Coolant maintenance: what to test, how often, and when to top up

Maintenance is a programme, not a product

Secondary cooling systems rarely fail because someone chose the wrong fluid on day one. They fail because a system that was correctly filled was then left alone for years, topped up with whatever was available, and inspected only after a leak appeared.

That matters more now than it did a decade ago. Refrigerant phase-down rules have pushed industrial and commercial refrigeration towards indirect architectures with a smaller primary charge and a larger circulating secondary loop. The secondary fluid is no longer a minor design detail; it is the part of the system a maintenance team actually touches. More circulating volume means more places for water chemistry, contamination and inhibitor depletion to matter.

The Glacier catalogue describes three maintenance product lines that are easy to confuse because they all arrive in drums and all claim to reduce corrosion. They address different systems, different failure mechanisms and different schedules. This article sets out what the catalogue says about each, and what it deliberately leaves to a site survey.

Brine systems: LMH

LMH is described as a corrosion inhibitor for brine, composed of film-forming agents, stabilizers, antioxidants and corrosion inhibitors, and stated not to contain chromium salts. The catalogue gives its pH as 7 to 11 and its density as 1.020 to 1.080 g/cm³, describes it as non-flammable, non-volatile and non-corrosive, and says it forms three layers of protective film on metal surfaces to slow pitting corrosion from chloride ions.

Its stated application is indirect refrigeration systems using calcium chloride or sodium chloride solution as the secondary refrigerant, and other situations where brine contacts metal, including brine drilling fluid. It is described as resisting corrosion of carbon steel, stainless steel and copper.

The usage instructions are the part worth reading closely. For first use, the catalogue states a dosage of about 1% of the total brine volume, weighed and added directly with the system circulating. During use, the pH value and anti-corrosion performance of the brine should be tested every three months, with pH adjusted and LMH replenished according to the technical standard — generally about 0.5%.

Note the structure of that instruction. The initial dose and the replenishment dose are different numbers, and the replenishment is conditional on a measurement. It is not a fixed annual top-up. The catalogue also classifies LMH as a hazardous chemical and points to the safety data sheet, which is a reminder that an additive used to protect metal is still a chemical requiring handling controls.

Circulating cooling water: LMT

LMT is a different product for a different loop. The catalogue describes the series as composed of rust inhibitor, corrosion inhibitor, scale inhibitor, bactericide and algaecide, supplied as light yellow non-combustible liquids for circulating cooling water systems in chemical, pharmaceutical and other industries. It addresses scale and biological growth alongside corrosion, which brine inhibitors do not.

Table 16 gives two grades:

The catalogue states the products can be added directly during use at approximately 1% of the system's water capacity, with proportional replenishment carried out regularly according to the amount of make-up water added later.

That last clause is the design principle. In an open circulating system, additive concentration is diluted by make-up water, so the replenishment rate tracks water loss rather than calendar time. A site with high evaporation or frequent topping up needs a different rhythm from one that is tightly closed. The catalogue also classifies LMT as a hazardous chemical.

Alcohol-based systems already in service: LMZ

The third line solves a different problem. LMZ synergists are described as concentrated additives for manufacturers who have already installed a large volume of alcohol-based secondary refrigerant and either cannot conveniently add Glacier coolant directly or face transport constraints. The catalogue describes adding them directly to the alcohol-based aqueous cooling medium at a dosage of 0.5% to 2%.

Table 17 gives four grades with different forms and compositions:

The catalogue also describes a comparative corrosion test: one gram of LMZ added to 100 mL of a 25% ethylene glycol solution in a conical flask with a polished carbon steel test piece and a copper test piece, against a control flask of the same glycol solution and the same test pieces, with corrosion observed the following day and over a longer period.

That comparator is a useful model for a site trial, and it is worth being explicit about what it is not. It is a small, short check of whether an additive changes visible corrosion behaviour in one specific fluid. It is not a corrosion rate, not a service-life prediction and not a substitute for testing the actual system fluid at its actual concentration. Three of the four grades — LMZ, LMZ-1 and LMZ-2 — are classified as hazardous chemicals.

What the intervals have in common

Read together, the three programmes share a shape that is more useful than any individual figure:

• The first dose and the ongoing dose are different. LMH is about 1% initially and about 0.5% for replenishment.
• Replenishment is tied to a measurement, not to a date. Brine pH and anti-corrosion performance every three months; cooling-water treatment matched to make-up water volume.
• The measurement comes before the decision. Without a baseline reading taken before treatment starts, a later result cannot tell you whether the programme is working.
• Every one of these products carries a hazard classification. Protection chemistry is still chemistry; the safety data sheet governs handling, storage and disposal.

What this article does not do

It does not give a dosing instruction for your system. Reference dosages in a catalogue are calculated against an assumed system volume and an assumed fluid condition, and neither is known until someone surveys the plant. Nor does it diagnose a specific corrosion problem: pitting from chloride ions, general corrosion from low pH, scale from hard make-up water and microbiological growth have different causes and different remedies.

What it should prompt is a short list of questions for the next maintenance review. What is actually circulating, at what concentration? When were pH, conductivity or inhibitor levels last recorded, and against what limits? How much make-up water does the system take, and what is in it? Who acts when a reading drifts, and how quickly?

If the answers are unclear, the useful next step is a fluid condition review rather than a drum of additive. The system protection solution page sets out that workflow, and the technical document request page covers obtaining current product documentation.