Testing Guide

DOWTHERM and DOWFROST heat transfer fluids

The free Fluid Analysis Program is offered to customers currently using over 250 gallons (10,000 Liters) of DOWTHERM™SR-1, DOWTHERM 4000, DOWFROST™, DOWFROST HD heat transfer fluids.

The analysis includes appearance evaluation, tests on corrosion inhibitors and freezing point.

This simple guide helps you to interpret what each test means and provides a profile of fluid changes over time, which allows you to identify trouble from product contamination or thermal decomposition that may occur in DOWTHERM or DOWFROST heat transfer fluids.

Appearance

Test Test Significance (HTF)
Color Describes the color of the sample as it was received. Brand new DOWTHERM or DOWFROST inhibited glycol based heat transfer fluids are dyed (pink, orange, yellow) or are colorless depending on product type. Fluids which are dark brown or black indicate substantial glycol degradation products, excessive contamination, and/or corrosion by-products.
Clarity Properly installed and maintained fluid will be clear or only slightly hazy. Fluids with a hazy appearance either contain suspended solids or insoluble liquids (oils). Suspended solids may be due to fabrication debris or may form by precipitation with hard water ions (calcium or magnesium). The presence of oils may suggest leakage of oil cooled equipment has occurred, or that residual oils or greases were not removed prior to fluid installation. It may mean that excessive degradation of the glycol base fluid has occurred. The presence of haziness or sediment is not typically cause for fluid disposal since this problem can normally be remedied by on-line filtration. However, samples with gross levels of suspended material or insoluble liquids at more than 5% by volume means the material is no longer suitable as a heat transfer fluid for the system.
Sediment Fabrication debris is commonly found in fluids which were not cleaned prior to installation, e.g. welding flash, pipe scale, corrosion deposits, even dirt, sand and other contaminants can be present. Fluids re-circulating with high levels of sediment can cause erosion of piping and premature wearing of mechanical pump seals. The presence of sediment is not typically cause for fluid disposal since this problem can normally be remedied by on-line filtration. However, samples with gross levels of suspended material or insoluble liquids i.e. more than 5% are no longer suitable as a heat transfer fluid for the system.

Concentration & Freeze Point

Test Test Significance (HTF)
Ethylene Glycol Desired range is between 25%-60%. Gas chromatography is used to determine actual concentration of ethylene glycol and propylene glycol, as well as the presence of other contaminant glycols not used (i.e. diethylene glycol or triethylene glycol). In addition to providing the necessary freeze protection, the concentration of glycol is important for other reasons. With too low of a concentration, i.e. less than 25%, fluids are subject to bio-organism contamination and bio-film fouling. At too high of a glycol concentration, i.e. above 60%, no additional freeze depression is realized but heat transfer efficiency will fall off substantially.
Freeze Point Dow recommends selecting a glycol concentration which freezes at least 5ºF below your lowest anticipated operating/exposure temperature. We calculate freeze point based on the measured amount of glycol.

Corrosion Inhibitors

Test Test Significance (HTF)
Iron inhibitor We test for the specific corrosion inhibitors we know to be present in our fluids, plus a few others. We report the fluid’s ability to protect iron (ferrous metals) from corrosion by listing the status of the iron inhibitors as either “high”, “acceptable”, “low”, “exhausted” or “inadequate”.
High iron inhibitors A “high” level means too much inhibitor has been added and further increases in concentration could have detrimental effects on fluid performance.
Acceptable iron inhibitors An “acceptable” level means the iron inhibitors are within our acceptable range and it is not necessary to increase their concentration.
Low iron inhibitors A “low” level means the fluid should be restored to an acceptable condition by adding more inhibitor. A recommendation of the type of inhibitor and how much inhibitor to add per 100 gallons of system volume will be given.
Exhausted iron inhibitors Fluids which have an “exhausted” level of inhibitors are recommended for disposal, i.e. the fluid has reached the end of its useful life.
Inadequate iron inhibitors A status of “inadequate” is where the inhibitors are within normal concentration ranges, but chlorides and/or sulfates are excessively high. This is inadequate corrosion protection when system temperature is at or more than 190ºF.
Copper inhibitor We test for the specific corrosion inhibitors we know to be present in our fluids, plus a few others. We report the fluid’s ability to protect copper from corrosion by listing the status of the copper alloy corrosion inhibitors as either “high”, “acceptable”, “low”, “exhausted” or “inadequate”.
High copper inhibitors A “high” level means too much inhibitor has been added and further increases in concentration could have detrimental effects on fluid performance.
Acceptable copper inhibitors An “acceptable” level means the copper inhibitors are within our acceptable range and it is not necessary to increase their concentration.
Low copper inhibitors A “low” level means the fluid should be restored to an acceptable condition by adding more inhibitor. A recommendation of the type of inhibitor and how much inhibitor to add per 100 gallons of system volume will be given.
Exhausted copper inhibitors Fluids which have an “exhausted” level of inhibitors are recommended for disposal, i.e. the fluid has reached the end of its useful life.
Inadequate copper inhibitors A status of “inadequate” is where the inhibitors are within normal concentration ranges, but chlorides and/or sulfates are excessively high. This is inadequate corrosion protection when system temperature is at or more than 190ºF.
Fluid pH New Dow heat transfer fluids with a pH of more than 9.0. Fluid pH will typically decrease with time because of thermal-oxidative degradation of the glycol base fluid. Degradation of glycol produces acidic compounds which cause the pH of your fluid to decrease with time. The buffers present in our fluids minimize pH drop by neutralizing these acid compounds. Meanwhile the corrosion inhibitors will protect your system from corrosion as long as fluid pH remains above 8.0 and below about 10.5. Fluids with pH above 10.5 may require special attention and assistance from Dow Technical Service.

Fluids will pH between 7.0 and 8.0 can be re-adjusted back to acceptable ranges by suitable addition of 50% caustic. When such pH adjustment is necessary, we provide specific directions on how to do so. Should fluid pH ever fall below 7.0, we recommend fluid disposal because insoluble (oil-like) glycol degradation products will form at this low pH range, meaning it is no longer possible to restore the fluid to acceptable condition by simple pH adjustment i.e. does not remove the contaminants.
Reserve Alkalinity Alkalinity above pH 5.5 found in 10 mLs of fluid sample. RA is a measure of the buffering capacity of the fluid.

Corrosives & Scale Promoters

Test Test Significance (HTF)
Chloride A corrosive ion. Properly installed DOWTHERM or DOWFROST fluids will have less than 25 ppm chloride. At high enough concentrations, the presence of chloride can render the inhibitor package ineffective. High chloride is caused by failure to use de-ionized or distilled water during system top-ups /dilutions. Its presence can increase the corrosion rate (most particularly pitting corrosion) of most metals. Systems containing more than 100 ppm chloride may experience excessive corrosion if other fluid parameters are also outside recommended ranges. The corrosive effect of chloride is more severe at higher fluid temperatures. Excessive corrosion rates caused by elevated chloride levels often can only be corrected by removal and replacement of the contaminated fluid.
Sulfate A corrosive ion. Properly installed DOWTHERM or DOWFROST fluids will have less than 25 ppm sulfate. Sulfate is also caused by failure to use de-ionized or distilled water. In addition sulfates may also form by using sulfur-based (non-Dow) corrosion inhibitors such as MBT. It can substantially increase the corrosion rate of your fluid, although less so than chlorides. Systems containing more than 250 ppm sulfate may experience excessive corrosion if other fluid parameters are also outside recommended ranges. The corrosive effect of sulfate is more severe at higher fluid temperatures. Excessively high corrosion rates caused by elevated sulfate levels often can only be corrected by removal and replacement of the contaminated fluid.
Total Hardness Expressed in ppm as calcium carbonate, with <100 ppm as CaCO3 being desirable. It is the amount of calcium and magnesium ions present in your fluid. High hardness is caused by using a poor quality water such as river water, well water or even tap water. Hard water ions, like calcium and magnesium, will react with most corrosion inhibitors, but particularly phosphates, to form insoluble scales on heat transfer surfaces. This reduces the active concentration of corrosion inhibitors as well as decreasing heat transfer efficiency. Systems are susceptible to localized hot spots and excessive corrosion. To correct this problem, the fluid should be dumped, drained and re-filled. The system should be cleaned with industrial cleaner prior to re-filling with new fluids.
Ferrous metal corrosion rate A calculated value based on the overall condition of your fluid. As a point of reference, new Dow fluids exhibit a ferrous metal corrosion rate below 0.05 mils per year, whereas the recommended maximum corrosion rate as established by ASTM is 0.5 mils per year. Dow Chemical has developed an extensive library for all of our fluids based on thousands of corrosion testing measurements. Dow reliably predicts the corrosion rate for our fluids to within plus or minus 0.1 mils per year (MPY). However it is not possible for us to accurately calculate corrosion rates for non-Dow fluids, mixtures which are predominately non-Dow in nature, or Dow fluids which have been altered significantly from their original design. The reported corrosion rate is an excellent tool in assessing the overall health of your system.
Copper alloys corrosion rate A calculated value but data is specific to copper and copper alloys such as brasses and bronzes. Again, newly installed Dow fluids will exhibit a corrosion rate below 0.05 mils per year, while the recommended ASTM maximum is 0.5 mils per year.

Contaminants & Other Glycols

Test Test Significance (HTF)
Nitrite Nitrite is not present as a corrosion inhibitor in DOWTHERM or DOWFROST heat transfer fluids. For properly installed Dow fluids, nitrite should be zero or at worst no higher than 100 ppm. If you desire to utilize a heat transfer fluid which contains nitrite, we recommend the use of NORKOOL SLH. If you are not using Norkool SLH then the presence of nitrite may indicate the use of the “wrong” product e.g. an automotive coolant or the use of water treatment chemicals. HVAC systems perform best when a fluid that is specifically designed for HVAC systems are used. Even the mixing of two different fluids with different types of inhibitor packages can sometimes be antagonistic (means the resulting mixture will have a higher rate of corrosion than either of the fluids left unmixed).
Nitrate Nitrate should not be present in any Dow fluid, not even NORKOOL SLH. Its presence typically signals the use of non-Dow products such as automotive coolants or the use of water treatment chemicals. While the presence of nitrates themselves are not normally detrimental, they are a good indicator of non-Dow fluid or atypical operation i.e. they should be zero or and no higher than 100 ppm.
Mercaptobenzothiazole (MBT) Mercaptobenzothiazole (MBT) or mercaptobenzothiazole is a sulfur based, non-Dow additive, which is commonly used as a corrosion inhibitor by many water treatment companies owing to its low cost. MBT oxidizes readily to form disulfides and eventually corrosive sulfates.
Diethylene Glycol (DEG) A contaminant glycol found in lower grade products such as automotive antifreeze, or those based on recycled ethylene glycols. In special circumstances, DEG may also form by excessive thermal degradation of mono-ethylene glycol. Thus, its presence always indicates an undesirable contaminant, and it should be less than 1%.
Triethylene Glycol Typically used in gas dehydrators and may also be used in non-HVAC, industrial type heat transfer fluids such as Tritherm™. It is not present in new DOWTHERM or DOWFROST heat transfer fluids so its presence indicates a contaminant product.