Notes On Pipe Corrosion - Mitsubishi Electric QAHV Série Manuel D'installation & D'instructions

[2] Notes on Pipe Corrosion

Water treatment and water quality control
Poor-quality circulating water can cause the water-side heat exchanger to scale up or corrode, reducing heat-
exchange performance. Properly control the quality of the circulating water.
• Removing foreign objects and impurities in the pipes
During installation, keep foreign objects, such as welding and sealant fragments and rust, out of the pipes.
• Water Quality Control
(1) Poor-quality water can corrode or scale up the heat exchanger. Regular water treatment is recommended.
Water circulation systems using open heat storage tanks are particularly prone to corrosion.
When using an open heat storage tank, install a water-to-water heat exchanger, and use a closed-loop circuit
on the air-conditioner side. If a water supply tank is installed, keep contact with air to a minimum, and keep the
level of dissolved oxygen in the water no higher than 1 mg/ℓ.
(2) Water quality standard
pH (25ºC) (77ºF)
Electric conductivity
Chloride ion
Standard
Sulfate ion
items
Acid consumption
Calcium hardness
Ionic silica
Iron
Copper
Sulfide ion
Reference
items
Ammonium ion
Residual chlorine
Free carbon dioxide
Reference: Guideline of Water Quality for Refrigeration and Air Conditioning Equipment. (JRA GL02E-1994)
(3) Please consult with a water quality control specialist about water quality control methods and water quality
calculations before using anti-corrosive solutions for water quality management.
(4) When replacing an air conditioner (including when only the heat exchanger is replaced), first analyze the water
quality and check for possible corrosion.
Corrosion can occur in water systems in which there has been no signs of corrosion. If the water quality level
has dropped, adjust the water quality before replacing the unit.
(5) Suspended solids in the water
Sand, pebbles, suspended solids, and corrosion products in water can damage the heating surface of the heat
exchanger and cause corrosion. Install a good quality strainer (60 mesh or better) at the inlet of the unit to filter
out suspended solids.
(6) Connecting pipes made from different materials
If different types of metals are placed in direct contact with each other, the contact surface will corrode.
Install an insulating material between pipes that are made of different materials to keep them out of direct
contact with each other.
Higher mid-range temperature
Water Temp. > 60ºC (140ºF)
Items
(mS/m) (25ºC)(77ºF)
(µs/cm) (25ºC)(77ºF)
-
(mg Cl /ℓ)
2-
(mg SO4 /ℓ)
(pH4.8) (mg CaCO /ℓ)
3
(mg CaCO /ℓ)
3
(mg SiO /ℓ)
2
(mg Fe/ℓ)
(mg Cu/ℓ)
2-
(mg S /ℓ)
+
(mg NH /ℓ)
4
(mg Cl/ℓ)
(mg CO /ℓ)
2
water system (with secondary side control enabled)
Recirculating water
6.5 ~ 8.0
30 or less
[300 or less]
30 or less
30 or less
50 or less
6.5 ≤ pH ≤ 7.5 : 90 or less
7.5 ≤ pH ≤ 8.0 : 50 or less
30 or less
0.3 or less
0.1 or less
Not to be detected
0.1 or less
0.1 or less
10.0 or less
GB-15
Make-up water criteria
Water Temp. > 60ºC (140ºF)
Recirculating water Corrosive
6.5 ~ 8.0
30 or less
[300 or less]
30 or less
30 or less
50 or less
250 or less
30 or less
0.3 or less
0.1 or less
Not to be detected
0.1 or less
0.1 or less
10.0 or less
Tendency
Scale-
forming