WO2002025256A1

WO2002025256A1 - Method to determine the corrosion protection in engine coolants

Info

Publication number: WO2002025256A1
Application number: PCT/SE2001/002053
Authority: WO
Inventors: Veli Sederholm
Original assignee: Scania Cv Ab (Publ)
Priority date: 2000-09-25
Filing date: 2001-09-24
Publication date: 2002-03-28
Also published as: DE10196665T1; SE0003402D0; SE0003402L; AU2001290452A1; SE519951C2

Abstract

In a method for determination of corrosion protection in a combustion engine coolant, both the coolant's refractive index and its conductivity are measured on a small quantity of coolant taken from the engine. The values thus obtained are used together to arrive at a measure of the corrosion protection of the coolant. Lightweight handheld instruments, namely a refractometer and a conductivity meter respectively, are used for the measurements. These instruments are simple and inexpensive and quickly provide measured values of sufficient accuracy for a quick answer as to whether the corrosion protection of the coolant does or does not meet specified requirements to be achievable by means of tables, diagrams or by simple formulae or by putting these into a computer.

Description

Method to determine the corrosion protection in engine coolants

The present invention relates to a method according to the preamble to patent claim 1.

Background and state of the art

Combustion engines, e.g. a diesel engine powering a truck, may have cooling systems that usually contain between 30 and 100 litres of coolant, although certain extra equipment may increase this to more than 100 litres. Engine coolants need a certain amount of corrosion protection, which is achieved by adding corrosion protection agents to the water. Coolants on markets with cold climates also need some degree of frost protection, which is provided by adding antifreeze glycol to the coolant. Antifreeze glycol also usually contains agents with corrosion inhibiting effects. The corrosion protection of coolants is often measured simply by their antifreeze glycol content, which is typically between 30 and 60% by volume of antifreeze glycol added to potable water. However, the total corrosion protection is usually^' a combination of the protection provided by antifreeze glycol and that due to the corrosion ^"protection agent which usually takes the form of a liquid or powder added via a coolant filter forming part of the engine cooling system. The amount of corrosion protection agent currently added to the cooling system of a truck engine in the form of a so-called inhibitor package is typically approximately between 5 and 10% by volume. During subsequent operation of the vehicle, various circumstances such as leakage, ageing of ingredients etc. may alter both the corrosion protection content and the antifreeze glycol content, thereby affecting both corrosion protection and frost protection.

A practice known from, for example, American patent specification US 4147596 is determination of the content of corrosion inhibitors in the coolant of a combustion engine by measuring the conductivity of the liquid. Also known from US 5870185 is determination of the content of contaminants in a cooling medium (forming part of an air conditioning system) by measuring the refractive index of the medium. In practice there has also been previous use of test strips which react to the content of corrosion inhibiting nitrites, but that method provides only an approximately idea of corrosion protection content, owing inter alia to the fact that nitrite converts to nitrate. Moreover the use of nitrite as corrosion protection is declining because of its toxicity and the risk of aluminium components of combustion engines being attacked by pitting.

Object and most important characteristics of the invention The object of the present invention is to provide a relatively simple and reliable method of measuring corrosion protection in coolants which contain both corrosion protection agents and antifreeze glycol. The method needs to be better suited than previously used methods to field use by service personnel. In vehicle workshops, particularly in truck servicing, it is important to have a method which can be used relatively quickly to obtain a reliable measurement of corrosion protection. Standstills caused by lengthy measuring procedures cause loss of revenue to truck owners: Incorrect results may lead to unnecessary addition of expensive supplemental coolant corrosion inhibiting additives or rapid corrosion of engine cooling systems. Overdosing may also cause silicate precipitation resulting in sludge formation and^' reduced cooling capacity.

The object described above is achieved by what is indicated in the characterising part of patent claim 1.

Using measured values of not only the refractive index of a coolant but also its conductivity makes it easy to obtain by simple means a relatively reliable value for the corrosion protection of the coolant.

In one embodiment of the invention, if the measured conductivity value of the coolant is above a certain level it is used for correcting the refractive index. The thus corrected refractive index value then corresponds to a certain value for the frost protection agent content of the coolant. The conductivity value is also used for deriving a measurement of the corrosion protection agent content. This measurement, expressed as a certain quantity of frost protection agent together with the antifreeze content which corresponds to the corrected refractive index value, provides a final answer about the corrosion protection of the coolant. Using this method, relatively simple and inexpensive measuring instruments which are easy to handle are adequate to provide sufficient accuracy of measurement of coolant corrosion protection. Brief description of the drawings

Figure 1 is a diagram of an example of a refractometer calibration curve for a certain type of antifreeze glycol in predetermined contents in water.

Figure 2 shows a corresponding curve for various contents of a certain type of corrosion inhibitor agent in water. Figure 3 shows examples of conductivity meter calibration curves for various corrosion inhibitor agent contents in water relative to various antifreeze glycol contents in water. Figure 4 shows in a different way the same set of parameters as Figure 3. Figure 5 shows the conductivity for various antifreeze glycol contents in water without other corrosion inhibitor additives.

Finally, Figure 6 shows the degree of inhibition which the combined corrosion protection arising from the pure antifreeze glycbl content and the pure corrosion inhibitor agent content causes, expressed in % by volume of concentrated antifreeze glycol.

Description of an embodiment of the invention

Engine servicing involves checking coolant corrosion protection at regular intervals, particularly where there is leakage or some other particular reason. This corrosion protection is measured as that provided by the content of a predetermined antifreeze glycol in water. Said antifreeze glycol contains a predetermined amount of corrosion inhibitors. In addition, the coolant may contain a certain amount of extra corrosion protection agents which thus consist of separate corrosion inhibitors also known as inhibitor packages.

Corrosion protection agents are hereinafter also referred to as corrosion inhibitors, and antifreeze glycol is also referred to as frost protection agent.

According to the present invention, coolant corrosion protection checking is done by using as measuring instrument a refractometer by which the refractive index of the liquid can be measured, and a conductivity meter by which the conductivity of the liquid is measured.

The refractometer may be of laboratory instrument type with relatively good accuracy but it is advantageous according to the invention to use a simple handheld battery-powered refractometer, e.g. an instrument which is on the market with the designation Leica DC 60 manufactured by the company Leica Inc., Buffalo, NY, USA.

In that case the conductivity meter may also be a meter with superior or inferior accuracy, but here again it is advantageous to adopt a meter which is easy to handle, such as the battery-powered TDScan WP4 meter manufactured by the company Eutech Instruments Ptc Ltd, Singapore.

Before using the refractometer, its refractive index scale has to be calibrated relative to distilled water that gives the value of zero. The conductivity meter likewise needs calibrating relative to a predetermined solution of water containing a corrosion inhibitor which has a conductivity somewhat higher than the recommended corrosion inhibitor reference content of the liquid. If possible, the type of corrosion inhibitor used at this stage should be that contained in the liquid which is to be tested. Water here means ordinary potable water or tap water used as liquid in the workshop or the like which is to use the measuring method concerned. Said solution has to correspond to a certain value on the scale of the conductivity meter. However, calibration may also be done relative to special calibration solutions available on the market which are recommended by the instrument manufacturer.

A one-off operation which needs to be performed for both the refractometer and the conductivity meter is to develop calibration curves which are used for deriving relevant measured corrosion protection values. These calibration curves show not only the refractometer' s refractive index value but also the conductivity meter's conductivity value as a function of both the antifreeze glycol content of the water and the corrosion protection agent content of the water. Here again water means ordinary potable water of the kind mentioned above.

The diagram in Figure 1 shows an example of a refractometer calibration curve relative to a certain type of antifreeze glycol in predetermined contents in water. From Figure 1 the following relationship can be derived for the measuring method according to the invention:

B = F1* G (formula 1) where B = refractive index value, G = antifreeze glycol content and FI is a constant factor. In antifreeze glycol available on the market with the designation BASF G 48-24 from the company BASF, Germany, B varies in a substantially linear manner between 0 and 55 refractive index value units (Brix) while G varies from 0 to 100 vol% of antifreeze glycol. The corresponding value of the constant FI is approximately 0.7. Instead of indicating the refractive index value, the refractometer may express it directly as the antifreeze glycol content or the freezing temperature of the coolant.

Figure 2 shows a curve corresponding to various corrosion inhibitor contents in water. From Figure 2 the following relationship can be derived within a certain measuring range which is appropriate to the measuring method according to the invention:

B = F2* I (formula 2) where B = refractive index value, I = corrosion inhibitor content and F2 is a constant factor. A corrosion inhibitor available on the market with the designation BASF 93-94 was used to make measurements and the corresponding diagram according to Figure 2 shows the refractive index value varying in a substantially linear manner with the corrosion inhibitor content. Thus the refractive index value ranges from 0 to 8 Brix, while the corrosion inhibitor content ranges from 0 to 17 vol%. F2 corresponds to approximately 0.5, i.e. 1 vol% of corrosion inhibitor corresponds to about 0.5 Brix.

It may thus be observed from Figures 1 and 2 that the refractive index is affected to different degrees by the corrosion inhibitor content and antifreeze glycol content respectively. A measured refractive index value for a certain coolant is therefore not a reliable value for its corrosion protection. This means that the refractive index value obtained needs correcting before a correct corrosion protection value can be arrived at.

The diagram in Figure 3 shows an example of conductivity meter calibration curves with various antifreeze glycol contents in water and incorporates curves for a predetermined type of corrosion inhibitor in predetermined contents in water.

It may be observed from Figure 3 that the conductivity (expressed in mS/cm) is affected both by the antifreeze glycol content and the corrosion inhibitor content. A measured conductivity value for a certain coolant can obviously not be a reliable value for its antifreeze glycol content but may represent a relatively good value for the corrosion inhibitor content.

This situation is also reflected in the diagram according to Figure 4. Although the value for the corrosion inhibitor content depends on how large the antifreeze glycol content is, this dependency is small enough to enable the requirements specified for a method according to the invention to disregard it. Figure 4 shows that within a certain measuring range, e.g. between 6 and 10 mS/cm, which is relatively suitable for the measuring method according to the invention, the corrosion inhibitor content may range in an almost linear manner between 5 and 11 vol%. Then the following relationship can be derived:

K = F3*(I - rB) + KB (formula 3) where K = conductivity value, I = corrosion inhibitor content, KB is a conductivity base value from Figure 4, IB is a corrosion inhibitor content base value from Figure 4 and F3 is a constant factor. In corrosion inhibitors available on the market, said factor F3 has a value of between 0.6 and 0.8 and advantageously 0.7. In the example illustrated, KB = 6 mS/cm, IB = 4 vol% of corrosion inhibitor and F3 = 0.7, resulting in

K = 0.7*1 + 1.4 (formula 4)

Conductivity measurement for various antifreeze glycol contents in water without any separate corrosion inhibitors produces a curve as depicted in Figure 5 which shows the conductivity rising initially to reach a maximum value K2 at an antifreeze glycol content

G2. With the particular antifreeze glycol taken as example, the value K2 arrives at approx. 4 mS/cm when G2 assumes the value of about 35 vol% of antifreeze glycol.

Thereafter the conductivity decreases as the antifreeze glycol content of the water increases. This again shows that a conductivity value alone is not sufficient for determining the antifreeze glycol content and hence the corrosion protection of a coolant.

The conclusion may also be drawn that if the conductivity value exceeds K2, then the coolant contains separate corrosion inhibitors;

Testing a coolant to measure its corrosion protection involves using a measuring instrument calibrated in one of the ways described above. The test needs to be carried out at room temperature, a small quantity of the sample is placed in the refractometer and the resulting refractive index measurement, a value Bl (18 Brix in the example of Figure 1) is recorded. From Figure 1 a certain antifreeze glycol content Gl (about 27 mS/cm in this case) can be read off against the measured refractive index value Bl. It is nevertheless not possible to exclude the possibility that the coolant may contain corrosion inhibitors which according to Figure 2 would call for correction of the antifreeze glycol content measured according to Figure 1 in order to arrive at a correct value representing the total corrosion protection in the coolant.

The conductivity of the sample is therefore also measured with the conductivity meter, resulting in a value Kl. In the example illustrated in Figures 3 and 4, Kl has a value of about 7.5 mS/cm. If the Kl value exceeds the above K2 limit value, it is obvious from Figure 5 that the coolant tested has such a large corrosion inhibitor content that this needs taking into account in assessing to what extent the B 1 value can or cannot be regarded as representing a correct value of the corrosion protection in the coolant. If it cannot, then the B 1 value needs correcting.

Correction is achieved by using the measured conductivity value Kl in formula 3 or 4 or in Figure 3 or 4 to arrive at a corrosion inhibitor content measurement II. In the example of Figures 3 and 4 the corrosion inhibitor value II corresponding to the Kl value of 7.5 mS/cm is approximately 7.5 vol%. Figure 2 then provides information on the refractive index B2 to which II corresponds, which in the example of II = approx. 7.5 vol% makes B2 about 3.5 Brix. This can also be expressed by incoiporating Kl, II and B2 in the previously indicated formulae 2 and 3 as follows:

Kl = F3*((B2 F2) - IB) + KB, in other words B2 = F2*(((K1 - KB)/F3) + LB) (formula 5)

B2 may be regarded as the refractive index which derives from the corrosion inhibitor content. The following formula is used to arrive at the refractive index value B3 corresponding to the antifreeze glycol content alone:

B3 = B1 - B2, in other words

B3 = B 1 - (F2/F3)*(K1 - KB) - F2*IB (formula 6) In the above example, taking (F2 F3) = 0.4/0.7 = approx. 0.6, KB = 6 mS/cm and IB = 5 vol% of corrosion inhibitors, formula 6 results in

B3 = B1 - 0.6*K1 + 1.6 Incorporating the Bl and Kl values of the example illustrated in the diagrams results in a B3 value of about 15 Brix. From Figure 1 or formula 1 it is therefore possible to derive an antifreeze glycol content value G3 uninfluenced by the corrosion inhibitor content corresponding to the B3 value. In the given example with a B3 value of 15 Brix, G3 arrives at approx. 21 vol% of antifreeze glycol.

The II value taken from Figure 3 (or from Figure 4 if so desired) which corresponds to the conductivity value Kl constitutes a corrosion inhibitor content measurement uninfluenced by the antifreeze glycol content. The antifreeze glycol content value G3 and the conductivity value Kl read off can be used to derive from Figure 6 a measurement of coolant corrosion protection, also called the degree of inhibition, i.e. the combined corrosion protection arising partly from the purely antifreeze glycol content and partly from the purely corrosion inhibitor content. The degree of inhibition is based on the fact that as regards corrosion protection effect there is for each % by volume of corrosion inhibitor, and hence for each unit of conductivity value, a corresponding number representing the % by volume of antifreeze glycol. This number is designated here F4 and has approximately a value of about 3 to 5 for antifreeze glycols and corrosion inhibitors available on the market. For the antifreeze glycols and corrosion inhibitors indicated above, F4 = approx. 4, hence

IG = 4*1 (formula 7) where IG = degree of inhibition expressed in vol% of pure antifreeze glycol and I = corrosion inhibitor content.

The following may be derived from formula 3:

I = ((K - KB)/F3) + IB (formula 8) and its incorporation in formula 7 using the KB, F3 and IB values of the example described above results in

IG = 4*(1.4(K- 6) + 5 The exemplified value Kl = 7.5 mS/cm thus results in an IG1 value of 28.4 representing the degree of inhibition expressed in vol% of pure antifreeze glycol which pertains to the separate amount of corrosion inhibitors.

The corrected refractive index value B3 is used to obtain directly the G3 value which is the same as IG2, i.e. the degree of inhibition expressed in vol% of pure antifreeze glycol which pertains to the antifreeze glycol in the coolant. In the example described, G3 = IG2 = approx. 21 vol% of pure antifreeze glycol.

The combined corrosion protection of the coolant tested, expressed as the degree of inhibition IG3 as above, is then

IG3 = IG1 + IG2 (formula 9)

With the values of the example described, IG3 is thus about 49 vol% of antifreeze glycol.

The Kl and B3 values can thus be used with the formulae as above to arrive at an IG3 value for the degree of inhibition expressed in vol% of pure antifreeze glycol which may be regarded as applying to the coolant concerned. This can also be derived from Figure 6 by using the G2 and Kl values.

Experience shows that in engines for heavy vehicles it is possible to indicate a range bounded by the values IG4 and IG5 expressed in vol% of concentrated antifreeze glycol which represents the region within which the value of the degree of inhibition achieved has to be if the corrosion protection in the coolant concerned is to be regarded as acceptable. In practice, IG4 = approx. 30 vol% of pure antifreeze glycol and IG5 = approx. 60 vol% of concentrated antifreeze glycol has proved to be a suitable range. The lower end of this range is bounded by the curve shown in Figure 5 for the antifreeze glycol content in water without corrosion inhibitors.

As may be seen, with the values exemplified above of Kl = 7.5 mS/cm and G3 = 21 vol% of antifreeze glycol, the IG3 value of 49 vol% of antifreeze glycol falls within the acceptable range in Figure 6.

The above example concerns situations where the Kl value exceeds the K2 limit value. If such is not the case, then according to Figure 5 the antifreeze content may be either above or below the Gl value. The Kl value may also comprise both an antifreeze portion and a corrosion inhibitor portion or only one of them. However, the Kl value means that it is possible to obtain from Figure 3 or from formulae 3 and 8 an indication of the magnitude of the corrosion inhibitor content II. The II value will be relatively low and incorporating it in Figure 2 or formula 2 will result in a correspondingly low refractive index value B2. The correction of the previously measured refractive index value Bl according to the formula B3 = Bl - B2 will likewise be relatively small and will not markedly affect the final result arrived at when deriving the value IG1 for the degree of inhibition from Figure 6 by means of Bl and Kl. In other words, in such cases the previously measured refractive index value Bl can be used directly together with the conductivity value Kl in Figure 6 or in formula 9 to obtain the corrosion inhibition value IG3 expressed in vol% of antifreeze.

The curves and formulae used for the method according to the invention are extremely suitable for storage in the memory of a simple computer. The computer can use input data from the conductivity meter and the refractometer to indicate quickly to what extent the corrosion inhibition of a coolant is acceptable or not. It is also easy to make the computer indicate a recommended amount of antifreeze or corrosion inhibitor to be added for a normal situation on prevailing markets. The measuring instruments used in the present invention are simple and inexpensive and quickly provide measured values of perfectly sufficient accuracy for obtaining a relevant answer about coolant corrosion protection. Hence the invention's advantages set out at the beginning of the description above can be obtained.

Claims

Patent claims

1. A method for determination of corrosion protection in a combustion engine coolant containing corrosion protection agents, characterised in that a small quantity of coolant is taken from the engine, that both the refractive index and the conductivity of the coolant are measured and that the values thus obtained are used together for providing a measure of the corrosion protection of the coolant.

2. A method according to patent claim 1, characterised in that the refractive index of the coolant is measured with a lightweight handheld refractometer, and the conductivity with a lightweight handheld conductivity meter.

3. A method according to patent claim 1 or 2, characterised in that the conductivity of the coolant is compared with a limit value (K2) in order to decide whether the coolant contains separate corrosion inhibitors or not.

4. A method according to patent claim 3, characterised in that when the measured conductivity value (Kl) is equal to or below the limit value (K2), a refractive index value (Bl) measured for the coolant represents a value (Gl) of the frost protection content in the coolant, while the conductivity value (Kl) represents a value (II) for the corrosion inhibitor content in the coolant, which values are used together for obtaining a measure (IG3) of the total corrosion protection of the coolant.

5. A method according to patent claim 3, characterised in that when the conductivity value (Kl) is above the limit value (K2), the conductivity value (Kl) is used for correcting a refractive index value (Bl) measured for the coolant, and the corrected refractive index value (B3) represents a value (G2) for the frost protection agent content in the coolant, while the conductivity value (Kl) represents a value (II) for the corrosion inhibitor content in the coolant, and these values are used together to obtain a measure (IG3) of the total corrosion protection of the coolant.

6. A method according to patent claim 5, characterised in that between the conductivity value (Kl) and the corrosion inhibitor content there is assumed to be a linear relationship whereby for each unit of the corrosion inhibitor content the conductivity value (Kl) changes by a constant value of between 0.6 and 0.8.

7. A method according to patent claim 5 or 6, characterised in that for each unit of the value (II) for the corrosion inhibitor content in the coolant there is a corrosion protection effect which corresponds to a predetermined constant number of units of the value for the frost protection agent content in the coolant, and this value is between 3 and 5.

8. A method according to patent claim 4, 5, 6 or 7, characterised in that the measure (IG3) obtained for the total corrosion protection of the coolant is compared with lower and upper limit values (IG4 and IG5) representing limits within which the measure obtained (IG3) has to be if it is to be considered that there is acceptable corrosion protection in the coolant.