Danfoss Guidelines for water quality in Danfoss brazed heat exchangers User guide

Danfoss A/S

Danfoss Heating Segment - DEN

BU HEX - Local Inspection Center KamnikDanfossSlovenia

Guidelines for water quality in Danfoss brazed heat exchangers with plates of EN 1.4404 ~ AISI 316L

Danfoss has prepared this guideline for the water quality of tap water and district heating water used in plate heat exchangers of stainless steel (EN 1.4404 ~ AISI 316L) brazed with pure copper (Cu), copper -nickel (CuNi) or Stainless Steel (StS). It is important to point out that the water specification is not a guarantee against corrosion, but it must be considered as a tool to avoid the most critical water applications.

Plate

Brazing material

Parameter

Unit

Value or concentration

AISI 316L

CuNi

StS

W.Nr. 1.4404

< 6.0

6,0 – 7.5

o/-

7.5 – 10.5

>10.5

<10

Conductivity

µS/cm

10 – 500

500 – 1000

>1000

<0.5

Free Chlorine

mg/l

0.5 – 1

1 – 5

Ammonia (NH3, NH4+)

mg/l

2 – 20

>20

<60

Alkalinity (HCO3-)

mg/l

60 – 300

>300

<100

Sulphate (SO42-)

mg/l

100 – 300

o/-

>300

HCO3- / SO42-

mg/l

>1.5

<1.5

o/-

Nitrate (NO3)

mg/l

<100

>100

Manganese (Mn)

mg/l

<0.1

>0.1

Iron (Fe)

mg/l

<0.2

>0.2

* Hardness ratio

0 – 0.3

0.3 – 0.5

o/-

[Ca2+, Mg2+]/[HCO3-]

>0.5

Good corrosion resistance

**Corrosion could happen when more parameters are evaluated with o

o/-

Risk of corrosion

Use is not recommended

*Hardness ration limits defined per experience and internal tests in Danfoss laboratory

**In case of three or more parameters evaluated with o consultancy is needed with Consultant for Corrosion & Microbiology or BU HHE Representative

Recommended Chloride concentration to avoid Stress Corrosion Cracking (SCC) in the stainless-steel plates:

Application temperature	Chloride concentration
at T ≤ 20°C	max 1000 mg/l
at T ≤ 50°C	max 400 mg/l
at T ≤ 80°C	max 200 mg/l
at T ≥ 100°C	max 100 mg/l

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