Part 2: Four influencing factors and the material selection sequence

Knowing that particles are harder than the surface and can cut into the material addresses only one part of the selection problem.

At an actual operating location, three other factors also need to be considered simultaneously: temperature, impact, and corrosion. The important point is that these four factors are not simply added together. Each factor plays a different role in eliminating or retaining material groups during the selection process.

Therefore, even when all field measurements are correct, following the wrong screening sequence can still lead to the selection of an unsuitable material group.

1. The roles of four factors in the selection process

The four factors to be considered include:

abrasion
temperature
impact
corrosion

During material selection, these four factors are not treated equally.

Factor	Role in the selection process
Temperature	Eliminate material groups that can no longer operate within the actual temperature range
Abrasion	Establish the lower hardness limit
Impact	Establish the upper hardness limit
Corrosion	Further eliminate options from the remaining material groups

1.1. Temperature is checked first because it can eliminate an entire material group

A material group may be suitable in terms of hardness or abrasion resistance, but if the temperature at the location exceeds its operating limit, the remaining advantages are insufficient to retain that group as an option.

Therefore, the upper operating temperature limit needs to be checked before comparing other properties.

1.2. Abrasion establishes the lower hardness limit, while impact establishes the upper limit

Abrasive wear caused by scratching particles requires the surface to be sufficiently hard relative to the particles acting on it.

Impact, however, establishes an upper limit. As hardness increases, the ability to deform and absorb impact may decrease.

This creates two boundaries:

lower hardness limit: the minimum hardness required to limit particle cutting of the surface
upper hardness limit: the maximum hardness that can be used before the material no longer has sufficient toughness for the impact conditions

If the lower hardness limit exceeds the upper hardness limit, a single material may not satisfy both requirements simultaneously.

This result does not mean that the selection process is incorrect. It indicates the need to consider combining multiple material groups or changing the conditions acting on the location.

You can learn more about the relationship between hardness, toughness, and the applicable limits of each parameter in Part 1: Material properties and trade-offs in material selection.

2. Four groups of data are required before evaluating material options

The selection process is only meaningful when the input data accurately reflect the conditions at the location.

At a minimum, the following need to be recorded:

Factor	Required data
Abrasion	Particle size, particle hardness, solids concentration, flow velocity
Temperature	Operating temperature and peak temperature
Impact	Drop height, maximum lump size, impact frequency
Corrosion	Moisture content, pH, chemical composition

Omitting one factor does not merely make the result less accurate. Each omitted data group can lead to a different type of incorrect material selection.

For example:

failure to record peak temperature may result in retaining a material group whose temperature limit has already been exceeded
failure to record lump size or drop height may result in selecting an excessively hard material for a location subjected to severe impact
failure to record the chemical environment may overlook the risk of corrosion
failure to determine particle hardness leaves the lower hardness limit without a sufficient basis

If sufficient data are not yet available, the appropriate approach is to return to the survey stage rather than filling in missing information with assumptions.

3. Step 1: Eliminate material groups that do not meet the temperature requirements

Operating temperature and peak temperature are used to eliminate material groups that no longer fall within a suitable operating range.

When the temperature exceeds	Material groups to eliminate during initial screening
80 °C	Polymeric materials
250 °C	Conventional wear-resistant steels
350 °C	Cast basalt, standard-grade cast ceramics and porcelain, bimetallic steel, hard cast alloys
400 °C	Standard-grade hard compounds
550 °C	Smooth stainless steel
750 °C	All metallic material groups
1,000 °C	Standard-grade alumina ceramics, cast zirconium-corundum ceramics
1,200 °C	Heat-resistant hard compounds, sintered zirconium-corundum ceramics
Above 1,200 °C	High-temperature ceramic groups remain, such as silicon carbide and certain high-purity alumina grades

The temperature thresholds above are used for screening by material group and do not replace the technical specifications of individual grades.

Within the same group, individual grades may have significantly different temperature limits. After narrowing down the material groups, the current technical documentation for the intended grade still needs to be consulted.

4. Step 2: Establish the lower hardness limit according to abrasion severity

After eliminating material groups that are unsuitable in terms of temperature, the next step is to compare the hardness of the abrasive particles with the hardness of the remaining material groups.

If the particles are harder than the surface, they can still cut into the surface and remove material.

This does not mean that the material must be eliminated immediately. However, the person making the selection needs to clearly understand that the surface remains softer than the particles and that the scratching mechanism has not been eliminated.

In that case, service-life evaluation must be based on these actual conditions rather than assuming that a material described as “wear-resistant” can no longer be affected by the particles.

You can learn more about comparing particle hardness with material hardness, as well as the differences between Mohs, Brinell, Vickers, and declared value categories, in Part 1: Material properties and trade-offs in material selection.

5. Step 3: Establish the upper hardness limit according to impact conditions

This step proceeds in the opposite direction to the abrasion-resistance requirement.

Greater drop height, larger lump size, and higher impact frequency increase the requirements for toughness and impact resistance.

If hardness is continually increased solely to resist abrasion, the material may move outside the range suitable for the impact conditions.

An indication requiring attention is a change in failure mode from progressive thickness loss due to wear to cracking or spalling.

In that case, the following need to be rechecked:

drop height
maximum lump size
impact frequency
impact resistance of the material

This failure mode indicates that the problem is no longer simply one of “insufficient hardness.”

6. Step 4: Continue screening according to corrosion conditions

After temperature, abrasion, and impact have been evaluated, the remaining material groups are further assessed according to the actual chemical environment.

Three required data points include:

moisture content
pH
chemical composition

If the environment changes significantly with the season, the data also need to be considered under the corresponding operating conditions at each point in time.

Dry-season data should not automatically be used to represent rainy-season conditions if moisture content or material condition has changed significantly.

Similarly, describing a material as “corrosion-resistant” or “chemically inert” is only meaningful when associated with a specific environment.

7. After the four screening steps, the result generally falls into four cases

The selection process does not necessarily have to return a single material group.

Result	Meaning	Next course of action
One group remains	The conditions have clearly narrowed down the options	Develop a specific solution
Multiple groups remain	Several options are technically suitable	Compare service life, installation feasibility, and budget
No single group meets all requirements	The requirements at the location are conflicting	Consider combining multiple material groups
Insufficient data	Input data are insufficient for selection	Return to the survey stage

If multiple groups remain, the next step is not to continue eliminating options until only one material name remains. The options can be further compared based on:

expected service life
installation feasibility
fastening method
equipment downtime
budget

If no single group meets all requirements, you can learn more about dividing the working surface into zones and addressing transition areas in Part 5: Combining multiple materials at one location: design principles and interface control.

8. Material-group selection table according to operating conditions

The table below is intended for screening and relative comparison between material groups, not for use as a calculation formula.

Material group	Abrasion resistance	Upper temperature limit	Thermal shock	Impact	Maximum flow velocity	Points requiring attention
Wear-resistant steel, quenched and tempered plate	+++	Approximately 250 °C, with heat-resistant grades up to approximately 500 °C	++	+++	Not specified	Can be welded, bent, and formed
Powder-sintered bimetallic steel	++++	350 °C, with heat-resistant grades up to 750 °C	+++	+++	20 m/s	High abrasion and impact resistance among metallic materials
Hard cast alloys	++++	350 °C	+++	++	20 m/s	Can be cast into complex, self-supporting shapes
Fused cast basalt	+++	350 °C	+	+	20 m/s	Hardness of approximately 8 Mohs, durable smooth surface
Cast ceramics, porcelain	++	350 °C, with heat-resistant grades up to 1,000 °C	+	+	20 m/s	Smooth surface
Cast zirconium-corundum ceramics	++++	1,000 °C	++	++	30 m/s	Durable smooth surface, corrosion-resistant
Sintered zirconium-corundum ceramics	+++	1,200 °C	+++	++	25 m/s	Better thermal-shock resistance than cast grades
High-alumina ceramics	++++	1,000 °C, with high-purity grades up to 1,400 °C	+	+	30 m/s	Can be manufactured from 1.5 mm thickness
Nitride-bonded silicon carbide ceramics	+++	1,550 °C	++++	+	25 m/s	High upper temperature limit and thermal-shock resistance
Silicon-infiltrated silicon carbide ceramics	++++	1,250 °C	++++	++	35 m/s	Highest flow-velocity range in the table
Hard compounds, sprayed, trowelled, or cast	++++	400 °C, with heat-resistant grades up to 1,200 °C	++	++	20 m/s	Do not create numerous joints; can be repaired in situ
Smooth stainless steel	++	550 °C	Not rated	++	Not specified	Can be used where abrasion and material sticking occur simultaneously
Polymeric materials	+	80 °C	Not rated	Not rated	Not specified	High material-flow promotion capability, lightweight

The + symbols in the table represent a relative comparison scale between material groups, not a unit of measurement.

“Not rated” means that the technical documentation does not evaluate that parameter for the corresponding group; it does not mean that the capability is zero.

The velocity in the table refers to material-flow velocity, not conveyor-belt speed or equipment rotational speed.

9. Damage patterns can guide measurements before sufficient data are available

When sufficient measurements are not yet available, surface damage patterns can help determine which parameters should be checked first.

Observed indication	Mechanism to consider	Data requiring verification
Parallel marks aligned with the flow direction	Abrasive wear caused by scratching particles	Particle size, particle hardness
Indentations with craze cracking around the indented areas	Fatigue wear under impact loading	Drop height, lump size
Uniform, fine surface ripples aligned with the flow direction	Abrasive wear caused by particle-laden flow	Flow velocity, solids concentration, angle of incidence
Scattered pitting without a clear directional pattern	Chemical action	Moisture content, pH, chemical composition
Widespread lining detachment after a period of operation	Both the fastening system and environmental conditions need to be checked	Temperature, moisture content, solids concentration
Wear and material build-up occurring at the same location	Two problems occurring simultaneously	Both wear data and material-sticking data
Damage over a large area, with multiple joints failing simultaneously	The influence of the lining structure needs to be considered	Area, geometry, and installation method

This table only helps determine the direction of further investigation. The final conclusion must still be based on data from the actual operating location.

10. Example of applying the complete selection sequence

Assume that an iron ore silo during the rainy season operates under the following conditions:

particle hardness of approximately 6 Mohs
temperature at ambient conditions
material falling from a conveyor at a moderate drop height
seasonally high moisture content

The sequence can be applied as follows:

Step 1 – Temperature: no significant material groups are eliminated based on the temperature conditions.

Step 2 – Abrasion: particles with a hardness of approximately 6 Mohs establish a surface-hardness requirement.

Step 3 – Impact: the impact severity is not high, so the upper hardness limit remains relatively broad.

Step 4 – Corrosion and moisture: the moist environment further narrows down the remaining material groups.

According to the example in the source, the groups retained for consideration include cast basalt or ceramics.

This is an example of how to apply the screening sequence, not a general recommendation for every iron ore silo. When the data at the location change, the selection result may also change.

11. Responsibilities of the departments

Activity	Person or department responsible
Record the four groups of input data	Survey engineer
Carry out the screening process and identify material groups	Materials engineer or solution provider
Confirm that the operating conditions accurately reflect actual conditions	Operations supervisor at the location
Compare and select among the remaining options	Operating party

The verification of operating conditions directly determines the reliability of the entire process.

Even a correct selection table can lead to an unsuitable solution if the input data do not accurately reflect the actual operating conditions.

12. Notes when applying this knowledge

First, the plus signs in the table indicate only relative comparison levels between material groups. The plus signs must not be used as quantities in calculations.

Second, the temperature thresholds are presented by material group. Within the same group, individual grades may have different limits. Once the material groups have been narrowed down, the current technical specification for the specific grade needs to be consulted.

Third, the selection sequence in this article first determines technical suitability; it does not directly establish the most economically advantageous solution. Service life, budget, and shutdown cycles need to be evaluated in the next step.

Fourth, installation feasibility is not fully reflected in the selection table. A material group that is suitable for the operating conditions may still be unsuitable for the equipment geometry, fastening method, or available downtime.

The selection sequence can be summarized in four steps: temperature eliminates material groups that can no longer operate under the conditions, abrasion establishes the lower hardness limit, impact establishes the upper hardness limit, and corrosion further narrows down the options. When the input data are complete and accurately verified at the location, this process helps narrow a very broad list of materials down to a number of groups with a technical basis for further comparison.