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The Chemical Cleaning of pipelines.
What we have learn from previous projects.

By: John Pitsilos, Dipl. Chemical Engineer

Introduction
In this issue we are dealing with the pipelines where a chemical cleaning process is obligatory as a pre-commissioning step; e.g. in gas turbines lines, in steam turbine lines, in the transfer of pharmaceutical gasses like oxygen lines, in the de-mineralized water lines, etc
In these cases a surface 100% free of loose foreign materials is required, so the chemical cleaning designates the formation of a bare metal surface with a good passive layer.
The author has been supervisor in some major projects both in Greece and Abroad.
Therefore hereafter some know-how and experience lessons are provided.

(1) Key Chemical words and phrases:
a. Foreign materials to be removed
b. Bare metal
c. Passive layer
d. Carbon steel pipelines
e. Stainless steel pipelines
f. Quality of water
g. Alkaline cleaning or degreasing
h. Acid cleaning or pickling
i. Neutralization
j. Monitoring with hand-held test instruments
k. Lab Tests to be carried out
l. Test coupons and test samples
m. Inspection and acceptance criteria
n. Wastes consideration

(2) Key Engineering words and phrases:
a. Pipe sizes
b. Capacity of pipelines in m3 of water
c. Flow velocity and Pumps requirements
d. Supply time and requirements to fill a pipeline with water
e. Heating of cleaning solution
f. The cleaning loop, blank flanges, inlet /outlet auxiliary pipes
g. Venting and gas releasing
h. Temporary cleaning lines
i. Wastes disposal
j. Drying

Evaluating a pipelines chemical cleaning project

(1e) Stainless steel pipelines
For a chemical cleaning specification of stainless steel pipe lines the best valid standard is the ASTM designation A967-01

(2b) Capacity of pipelines in m3 of water
By increasing the size of a pipe line, the capacity in water is dramatically increased.
100 meters of ½ inch pipe contains approximately only 10 kg of water.
100 meters of 1 inch pipe contains approximately only 60 kg of water.
100 meters of 4 inches pipe contains approximately 780 kg of water.
100 meters of 8 inches pipe contains 3140 kg, or 3.14 tons of water.
100 meters of 12 inches pipe contains approximately 7.06 tons of water
100 meters of 16 inches pipe contains approximately 12.56 tons of water
It is not surprise that:
100 meters of 32 inches pipe contains approximately 50.20 tons of water
100 meters of 40 inches pipe contains approximately 80 tons of water
100 meters of 48 inches pipe contains approximately 115 tons of water
100 meters of 64 inches pipe contains approximately 200 tons of water
100 meters of 80 inches pipe contains approximately 320 tons of water

(2c) Flow velocity and Pumps requirements
Practically on small dimension pipes up to 6 inches a volume flow rate pump
of 10-50 m3/hour is enough.
On medium side pipe lines 8-12 inches, a big volume flow rate pump of 300 m3/hour is required
On large side pipe lines 16-40 inches, a huge volume flow rate pump of about 1000 m3/hour is required
Finally on extra large pipe lines as 40-80 inches, even a huge volume flow rate pump of about 1000 m3/hour is not sufficient; therefore, in addition to the application of the bigger possible pump, other engineering techniques during chemical cleaning should be tried, with the scope to accelerate flow and mixing rate of chemical solution and mainly during the final water rinse, like injection of nitrogen gas under big pressure.

(2d) Supply time and requirements to fill a pipeline with water
To carry out a chemical cleaning, a solution of water with chemicals should be prepared and re-circulated through a pipelines cleaning loop.
By increasing the size of a pipe line, the capacity in water is dramatically increased.
From the (2b) parameter of above lines, it is obvious that, huge quantities of water are required to fill up a line, to water flash and to rinse a line with water.
Therefore the first priority in a project is to have sufficient quantity availability and supply rate of water. For example in case that a system requires 300 m3 of water to be filled up, both a high volume storage tank of water is required and a high flow pump is required with the scope to fill up the cleaning loop in less than hour. You cannot be based on external supply water with lorry tanks as the normal capacity of these lorry tanks is only 20 m3. To avoid big delays therefore, it is first priority to manage water supply facilities operation.

(2e) Heating of cleaning solution
In many cases in order the best cleaning results to be obtained a sufficient heating of the cleaning solution, sometimes up to 90 degrees C, is required.
If not steam supply is not available in the site/ factory, the cleaning contractor is obliged to provided auxiliary boiler and sufficient Heat Exchanger/ Heating Coils in order to succeed in the require heating rate.
It is obvious that to obtain, to install and to operate such heating facilities is a major cost factor in the whole project.
In addition great attention should be paid that in long and big pipelines the requested heating probably will be not effected in the case of non insulation of the pipelines. Therefore such investigation of insulation should be done in advance and should be anticipated. If no insulation is possibly the chemical cleaning parameters such as chemicals concentration should be sufficiently modified by very experienced Chemical Engineers, the cleaning acceptance criteria should be specified and the expected metal corrosion rate to be foreseen.

(2f) Preparing the chemical cleaning loop (Chemical cleaning circuit)
An installation line as a pipeline can be chemical cleaned by continuous circulation (Re-circulation) of a chemicals cleaning solution with pumping facilities, while the installation is remaining full up, so the whole surfaces are in contact with the cleaning agent.
A supply (inlet) line to the system and a return line (outlet) as well as should be therefore connected to the pumping facilities, together with some isolating blanc flanges to the beginning and the end of the subject pipeline.
The above flanges, a temporary devise, should be prepared in advance, should have fixed size and thickness and should be bolded fixed to the line achieving no leakage.
The above inlet and outlet lines should be in sufficient size to achieve the required flow velocity and should be accompanied with proper valves.
It is obvious that, especially in big size pipelines as over 16 inches or bigger size, the purchase or the construction, the installation and the final dismantling of these temporary devises is a process of high cost and long time. This process in a high size pipe probably requires reasonable number of man-working hours. In case that a good management of this process is not well anticipated, major delays and problems will be faced.

(2g) Vents and gas release
Another major concern during any chemical cleaning project is the management of releasing all gasses which are producing with chemical cleaning reactions. Otherwise the pipe will remain partly full up and the results will not be satisfactory.
Therefore proper arrangements in the vents should be anticipated and new proper vents with proper valves should be applied and connected to the ground or to the re-circulation tank or the ground storm water lines.
During the cleaning process all these venting lines should be in full operation and under control by the cleaning contractor’s team.

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Page Updated Fri Dec 12, 2008 8:48am EST