API 936: Refractory Installation, Inspection and Testing
PART - III
IMPORTANT POINTS FROM STANDARD
API 936
This standard provides installation quality control procedures for monolithic refractory linings. The responsibilities of inspection personnel who monitor and direct the quality control process are also defined in the standard.
Definitions
1. Abrasion resistance: The ability to withstand the effects of eroding particles for an extended period without significant loss of material or other damage.
2. As-installed testing: Testing of refractory materials sampled from the
installation to confirm that they meet specified physical property standards.
3. Biscuit: A refractory piece formed within an area completely enclosed by
the anchoring system.
4. Cold Crushing Strength: (CCS) A measure of a refractory's ability to
resist failure under a compressive load as determined at room temperature after drying and/or firing.
5. Cold wall: An insulating refractory lining system with a metal shell temperature
less than 500°F (260°C).
6. Dry-out: The initial heating of a newly installed castable lining in which heating
rates and hold times are controlled to safely remove retained water without explosive spalling and to form a well distributed network of shrinkage cracks in the lining.
7. Firing: The process of heating refractories to develop desired properties.
8. Gunning: The application of monolithic refractories by means of air placement
guns.
9. Hot wall : A thin refractory lining system with a metal shell temperature greater than
10. Pre-wetting (gunning): A technique used with dry gunning machines
where a small quantity of water is mixed into the dry refractory before charging into the gun to reduce rebound and dust, and to improve wetting of the
cement in the gunning operation.
11.Wet gunning: Pneumatic placement of premixed castables (including
water) where flocculating agents and placement air are added at the nozzle.
Responsibilities
1.Owner
1. The owner shall prepare a detailed specification. The specification shall include the following design details.
a) Lining products, thickness, method of application, and extent of coverage.
b) Anchor materials, geometry, layout and weld details. Suggested color coding for metallic anchors is provided in Annex B.
c) When used, details of metal fiber reinforcement including dimensions, concentration, type, and metallurgy.
d) Curing and dry-out procedures, including constraints on dry-out heating (e.g. design temperature limits and/or maximum differential temperatures that shall be maintained to avoid damaging the unit and/or components).
2. The owner shall provide quality requirements covering the following.
a) Physical property requirements to be used for qualification and installation quality control by specific product, installation method and location where the product will be utilized. These requirements shall be in accordance with Annex C unless amended by prior agreement with owner.
b) Sampling frequency as applicable for the product’s intended use in either erosion service or other service.
c) Required lining thickness tolerances.
d) Criteria for hammer testing and the extent of cracking and surface voids permitted. 3. The owner shall approve the engineering drawings, execution plan and dry-out
2.Contractor: The contractor shall prepare a detailed execution plan in accordance
with this standard and the requirements of the owner's specification and quality standards.
3.Inspector: The inspector shall be responsible for the following.
a) Ensure that material and applicator qualification test results are fully documented.
b) Monitor qualification, production work and dry-out (when applicable) conducted by the manufacturer(s) and contractor to ensure compliance with job specifications and agreed-to quality practices.
4.Inspector Qualifications
The inspector shall have no commercial affiliations with the contractor or manufacturer(s). The inspector shall be certified in accordance with API 936 Annex D.
The inspector shall possess this standard, owner specifications, the project execution plan, and other job specific requirements outlined by the owner, contractor, and/or manufacturer. The inspector shall have working knowledge of these documents.
Refractory materials Storage and Testing
1.Temperature
Refractory materials shall be stored at a temperature of 40°F to 100°F (5°C to 38°C).
2. Testing
General : Testing of refractory lining shall be in strict accordance with ASTM procedures
as modified below. The laboratory conducting the test procedures shall be subject to audit and approval by the owner. Quality control testing shall consist of density, cold crushing strength (CCS), permanent linear change (PLC), abrasion loss (when applicable), and workability index (plastics only).
3.Abrasion (Erosion) Resistance
Testing shall be in accordance with ASTM C704 and API 936 the following.
4.Permanent Linear Change (PLC)
5.Pre-shipment Refractory Qualification Testing
Refractories to be installed by gunning, casting, or hand/ram packing shall be tested to ensure that they comply with specified physical property requirements
6.Forming of Refractory Test Specimens
For cast installations, refractory shall be cast in the same manner as the installation. For vibration cast installations, vibration shall be used in the forming of the test specimens.
a) For pump cast installations, refractory shall be poured into forms. b) For hand packed installations, refractory shall be hand packed.
c) For gunned installations, refractory shall be gunned to produce a large panel.
7.Application Period
Refractory shall be applied within four months of the initial qualification tests.
8.Casting :
A mock-up shall be prepared by each applicator, for each mixing/installation procedure, and for each refractory being installed. Refractory cast in the mock-up shall be cured for 12 hours minimum prior to stripping the forms. Heat-setting, plastic refractories shall be allowed to air dry for a minimum of 24 hours followed by oven drying in a form suitable for drying temperatures.
9.Oven dry:
hold for 12 hours minimum at 220°F to 230°F (104°C to 110°C) in a forced air, convection dryer. Heating to this level shall be in accordance with manufacturer's recommendations. Heat setting plastics shall be oven dried in the forms.
10.Oven fire:
heat at 300°F/h (170°C/h) maximum to 1500°F (815°C), hold for five hours at 1500°F (815°C); cool at 500°F/h (280°C/h) maximum to ambient. Remove heat setting plastics from the molds after oven drying and before oven firing.
Water used for mixing in the refractory shall be potable. The chloride content of the water shall not exceed 200 ppm. When refractory is installed on stainless steel surfaces the chloride content shall not exceed 50 ppm.
Refractory installation
1. Refractory installation shall not begin until completion of welding, postweld heat treatment, and pressure testing.Structural members, nozzle extensions, and other items within the limits of the lining shall be wrapped with 1/8 in. (3 mm) thickness of a nonabsorbent material to prevent moisture absorption from, or bonding to, the refractory lining. The wrapping shall be taped smoothly into place.
2..Application Temperature
The temperature of the air and shell at the installation site shall be between 50°F and 90°F (10°C and 32°C).Temperature limits for refractory and mix water shall be in accordance
with the manufacturer's requirements. In the absence of manufacturer's mix temperature limits, mix temperature shall be between 60°F and 80°F (15°C and 27°C). During dry-out heating shall be controlled using temporary thermocouples to monitor gas temperatures throughout the lined area(s). Thermocouples shall be located within 1/2 in. (13 mm) of the refractory surface.
Points from Report A
C
I -547
1. The report presents background information and perspective on the history and current status of the technology.
2. Scope of report Refractory concrete is concrete suitable for use at temperatures up to about 3400 F (1870 C).
Following types of refractory are covered
a) Acid Refractories
b) Apparent Porosity (Astm C20) c) Basic Refractories
d) Calcium Aluminate Cement e) Castable Refractory
f) Ceramic Bond g) Explosive Spalling
h) Heat Resistant Concrete i) High Alumina Cement j)Refractory Aggregate
3. Brick has a number of disadvantages when compared to monolithic refractories. These disadvantages include multiple joints, complicated anchoring, higher placement costs, more difficult repair procedures, the need to maintain expensive inventories of special or scarce items, a certain inflexibility in structural design, and higher fuel requirements during manufacture.
4. Plastics are generally placed without use of forms. With the exception of some specialized tabular alumina castables, plastics have a somewhat higher service limit than castable refractories. Their main disadvantages are greater shrinkage and crack development.
5. Gunning mixes generally have low rebound loss, are predominately used for patching or resurfacing brick or other refractories, have a strong internal bond, and exhibit excellent adhesion or bond to the existing refractory lining. They find extensive use in basic oxygen, electric arc and open hearth furnaces, among other applications.
6. Alkalies can effect the service life of refractory concretes. The furnace charge can give
off both alkalies (K2O) and the fuel sulfur compounds (SO2) as vapors. These can penetrate into the pores of the refractory concrete and react; their reaction products cool, solidify, and expand, sometimes causing the hot face of the refractory to peel or shear away. 7. Binders The binders principally used in refractory concretes are calcium aluminates
cements.
8. Temperature stability of the aggregate determines the maximum service conditions below approximately 24000 F (13200 C).. For conditions above 24000 F (13200 C), binder purity also becomes a design factor. Generally, the low purity binder can be used with proper aggregates up to 2700 F (1480 C), intermediate purity to 30000 F (16500 C) and high purity to 34000 F (18700 C).
9.The recommended maximum service temperature will normally assume that the castable will be used in a clean, oxidizing atmosphere, such as is present when firing with natural gas. The maximum service temperature is usually determined as the point above which excessive shrinkage will take place. It is about 150-200 F (70-90 C) below the actual softening point of the concrete.
