Pipe fittings are a kind of connectors widely used for connecting pipes, changing direction, or leading pipe out in pipeline systems and pipeline installations of machinery, oil, chemical, electric power, water conservancy, light industry, pharmaceuticals, urban construction, nuclear industry, etc. A pipe fitting is a leakage-proof part connecting the pipeline to the pipeline or another component.
Type of Pipe Fittings
Most pipe fittings have been standardized. They can be divided into two categories by function: one is the hydraulic pipe fittings used in pipeline systems with liquid or gas as a medium; the other is those used in multi-medium pipeline systems.
Hydraulic Pipe Fittings
Hydraulic pipe fittings, as a kind of sealing parts for small pipe connection, is widely used in various hydraulic transmission machines, with an appropriate working temperature range of –20 – 100 ℃ and a nominal pressure of PN≤40MPa; generally, it applies to small pipes with an outer diameter of 4-34mm.
Hydraulic pipe fittings mainly include below:
Bite type fittings,
Hose fittings used for welding, cutting, and relevant processing equipment;
Piping Connectors in Multi-medium Pipeline Systems
This kind of pipe fittings is used for transmitting different media such as seawater, freshwater, cold and hot water, drinking water, domestic sewage, crude oil, fuel oil, lubricating oil, product oil, air, gas, steam, and particle powder with temperature no higher than 170℃. They are commonly used in pipes and pipeline installations of urban construction water supply systems, ship, and petrochemical industry, with a wide range of specifications that apply to pipes with a nominal diameter DN of 10-3,000mm.
Piping Connectors for multi-medium pipeline mainly include below:
Clamp-type flexible pipe fittings,
Pipeline compensating fittings,
Pipe fittings for corrugated metal hose,
(including fittings made of alloy steel and stainless steel),
Stainless steel thread pipe fittings for food and water supply industries.
Pipe Fittings Structure
A pipe fitting is generally composed of a fitting body, a connecting sleeve or a connecting nut, and a sealing element. As an assembled sealing element, it is used for connecting pipes, changing direction, leading pipe out, etc. A pipe fitting is a leakage-proof part connecting the pipeline to the pipeline or another component. The fitting body is the main connecting part, which may be the fitting itself or a part of the fitting. The sealing element in the pipe fitting is mainly made of metal or non-metal material. The former is commonly known as metal seal fitting, and the latter is commonly known as elastomer sealing fitting.
Piping Fittings Definition
The ways and methods of energy conversion, transmission, control and distribution using pressurized fluid as a medium, which are called hydraulic and pneumatic for short.
The pressure under which the installation is operating.
Maximum Working Pressure
The maximum working pressure under which a hose fitting can ensure the normal operation of the system under the specified service conditions.
The bearing capacity of a hose fitting under twice the maximum working pressure.
Minimum Burst Pressure
The minimum failure pressure that a hose fitting should be able to bear, which is 3 times its maximum working pressure.
A leakage-proof part for connecting pipeline to pipeline or another component.
A part that plays the main role of connection in the fitting. The fitting body may be the fitting itself or a part of the fitting.
External thread connected with the threaded hydraulic fluid port.
Torque applied for satisfactory installation.
Adjustable Column-end Fittings
A column-end attachment fitting allows the fitting to adjust direction to complete the connection before tightening the nut. This type of column-end fitting is generally used for tee, cross, elbow, and other similar fittings only.
Fixed Column-end Fittings
A column-end attachment fitting that doesn’t require special direction adjustment before tightening the connection, which is used for straight fittings only.
1. Flare Fittings
Flare fittings are widely used in some medium- and high-pressure hydraulic pipeline systems. This kind of fittings usually has two types of structure: one is composed of a fitting body with a 74° outer conical surface, a nut (A-nut) for pressing and a flare fitting sleeve with a 66° tapered bore; the other is composed of a fitting body with a 90° outer conical surface and a nut (B-nut) with a 90° tapered bore. The flare pipe with a 74° or 90° inner conical surface after cold-drawn processing is placed between the outer conical surface of the fitting body and the tapered bore of the sleeve (or B-nut). Tighten the nut to press the flare of the pipe and squeeze it into the gap between the outer conical surface of the fitting and the tapered bore of the pipe sleeve (or B-nut) to play a sealing role.
Flare pipe fittings have been standardized and widely used in many industries. At present, there are 27 typical national standards such as GB/T 5625-GB/T 5635—2008, GB/T 5637-GB/T 5639—2008及GB/T 5641-GB/T 5653—2008.
Flare Fittings Application
Flare fittings are applicable to the pipes with 4-34mm outer diameter and 3.5-16MPa maximum working pressure, which are used for hydraulic fluid transmission and other general purposes.
Categories of the Flare Pipe Fittings
Straight Flare Pipe Fittings
Flare Taper Thread Straight Pipe Fittings
Flare Taper Thread Long Pipe Fittings
Flare Straight Pipe Fittings
Flare Taper Thread Elbow Pipe Fittings
Flare Elbow Pipe Fittings
Flare Adjustable Elbow Pipe Fittings
Flare Combined Elbow Pipe Fittings
Flare Adjustable Union Tee
Flare Combined Elbow Union Tee
Flare Taper Thread Union Tee
Flare Adjustable Elbow Union Tee
Flare Combined Union Tee
Flared Union Tee
Flare Union Cross
Flare Welded Pipe Fittings
Flare Cross-plate Straight Pipe Fittings
Flare Cross-plate Elbow Pipe Fittings
Flare Pressure Gauge Pipe Fittings
Flare Pipe Fitting Sleeve
A-nut for Flare Pipe Fittings
B-nut for Flare Pipe Fittings
Locknuts and Washers for Pipe Fittings
Hollow Bolts for Flare Pipe Fittings
Sealing Gaskets for Flare Pipe Fittings
Size of Flared End of Flare Pipe Fittings
Material of Flare Pipe Fittings
The material of the fitting body shall be compatible with the transmitted medium and ensure an effective connection.
The fitting body made of carbon steel shall meet the pressure-temperature requirements specified in Article 1.3.2; the pressure-temperature grade of that made of stainless steel or copper alloy shall be specified by the manufacturer.
Unless otherwise agreed by the supplier and the buyer, the nuts matching with the carbon steel fitting body shall be made of carbon steel, those matching with the stainless steel fitting body shall be made of stainless steel, and those matching with copper alloy fitting body shall be made of copper alloy.
The pipe sleeve material shall be compatible with the transmitted medium and ensure an effective connection.
The carbon steel pipe sleeve shall match with the carbon steel fitting body and carbon steel pipe. Stainless steel sleeve shall match with stainless steel fitting body and stainless steel pipe. The copper sleeve shall match with copper fitting body and copper pipe; The combined use of different types of materials shall be determined by the supplier and the buyer through negotiation.
Unless otherwise specified, O-rings used for petroleum-based hydraulic oil and complying with the pressure-temperature requirements specified in Article 1.3.2 shall be made of NBR with a hardness of (90±5) IRHD that is measured according to GB/T 6031-1998 Rubber, Vulcanized or Thermoplastic-Determination of Hardness (Hardness between 10IRHD and 100 IRHD), and its appearance quality shall not be lower than the N-level requirements of GB/T 3452.2-2007 Hydraulic and Pneumatic Rubber Sealing O-Ring Part 2: Code for Appearance Quality Inspection. O-rings used beyond the scope of Article 1.3.2 or for non-petroleum-based hydraulic oil systems may be made of other materials that shall be consulted with the pipe fittings manufacturer.
2. Cone Connectors
The 24° cone connector is a kind of rigid sealing connector invented in the 1930s. It has been widely promoted due to its easy production process, easy installation, and satisfactory pressure-resistant performance. Meanwhile, the 24° cone connectors can be made in various patterns to fit different design requirements well in most regions of the world.
This rigid sealing cone connector is mainly composed of three parts: the connector body with 24° tapered bore, the connecting sleeve (surface hardened) with inner blade, and the fastening nut. When the nut is screwed down, the connecting sleeve could be pushed into the tapered bore of the connector body under the nut pressure. And with the elastic deformation, the sealing bevel of the connecting sleeve and the tapered plane of the connector body squeeze each other to form rigid sealing. Meanwhile, the inner blade in the connecting sleeve clips into the outer wall of the connecting pipe, while the end of the connecting sleeve shrinks radially to wrap the pipe, thereby achieving reliable connection between the steel pipe and the connector.
This is actually a small-sized medium/high-pressure joint commonly used in hydraulic lab and hydraulic transmission machine. It is now a standard component in China and has been commonly used in various sectors. Up to now, a total of 30+ standards are made available and applicable to this product, including GB/T 3733-3760—2008, GB/T 3763-3765 2008, etc.
Application of Cone Pipe Connector
This cone connector is mainly applicable to hydraulic power and general purpose pipeline systems, which are featured in 4-42mm pipeline outer diameter and 10-36MPa max. working pressure.
Cone Fittings Materials
The connector body material should be compatible with the transmission medium. And the connector shall be effectively connected.
The connector body made of carbon steel shall meet the pressure-temperature requirements specified in 2.3.2; the pressure-temperature value of the connector body made of other materials like stainless steel or copper alloy shall be specified by the manufacturer.
Unless otherwise agreed between the supplier and the buyer, the connecting nut used together with the carbon steel connector body shall be made of carbon steel; the connecting nut used with the stainless steel connector body shall be made of stainless steel; and the connecting nut used with the copper alloy joint body shall be made of copper alloy.
The sleeve material should be compatible with the transmission medium. And the sleeve should be effectively connected.
Carbon steel sleeves should be used together with the carbon steel connector bodies and the carbon steel pipes; stainless steel sleeves should be used together with the stainless steel connector bodies and the stainless steel pipe; and copper sleeves should be used in conjunction with copper connector bodies and copper pipes. The coordinated use of products made of different materials should be based on the negotiation between the supplier and the buyer.
Unless otherwise specified separately, the O-ring used in petroleum-based hydraulic oil should be made of nitrile butadiene rubber (NBR), with a hardness of (90±5) IRHD. When measuring according to the requirements in GB/T 6031, its appearance quality should be no lower than Grade-N requirements in GB/T 3452.2. As for O-rings used outside the pressure and temperature ranges, or in non-petroleum hydraulic oil systems, other hardness or materials can be selected under the precondition of consulting the connector manufacturers.
Pressure and temperature for cone connector
(1) The 24°cone connectors made of carbon steel should be able to bear the required working pressure when the medium temperature ranges between -40-120℃.
(2) Unless otherwise specified separately, pipe connectors with elastic seals should be designed with special operating temperature range if they are used in petroleum-based hydraulic oil systems. Its operating temperature range may be reduced or may be totally inapplicable to other fluids. The manufacturer can provide elastic seals that are suitable for different media and can meet the temperature range requirements.
3. Welding Cone Adapter
The welding cone connector, which is a 24° welded joint, has been widely used in the heavy machinery industry of China. It is generally composed of three parts: connector body with a hexagonal head support plane (24° cone inside the connector), the cone tube (24° outer cone of the cone tube head), and the tightening nut. When installing the product, the welded tapered tube end of the connector should be butt welded to the nozzle of the pipe firstly; and then, the O-ring should be put into the O-ring groove in the tapered tube head. After that, the 24° outer tapered plane of the cone should be connected to the 24° inner tapered plane of the connector body. And finally, the nut should be screwed down to achieve sealed connection.
Application of Welding Cone Adapter
Welding cone connectors are applicable to the pipeline systems which take oil or gas as the media, with PN≤31.5MPa nominal pressure (315bar), and -25～90°C working temperature range.
Type of Welding Cone Adapter
Straight 55° non-sealed pipe threaded adapter;
Straight 55° sealed pipe threaded adapter;
Straight 60° sealed pipe threaded adapter;
90° elbow adapter;
55° non-sealed pipe thread 90° elbow adapter;
55° sealed pipe thread 90° elbow adapter;
60° sealed pipe thread 90° elbow adapter;
Both-ends welded straight adapter;
Welded angular adapter;
Welded tee adapter;
Welded angular bulkhead adapter;
Welded straight bulkhead adapter;
Welded connector for pressure gauge.
4. O-ring plane sealed connector
The O-ring plane sealed connector, which takes hydraulic oil (liquid) as its working medium, is a metal connector used for general purposes. Its working temperature is between -20-100°C. And it is used for connection that requires O-ring plane sealed connector under working pressure between 6.5kPa absolute vacuum pressure to the pressure specified in Table 4-12.
The O-ring plane sealed connector is mainly composed of three parts, namely the connector body, welding pipe, and connecting nut. The thread end surface of the connector body is a plane with O-ring groove, that is: the sealing plane. The nozzle of the welding pipe is processed into a sealing plane by rolling and flaring. When installing the product, the nozzle that has been processed into plane should be connected to the end of the connector body first. And then, the nut should be screwed down to form elastic sealing.
Connection mode and structure of the O-ring plane sealed connector
O-ring plane sealed connection end
Categories of O-ring plane sealed connectors
Straight, angular, tee, and cross connectors
Straight, angular,45°, tee branch, tee main partition connector
Column-end straight connector, 45°, angular, tee branch, tee main adjustable column-end connector
Union connector and union connector end
Straight and angular welded connector
5. Hose Adapters
It includes two parts: one is the hose connectors used on equipment of welding, cutting, and relative processes, and the other one is the.non-alloy and stainless steel connectors.
Hose connectors for equipment of welding, cutting, and relative processes
Application of Hose Adapter
This hose connector is applicable to the hose connection of the metric thread welding, cutting, and relative process equipment with 6.3～12.5mm inner diameter rubber tube, and applicable to the hose connection of the 55°non-sealing pipe thread welding, cutting, and relative process equipment with 3.2-20mm inner diameter rubber tube.
Categories of Hose Connectors
Inner-cone sealed thread connector
Ball-type sealed hose connector
Inner-cone sealed thread connector
Ball-type sealed hose connector core
6.Non-alloy steel and stainless steel connectors for corrugated metal hoses
Metal hoses used in petroleum and chemical industrial pipelines and devices are commonly connected by non-alloy steel and stainless steel connectors. These connectors are within DN6～DN300. And for the flange connectors, the nominal pressure ranges between PN0.6MPa～PN26.0MPa.
External thread connector
Spherical sealing loose nut joints
External thread transition connector connected to loose nut connector
Internal thread transition connected to loose nut connector
Butt welded pipe
Bulkhead loose flange
Loose hubbed flange
Bulkhead flat-welded flange
Butt welded flange
Lapped ring loose flange (type-B1)
Lapped ring loose flange (type-B2)
7. Hydraulic Quick Action Connector
Application of Hydraulic Quick Action Connector
Requirements on size and performance of the quick action connector were made in order to guarantee that the connector can be quickly connected or disconnected in the hydraulic pipeline system without any tool or special devices. In this standard, two widely-used series of quick action connectors, which are with similar processes, are specified, namely Series-A and Series-B quck action connectors. Requirements herein are equivalent to those in ISO 7241-1:1987 Quick Action Connectors for Hydraulic Transmission; Part 1: Dimensions and Requirements. Series-A connectors are usually used in Europe, while Series-B connectors are usually used in the Americas.
8.Clamp-type Flexible Connector
It is widely used in water supply/drainage systems and material conveying systems in the mining operation field.
Application of clamp-type flexible connector
The clamp-type flexible connector is a standard and removable connecting component, which is mainly used for connecting pipelines to convey gas, fluid, slurry, and dust. It can be designed and manufactured into 4 types of connectors with nominal pressure of PN10～PN100 (measured in ‘bar’), including the clamp-type flexible ring connector, the flexible widened connector, the flexible groove connector, and the flexible shoulder-type connector.