LU80891A1 - SANITARY TUBES OF PHOSPHORUEX COPPER OR CORROSION-RESISTANT PHOSPHORUS COPPER ALLOYS AND PROCESS FOR THEIR PRODUCTION - Google Patents

Description

I BL - 2 S 7 3 / EM / BM

. i 'Descriptive memorandum filed in support of the patent application for: SANITARY TUBES IN PHOSPHORUS COPPER OR CORROSION-RESISTANT PHOSPHORUS COPPER ALLOYS AND PROCESS FOR THEIR PRODUCTION.

formed by ί

| Public limited company of copper and zinc factories

i at B-4020 Liège.

i ________________: __________________________________: ________________________

Inventors: Yves AKDRIEN, Engineer and Christian TRIQUET, Engineer.

The present invention relates, as new products, to tubes for sanitary use made of copper or copper alloys. phosphorous copper, with good resistance properties; corrosion. The invention also relates to a process for the production of such tubes.

In the field of sanitary tubes, in particular hot and cold water pipes, copper tubes or copper alloys r-hosnh. OrsUX SOzlt 1δΐ2? £! ΘΠ! 6Ι! Ϊ used. These products generally come in two forms, either in rolls of annealed copper, or in straight lengths, generally made of non-annealed or semi-annealed copper.

These tubes can be bare or isolated from a PVC sheath, especially when they are intended to be embedded in concrete.

u "ί: 'au cour, ·; <·; leux- manufacture, which comprises an et-irage between an iî ^ xère and a mandrel forming an ecjjacc i \ annulaire, the tubes brought into contact with oil drawing | (generally consisting of hydrocarbons) necessary for the manufacture. When such tubes are used in the presence of aggressive water, one generally notes the appearance of pitting or pustules and studies have proved that the carbon content of the internal surface of these tubes, resulting from the distillation and decomposition of drawing oils, in particular during annealing, generally increases the susceptibility to corrosion of pipes. It is generally accepted that the carbon content that it is desirable not to exceed is-de-2 2 mg / dm.

Different methods have therefore been proposed to remove the residues of drawing oils and in particular: to avoid the formation of carbon deposits from these oils.

J

! It is known in particular that it is possible not to | exceed the level of 2 mg / dm of carbon by injecting into them! tubes, in particular in tubes in the form of rolls,! before their annealing, a degreasing product such as trichlor-1,,! ethylene, to decrease the amount of residual oil likely! '' cause carbon deposits. After passing this; degreasing liquid, a stream of water vapor is injected inside the tube intended to entrain residual traces of solvent.

A method is also known which makes it possible to reduce the residual carbon content of the tubes after annealing by injecting therein, at high speed, a mixture of air and of abrasive particles such as alumina or carbide. of silicon, of.!: This process is however not applicable to tubes in rolls i and is used only for tubes with straight length. Indeed, · the drop in speed of the abrasive particles caused by their impact in the curves of the roller is too high for the abrasive particles to be able to remove deposits of. carbon or the like in tubes in the form of rolls.

Finally, it is known to achieve a residual carbon content reaching values as low as 2 0.5 mg / dm by injecting into the tubes, before their heat treatment, a gaseous mixture containing oxygen and inert gases. -

During annealing in an oven, generally in a reducing atmosphere, the oxygen reacts with the residual drawing hydrocarbons remaining inside the tube, forming volatile gases such as carbon monoxide or carbon dioxide which are then easily eliminated. of the tube. In this process, the oxygen content is adjusted in the atmosphere injected into the tube so as to particularly prevent the formation of powdery oxide deposits during annealing.

It is known in fact that a thick layer of oxides is generally porous, brittle and not very adherent to the underlying metal and that it can act in a similar manner to a carbon film and therefore be a cause of a pitting corrosion. Studies have shown that these copper tubes containing even less than 1 mg / dm of carbon and covered on their internal surface with oxides formed during annealing. slightly oxidizing condition have a susceptibility to pitting corrosion due in particular to the presence of film oxides.

It is for this reason that the current state of knowledge aims - to develop processes capable of reducing the residual carbon content while avoiding the formation of internal oxide layers. Tests (Pitting Corrosion in Copper Tubes in cold water Service FJ CORNWELL, G. WILDSMITH, PT GILBERT British Corrosion Journal, 1973j Vol. 8 September) indicate that when, over time, in a tube of the type described, the potential difference measured in minivolts between an electrode placed axially at the inside of the tube and the internal wall of this tube remains less than 170 millivolts, a susceptibility to corrosion by pitting in cold water is not observed, even in the presence of aggressive water.

The present invention is based on the observation that a satisfactory product according to the pre-indicated tests can be obtained when simultaneously carrying out a residual carbon content less than or equal to 0.05 mg / dm and an internal coating d '' a thickness between 0.1 and 5 microns made of oxides! } f | adherent to the base metal.

i! j An oxy deposit is described as an adherent to the base metal.

i des when it is possible to make a folding without without! visible cracks on visual examination.

i î Such a tube made of phosphorous copper or copper alloy i i ^ i phosphorous in the presence of particularly aggressive cold water does; does not have a potential difference greater than 170 Millivolts in the indiaue test, in particular in the presence of cold, hard and aggressive water whose pH is greater than or equal to 7 and whose electrical conductivity is between 650 and 800 vil / cm .

It is also observed that even after a year of use, it does not present on its internal surface the start of pitting. On the other hand, a copper tube whose carbon content is low (for example 0.15 mg / drn '.), That is to say clearly lower than the vanity generally /? ,! admitted 2 mp / dm “but it does not contain a layer of oxides,

An .s is observed if in this case the difference in electrode potential K

axial-surface area of the tube is greater than 170 millivolts g

and that after δ, service no., starts of punctures can B

happen. B

We note that there is a relationship between the content g

carbon and the thickness of the oxide layer and as a general rule, B

the lower the carbon content, the more the oxide layer can B

be reduced. A preferred range of carbon content is h

'' between 0.01 and 0.025, while the thickness of the oxide layer ES

can advantageously be between 0.1 and 3 microns. ||

According to the invention, the tubes can be produced I

i by a process in which they are subjected after the conventional annealing f i at 7'00 ° C following a solvent degreasing, a second annealing at a temperature of about 650 ° C in a Ë

separate oven. An atmosphere containing a percentage by volume K

oxygen of about 15% and a percentage by volume i

additional · - a gas mixture consisting of 25% helium E

and 75% of argc'n is injected inside the tube before the second day

annealed. The oxygen in the indicated mixture reacts with the I

last traces of carbon left by the first annealing and I

do rts and wait for such low residual carbon values f? t, 2 1 as 0.05 mg / dr while forming the layer of adherent oxides according to j

And invention.

i the first annealing treatment takes place as a result!

of a degreasing carried out in the conventional manner by .injection | solvent according to the process described in the ► patent; mechanism which allows both to obtain the 5 * reduction in carbon content combined with the formation of an l f? t. ’. · Desired characteristics in particular the adhesion of the deposit of oxides forming in the second annealing operation. It should be noted, however, that this is only a hypothesis and that the Applicant does not intend to bind to any explanation of the reaction mechanism that occurs, any more than it intends to bind specifically to a particular process making it possible to obtain the product of the invention, because modifications of the operating conditions could make it possible to obtain products similar to those described.

By way of illustration of the invention, reference will be made to the annexed graph (FIG. 1) which represents as a function of time, the evolution of the potential difference between an axial electrode and the internal surface of tubes as a function of their quantity i of carbon in the presence of aggressive water, the characteristics of which are as follows: pH 7.50

i ΤΗ ^ 0 ° F

TA 0 ° F

J TAC 26 ° F

- · S0; ~ ^ 5 mg / liter - Cl 70-135 mg / liter

Co ^ h mg / liter i * sf Conductivity 650 to gOO -μ.fl / cm.

Ί .I Curves 1, 2 and 7 correspond to tubes from! 2 '5 ‘trade in carbon characteristics respectively 0, ^ 5 mg / dm, | _ 0.16 mg / dm and 0.11 mg / dm (i.e. well below the Λ ... 2 I ï limit of 2 mg / dm) which have not been treated according to the invention

i i

I / and which are free from any internal oxide deposit.

Λ 1 * V - * - v t h * v.

î. ; - 7 - \} j

Curves 3, 5, 6 correspond to products in accordance with the invention all having a carbon content of • 0.05 mg / dra and an internal oxide coating with an average thickness of 1 micron. i 'i

The improved product features of '

the invention clearly appears. I

Figure 2 illustrates a photomicrograph (magnification x ^ 750) showing the oxide adhering to the surface; i internal. if ; Iß ’7! b! 't • ί [; , \ * · F;

Claims (3)

1. Tubes for sanitary use made of phosphorous copper or. phosphorous copper alloys having good corrosion resistance properties, in particular corrosion by pitting in aggressive waters, characterized by a carbon content less than 2 or equal to 0.05 mg / dm and the presence of an internal coating d '' a thickness of 0.1 to 5 microns consisting of oxides adhering to the base metal. 2. Tubes according to claim 1 characterized in that they are formed of copper or copper alloys annealed after drawing. 3 * Tubes according to claim 1 characterized in that | if they are formed from copper or copper alloys not annealed i »J | after stretching. | h. Tubes according to any one of the claims | 1 to 3 characterized in that the potential difference between the axial electrode and the internal surface of the tube according to the test described in Pitting Corrosion! | in Copper Tubes in cold water Service F.J. CORNWELL, G. WILDSMITH, i * P.T. GILBERT British Corrosion Journal, 1973> Vol. g September, remains below 170 rnV, even in the presence of cold, hard and aggressive water, the pH of which is greater than or equal to 7 and the electrical conductivity between 650 and gOO uJl / cm . IK 5 · Process for the production of tubes according to one I Any of claims 1 to h, characterized in that i · proceeds after conventional annealing at 700 ° C, degreasing by ί solvent followed by drying and then again annealed at a temperature of about 650 ° C, an atmosphere containing a pour; contage in volume of oxygen of approximately 1 j fi and u1 a percentage - 9 - t "of 25% of helium and 75 ° / ° of argon having been produced in the tube before this second annealing . t î ^ —— \