39 Recovery Analysis of Domestic Electric Storage Water Heaters
595
We suggest below a guide for the inspection process of a used DESWH in order
to determine whether it is or not remanufacturable, and to what extent.
Step 1—External review: Thoroughly examine the outside of the DESWH for
any signs of corrosion, denting or breakage. If there is corrosion, grade the DESWH
as non-remanufacturable. If there is not corrosion, but there is an appreciable dent
or break, go to Step 2.2. Otherwise, go to Step 2.1.
Step 2.1—Non-destructive disassembly: Open the DESWH in order to access the
storage tank. Go to Step 3.
Step 2.2—Destructive disassembly: Remove the outer case and the insulation
coverage of the DESWH in order to access the storage tank. Go to Step 3.
Step 3—Hydraulic test: Verify the tank can resist a critical pressure value without
suffering water loss for a certain period of time. If it is, go to Step 4, otherwise grade
the DESWH as non-remanufacturable.
Step 4—Rust evaluation: If the sacrificial anode and/or the inside of the tank show
hints of corrosion, go to Step 5, otherwise grade the DESWH as remanufacturable.
End.
If the anode is completely consumed, this will be a sign that the tank is corroded.
In this case the condition of the tank cannot be guaranteed, and a second level rust
evaluation must be carried out. Go to Step 5.
Step 5—Rust study: Carry out a non-destructive study in order to determine if the
tank is or not corrupted by rust. If it is not, grade the DESWH as remanufacturable,
otherwise grade it as non-remanufacturable. End.
From Step 3, we note that in order to grade a used DESWH as a remanufacturable,
it must verify the hydraulic test. Compliance is verified by subjecting the device to
a hydraulic pressure equal to twice the nominal pressure. If the DESWH is fed by
means of a pressure reducing device, instead of subjecting the DESWH to pressure,
it is subjected to twice the service pressure (Standard UNIT-IEC 60335-2-21:2012
with adoption of UNIT in 2015 Safety of household appliances and similar ones—
Part 2: Particular requirements for storage water heaters). The hydraulic test of Step
3 should be the same that the one carried out for a newly manufactured DESWH. The
conformity of the test guarantees that the tank is not punctured and that the original
structure is maintained.
To carry out Step 5, there are different alternatives, but here we propose two of
them. One of them is to measure the corrosion between the anode and the point on the
surface that is presumed most affected. Through a quantitative study it is possible to
obtain the difference of potentials, and thus estimate the internal DESWH corrosion.
Another feasible procedure for the non-destructive rust study of the tank is to measure
the thickness of the most affected area by the oxide, for example using an ultrasonic
thickness gauge, and compare the value obtained with a nominal thickness value.
In order to summarize the inspection guide of above, a diagram is provided
in Fig. 39.2. The diagram depicts the flow of activities in order to determine
the quality level of a used DESWH returned to the origin. Boxes and arrows in
Fig. 39.2 represent the steps and the order of them. Dashed lines as well as dashed
boxes indicate the classification of an inspected DESWH, i.e. remanufacturable or
non-remanufacturable.
595
We suggest below a guide for the inspection process of a used DESWH in order
to determine whether it is or not remanufacturable, and to what extent.
Step 1—External review: Thoroughly examine the outside of the DESWH for
any signs of corrosion, denting or breakage. If there is corrosion, grade the DESWH
as non-remanufacturable. If there is not corrosion, but there is an appreciable dent
or break, go to Step 2.2. Otherwise, go to Step 2.1.
Step 2.1—Non-destructive disassembly: Open the DESWH in order to access the
storage tank. Go to Step 3.
Step 2.2—Destructive disassembly: Remove the outer case and the insulation
coverage of the DESWH in order to access the storage tank. Go to Step 3.
Step 3—Hydraulic test: Verify the tank can resist a critical pressure value without
suffering water loss for a certain period of time. If it is, go to Step 4, otherwise grade
the DESWH as non-remanufacturable.
Step 4—Rust evaluation: If the sacrificial anode and/or the inside of the tank show
hints of corrosion, go to Step 5, otherwise grade the DESWH as remanufacturable.
End.
If the anode is completely consumed, this will be a sign that the tank is corroded.
In this case the condition of the tank cannot be guaranteed, and a second level rust
evaluation must be carried out. Go to Step 5.
Step 5—Rust study: Carry out a non-destructive study in order to determine if the
tank is or not corrupted by rust. If it is not, grade the DESWH as remanufacturable,
otherwise grade it as non-remanufacturable. End.
From Step 3, we note that in order to grade a used DESWH as a remanufacturable,
it must verify the hydraulic test. Compliance is verified by subjecting the device to
a hydraulic pressure equal to twice the nominal pressure. If the DESWH is fed by
means of a pressure reducing device, instead of subjecting the DESWH to pressure,
it is subjected to twice the service pressure (Standard UNIT-IEC 60335-2-21:2012
with adoption of UNIT in 2015 Safety of household appliances and similar ones—
Part 2: Particular requirements for storage water heaters). The hydraulic test of Step
3 should be the same that the one carried out for a newly manufactured DESWH. The
conformity of the test guarantees that the tank is not punctured and that the original
structure is maintained.
To carry out Step 5, there are different alternatives, but here we propose two of
them. One of them is to measure the corrosion between the anode and the point on the
surface that is presumed most affected. Through a quantitative study it is possible to
obtain the difference of potentials, and thus estimate the internal DESWH corrosion.
Another feasible procedure for the non-destructive rust study of the tank is to measure
the thickness of the most affected area by the oxide, for example using an ultrasonic
thickness gauge, and compare the value obtained with a nominal thickness value.
In order to summarize the inspection guide of above, a diagram is provided
in Fig. 39.2. The diagram depicts the flow of activities in order to determine
the quality level of a used DESWH returned to the origin. Boxes and arrows in
Fig. 39.2 represent the steps and the order of them. Dashed lines as well as dashed
boxes indicate the classification of an inspected DESWH, i.e. remanufacturable or
non-remanufacturable.