EP1930462B1 - Fittings for drinking water carrying assembly sections - Google Patents

Description

The invention relates to a method for the production of screw or plug fittings, fittings or compression connectors for drinking water leading trades, which are made of a steel alloy, as well as screw or push fittings, fittings or press connectors, made of a steel by laser shearing.

Typically, high-copper-containing non-ferrous metal alloys, such as bronze or gunmetal, are used today for producing media of leading components of, for example, gas or drinking water of leading industries. The non-ferrous metal alloys used are subject to stringent requirements, especially in the case of trades intended for drinking water supply. On the one hand, the non-ferrous metal alloys must have a particularly high corrosion resistance, since the components in contact with drinking water, for example, should not corrode even after many years of use. In addition to a low migration tendency of metal ions in the medium, the components should also be easy to produce and can be mechanically processed well. Due to the rising raw material prices for copper, the main constituent of the previously used non-ferrous metal alloys, alternatives are increasingly being sought which, in addition to good processing properties, ensure similarly high corrosion resistance cost-effectively. When Austenitic steels, for example 1.4301 or 1.4401 steels, have been used to date for stainless steel alloys Although they are characterized by good formability, so that fittings, fittings or compression connectors could be produced economically. However, their corrosion resistance, especially in thick-walled parts that are in constant contact with, for example, drinking water, can be improved. Although ferritic steels, which in principle have an equivalent corrosion resistance, are known, they have not hitherto been used for the production of fittings, fittings and press connectors, since on the one hand they tend to coarse-grained during welding, which leads to a reduced corrosion resistance. On the other hand, the production of thick-walled parts, such as fittings, is problematic due to the reduced formability of the ferritic steel alloys.

The publication JP01180946A discloses, for example, the use of ferritic steel for the manufacture of pipes for conducting high purity water. A high corrosion resistance is achieved according to the teaching of this document both by the alloy composition used and by an additional coating of the inner wall of the tube.

JP-A 9 143 630 . WO 99/25890 and JP-A 8 333 656 disclose steels for making tubes with improved welding properties.

Proceeding from this, the object of the present invention is to propose a method which enables economical production of fittings, fittings and press connectors with improved corrosion resistance.

• C ≤ 0,05 %,
• 11 % ≤ Cr ≤ 25 %,
• Ni < 5 %,
• Mn ≤ 2 %,
• N ≤ 0,25 %,
• Rest Eisen,
• optional: 0,15 % ≤ Ti ≤ 0,8 %,
• optional: 1 % ≤ Mo ≤ 2,5 %,

und bei dem ein Laserschweißschritt durchgeführt wird.According to a first teaching of the present invention, the above-mentioned object is achieved by a method for producing threaded or plug-in fittings, fittings or press connectors for drinking water-bearing industries, which are made of a steel alloy, wherein the steel alloy of the following alloying ingredients in weight percent consists:

• C ≤ 0.05%,
• 11% ≤ Cr ≤ 25%,
• Ni <5%,
• Mn ≤ 2%,
• N ≤ 0.25%,
• Rest of iron,
• optional: 0.15% ≤ Ti ≤ 0.8%,
• optional: 1% ≤ Mo ≤ 2.5%,

and in which a laser welding step is performed.

It has surprisingly been found that by the use of the steel alloy of the specified composition fittings, fittings or press connectors can be produced in an economical manner by laser welding. So far, it has been assumed that corresponding ferritic or austenitic-ferritic steel alloys were not suitable for the production of corresponding components, since these problems on the one hand in terms of formability and on the other hand strongly tend to coarse grain formation during welding, so that the corrosion resistance in these areas is no longer given is. Due to advances in laser welding, the heat input during welding could be reduced so much that a reduction in corrosion resistance now almost no longer occurs. In addition, advances in the field of forming processes, which allow the material to flow, have led to the fact that fittings, fittings or press connectors can be produced economically despite their thick walls and the high degree of forming required for their production. When using a steel alloy according to the invention is due to the low carbon content of max. 0.05 wt .-% significantly reduces the intercrystalline corrosion of the ferritic or ferritic-austenitic steel alloy. Of the Chromium content of 11 wt .-% to 25 wt .-% also leads to an improvement in corrosion resistance, with higher chromium contents in principle increase the corrosion resistance. However, with increasing chromium content, the processing of the steel alloy into fittings, fittings and press connectors more difficult. Nickel is considered austenite former and thus determines the proportion of austenitic structure in the steel alloy. At less than 5%, the austenitic portion is about 50% of the steel alloy. The lower the nickel content, the higher the ferritic fraction of the microstructure. About the addition of max. 2% manganese, the formability of the steel alloy can be improved. In contrast, a higher manganese content would worsen the corrosion resistance of the steel alloy. With a nitrogen content of N ≤ 0.25 wt .-% is achieved that on the one hand by the presence of nitrogen, the resistance to pitting of the steel alloy is improved. On the other hand, limiting the nitrogen content to the stated value does not adversely affect the formability of the steel alloy.

in Gewichtsprozent auf. Durch den erhöhten Chromgehalt der Stahllegierung kann insbesondere die Beständigkeit gegen Korrosion deutlich verbessert werden.According to a next embodiment of the use according to the invention, the steel alloy has a Cr content of $$16\%\le \mathrm{Cr}\le 23\%$$

in percent by weight. Due to the increased chromium content of the steel alloy in particular the resistance to corrosion can be significantly improved.

In order to achieve a sufficient stabilization against intercrystalline corrosion of the steel alloy even with larger wall thicknesses, the steel alloy has a titanium content of 0.15% by weight to 0.8% by weight.

Limiting the molybdenum content to less than or equal to 0.5% by weight lowers the cost in use steel alloy for the production of fittings, fittings or press connectors.

in Gewichtsprozent begrenzt ist.However, a significant improvement in corrosion resistance can be achieved by the alternative addition of molybdenum, so that the Mo content in the steel alloy on $$1.0\%\le \mathrm{Not\; a\; word}\le 2.5\%.\mathrm{Preferably\; not}1.5\%\le \mathrm{Not\; a\; word}\le 2.5\%$$

is limited in weight percent.

in Gewichtsprozent beschränkt, um das Umformverhalten der Stahllegierung zu verbessern.Preferably, the nitrogen content of the steel alloy on $$\mathrm{N}\le \mathrm{0}.\mathrm{03}\%.\mathrm{preferably\; N}\le \mathrm{0}.\mathrm{015}\%$$

limited in weight percent to improve the forming behavior of the steel alloy.

in Gewichtsprozent aufweist, verwendet. Über den Ni-Gehalt wird der Anteil zwischen ferritischem und austenitischem Gefüge eingestellt. Vorzugsweise beträgt der Anteil an austenitischem Gefüge maximal 50 %. Bei ähnlich guter Korrosionsbeständigkeit, wie die der ferritischen Stähle mit sehr geringerem Ni-Gehalt, weist die austenitisch-ferritische Stahllegierung verbesserte Zähigkeitskennwerte und Dauerfestigkeitseigenschaften in korrosivem Medium im Vergleich zu austenitischen Stählen und eine verbesserte Umformbarkeit im Vergleich zu den ferritischen Stahllegierungen auf.According to a further developed embodiment of the invention, a steel alloy having a nickel content of $$1\%\le \mathrm{Ni}\le 3\%$$

in weight percent used. The proportion between ferritic and austenitic structure is set via the Ni content. The proportion of austenitic structure is preferably at most 50%. With similarly good corrosion resistance as ferritic steels with very low Ni content, the austenitic-ferritic steel alloy has improved toughness characteristics and fatigue properties in corrosive medium Compared to austenitic steels and improved formability compared to the ferritic steel alloys.

The use of steel alloy and laser welding for the production of screw or push fittings, fittings or press connectors for drinking water utilities can be provided in an economical manner very corrosion-resistant trades.

According to a second teaching of the present invention, the above-described object is achieved by screw or push fittings, fittings or press connectors for drinking water leading trades, that they have been prepared by the method and the steel alloy according to the invention. With regard to the advantages of the fittings, valves and press connectors thus produced, reference is therefore made to the previous statements on the method according to the invention for the production of screwed or plug-in fittings, fittings or press connectors.

Fig. 1 a)-d)

perspektivische Ansichten von vier Ausführungsbeispielen von erfindungsgemäßen Fittings, Armaturen und Pressverbindern.

There are now a variety of ways to design the inventive method and the components of the invention and further. Reference is made to the claims subordinate to claim 1 and to the description of embodiments in conjunction with the drawings. The drawing shows in

Fig. 1 a) -d)

perspective views of four embodiments of fittings according to the invention, fittings and press connectors.

An embodiment of valves according to the invention is for example the in Fig. 1a The valve housing 1, which is part of the fittings, has partly very high wall thicknesses and can be made of solid material, for example by machining, but also by drop forging the ferritic or ferritic-austenitic steel alloys with the alloy components specified above.

In particular, a titanium content of 0.15 wt .-% to 0.8 wt .-% ensured despite the high wall thicknesses a good corrosion resistance of the valve housing 1 against intergranular corrosion. When laser welding the valve housing 1 according to the invention care must be taken that the heat input is as low as possible, otherwise the steel alloy tends to strong grain growth and intercrystalline corrosion. According to the invention is therefore welded by laser welding, which are optimized for the lowest possible heat input. In addition, by adding up to 2.5% by weight of molybdenum, the valve housing 1 can additionally be stabilized against intergranular corrosion.

Although the ferritic or ferritic-austenitic steel alloy according to the invention is limited in its formability in comparison with deep-drawing steels, the forming capability nevertheless leaves the production of end caps 2 (FIG. Fig. 1b )), which was produced by deep drawing from a strip of a corresponding steel alloy, provided that during the forming a flow of the material is ensured. In a further cold forming step, for example, an O-ring groove 3 can be introduced into the end cap 2.

A compression connector 4 shows the Fig. 1c ). The press connector 4 consists of a tube with an overbend 5 and two-sided connection ends 6. The overbend 5 is produced by bending, whereas the connecting pieces 6 are introduced into the compression connector 4, for example, by an upsetting and widening step but also by using a hydroforming process , The connecting pieces 6 can be pushed onto a corresponding connecting piece, for example a pipe, and pressed with this, so that a tight connection is formed.

This in Fig. 1d ) shown T-piece 7 has at the two opposite terminal ends O-ring grooves 3, which serve for connection, for example with press connectors. For example, the T-piece 7 can be made by a hydroforming of a longitudinally welded pipe, the thread 8 is introduced, for example, by machining. However, the thread 8 can also be produced by rolling. As further forming steps, the upsetting, flanging, necking and widening can be mentioned. The inventive use of ferritic or ferritic-austenitic steel alloy allows the use of not only the conventional forming techniques, but results in the result particularly corrosion-resistant and economically producible screw or plug-in fitting, fittings or compression connectors for drinking water leading trades.

Claims (6)

1. Method for the production of screw- or push-fit fittings, valves or compression joints for drinking water ducting systems, which are produced from a steel alloy having the following content of alloying constituents in weight percent:

   C ≤ 0.05 %,

   11 % ≤ Cr ≤ 25 %,

   Ni < 5 %,

   Mn ≤ 2 %,

   N ≤ 0.25 %,

   optionally: 0.15 % ≤ Ti ≤ 0.8 %,

   optionally: 1 % ≤ Mo ≤ 2.5 %,

   the remainder being iron,

   and wherein a laser welding step is carried out.
2. Method according to claim 1, characterized in that the steel alloy has a Cr-content of $$16\%\le \mathrm{Cr}\le 23\%$$

   

   
   in weight percent.
3. Method according to claim 1 or 2, characterized in that the steel alloy has a Mo-content of $$1.8\%\le \mathrm{Mo}\le 2.5\%$$

   

   
   in weight percent.
4. Method according to anyone of claims 1 to 3, characterized in that the steel alloy has a N-content of $$\mathrm{N}\le \mathrm{0.03}\%,\mathrm{preferably\; N}\le \mathrm{0.015}\%$$

   

   
   in weight percent.
5. Method according to anyone of claims 1 to 4, characterized in that the steel alloy has a Ni-content of $$1\%\le \mathrm{Ni}\le 3\%,$$

   

   
   in weight percent.
6. Screw- or push-fit fitting, valve or compression joint for drinking water ducting systems, which consist of a steel alloy having the following content of alloying constituents in weight percent:

   C ≤ 0.05 %,

   11 % ≤ Cry 25 %,

   Ni < 5 %,

   Mn ≤ 2 %,

   N ≤ 0.25 %,

   optionally: 0.15 % ≤ Ti ≤ 0.8 %,

   optionally: 1 % ≤ Mo ≤ 2.5 %,

   the remainder being iron,

   characterized in that the fitting comprises a laser-welded seam.

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