires that all such welds remain unlined and exposed to the test medium until the pressure test is successfully completed.

A. be lined with coal tar epoxy.

This is incorrect because any coating, including epoxy, would cover the weld and prevent the required visual inspection for leaks during the pressure test.

B. include additional anchors.

This is incorrect as anchors are for securing the refractory lining; they do not contribute to verifying the pressure boundary's integrity or enabling weld inspection.

D. be gunned with no needles.

This is incorrect because it describes a specific refractory application technique, which is irrelevant to the essential requirement of keeping welds exposed for inspection during testing.

1. American Petroleum Institute (API) Standard 936

Refractory Installation Quality Control—Inspection and Testing Monolithic Refractory Linings and Materials

4th Edition

June 2014.

Section 6.3.3

"Coordination with Other Work

" explicitly states: "If the refractory lining is required before pressure testing

all pressure-retaining welds shall remain unlined and exposed to the test medium. The owner/operator shall specify the width of the unlined area over the welds." This directly supports the correct answer.

API Standard 936 specifies the quality control requirements for monolithic refractory linings, including material qualification testing. Table 2, "Required Laboratory Physical Property Testing for Material Qualification," explicitly lists the number of specimens required for each test. For the "Workability index" test, which is performed in accordance with ASTM C181, the standard mandates that each sample shall consist of three specimens. The final workability index is reported as the average of the three individual measurements, ensuring a representative value for the material lot.

A. 1: A single specimen does not provide a statistically reliable result and fails to meet the standard's requirement for averaging multiple measurements.

B. 2: Two specimens are insufficient as API 936 and the referenced ASTM C181 procedure are based on an average of three determinations.

D. 5: Testing five specimens is excessive and not required by the standard for this specific property, leading to unnecessary material and time expenditure.

1. API Standard 936

Refractory Installation Quality Control—Inspection and Testing Monolithic Refractory Linings and Materials

Fourth Edition

December 2014. Table 2—"Required Laboratory Physical Property Testing for Material Qualification

" page 11.

2. ASTM C181-11(2021)

Standard Test Method for Workability Index of Fireclay and High-Alumina Plastic Refractories. Section 7.2 states

"Take the average of the three individual measurements as the workability index."

The term "friable" is officially defined within the context of refractory materials as being easily reduced to a granular or powdery condition. This property is often assessed after the refractory material has been placed, cured, and/or fired. A friable condition can indicate improper mixing, curing, or material degradation, which compromises the integrity and performance of the refractory lining. The term directly corresponds to the description provided in the question.

B. calcined frits: Calcination is a high-temperature heating process, and frits are fused ceramic materials. This term describes a material's processing history, not its physical tendency to crumble.

C. mineral additives: These are materials added to a refractory mix to impart specific properties (e.g., plasticity, sintering). The term does not describe the final physical state of being easily crumbled.

D. granular grog: Grog is a pre-crushed and sized refractory aggregate used as a raw material in the mix. It is already granular before placement, not a condition that develops afterward.

1. API Standard 936

Refractory Installation Quality Control—Inspection and Testing Monolithic Refractory Linings and Materials

4th Edition

May 2014.

Section 3.1.24: Defines friable as: "Easily reduced to a granular or powdery condition."

2. Schacht

C. A. (2004). Refractories Handbook. CRC Press.

Glossary

page 481: Defines friable as: "Easily crumbled or pulverized." This general materials science definition aligns with the specific use in the API standard.

3. Sarkar

R. (2014). Refractory Technology: Fundamentals and Applications. CRC Press.

Chapter 2

Section 2.3.2: Discusses refractory aggregates like grog

differentiating them from the final properties of the installed refractory

such as friability

which relates to the strength of the ceramic bond.

According to API Standard 936, forms used for monolithic refractory installation must be self-supporting. This is a critical requirement to ensure the form maintains its own structural integrity and the intended geometry of the lining without relying on the vessel shell or casing for support, unless specifically permitted by the design drawings. This characteristic prevents the transfer of unintended loads to the shell or anchor system and ensures the final refractory lining has the correct dimensions and profile after the form is removed. The standard explicitly lists this as a mandatory characteristic for formwork.

A. Resist chemical attack: Forms are in temporary contact with the uncured refractory, so significant chemical resistance is not a primary design requirement.

B. Resist mechanical loads: While forms must be rigid and braced to resist loads from the wet refractory, "self-supporting" is a more specific and distinct requirement explicitly stated in API 936.

D. Transparent: Transparency is not a requirement for forms. They are typically constructed from opaque materials like wood, steel, or plastic.

1. API Standard 936

Refractory Installation Quality Control—Inspection and Testing Monolithic Refractory Linings and Materials

4th Edition

December 2014.

Section 6.3.4.2: "Forms shall be self-supporting and not attached to the shell or casing unless specified on the drawings." (This directly supports the correct answer

C).

Section 6.3.4.1: "Forms shall be rigid

tight-fitting

and adequately braced to prevent bulging or distortion." (This supports the concept in option B but shows that "self-supporting" is a separate

distinct requirement).

According to API Standard 936, the primary purpose of pre-installation testing (which includes casting sample mock-ups) is to qualify the installation procedures (the method) and the personnel (the installation crew or "fabricator") before actual work begins. The testing demonstrates that the specific combination of materials, equipment, procedures, and personnel can produce a refractory lining that meets the project specifications.

Other options like "mixing time" and "mix water levels" are variables that are established, optimized, and recorded during the testing to define the procedure, but they are not the entity being "qualified" in the certification sense. The "quality of the inspection equipment" is verified through calibration, not by the mock-up itself.

API Standard 936, Refractory Installation Quality Control—Inspection and Testing Monolithic Refractory Materials. Section: Pre-Installation Testing (Qualification of Installation Procedure and Crew).

Quote: "Pre-installation testing shall be performed to qualify the material, installation equipment, installation procedures, and personnel (installation crew)."

API 936 Body of Knowledge, Quality Control - Qualification, American Petroleum Institute.

This sequence represents the industry best practice for minimizing thermal stress and the risk of explosive spalling. A 24-hour ambient air cure allows the hydraulic bonds of the low-cement castable to develop initial strength. The subsequent slow, controlled heating ramp (50°F/h) through the critical temperature range (up to 600°F or 315°C) is essential. This controlled rate allows free and chemically bound water to be safely removed as low-pressure steam, preventing pressure buildup within the refractory's pore structure, which is the primary cause of cracking and spalling during dryout.

A. Firing directly to 1500°F without a controlled ramp-up induces extreme thermal shock and would almost certainly cause catastrophic failure of the lining due to rapid steam generation.

C. Accelerated drying with high-temperature forced air can cause surface sealing or "case hardening," trapping moisture within the lining and significantly increasing the risk of explosive spalling.

D. Using open flame burners with direct impingement on the refractory surface creates severe, localized thermal gradients, which is a well-documented cause of cracking and spalling.

1. API Technical Report 980

Monolithic Refractories: Installation and Dryout

2nd Edition

May 2018.

Section 6.1.1 (Curing): States

"For conventional castables

this curing period is typically a minimum of 24 hours..." This supports the initial step in the correct answer.

Section 6.2.2 (Heating Rate): Specifies

"The most critical part of any dryout is the initial heating phase where free water is removed... A typical heating rate in this range is 25 °F/hr to 50 °F/hr (14 °C/hr to 28 °C/hr)." This directly validates the heating ramp in the correct answer.

Section 6.2.3 (Burner Operation and Placement): Warns

"Direct flame impingement on the refractory lining shall be avoided as this can cause localized overheating

resulting in cracking or spalling of the refractory." This directly refutes option D.

2. Schacht

C. A. (2004). Refractories Handbook. Marcel Dekker

Inc.

Chapter 5

Section 5.4.2 (Drying and Firing): This chapter explains that the initial heating rate for monolithic refractories must be slow and controlled

particularly below 300°C (572°F)

to safely evaporate free water and water of hydration without generating destructive steam pressures. This principle supports the controlled ramp in option B and highlights the danger in options A and C.

3. VDI-Guideline 3470

Heat Treatment of Refractory Linings

Verein Deutscher Ingenieure

2012.

Section 5.2 (Heating-up): This guideline emphasizes that for hydraulically bonded refractories

the heating rate in the range up to 300°C should not exceed 20-30 K/h (36-54 °F/h) to prevent damage from steam pressure

aligning with the rate specified in option B.

According to API Standard 936, when a sample fails to meet the required specifications, retesting is permitted to validate the result. To ensure the retest is scientifically valid and comparable to the original failed test, variables must be minimized. The standard explicitly states that retesting shall be performed using specimens drawn from the same batch, same pallet, and the same sample (the original quantity of material extracted) as the original test. Furthermore, the same testing procedure (methodology) must be utilized to ensure the results are correlated. Inspection methods (which typically refer to visual field monitoring or installation oversight) are distinct from the specific laboratory testing protocols and are not a variable that applies to the retesting of a specific material sample.

API Standard 936, Refractory Installation Quality Control—Inspection and Testing Monolithic Refractory Materials, Section: Testing and Quality Control (specifically subsections on Sampling and Retesting/Resampling).

Note: The standard dictates that to confirm compliance or failure, the re-evaluation must rule out material variation; thus, the original source material (Batch/Pallet/Sample) and the yardstick (Testing Procedure) must remain constant.

API 936 Body of Knowledge, Quality Control - Testing Variables, American Petroleum Institute.

According to API Standard 936, if the application of hydraulic-bonded or chemical-setting refractory is interrupted, immediate action is required to prevent the formation of a weak "cold joint." The standard mandates that the installed refractory be cut back to its full depth (to the shell) and shaped between the anchors. This procedure creates a keyed or dovetailed joint, which provides a strong mechanical interlock for the material applied once work resumes, ensuring the monolithic integrity of the final lining.

A. cut back within 1 hour: This is incorrect. The standard specifies the action must be taken "immediately," not after a delay of up to one hour, as the material begins to set quickly.

B. cut back within 30 minutes: This is incorrect. The requirement is for immediate action. Waiting 30 minutes allows the material to partially set, making a proper joint difficult to achieve.

D. cut back to the shell in a straight line: This is incorrect. A straight-line cut creates a vertical plane of weakness, which is prone to cracking. The correct method is to cut between anchors to form a key.

1. API Standard 936

Refractory Installation Quality Control—Inspection and Testing Monolithic Refractory Linings and Materials

4th Edition

December 2014.

Section 6.3.3.5 Delays/Interruptions: "If the application of hydraulic-bonded or chemical-setting refractory is interrupted

the refractory lining shall be immediately cut back to the shell between anchors to form a key for the subsequent cast." This clause directly supports the correct answer.

While the value presented in the option is incorrect, the principle is the most accurate among the choices. According to API 936, Section 4.2.2, for material qualification testing, the amount of mixing liquid (water) must be controlled within a strict tolerance of the manufacturer's recommendation to achieve the required physical properties. This control is critical because slight variations in water content can significantly impact the castable's density, strength, and shrinkage. The correct tolerance specified in the standard is ±0.5%, not ±1.0%. However, the other options contain more significant procedural or fundamental errors.

B. The standard firing hold time for qualification specimens is 5 hours, not 3 hours, unless otherwise specified by the owner (API 936, Section 4.2.3).

C. Acceptance criteria are based on meeting the values published on the manufacturer’s data sheet, not the average values from the general classification standard ASTM C401 (API 936, Section 4.3.1).

D. Specimens are dried at 220°F to 230°F (104°C to 110°C) until a constant weight is achieved, not for a prescribed minimum of 48 hours (API 936, Section 4.2.3).

---

1. American Petroleum Institute. (2014). API Standard 936: Refractory Installation Quality Control—Inspection and Testing Monolithic Refractory Linings and Materials (4th ed.).

For Correct Answer (Principle): Section 4.2.2

Page 10. "The amount of mixing liquid shall be within ±0.5 % of the amount recommended by the manufacturer to achieve the required physical properties." (Note: This confirms the principle of a strict water content tolerance but shows the value in option A is incorrect).

For Option B: Section 4.2.3

Page 10. "After drying

the specimens shall be fired at 1500 °F (815 °C) for 5 hours unless otherwise specified by the owner."

For Option C: Section 4.3.1

Page 11. "The average results for permanent linear change

cold crushing strength

and abradability shall meet the manufacturer’s published data. The average bulk density shall be within ±5 % of the manufacturer’s published data."

For Option D: Section 4.2.3

Page 10. "The specimens shall be dried at 220 °F to 230 °F (104 °C to 110 °C) until constant weight is achieved."

2. Schacht

C. A. (2004). Refractories Handbook. Marcel Dekker

Inc. (Peer-reviewed academic publication).

Chapter 5

Section 5.4.1

"Water Content

" emphasizes that for low-cement castables

"the amount of gauging water is critical" and must be controlled precisely as per the manufacturer's instructions to develop optimal properties. This supports the fundamental importance of the principle in option A.

According to API Standard 936, the primary purpose of constructing a gunning test panel with a removable back is to facilitate a critical quality control inspection. After the refractory material has been installed and has set, the back panel is removed to allow for a thorough visual examination of the material at the interface that simulates the vessel shell. This inspection is specifically to identify hidden defects such as voids, laminations, or areas of poor compaction that would not be visible from the gunned surface. These defects can significantly compromise the integrity and performance of the final refractory lining.

A. The design's purpose is quality control of the refractory installation, not the economic consideration of reclaiming anchors from a test piece.

C. Green-to-fired weight changes are determined by testing smaller, specifically prepared samples (e.g., cubes or bars), not by inspecting the main test panel.

D. A hammer test is a form of physical inspection performed on the exposed, hardened surface of the refractory, not on the back side against the panel.

1. API Standard 936

Refractory Installation Quality Control—Inspection and Testing Monolithic Refractory Linings and Materials

4th Edition

June 2014.

Section 6.3.3: "The test panel shall be constructed with a removable back to permit inspection of the castable for voids and laminations after installation." This clause directly supports the correct answer.

Section 8.2.2: This section on visual inspection details the types of defects to look for

including voids and laminations

which the removable back panel is designed to expose for examination on the test piece.