US-12624459-B2 - Method of chemically cleaning pipework systems

US12624459B2US 12624459 B2US12624459 B2US 12624459B2US-12624459-B2

Abstract

A process for chemical cleaning and corrosion inhibition of pipework, typically in closed loop systems, that avoids or significantly minimises the requirement for wastewater discharge where the system is first acidified using a mixture of cleaning agents capable of dissolving metal oxides. The method then precipitates any dissolved contaminants and separates the precipitate from the carrying fluid. Further elements of a combined corrosion inhibitor package are then added to any cleaning agent ions that remain in solution to develop a fully functional corrosion inhibition package to protect the metals of the system.

Inventors

David Sevier

Assignees

David Sevier

Dates

Publication Date: 20260512
Application Date: 20210628
Priority Date: 20200628

Claims (14)

1 . A method of chemically cleaning pipework systems that comprises the following steps in order: A) cleaning the metal surfaces using a water-based acidic cleaning fluid that includes a source of one or more of the following ions: phosphate, pyrophosphate, metaphosphate, polyphosphate to produce dissolved metal ions; B) raising the pH using an alkali metal salt hydroxide/oxide/carbonate to cause precipitation of the dissolved metal ions; C) separating insoluble minerals and suspended debris by passing at least a part of the cleaning fluid through at least one filter or separator to produce filtered cleaning fluid, wherein the filtered cleaning fluid contains non-metal dissolved ions; D) adding chemical compounds and/or elements to the non-metal dissolved ions that remain in the filtered cleaning fluid to assemble a corrosion inhibitor package to protect the metal surfaces from corrosion; and E) retaining the filtered cleaning fluid and corrosion inhibitor package in the pipework system as a heat transfer fluid.
2 . A method according to claim 1 , wherein the source of phosphate ions is either phosphoric acid or a phosphate salt, and the source of pyrophosphate ions is a pyrophosphate salt, and the source of metaphosphate ions is a metaphosphate salt, and the source of polyphosphate is polyphosphate salt.
3 . A method according to claim 1 , wherein the filtration or separation is carried out after the pH has been raised.
4 . A method according to claim 1 , which includes, prior to raising the pH, removing at least part of the cleaning fluid from the pipe work system in order to pass the cleaning fluid through at least one filter or separator in step (C).
5 . A method according to claim 4 , further comprising the step of returning the filtered cleaning fluid back to the pipework system.
6 . A method according to claim 1 , wherein the alkali metal salt used is either calcium or magnesium oxide/hydroxide/carbonate.
7 . A method according to any of claim 1 , wherein the alkali metal salt used includes one or more of the following compounds: calcium oxide, calcium hydroxide, calcium carbonate, magnesium oxide, magnesium carbonate, magnesium hydroxide, barium oxide, barium carbonate, barium hydroxide, manganese oxide, manganese carbonate, manganese hydroxide, strontium oxide, strontium carbonate, sodium and potassium oxides, hydroxides and carbonates and strontium hydroxide.
8 . A method according to claim 7 , wherein the alkali metal salt is added in a separate step to the calcium or magnesium oxide/hydroxide/carbonate.
9 . A method according to claim 1 , wherein step B of claim 1 raises the pH to above 7.
10 . A method according to claim 1 , which includes, prior to reducing the pH, removing at least part of the cleaning fluid through at least one filter or separator in step (C), further comprising the step of returning the filtered cleaning fluid back to the pipework system and further comprising a step of introducing an acid into the cleaning fluid to reduce the pH prior to returning the cleaning fluid into the pipework system.
11 . A method according to claim 1 , wherein the corrosion inhibitor package includes one or more of the following: molybdate, nitrite, nitrate, cerium, azole, polymer and triethanolamine.
12 . A method according to claim 1 , wherein the filtered cleaning fluid is first returned to the system prior to the addition of the chemical compounds and/or elements to assemble the corrosion inhibitor package.
13 . A method according to claim 1 , wherein step A of claim 1 includes recirculating the cleaning fluid within the pipework system.
14 . A method according to claim 1 , further comprising, in either step A or step B of claim 1 , introducing a flocculating agent into the pipework system or to the fluid being passed to filters or other separators to cause larger particles of precipitate to form.

Description

FIELD OF THE INVENTION This invention relates to a method of chemically cleaning pipework systems, which may be either open or closed loop systems, and which avoids or significantly minimises the requirement for wastewater discharge. The pipework systems are typically systems that, in use, carry water-based fluids. More specifically, the invention covers a process for chemical cleaning and corrosion inhibition of pipework, typically in closed loop systems, that avoids or significantly minimises the requirement for wastewater discharge where the system is first acidified using a mixture of cleaning agents capable of dissolving metal oxides. The method then precipitates any dissolved contaminants and separates the precipitate from the carrying fluid. Further elements of a combined corrosion inhibitor package are then added to any cleaning agent ions that remain in solution to develop a fully functional corrosion inhibition package to protect the metals of the system. BACKGROUND Chemical cleaning of pipework systems is necessary to remove debris and mill scales from metal and system services. This issue is most prevalent in closed loop systems where physical access to the inside surfaces of the pipes is more difficult. Such systems might include heated or chilled fluid systems, pipelines, heating or chilled systems, tank systems and such systems may be part of for example a ground source heating system. When pipe and formed metal parts are made, the process can produce mill scales that chemical cleaning removes. Often the pipework can be oil or grease coated to a degree. Plastic pipe can be formed with sparingly soluble fatty acids in the plastic to help lubricate the pipework formation dies. There are all kinds of “other fouling elements” which might end up inside pipework. The pipes themselves can corrode. This can happen whether the system is wet or dry. Other fouling sources include, but is not limited to bark chips, stones, floating foam insulation, and parts of dead animals. Failure to adequately clean pipework before bringing into service can result in reduced equipment performance, increased maintenance, and reduced equipment and system working life. Current practices for chemical cleaning a system involve adding a cleaning agent that dissolves/emulsifies or suspends metal oxides, debris, and other fouling elements. After the cleaning agent has finished its process of cleaning, it is then fully flushed out of the system with the system then being treated with a corrosion inhibitor package. Typically it requires a water volume of ten times or greater that of the system total volume to fully flush out the cleaning agent so that the system water conductivity is no more than ten percent greater or ten percent less than that of the conductivity values of the water being used to fill the closed loop. Few cleaning agents are compatible or helpful to the final corrosion inhibitor packages that are later used to preserve the system. Most cleaning agents and dissolved metal ions such as iron and copper have strongly negative impacts on the corrosion inhibitor package performance. Traces of cleaning agents can increase system corrosion rates ten times or more. Corrosion inhibitor packages for aluminium are very adversely affected by the presence of copper ions. Excessive iron levels can lead to iron bound hardness scale formation on hot heat transfer surfaces which adversely impact heat transfer. Many other adverse impacts of failing to fully remove cleaning agents and/or not producing low iron and copper water at the end of a pipework clean are well documented and widely known to those involved in chemical cleaning and maintenance of water systems. It is therefore important that the cleaning agent and the released contaminants are fully removed before adding corrosion inhibitors to a closed loop system. The volume of water supply required to fully flush closed loop systems following chemical cleaning and the requirement to treat the produced effluent has negative environmental and financial impacts. Dissolved copper and zinc levels can rise to values of over 100 ppm during chemical cleaning under acidic conditions. Typical discharge permits within Britain require that copper discharge be limited to a maximum of 3 ppm. The issue of treating effluent contaminated with dissolved metal ions such as copper and zinc is non-trivial. Increasing attention is being paid to ensure that conditions of issued discharge permits are adhered to. Increased awareness of the costs associated with water supply and the cleaning up of discharge water has created a desire to find a way to clean closed loop systems that either reduces or eliminates the large volume of water required and the associated discharge. Efforts have been made to try to eliminate the use of cleaning agents associated with chemical cleaning of closed loop systems. GB2468211A describes a method that seeks to deliver only water to the closed loop system that has be