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Guide to Purchasing Monolithic Refractory Materials Author: Jan Theron This work by Ceram is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License

Guide to Purchasing Monolithic Refractory Materials

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Guidelines and good practice for refractory users is provided to ensure that the materials specified by the designer are delivered and meet the quality required for the application. The differences between data sheets, product specifications and test certificates are discussed. A series of suggested checks to be made during the various procurement and supply process stages is also given. Courtesy of Jan Theron, Ceram.

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Page 1: Guide to Purchasing Monolithic Refractory Materials

Guide to Purchasing Monolithic Refractory Materials

Author: Jan Theron

www.ceram.com

This work by Ceram is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License

Page 2: Guide to Purchasing Monolithic Refractory Materials

Introduction

This paper provides guidelines and good practice for the refractory user to ensure that the material specified by the designer is delivered on site according to the quality required for the application. The differences between data sheets, product specifications and test certificates are discussed. A series of suggested checks to be made during the various procurement and supply process stages is also given.

Ideal Life Cycle of a Refractory Lining

1. For a refractory lining design, the lining thickness, anchorage, expansion joints, material selection, etc., are all to be carefully considered, based on the process conditions and vessel design given to the designer.

2. The final design is then presented as a drawing to the client. The commercial department will purchase the recommended material from a selection of suppliers based on the specifications set out in the design.

3. During the next stage, a qualified refractory installer will install the materials according to the specifications given in the drawing, making use of best practices.

4. The dry-out or start-up is then carried out to the recommended heat-up profile supplied by the material manufacturer. Once the unit goes into production, the refractory lining is then exposed to the design conditions anticipated by the process engineers and will remain in place until the end of its lifetime.

Main Categories of Failure

From the life cycle highlighted above it is evident that there are four main areas where premature failure can originate:

1. Design2. Material3. Installation4. Operation.

There are many reasons for failure in all of these areas. Following are some of the reasons why problems can occur during each stage of the lifetime of a refractory lining.

1. During the design process, assumptions relating to the process conditions may be incorrect or incomplete. This may result in the wrong choice of refractory material. The steel shell designs have normally been made without taking the properties of a refractory lining into consideration and this may lead to complex and impractical refractory shapes.

2. During the purchasing of the material, a general specification of material may be used by the buyers with the result that, possibly, the cheapest alternative may be acquired. This may not be the material best suited to that application. During the purchasing of materials, the documentation from the supplier is often solely relied upon. In addition, materials are often delivered to site without ensuring that the correct material was supplied.

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3. During installation there can be many difficulties to overcome which can lead to installation-related failure. Mistakes may be due to an installer’s lack of familiarity with the specific material or design, unavailability of correct equipment, harsh environmental conditions and/or time constraints.

4. During operation the lining is expected to perform under a defined set of conditions. However, many production processes do not continuously operate under a set of constant conditions. This inconsistency may be a result of impurities in the feed streams, plant trips as well as temperature and pressure fluctuations.

Failure Investigations Where the Material Used is Suspected of Causing the Failure

When a failure occurs, often very limited information is available on material and installation. Inadequate and inappropriate records are kept on material quality and/or installation quality. This obviously points to the material as the main suspect of the failure. Determining properties of material recovered from the failed area can incur considerable costs.

These post-mortem costs are significantly higher than the costs that would have been incurred when establishing material properties prior to installation. Quality control measures may be seen by many end users as a waste of time and/or money. QC is often seen as simply a paper exercise to satisfy legal requirements, instead of a dedicated task to ensure lining integrity.

Best Practice Guidelines When Choosing a Supplier

The designer may have chosen a specific product from a specific supplier. However, in some cases, the buyer, who may not have sufficient knowledge of refractory materials, may choose an “equivalent” supplier to reduce project costs or perhaps to shorten delivery times. It should be appreciated that there are not equivalent materials in the refractory industry compared to, for instance, the steel industry. (Stainless steel 310 has a worldwide recognised specification that it has to conform to, whereas there are no such specifications for refractory materials). Purchasing an “equivalent” may therefore be risky.

In most cases the manufacturers’ data sheet will be used to compare different products. However, a refractory specification is not the same as a data sheet. A data sheet is a very incomplete summary of the composition and properties of the specific material. Manufacturers publish limited data in order to prevent competitors from duplicating material too easily; by doing this though they are also able to change raw materials without changing data sheets.

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Properties in a data sheet are often related to quality assurance parameters and are based on values obtained from many different batches - which means that what you receive in one delivery may vary significantly from what you receive in the next delivery batch.

Best Practice Guidelines When Placing an Order

As best practice during a refractory replacement project, any material specified, ordered and manufactured, should be quality checked before clearance for delivery is given. This is something that could be adapted as a standard commercial practice in placing a refractory material order. Normally the quality conformance tests that are carried out by the manufacturer are often limited to bulk density, apparent porosity and cold crushing strength. In the petrochemical industry, where high temperatures, high pressures and flammable gases are involved, careful selection of good quality materials is imperative.

1. The main objective of quality-checking prior to delivery is to firstly to ensure that the material manufactured complies with the specifications set out by the designer. For this, the material should be tested for the properties that are very specific to the critical criteria of the design, e.g.:

a. Erosion-resistant material should be tested for strength and erosion.b. Insulating material should be tested for insulating properties.c. Material used in reducing atmospheres should be tested for CO-resistance.

2. Another objective of the quality checking exercise is to obtain a set of reference data based on laboratory tests under ideal conditions for that specific batch of material. The properties of samples taken during installation can then be compared to these reference values and hence problems can be identified early.

As an example:During higher ambient temperatures the likelihood would be that the installer would add more water to aid installation. The final properties of some materials are very sensitive to changes in water addition. This may reduce, for example, the values of cold crushing strength compared to laboratory reference samples. However, this data needs to be compared with actual values from the particular batch of material as well as the general data sheet values from the supplier. Should the addition of more water jeopardise the final integrity of the lining, a decision can be made to invest in cooling the material prior to installation.

3. Lastly, casting samples of the material prior to installation gives valuable information about the workability and behaviour of the material, which is very important when planning the installation schedule. Mixing characteristics, water sensitivity, flowability, the effect of vibration, working time, setting time and strength development are all important parameters that the installation team should be aware of. Sometimes an agent from the material manufacturer oversees the installation, but, as previously stated, not all batches may behave in the same manner. Therefore, this knowledge is essential, even though the material expert may be on site.

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Page 5: Guide to Purchasing Monolithic Refractory Materials

Testing Programme

A typical test programme for the castable material to be used in a petrochemical vessel would look something like this:

1. Measurement of the permanent linear change and thermal expansion, as these will indicate whether the material in the vessel will be in compression and that all joints will be tightly closed during operation.

2. Measurement of CO-resistance, as in a reducing atmosphere, with the presence of carbon monoxide, the reaction of free iron oxide can cause carbon bursting and lead to material deterioration.

3. A full chemical analysis to ensure no unnecessary contaminants are present in the material.

4. Strength development under a range of water additions to determine the time required for material to harden. This information is important for decisions made on when shuttering can be removed or vessels transported. Bulk density and cold crushing strength would be used as indicators.

5. General workability properties of the material such as setting time and flow tests which will assist with the general planning of the installation such as mixing sizes, etc.

Testing Procedure

1. Identify the different batches of material supplied. Do not rely only on a serial number. A batch is a bulk of material which, under the mixing conditions of the specific manufacturing plant, should have the same properties. For such an installation the material would most probably be in 25Kgs bags. Select three bags per batch.

2. Empty the bags into a mixer and dry mix to ensure homogeneity then split the material into three equal, homogenous parts of roughly 15Kgs each.

3. Mix each 15Kgs sample with different amounts of water – the minimum, that recommended by the manufacturer and a realistic excess.

4. Cast each 15Kgs sample into eighteen 50mm cubes, three 125 x 25 x 25mm bars, a 230 x 114 x 76 standard brick, two 75 x 50 x 50 cubes and use the remaining material for setting and flowability testing.

The following tests should then be conducted on the samples:

1. From the excess material, the working time and the setting time of the material will be determined. Working time is considered to be the time at which the material can still be vibrated effectively into a former; setting time is when sufficient strength has developed to allow mould removal.

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2. From the 50mm cubes the strength development will be tested under temperatures similar to expected installation conditions.

a. Three cubes will be left for 6 hours before cold crushing is performed.b. Three cubes will be left for 12 hours before cold crushing is performed.c. Three cubes will be left for 24 hours before cold crushing is performed.d. Three cubes will be left for 48 hours before cold crushing is performed.

3. Also, from the 50mm cubes, standard cold crushing, bulk density and apparent porosity will be carried out on three cubes dried out at 110°C.

4. Similarly, for three cubes, cold crushing, bulk density and apparent porosity will be carried out on the material dried out and fired to a temperature close to that of operation.

5. The one standard brick will be used to determine permanent linear change at 110°C, 350°C and then at the design temperature of the unit.

6. The one 125 x 25 x 25mm bar will be used to determine thermal expansion up to operating temperature.

7. One chemical analysis will be carried out on dry material.

8. One CO-resistant test will be done with the two samples of 70 x 50 x 50mm for 200 hours.

Conclusion

Buying a refractory material seems to many as just another materials purchase, in that they choose either the cheapest product, the best branded one or the best selling one. Users of refractory materials should, however, be much more cautious about what and how they buy.

The first step is to ensure that the best product is chosen for that specific application based on how it will perform in the unit. Should it be specified by the designer, the buyer should ensure that they are in possession of proper technical specifications for the product.

The second step is to make sure that what is ordered is what is received. The best option is to check that the material is made to a proper specification, and has been tested, before it leaves the supplier. This has many advantages, such as that the manufacturer will be much more careful with the order and possible defects will automatically be reduced.

The installer will appreciate the effort and will pay much more attention to the installation as he will not have the ability to blame the material, in the event of a failure.

The cost of proper pre-qualification ensures peace of mind and is also minimal to costs that can be incurred at a later stage if failure occurs.5

by Ceram.

Page 7: Guide to Purchasing Monolithic Refractory Materials

About Ceram

Ceram is an independent expert in innovation, sustainability and quality assurance of materials.

With a long history in the ceramics industry, Ceram has diversified into other materials and other markets including aerospace and defence, medical and healthcare, minerals, electronics and energy and environment.

Partnership is central to how we do business; we work with our clients to understand their needs so that we can help them overcome materials challenges, develop new products, processes and technologies and gain real, tangible results.

Headquartered in Staffordshire, UK, Ceram has approved laboratories around the world.

About the Author

Jan TheronExpertise in: RefractoriesRefractories Specialist

Jan has a BTech Chemical Engineering Degree from Cape Technicon and is a member of the Refractories Association of South Africa and Institute of Refractories Engineers.

Jan has over twelve years of industry experience and specialises in refractory maintenance management. His career has been focused on cost-effectively improving lining integrity which encompasses failure analysis, refractory selection, quality control, design evaluation and commercial contracts. Jan’s experience is diverse – from incinerators, reformers, heaters, arc furnaces, induction furnaces, through to rotary kilns, shaft kilns, sulphur burners, boilers, CFB reactors and FCC units.

He is also involved in the training of inspectors, commercial personnel and plant managers to increase their awareness of refractory applications within their organisations.

www.ceram.com by Ceram