NO158349B - BITUMINOES MIXING FOR COATING OF PIPES OR PIPES - Google Patents

Description

The invention relates to a bituminous mixture for coating pipes or pipelines.

It is known to coat pipes, e.g. metal pipes, e.g.

pipes of steel or cast iron, which are to be used as transport lines for oil, gas, etc., with a layer of a bituminous or asphalt mixture. Such layers are usually between 3 and 10 mm thick. Due to the conditions encountered in connection with such coated pipes during transport, storage, laying and use, especially if such pipes are laid in the ground or in water, a number of standard specifications have been produced for testing the coating. Two such specifications are: (I) In a flow test, the flow from a coating layer 5 mm thick at 70°C and an angle of 45°

be less than 6 mm after 2o hours: and

(II) in an indentation test, the impression of a round piston having a surface area of 1 cm under a load of 2.5 kg, at a temperature of 25°C, shall not exceed 17 mm after 24 hours.

Additional claims are:

(I) In a bending test, the coating shall not crack at a deflection of less than 20 mm at a thickness of 2 mm, a temperature of 4°C and a bending speed of 1 mm/s: and (II) the coating compositions as such shall have acceptable corrosion protection properties.

One problem with selecting a pipe asphalt is that asphalt that has satisfactory mechanical properties occasionally provides incomplete corrosion protection and vice versa,

and the selection of a particular pipe asphalt is therefore a compromise between such conflicting requirements.

We have now discovered a pipe asphalt mixture that satisfies these conflicting requirements. The invention thus relates to a bituminous mixture as stated in the accompanying patent claim.

As indicated above, the pipe coating composition comprises a block copolymer which is preferably a thermoplastic rubber, having the general configuration:

The polymer blocks A preferably have a number average molecular weight in the range 2000-100,000, especially 5000-50,000. The polymer block B preferably has an average molecular weight in the range 25,000-1,000,000, especially 35,000-150,000.

Any time according to the branched configuration when two or more blocks B are immediately adjacent to each other, they are treated as a single block in terms of molecular weight. The amount of polymer blocks A in the block copolymer preferably varies from 10 to 70% by weight, especially from 20 to 50% by weight. As examples of monovinyl aromatics which are suitable for the production of the polymer blocks A in the block copolymers referred to here, styrene and α-methylstyrene can be mentioned. As conjugated dienes which are suitable for the production of the polymer blocks B in the block copolymers mentioned here, dienes with 4-8 carbon atoms per molecule, especially butadiene and isoprene. Polymer blocks B can also originate from the copolymerization of one or more conjugated dienes with one or more monovinyl aromatic compounds. The 1-alkenes which are applicable in the production of either the thermoplastic blocks A or the elastomeric blocks B include 1-alkenes with 2-12 carbon atoms per molecule, e.g. ethylene, propylene, butene-1, hexene-1 and octene-1.

Suitable examples of the block copolymers contemplated here are as follows: polystyrene/polyisoprene/polystyrene, polystyrene/polybutadiene/polystyrene, polyethylene-(ethylene/propylene copolymer)-polyethylene, polypropylene-(ethylene/propylene copolymer)-polypropylene , and their hydrogenated counterparts, particularly of the block copolymers containing diene homopolymer blocks.

The block copolymers can be prepared by a number of different types of processes including the following:

A vinyl aren, e.g. styrene, can be polymerized in a

in an essentially inert hydrocarbon environment in the presence of a mono-functional alkali metal hydrocarbyl initiator, e.g. a lithium-alkyl compound, to form a polyvinyl-arene block A terminated with a lithium ion. Immediately thereafter, and without further treatment, a conjugated diene is introduced, e.g. butadiene, and block copolymerization is performed to produce the intermediate block copolymer A-B associated with the lithium ion. Finally, a vinylaren is introduced, e.g. styrene, and the polymerization is continued to form the desired linear polymer

Linear polymers can also be formed by a coupling process where the first step is as described above,

to form the first lithium-terminated polymer block A, followed by introduction of the conjugated diene to form a polymer block having a molecular weight only half the final molecular weight of the conjugated diene polymer block in the finished product. At this point, a difunctional coupling rod part is added, e.g. dibromo-methane, to form the desired 3-block polymer A-B-(-B-A)n, where n is 1, in other words A-B-A, which may contain an insignificant coupling residue in the center block B. This coupling residue is ignored in the description of the block copolymers.

Non-linear, i.e. branched, block copolymers

is easily formed by using multifunctional coupling agents, e.g. trichlorobenzene and tetrachloroethane. Hydrogenation can be carried out under the usual conditions known to those skilled in the art, using a variety of hydrogenation catalysts, e.g. nickel and diatomaceous earth, Raney nickel, copper chromate, molybdenum sulphide, finely divided platinum, platinum oxide, finely divided palladium, copper chromium oxide, etc. The hydrogenation pressures usually vary from atmospheric pressure to approx. 211 kg/cm 2 , and typically varies between approx. 7 and 70.3 kg/cm 2.

The temperature can vary from approx. 10 to approx. 316°C, the maximum temperature being limited to avoid degradation of the polymer. The hydrogenation can be complete, i.e.

to reduce all unsaturation, or it may be randomized, ie to reduce unsaturation to a certain extent, e.g. 20%

of the original value. It is also possible to selectively hydrogenate exactly the center block so that e.g. the polyisoprene is converted into an ethylene/propylene rubber (EPR).

Preparation of the mixture can take place in a simple way by stirring the polymeric component as a finely dispersed solid or in the form of a solution in e.g. benzene or toluene, into a molten bituminous component. The solvent can then be evaporated.

As mentioned, the pipeline mixtures contain a wax

and optionally an inorganic filler. The. waxes or wax mixtures used are those which have a solidification point of at least 60°C. As mentioned, the wax is used in amounts of 1 to 60% by weight, preferably from 5 to 40% by weight, based on the weight of the bituminous component and the thermoplastic rubber. Animal, insect, vegetable, synthetic and mineral waxes can be used, with those derived from mineral oils being preferred. Examples of mineral oil waxes include bright stock slack wax (BSSW), medium machine oil slack wax (MMOSW), high melting waxes (HMPW) and microcrystalline waxes (MXW). Additives to increase the pour point of the wax may also be present.

A large variety of inorganic materials can be used as fillers, those having such a particle size

that at least 5% by weight is retained on an ASTM 200 sieve is preferred. The fillers that give the best results are talc and slate powder. Other suitable fillers include asbestos, silica fillers, e.g. silicates, and calcareous fillers. Mixtures of different fillers can also be used. Amounts of inorganic filler used are from 1 to 100% by weight, preferably from 20 to 80% by weight, based on the weight of bituminous component and thermoplastic rubber.

The coating agents are particularly suitable as a coating for water pipelines.

It is preferred that the pipe or pipeline is treated with a primer before a coating of the above-mentioned bituminous mixture is applied. Such primers are often similar to the mixtures described here, with the exception that they do not contain an inorganic filler and are usually dissolved in an aromatic-type solvent, e.g. kerosenes.

The bituminous mixtures are preferably applied in liquid form to form a coating of at least 3 mm thickness, preferably 3-10 mm thickness. It is therefore necessary to heat the mixture so that a sufficiently low viscosity is obtained. In general, it is preferred to apply the bituminous mixture in the form of a liquid with a viscosity below 1500 cS at 180°C.

After the pipe or pipeline has been coated by the above method, it can be further coated, e.g. with a layer of concrete, paper or plastic.

In what follows, the invention will be illustrated by means of examples. The ring and ball softening points are determined according to ASTM 36-26 and the penetration according to ASTM D5-61.

EXAMPLES

Various bituminous mixtures, the composition of which is given in the table, were produced and used for coating such objects as metal sheets and pipes. The objects were pre-treated with a primer consisting of bitumen, rubber and wax dissolved in an aromatic solvent.

The properties of the materials used were: Bitumen A:

Propane bitumen: softening point, ring and ball:

58°C: penetration : 12 (0.lmm) at 25°C.

Bitumen B:

Propane bitumen: softening point, ring and ball:

66°C penetration : 9 (0.lmm) at 25°C.

Bitumen C:

Blown propane bitumen: softening point, ring and ball:

87.5°C; penetration: 7 (0.1 mm) at 25°C.

Bitumen D:

Blown propane bitumen, softening point, ring and ball:

104°C; penetration: 1.5 (0.lmm) at 25°C.

Rubber A:

Styrene/butadiene/styrene block copolymer with molecular weight 14,000 - 65,000 - 14,000.

Rubber B:

Styrene/isoprene/styrene block copolymer with molecular weight 9,000 - 140,000 - 9,000.

Rubber C:

Styrene/hydrogenated butadiene/styrene block copolymer

with molecular weight 10,000 - 50,000 - 10,000.

HMPW:

High-melting wax, solidification point 84°C.

MXW:

Microwax, solidification point 62°C.

BSSW:

"Bright stock slack wax", solidification point 73°C.

MMOSW: Medium machine oil slack wax; solidification point 63°C. Slate dust:

Slate dust with 96% by weight particles with sizes from

20 to 149 µm.

The coatings were then subjected to a flow test, an incision test and a bending test. These tests are described above.

. The coating mixtures according to Examples I and II were also subjected to a corrosion test which included the coating of mild steel plates (8 x 8 cm 2 ), which had previously been sand-blasted and primed with a 0.5 mm thick coating of the mixture. Each metal plate was then sealed to one end of a "Perspex" cylinder whose other end consisted of a titanium anode fixed by means of an 0-ring. The metal plate was connected to the negative pole of a 3 V battery and the titanium anode to the positive pole. A solution of aerated saline was then pumped through the cylinder. The electrical resistance of the coating was measured

12 at regular intervals. The first value is usually approx. 10 10"^ ohms, and the coating is said to have failed in the test when this value falls below 10^ ohms. The number of days before failure was observed is the corrosion character of the coating.

The results are reproduced in the table below.

Claims (1)

Bituminous mixture for coating pipes or pipelines, comprising (a) 80-99% by weight of a propane bitumen and/or a blown propane bitumen having a ring and ball softening point of 55-100°C and a penetration of 2-15 (0.1 mm) at 25°C, (b) 1-20% by weight of a block copolymer of the general configuration: A-B - (-B - A)where A is a thermoplastic polymer block of a monovinyl aromatic hydrocarbon or a 1-alkene, B is an elastomeric polymer block of a conjugated diene or more than one 1-alkene, and n is an integer, preferably from 1 to 5, or a hydrogenated derivative of the block copolymer, and optionally ( c) 1-100% by weight, based on the weight of the bitumen and the block copolymer, of an inorganic filler, characterized in that the mixture additionally contains (d) 1-60% by weight, based on the weight of the bitumen and the block copolymer, of a wax with a solidification point of at least 60°C.