Part 6: Designing a test at a single location

Testing a new material at one location before wider implementation helps the plant reduce the risk associated with changing the solution. However, a trial is only meaningful when the trial location is sufficiently representative, a control location is available, a measurement schedule is established, and stopping criteria are agreed in advance.

If the wrong location is selected or no control location is available, the trial may still generate measurements and records but may not accurately reflect the material’s performance. In that case, the result from one location may be extrapolated to locations with different conditions, increasing the risk when the solution is implemented on a larger scale.

1. A trial requires a control location, monitoring cycle, and stopping criteria

The three components that determine whether a trial has a sufficient basis for evaluation are:

Required component	Role in the trial	Effect if omitted
Control location	Retain the existing material at a location with equivalent conditions for comparison	It becomes difficult to distinguish whether the result comes from the new material or from changes in operating conditions
Monitoring cycle	Define the measurement times and monitoring period	Only isolated measurements are available, which are insufficient to observe a trend
Stopping criteria	Define in advance which cases allow the trial to continue and which require it to be stopped or reassessed	Post-trial results can easily be interpreted in different ways

When these three factors are defined in advance, both favorable and unfavorable results have value.

A trial without a control location only produces results for the trial location itself. A favorable result may come from the new material, but it may also result from a lighter operating load, a change in the material being handled, or the trial location receiving more frequent inspection and attention during the monitoring period.

Therefore, the control location helps separate the effect of the material from the effect of the trial conditions.

2. The trial location must be representative of the group of locations to which the result is intended to be applied

The trial location should not be selected solely because it is the most severely damaged or the easiest to access.

Location that should not be prioritized	Reason
Most severely damaged location	It may not be representative of the majority of similar locations
Most easily accessible location	Accessibility does not reflect wear conditions
Location scheduled for modification	Structural or equipment changes may cause the trial to lose its basis for comparison partway through

A more suitable location is one with conditions similar to those of the majority of comparable locations in the production line.

Wear, temperature, impact, and corrosion can be compared between the proposed trial location and equivalent locations. When these four groups of factors are under similar conditions, the trial result has a stronger basis for application to similar locations.

3. The control location needs to be equivalent to the trial location

The control location is where the existing material is retained throughout the trial period for comparison with the location using the new material.

In practice, it is difficult to find two completely identical locations. Therefore, the degree of equivalence needs to be evaluated using four criteria:

Comparison criterion	Meaning in the comparison
Same type of material flow	Different materials may create different operating conditions
Similar conditions for the four groups of influencing factors	Provides a technical basis for comparing the two locations
Equivalent intervention cycle before the trial	Helps compare repair or replacement history
Same role within the production line	One location may affect the entire line while another may affect only one item of equipment

If one criterion is not equivalent, it is necessary to clearly record which criterion differs and the extent of the difference.

This does not eliminate the value of the trial entirely, but it helps the reader understand the scope within which the result can be used and avoids treating the two locations as fully equivalent when they are not.

4. The trial location and control location must be measured at the same time

At least three measurement milestones are required:

M0: immediately after installation
M1: after the first operating cycle
M2: after the second operating cycle

M0 establishes the initial reference point for the new material. M1 provides the first data on wear rate. M2 allows the wear trend to begin to be observed.

The important point is that the trial location and control location must be measured at the same time. If the two locations are measured at different times, operating conditions may have changed, reducing the value of the comparison.

The method for establishing measurement milestones and calculating wear rate is presented in Part 4: Measuring wear rate and establishing a baseline.

5. Stopping criteria must include both unfavorable results and unusually favorable results

Stopping criteria are not used only when the trial material performs poorly.

An unusually favorable result also needs to be checked before it is used to draw a conclusion or support wider implementation.

Situation during the trial	Condition requiring attention	Action
Result worse than the control	The wear rate at the trial location is worse than at the control location from M1	Stop the trial and reassess the diagnosis
Material loses its ability to perform	Detachment from the substrate, loss of bonding, or cracking down to the base metal	Stop the trial and investigate the cause
Unusually favorable result	The wear rate is much better than expected	Remeasure and check the operating conditions during the trial period

The third case is particularly important. If a favorable result occurs during a period of lighter load, a different material type, or lower-than-normal temperature conditions, applying that result to other locations may create inappropriate expectations.

6. Not every crack is a reason to stop the trial

The type of cracking needs to be identified before deciding whether to continue or stop the trial.

For some carbide-rich hardfacing overlays, small, regular cracks running across the weld bead may occur within the overlay to relieve shrinkage stress. Therefore, the stopping criterion should not simply state “cracking occurs”.

Observed crack or damage type	Recommended action
Small, regular cracks running across the weld bead and terminating within the overlay	Continue monitoring
Cracks propagating into the base metal	Stop and inspect the welding procedure
Uniform crack network across the ceramic lining	Stop and investigate the effect of thermal shock
Material layer spalling off in sections	Stop and inspect the fastening method or thickness

The trial record needs to describe the specific crack type or damage mode rather than using only the general criterion “cracking is present.”

7. The trial record must be agreed before the material enters service

The trial design needs to be completed before the new material is put into service.

The record needs to clearly define the trial and control locations, the operating conditions at both locations, the degree of equivalence between them, the materials used, the measurement schedule, stopping criteria, and the responsibilities of the parties.

The required content includes:

trial location and control location
the four groups of influencing factors at both locations
control criteria that are not equivalent and the degree of difference
trial material and the material retained at the control location
M0, M1, and M2 milestones together with the expected timing
stopping or reassessment criteria
the person taking the measurements, the person confirming the measurement method, and the person confirming the results
operating conditions throughout the trial period

Operating conditions need to be recorded throughout the trial because they provide the basis for verification when results are unusually favorable or unfavorable.

8. Results should only be applied to locations with equivalent conditions

A trial at one location has a specific scope of conclusion.

Result that can be used	Content that should not be automatically extrapolated
Wear rate of the new material at the trial location	Wear rate at a location with different conditions
Comparison with the existing material over the same period	Service life under a different temperature range
Basis for cost calculation for an equivalent type of location	Performance across the entire plant

A favorable result at one location does not mean that the material will produce the same result at every other location in the plant.

The scope of application needs to be determined according to the degree of equivalence of the operating conditions, not merely according to the equipment name or material name.

9. At least two operating cycles and three measurement milestones are required

Under this monitoring method, the trial requires at least two operating cycles and three milestones: M0, M1, and M2.

An initial assessment can be made after one cycle, but that result needs to be understood as a preliminary conclusion.

The wear rate is not necessarily linear. One cycle is also insufficient to exclude the influence of short-term variations such as changes in the material handled, operating load, or seasonal conditions.

10. Three changes can reduce the comparative value of the trial

During monitoring, it needs to be recorded if:

the control location is subject to intervention during the trial period
operating conditions change significantly, such as material type, capacity, or temperature
the trial location is inspected, cleaned, or operated differently from normal locations

These changes do not automatically invalidate the entire trial. However, they must be recorded so that the results can be interpreted correctly within the actual context.

Particularly for the control location, if the equipment fails during operation, the plant still needs to intervene. In that case, the intervention date, cause, and work performed need to be clearly recorded so that the trial can continue to be monitored on the new basis.

11. Responsibilities of the departments within the process

Trial design requires coordination between survey engineering, operations, and the parties directly monitoring the results.

Activity	Person or department responsible
Select the trial location and control location	Survey engineer in coordination with the operations department
Confirm that the trial location is representative of the group of locations to be evaluated	Operations department
Limit intervention at the control location during the trial period	Operations department
Agree on stopping criteria	Technical departments of both parties
Measure the trial and control locations at the same time	Project engineer
Confirm the trial results	Representatives of both parties

The control location may require intervention if an operational issue arises. Therefore, the record needs to define in advance how such a case will be documented rather than assuming that the control location will remain unchanged throughout the entire trial period.

12. Notes when designing a trial at a location

Four points need to remain clear.

First, results from one location should not be automatically extrapolated to locations with different operating conditions.

Second, in practice, the control location is unlikely to be completely identical to the trial location. The degree of equivalence needs to be evaluated using the defined criteria, and the remaining differences need to be clearly recorded.

Third, a conclusion after one cycle should only be regarded as a preliminary conclusion. At least two operating cycles are required to begin observing a trend and reduce the influence of short-term variations.

Fourth, unusually favorable results also need to be rechecked. A trial period with lighter-than-normal conditions may cause the material’s performance to be evaluated more favorably than under actual wider implementation.

The design of the control location and the method of establishing stopping criteria in both directions are methods used by GAC when organizing field trials and are not a general procedure applied identically to every case.

A trial is valuable not simply because the new material produces a favorable result. Its value lies in the result being generated at a sufficiently representative location, compared with a control under the same conditions, and monitored according to criteria agreed before the trial begins.