NO157744B - PROCEDURE FOR INTERIOR CLEANING OF PIPES. - Google Patents

Description

This invention relates to a new method for cleaning the internal surfaces of pipelines using aqueous, cross-linked, gelatinized blocks.

Pipeline efficiency and volume of product transported through the pipeline can be lost by the build-up of shell deposits on the inner surface of the pipe. Mechanical blocks and/or gelatinized chemical blocks - so-called "pigs" - have previously been used to remove shell deposits from the inner surface of a pipe. Mechanical blocks are usually fixed, ball-shaped devices with metal brushes or abrasive surfaces to physically scrape away the scale deposit adhering to the inner surface of the pipe. Gelatinized chemical blocks, on the other hand, remove surface deposits on the inner surface of a pipe by dissolving and/or picking up loose fragments as they pass through the pipeline.

In many cases, the shell deposits also contain bacteria that attack the product to be carried through the pipeline. For example, sulfate-reducing bacteria can develop copious amounts of gaseous hydrogen sulfide from certain crude oils, which causes severe corrosion of pipeline walls and also contaminates the product flowing in the pipeline. Hydrogen sulfide is also a harmful, toxic gas, and this makes it difficult and dangerous for personnel to handle and also difficult to pump. Gases in a liquid can cause the pumps to cavitate, lose drive or function less efficiently. Bacteria are also known to consume hydrocarbons, and this results in product loss.

Because water is an undesirable foreign substance in any oil or gas pipeline, the treatment of gelatinized blocks also includes their drying. A method for drying a pipeline is described by G.D.H. Crawford, Gas Journal, Volume 341, No. 5549, 282 (March 18, 1970). According to Crawford, the bulk of the water is removed from a pipeline with a conventional mechanical block, and then the interior of the pipe is dried by passing a quantity of methanol through the pipeline compressed between a pair of blocks. Crawford found it necessary to use this technique to remove residual water from pipelines that carried natural gas with a large proportion of methane. It was assumed that residual water formed hydrates with methane under certain temperature and pressure conditions and led to serious transfer difficulties.

From US patent no. 3,974,077, it is known to use galactomannan gum in connection with pumping a fluid into a borehole, but the patent does not state anything about driving a plug or block into a pipeline for efficient scraping and removal of residues of fluids and solids, as is done in connection with the present invention.

From US patent 4,003,393 a gel-like block is known, used e.g. for cleaning a pipeline, where the block is formed by mixing an organic liquid with a gel mixture comprising a metal salt of an aliphatic substituted orthophosphate ester, so that a self-supporting gel-like mass is formed. However, the use of galactomannan gum in such a block, as used in the method according to the present invention, is not mentioned in the patent document.

From US patent 3,744,880, a cleaning plug for an oil pipeline is known, comprising a solid binder of an oil-soluble material, and where the material can also contain a bactericide. In contrast to the aforementioned oil-soluble material, however, in the present method, an aqueous, gelatinized block of galactomannan gum is used.

The present invention thus relates to a method for internal cleaning of a pipeline, by passing a gel-like mass through the pipeline, driven by a fluid under pressure, and the method is characterized by using a gel-like mass in the form of a watery, gelatinized block containing an aqueous, crosslinked, gelatinized galactomannan gum, or derivative thereof.

The aqueous, gelatinized, crosslinked blocks used in the invention are superior to other blocks such as e.g. uses polyacrylamides or similar as gel mass. This superiority is shown by their shear stability, by their being easily hydrated in water, and by the convenient manner in which the gelatinized blocks are broken into pieces when the work is completed. This makes it easier to get rid of waste and increases its commercial viability.

It has also been discovered that pipelines can be cleaned and at the same time made sanitary by passing an aqueous, gelatinous block containing at least one bactericide through the interior of the pipe. The expression "make sanitary" means that the amount of bacteria in the pipeline surface that comes into contact with the watery, gelatinized block is reduced. Usually, the bacterial count is reduced to zero or some other, very low value.

The aqueous, gelatinized blocks used in the invention are easy to form, easy to use and eliminate the need to completely fill a pipeline with an antibacterial solution, thus representing an advance in the pipeline cleaning industry.

The method according to the invention can also comprise drying the internal surfaces of a pipeline, by successively passing through the pipeline an aqueous cross-linked, gelatinized block, a fluid mobility buffer, which comprises a non-cross-linked, gelatinized alkanol with from 1 to 3 carbon atoms, and a drying amount of a liquid alkanol having from 1 to 3 carbon atoms. The mobility buffer allows the consumer to enjoy the benefits of both the gelatinized aqueous blocks and a liquid drying alkanol.

The term "fluid mobility buffer" can be explained as follows: Such a buffer separates the gelatinized block from the alkanol. If the gelatinized alkanol is not present, the ungelatinized liquid alkanol behind the block is more "mobile" and will absorb water from the gelatinized water block, making it less apt to absorb water from the wall of the pipeline and break down the structure of the water-based gel mass. The gelatinized alkanol also does this to a certain extent, but because it is gelatinized to a high viscosity, its mobility is greatly reduced. Therefore, an interface of mixed gelatinized alkanol and water forms, but it is relatively short and becomes stable as the row moves down the pipeline. The front of the gelatinized water block continues to push out the majority of the water in the line, while the alkanol behind (both gelatinized and ungelatinized) absorbs the remaining water film. The gelatinized alkanol section also provides the "buffer" between the water-based gel and the bulk of the alkanol and reduces their "fluid mobility" in the block so that a relatively small amount of mixing between muds in the block occurs.

The water-based block composition comprises water, a galactomannan gum or a derivative thereof as a thickening agent, and a cross-linking agent. The block composition may optionally contain a bactericide as an additive. Other additives may include an abrasive in solid particulate form (eg, sand) to promote the cleaning ability of the block as it is passed through the pipeline, or other conventional additives that stabilize the block.

Galaktomannen gums and derivatives thereof are well-known thickeners for water and water-based fluids. Examples of such gums include natural gums (eg guar gum, acacia bean gum, endosperm seed gums and the like)

and derivatives thereof (eg hydroxyalkyl-galactomannans, carboxyalkyl-galactomannans, hydroxyalkyl-carboxyalkyl-galactomannans and the like). These are well-known groups of compounds, and essentially any can be used in the present invention.

The most commonly used commercially galactomannan gums are guar, hydroxypropyl guar, hydroxyethyl guar, hydroxyethyl carboxymethyl guar and carboxymethyl guar gums. Because the aforementioned gums are readily commercially available, these gums are preferred thickeners, and of these, guar gum and hydroxypropyl guar gum are the most preferred.

It should be noted that in some literature the galactomannan gums are referred to as polysaccharides and polysaccharide derivatives. Any compound in this known group of thickeners can be used in the present invention. Such thickeners are usually used in amounts of from 0.5 to 1.8 percent by weight. They are preferably used in amounts of 0.5 to 1.0 percent by weight. However, the actual quantity used can be adjusted so that it is convenient for the athlete.

Aqueous mixtures containing the above-mentioned thickeners are usually cross-linked using a polyvalent metal ion. The crosslinking agent is usually added as a soluble salt or as a soluble organometallic compound in an amount sufficient to achieve the desired degree of crosslinking. Borates, organotitanates and organozirconium salts are usually used. The cross-linking ability of such a compound is pH-dependent in many cases (eg the borate systems). This factor provides a convenient mechanism for treating the thickened fluids in a non-crosslinked form until the properties of a crosslinked fluid are desired. In the non-crosslinked state, the thickened aqueous fluids are usually pumpable at conventional pressure. Substantially elevated pressures are required to pump the fluids in the cross-linked state.

The galactomannan gums and cross-linking agents are, as indicated, known classes of compounds and are disclosed in US Patent Nos. 3,058,909, 3,974,077, 3,818,991, 3,779,914

and 3,696,035. Reference is also made to the publication by Davidson and Sittig, "Water-soluble Resins", 2nd edition (1968) and the publication by Smith and Montgomery: "The Chemistry of Plant Gums and Mucilages", Biograph Series No. 141 (1959).

Typically, the block is formed outside the pipeline as a pumpable mass and the crosslinking agent or crosslinking activator is added to the pumpable mass as it is pumped into the pipeline. This "on-kick" design has several process advantages, not least the easy application at conveniently low pressures. In this way, the block forms a cross-linked gel network after it enters the pipeline and adapts to the general shape and size of the pipeline. As an illustration, an aqueous block of a borate-crosslinked polysaccharide (or polysaccharide derivative) gel preferably comprises a block composition where the block can be subjected to considerable shear forces. Such block formation is conveniently formed and used by first mixing boric acid (from 0.24 to 0.48 kg) with an aqueous slurry or solution of the polysaccharide or polysaccharide derivative (from 7.19 to 9.59 kg) to form a pumpable homogeneous mass. Sufficient base (eg aqueous NaOH) is then added to change the pH to a basic pH (pH usually 8.5-10) when the homogeneous mass is pumped into the pipeline. The desired amounts of boric acid and polysaccharide or derivative are present per 1000 liters of water in each case in the pipeline. The gel time of these borate crosslinked systems is easily adjusted with the amount of added base (crosslinking occurs faster at higher pH values).

After the gelatinized block has been formed in the pipeline, it is usually driven through the pipeline with a driving force consisting of a fluid under pressure. This fluid can be a gas or a liquid and varies according to the consumer's needs. If e.g. the consumer wishes to leave the pipeline in a dry, empty state, a dry, inert gas will usually be used, such as e.g. nitrogen, carbon dioxide, ethane, propane or liquid petroleum gas. If the consumer wishes to refill the pipeline with a liquid product, such as e.g. crude oil or gasoline, the block may be propelled with a liquid product, as long as the product has no detrimental effect on the properties of the block before its task is completed or substantially completed in the pipeline.

Typically, the blocks are formed and used at or below ambient temperature, and are pumped through the pipelines at sufficient pressure to move the block at a reasonable speed. Temperatures are therefore usually below approx. 60°C. The pressures are usually below approx. 141 kg/cm<2>. The majority of pipelines will usually be cleaned at pressures below 35 kg/cm<2>. Linear flow rates of up to approx. 1.524 m/second is usually satisfactory from a commercial cleaning point of view. Velocities of from 0.229 to 0.381 m/second are preferred.

The size and shape of the pipeline is essentially irrelevant because the gelatinized blocks are capable of being pumped through the pipeline over long distances and their shape will adjust to fit the size of the pipeline during use. This makes the gelatinized block extremely effective due to the fact that stalactites and stalagmites in the pipeline do not cause its destruction by scratching and tearing, as they do with solid mechanical blocks.

The watery, gelatinized blocks can be used alone or as an element in a series of blocks in the cleaning process for pipelines. In the latter case, the aqueous, gelatinized block precedes and/or follows other chemical block segments or mechanical blocks. Such chemical block segments can be of the same or different composition. E.g. the block row may be formed with an aqueous gelatinized block, as described herein, as the leading segment to remove loose shell deposits or other fragments from the pipe, followed by a bactericidal gelatinized block to sanitize the pipe. This combination can therefore be effective, both in cleaning the pipelines and in making them sanitary. Segments of the block array may likewise include fluids (liquids or gases) or non-crosslinked gels containing various additives, such as corrosion inhibitors and the like.

After the aqueous crosslinked gelatinized blocks are passed through the pipeline, they can be recovered and disposed of as such, or "disruptors" can be added to the pipeline and cause the crosslinked gelatinized block to break up and lose its structure and viscosity. As noted above, this is a highly desirable property because it facilitates disposal of the waste. In many cases, moreover, the aqueous, gelatinized block is of essentially negligible volume in relation to the volume of the subsequent "product" and therefore has no deleterious effect on the material that follows. E.g. will not a few hundred liters of a block, used in accordance with the present invention and discharged into the hold of a ship carrying crude oil, have any detrimental effect on the properties of the many thousands of liters of crude oil also present in the hold.

Bactericides compatible with water-based compositions are also a known group of compounds.

Typical examples of such compounds are aldehydes, organic quaternary ammonium compounds or water-soluble salts of halogenated (especially chlorinated) phenols. Examples of such bactericides include formaldehyde gluteraldehyde, dodecyl-trimethyl-ammonium chloride and octadecyl-tris-(2-hydroxyethyl)-ammonium chloride. Bactericides effective against sulfate-reducing bacteria are particularly useful in the present invention because of the serious problems such bacteria can cause, especially in oil pipelines. If the special thickener used is exposed to bacterial attack, it may also be desirable to include a bactericide as a preservative for the block formed.

The fluid mobility buffer used in the invention for drying the inner surface of a wire comprises a non-crosslinked, gelatinized alkanol having from 1 to 3 carbon atoms. Preferred alkanols are methanol, ethanol and isopropanol. If desired, mixtures of alkanols can be used. The thickening agent for such alkanols can be galactomannan gums or derivatives thereof, but are preferably hydroxy-(lower alkyl) celluloses and are more preferably hydroxyethyl or hydroxypropyl cellulose. Such thickeners may be included in the alkanol at substantially any concentration which has the effect of gelatinizing the alkanol, thereby reducing its volatility and enabling the gelatinized material to be pumped as a viscous slurry through the pipeline. Concentrations of from 5.99 to 23.97 kg of thickener per 1000 liters of alkanol are usually used in the production of the puffer. Sodium hydroxide or other strong base can also be added to the puffer as a viscosity increaser.

The buffer used in the invention separates the aqueous, gelatinized block from the liquid alkanol and prevents mutual mixing of these two components, which would destroy or substantially reduce the effectiveness of each. The gelatinized alkanol does not appear to cause degradation of the gelatinized aqueous block, such as by dehydration, even though the gelatinized alkanol has the capacity to absorb significant amounts of water as it passes through the pipeline.

The desiccant used for drying the inner surfaces of a pipe comprises a liquid alkanol with from 1 to 3 carbon atoms. Preferred alkanols are methanol, ethanol and isopropanol. The alkanol(s) is used in an amount sufficient to dry the pipeline to a desired degree of dryness, that is to say a drying amount.

It is preferred that the alkanol drying agent and the puffer are the same agent, but they can be different when this suits the consumer. One will e.g. usually prefer to follow gelatinized methanol with liquid methanol, but it would also be satisfactory to follow gelatinized methanol with ethanol or isopropanol.

It is usually convenient to follow the liquid desiccant with a mechanical sponge or with a cross-linked hydrocarbon gel, such as the gelatinized hydrocarbon block described in U.S. Patent No. 4,003,393, or a non-gelatinized hydrocarbon block such as described in US Patent No. 4,152,289, but it is also useful to use an inert gas.

The aqueous, crosslinked, gelatinized block, the puffer, and the desiccant are typically driven through the pipeline with a driving force consisting of a pressurized fluid, as described above. If the consumer wishes to refill the pipeline with a liquid product, the "block row" can be advanced with the product as long as there is a satisfactory interface between the product and the alkanol so that the product does not adversely affect the drying ability of the alkanol before its task is completed or substantially completed in the pipeline.

The following examples will further illustrate the invention.

Example 1

A 64.36 km pipeline was cleaned by sequentially passing through it (a) 7570 liters of borate-crosslinked aqueous gelatinized block (pH 8.5-10) containing 45.359 kg of hydroxypropyl guar per 7,570 liters of water, (b) 3,785 liters of fresh water, (c) 60,560 liters of 15 percent hydrochloric acid, (d) 30,280 liters of a commercial passivator and neutralizing agent, and (e) several polyurethane blocks to control gas migration. This line was driven through the pipeline with fresh water pumped at 340.65 liters per minute. Samples were taken of the block as it was passed through the pipeline. Data obtained from such samples showed that the gelatinized, aqueous block retained its integrity during the 40-mile (64.36 km) transport. An excellent cleansing was the result of this treatment.

In example 1, the block row was driven through the pipeline at a speed of approximately 0.3 meters per second. second. This is a very satisfactory speed from a commercial point of view, but speeds of up to approx. 1.5 meters per second has been successfully applied. Rows with higher linear velocity usually require somewhat longer blocks or block segments to achieve the same degree of cleaning (considered to be primarily a function of contact time) and to minimize the propensity of the block segments to mix if one encounters turbulent flow.

Example 2

The effectiveness of a bactericidal gelatinized block was evaluated by passing 37.85 liters of an aqueous gelatinized block containing 250 ppm of a commercial quaternary ammonium bactericide (Dowell M 76) through a 19.812 meter test loop of 2.54 cm's of steel and a section of a 2.54 cm's polyvinyl chloride pipeline contaminated with bacteria-laden river water.

The gelatinized block was driven through the fresh water pipeline at approximately 15.2 cm per second. When the gel came out of the pipeline, it was flushed with approximately 151.4 liters of fresh water. Samples were taken of the river water, of the gelatinized block and of the flushing water. Culture tests showed an extremely large amount of bacteria, more than one million bacteria per cm<3>, in the river water, no bacteria were detected in the gelatinized block, and less than 10 bacteria per cm<3> was detected in the flushing water. The gelatinized block was prepared by mixing 27.216 kg of hydroxypropyl guar and 1.361 kg of boric acid and 250 ppm of the bactericide per 3785 liters of water, and adjust the pH of the solution to a pH of 9-10 with aqueous sodium hydroxide. The system became cross-linked when the pH became basic.

Example 3

Approximately 18.3 meters of 2.54 cm steel pipe containing 7.62 meters of clear polyvinyl chloride sections was filled with water, evacuated with compressed air, and then dried by passing through the following series of blocks: ( 1) A cross-linked, gelatinized water block was added first. It was prepared by mixing 45.42 liters of water, 354 g of hydroxypropyl guar, 16.5 g of boric acid and 350 ml of a 5 percent solution of sodium hydroxide in water. The sodium hydroxide was added on the kick as the block was pumped into the tube. The block was quickly cross-linked (2-5 seconds) after it entered

the tube, to a solid gel.

(2) A gelatinized methanol block - prepared by mixing 13.25 liters of methanol, 191 g of hydroxypropyl cellulose

(average molecular weight of approximately 1 million)

and 24 g of solid sodium hydroxide - were then added.

(3) Methanol - 56.78 liters.

The block row was then driven through the pipe at 0.3048 - 0.6096 meters per second with nitrogen under pressure (approximately 6.542 m<3> was used).

Visual inspection of the pipe before drying showed that the walls were wet with water and that there was some dirt in the low parts of the pipe. After drying with the block row, the surface walls had a dew point of -28.3°C, as measured by the dew point tester of the Bureau of Mines.

Claims (13)

1. Method for internal cleaning of a pipeline, by passing a gel-like mass through the pipeline, driven by a fluid under pressure, characterized in that a gel-like mass is used in the form of an aqueous, gelatinized block containing an aqueous, cross-linked, gelatinized galactomannan gum, or a derivative thereof, as well as possibly a drying alcohol and/or a bactericide and/or other known additives. 2. Method according to claim 1, characterized in that a galactomannan gum is used, or a derivative thereof, which is a guar gum or a hydroxypropyl guar gum. 3. Method according to claim 1 or 2, characterized in that a galactomannan gum is used, or a derivative thereof, which is cross-linked with borate, organo-titanate or organozirconium ions. 4. Method according to any of the preceding claims, characterized in that said rubber, or derivative thereof, is present in said gelatinized block in an amount of at least 5.4 kg per 1000 liters of water. 5. Method according to claim 1, characterized in that a gelatinized block is used which comprises hydroxypropyl guar gum in an amount of from 5.4 to 9.6 kg per 1000 liters of water cross-linked with borate ions and buffered at a pH of from 8.5 to 10.5. 6. Method according to claim 1, characterized in that a bactericide is used which is effective against sulphate-reducing bacteria and which is selected from aldehydes, organic quaternary ammonium compounds and water-soluble salts of halogenated phenols. 7. Method according to claim 6, characterized in that a bactericide selected from formaldehyde, gluteraldehyde, dodecyltrimethylammonium or octadecyltris(2-hydroxyethyl)ammonium chloride is used. 8. Method according to any of the preceding claims, characterized in that it includes the steps of passing through said pipeline in sequence: (a) an aqueous, cross-linked, gelatinized block, (b) a fluid mobility buffer comprising a non-crosslinked, gelatinized alkanol having from 1 to 3 carbon atoms, and (c) a drying amount of a liquid alkanol having from 1 to 3 carbon atoms. 9. Method according to claim 8, characterized in that an alkanol thickened with hydroxyethyl or hydroxypropyl cellulose is used as (b). 10. Method according to claim 8 or 9, characterized in that methanol, ethanol or isopropanol is used as (c). 11. Method according to claim 8, characterized in that in (b) and (c) the same alkanol is used in each case, namely methanol, ethanol or isopropanol. 12. Method according to claim 8, characterized in that (a) an aqueous, crosslinked, gelatinized block is used which comprises an aqueous, gelatinized guar gum or hydroxypropyl guar gum that is crosslinked with borate, titanate or zirconium -ions, (b) a fluid mobility buffer comprising methanol, ethanol or isopropanol thickened with hydroxypropyl cellulose, and . (c) methanol, ethanol or isopropanol. 13. Method according to claim 12, characterized in that (a) a hydroxypropyl guar gum cross-linked with borate ions is used, as (b) methanol thickened with hydroxypropyl cellulose and as (c) methanol.