AN INTRODUCTION TO CHEMICAL CLEANING OF INDUSTRIAL WATER SYSTEMS/طرق التنظيف الكيميائى لاجهزة معالجة المياه

AN INTRODUCTION TO CHEMICAL CLEANING OF
INDUSTRIAL WATER SYSTEMS

1. GENERAL GUIDANCE.

Chemical cleaning of water systems can be divided into two classifications:

pre-operational and remedial. Pre-operational cleaning is performed to prepare the water-contacted metal surfaces to receive chemical treatment, which provides protection from scale, corrosion, and microbiological growth.

Remedial cleaning is performed to restore water systems that have been fouled with scale, corrosion products, and microbiological growth due to inadequate or ineffective water treatment.

Cleaning, particularly remedial-type cleaning, is often performed by outside contractors familiar with cleaning procedures, techniques, and safety.

It should be noted that if the water system is significantly scaled, the chemical treatment program was obviously inadequate and was not properly designed, set-up, controlled, or applied.

After cleaning has been completed, the chemical treatment program and quality control (QC) program must be improved so the same problem does not recur.

Use of a well-designed quality assurance (QA) program would have produced identification and notification of potential and developing problems before they became serious.

Pre-operational cleaning is often performed by contractors responsible for the fabrication of the water system before turning it over to the owner. Water system operations personnel must assess the effectiveness of any cleaning process that has been performed.
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1.1

PRE-OPERATIONAL CLEANING.

Pre-operational cleaning can be performed on all new systems or pieces of equipment installed in any existing system, including new boiler tubes or new chiller copper tube bundles.

New piping and coils will usually be contaminated with materials such as mill scale, rust, oil, and grease resulting from the fabrication, storage, and installation of the equipment.

Pre-operational cleaning is performed to remove these materials and prepare metal surfaces to receive corrosion protection from chemical treatment.

Pre-operational cleaning agents that are used include detergents, wetting agents, rust removers, and dispersants.

These cleaning agents have a pH in the range of 9 to 11. Water systems containing piping or
components constructed of galvanized steel and aluminum should not be subjected to procedures that require high pH (greater than 8.5) because this would contribute to initiating corrosion of these surfaces.

The requirement for performing a pre-operational cleaning process is usually written into the specification for new construction of a water system that must be performed by a mechanical contractor.

The mechanical contractor is required to perform the work as directed in the specifications; however, if the specifications are not appropriate for the specific system, including consideration of all system metallurgy, the cleaning process may contribute to corrosion to mild steel, galvanized steel, copper, or aluminum, or it may result in incomplete cleaning of dirty and corroded metal surfaces.

The specifications should be reviewed by a qualified base inspector or qualified independent consultant to ensure that cleaning agents and procedures have been specified appropriately.

A contracting officer or other individual responsible for QA should inspect the equipment after cleaning and document the effectiveness of the cleaning process.
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1.2

REMEDIAL CLEANING.

Remedial cleaning is performed to restore a water system
that is fouled with scale, corrosion products, or microbiological biomass due to inadequate or ineffective water treatment.

The problem could have resulted from using improper chemical technology, failure to maintain treatment levels within control parameters, or the failure of pre-treatment equipment.

The cleaning agents used for remedial cleaning usually include acids, chelants, neutralizing agents, and specialty cleaning chemicals.

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1.2.1

SAFETY AND ENVIRONMENTAL ISSUES.

Remedial cleaning may pose safety
issues for personnel handling acids, caustics, and various chemicals.

There could also be environmental concerns associated with chemical disposal. Inexperienced personnel should not perform the chemical cleaning of an industrial water system.
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1.2.2

CONTRACTING CLEANING SERVICES.

For some cleaning jobs, such as large boilers and cooling towers, it may be advisable to engage a service company
specializing in chemical cleaning.

If the cleaning service is contracted, it is vital that adequate lines of communication be established, and that safety procedures employed by the service company comply with appropriate regulations.

An orientation meeting should be scheduled between appropriate personnel and the service company representatives.

At that time, the scope of the work can be defined, proper procedures initiated, and the nature of the hazards described thoroughly.

The use of proprietary cleaning chemicals or chemical formulations may be involved; disclosure of the use and nature of these chemicals should be made at the orientation meeting.

Appropriate policies and restrictions can also be explained.

The inspection of equipment after cleaning is usually the final step in the overall cleaning process.
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1.3

REASONS FOR CLEANING.

Maintenance of an effective water treatment program is essential to minimize scale and corrosion problems in industrial water systems; however, scale and deposits that form will require remedial cleaning (descaling).

If not removed, these scale and water-caused deposits may impact the safety of operations personnel, interfere with heat transfer, and cause excessive damage to (or destruction of) the water-using equipment.

Cleaning is not appropriate for the removal of deposits when corrosion of the system has advanced to the point where a large number of leaks may result from the removal of the deposits.
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1.4

TYPES OF DEPOSITS.

The deposits that occur in water systems can be inorganic mineral salts and corrosion products or organic (oily) or biological in nature.

Deposits range in composition from very dense crystalline structures, to very porous and loosely bound materials, to gelatinous slimes.

Most of the deposits formed from water constituents consist of corrosion products such as iron and copper oxides, mineral scales, or mixtures of these materials.
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1.4.1

WATERSIDE DEPOSITS LOCATED IN HEAT EXCHANGERS.

Water deposits located in heat exchangers are usually carbonate-based scales, while steamside deposits may be a mixture of metallic oxides and organic residuals from lubricating oil, particularly where reciprocating-type engines are used.

In steam systems, the oxides are usually iron and copper, resulting from aggressive condensate.

Microbiological
deposits may form in cooling systems from bacterial or algae growths, or from decomposition products
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1.4.2

BOILER DEPOSITS.

Boiler deposits may take various forms. In low-pressure boilers using a relatively hard feedwater, deposits are essentially calcium and magnesium, silicates, sulfates, carbonates, phosphates and hydroxides, plus some organics.

Deposits may also contain considerable amounts of silica, iron, and copper.

These deposits can be spongy or porous or relatively hard and glass-like.

Deposits of the latter characteristic occur where silica is present in appreciable quantities in the boiler water.

Deposits in medium-pressure to high-pressure boiler systems usually are mixtures of iron and copper oxides and phosphates.

Dense deposits may tend to form in high-heat transfer areas.

Considerable quantities of sludge-type accumulations may be found in downcomers, mud drums, waterwall headers, crossover tubes, and areas of low water circulation in the boiler.

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AN INTRODUCTION TO CHEMICAL CLEANING OF INDUSTRIAL WATER SYSTEMS/طرق التنظيف الكيميائى لاجهزة معالجة المياه Blue-w12

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AN INTRODUCTION TO CHEMICAL CLEANING OF INDUSTRIAL WATER SYSTEMS/طرق التنظيف الكيميائى لاجهزة معالجة المياه Uoo135

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