Pipes

What is a hydraulic pipe?

A hydraulic pipe, often called a hydraulic tube, is a rigid metal line used to carry hydraulic fluid under pressure between the components of a hydraulic system, such as pumps, valves, manifolds, cylinders, and motors. While hoses are flexible and used where parts move, rigid pipes are used for fixed runs where the line does not need to flex. They are common on machinery frames, hydraulic power units, and industrial installations, and anywhere a neat, durable, and pressure-stable line is needed.

Most hydraulic pipes are precision seamless steel tubes, made by cold drawing to give accurate dimensions, a smooth bore, and high strength. They are connected to the rest of the system using compression fittings, flared fittings, welded fittings, or flanges, and are usually bent to shape so they follow the machine with as few joints as possible.

Key features:

• High-pressure capability - depending on material, outside diameter, and wall thickness, hydraulic pipes can handle working pressures from low-pressure return lines up to several hundred bar
• Rigid construction - holds its shape, giving neat, stable, and well-supported routing
• Precision dimensions - accurate outside diameter and wall thickness ensure a reliable seal with compression and flared fittings
• Smooth, clean bore - reduces pressure loss and helps keep the system clean
• Low expansion under pressure - unlike hoses, rigid pipes hardly expand, giving a stiffer, more responsive system
• Long service life - pipes do not age like rubber hoses and can last for the life of the machine if properly supported and protected
• Corrosion protection - usually supplied with a zinc-plated, phosphated, or oiled finish, with stainless steel available for harsh environments
• Wide size range - commonly from 4 mm to 42 mm outside diameter for compression fitting systems, and larger for welded and flanged pipework

In simple terms, a hydraulic pipe is a strong, rigid, precision-made line that carries pressurised fluid along fixed routes in a hydraulic system.

Why are hydraulic pipes essential?

Hydraulic pipes are essential because many parts of a hydraulic system are fixed in place and need a line that is strong, stable, and long-lasting. Using hoses for every connection would mean more movement, more wear, more ageing, and more replacement. Rigid pipes provide a durable backbone for the system, while hoses are used only where movement is needed.

Their main benefits are:

• Durability - steel pipes do not age, crack, or perish like rubber hoses, giving a much longer service life on fixed runs
• Stable performance - low expansion under pressure gives a stiffer system with more precise and responsive control
• Lower pressure loss - smooth bores and gentle bends help fluid flow efficiently
• Better heat dissipation - metal pipes help release heat from the fluid, which can help keep oil temperatures down
• Neat and compact routing - pipes can be bent tightly and run close to the machine structure, keeping systems tidy and out of the way
• Fewer leak points - bending one length of pipe instead of using several fittings reduces the number of joints and possible leaks
• Cost-effective for long runs - pipes are often more economical than hoses over longer distances and in permanent installations
• Resistance to damage - rigid steel pipes resist abrasion and impacts better than hoses when properly supported and protected
• Cleaner systems - precision tubes are produced with clean bores, helping protect sensitive components

These qualities make hydraulic pipes important in a wide range of industries and equipment, including:

• Construction machinery - excavators, loaders, cranes, and telehandlers, along booms, chassis, and frames
• Agricultural machinery - tractors, loaders, sprayers, harvesters, and implements
• Hydraulic power units - connecting pumps, valves, filters, coolers, and reservoirs
• Industrial machinery - presses, injection moulding machines, machine tools, and production lines
• Mining and quarrying - heavy mobile and fixed equipment
• Marine and offshore - deck machinery, steering systems, winches, and offshore installations, often using stainless steel or copper-nickel pipe
• Commercial vehicles - tippers, cranes, refuse vehicles, and tail lifts
• Steel, paper, and process industries - large centralised hydraulic and lubrication systems
• Test benches and laboratories - where stable, precise lines are required

The main types of hydraulic pipes

Hydraulic pipes are usually grouped by material, manufacturing method, finish, and the type of connection they are used with.

By material:

• Carbon steel precision tube - the most common type, usually seamless and cold drawn. Typical grades include E235 and E355, which are often supplied in the normalised (+N) condition so the tube can be bent and fitted without cracking
• Stainless steel tube - usually 316 or 316L grades, used for marine, offshore, food-processing, chemical, and corrosive environments, and where cleanliness is critical
• Copper-nickel tube - used in marine applications for its excellent resistance to seawater corrosion
• Copper and aluminium tube - used for some low-pressure lines, lubrication systems, and lightweight applications

By manufacturing method:

• Seamless cold drawn tube - made without a weld seam, giving the best strength and pressure performance. This is the standard for most hydraulic systems
• Welded and drawn tube - made from welded strip, then drawn to size. Suitable for some lower-pressure applications
• Heavy wall pipe - thicker pipe used for large-bore, high-pressure systems, usually joined by welding or flanges

By finish:

• Zinc-plated with passivation - gives good corrosion resistance and a clean appearance, widely used on mobile machinery
• Phosphated and oiled - a light protective finish often used for tubes that will be painted or used indoors
• Black or plain finish - usually oiled for storage and painted or protected after installation
• Stainless steel - naturally corrosion resistant without extra coating

By connection type:

• Compression fittings with 24 degree cone - the most common system for metric hydraulic tube, defined in ISO 8434-1 (formerly DIN 2353). A cutting ring or progressive ring bites into the tube as the nut is tightened. These fittings are made in light (L) and heavy (S) series
• Formed or flared tube ends - the tube end is formed or flared using special tooling, then sealed with an elastomer seal or metal-to-metal contact. These reduce the risk of leaks and are popular on mobile machinery
• 37 degree flared tube (JIC) - common on inch-sized tube, especially on equipment built to American standards
• O-ring face seal (ORFS) with braze or formed sleeves - used for leak-free connections at high pressures
• Welded connections - weld-on fittings, weld nipples, and butt welds, used on larger pipes and permanent installations
• Flanged connections - SAE or other flanges welded or fitted to the pipe, used on large, high-pressure lines

By size system:

• Metric tube - sized by outside diameter and wall thickness in millimetres, such as 12 × 1.5 or 20 × 2.5
• Inch tube - sized by outside diameter and wall thickness in inches, commonly used with JIC and ORFS fittings
• Nominal bore pipe - larger pipes sized by nominal bore and wall schedule, such as Schedule 80 or Schedule 160, used in heavy industrial installations

How to choose the right hydraulic pipe?

Choosing the right hydraulic pipe means matching it to the pressure, flow, connection system, and environment. Work through these points in order:

• Outside diameter - choose an outside diameter that matches the fittings used. Compression fittings are sized by the tube outside diameter, so this must be exact
• Inside diameter and flow - check that the inside diameter is large enough for the required flow rate. Too small a bore causes high fluid velocity, pressure loss, and heat
• Wall thickness and pressure - choose a wall thickness that gives a safe working pressure for the system, including pressure spikes. A thicker wall gives a higher pressure rating but a smaller bore for the same outside diameter. Always check the manufacturer’s pressure tables
• Material - use carbon steel for most applications, and stainless steel or copper-nickel for marine, offshore, chemical, or food-processing environments
• Material condition - choose normalised (+N) precision tube where the pipe will be bent or used with compression fittings, as it is ductile and suitable for forming
• Connection system - make sure the tube suits the fittings, whether 24 degree cone compression fittings, formed ends, flared ends, ORFS sleeves, welded fittings, or flanges
• Light or heavy series fittings - heavy (S) series fittings are rated for higher pressures than light (L) series fittings of the same tube size, so match the fitting series to the system pressure
• Finish and corrosion protection - choose zinc-plated tube for mobile machinery and outdoor use, phosphated or oiled tube for painting or indoor use, and stainless steel for harsh environments
• Temperature - check that the tube and fittings are suitable for the operating temperature, as high temperatures reduce the allowable pressure
• Bending - plan bends so the pipe can be formed with a suitable bending radius, without flattening or kinking. Gentle bends reduce pressure loss and the number of fittings needed
• Support and clamping - plan clamp positions along the pipe and near bends and fittings to reduce vibration and stress
• Cleanliness - make sure the tube is clean and capped, and flush the system after installation to remove any debris
• Standards and quality - choose tube made to recognised hydraulic standards, such as EN 10305-4 for seamless cold drawn precision steel tubes, from reputable suppliers

FAQ: all you need to know about hydraulic pipes

What is the difference between a hydraulic pipe and a hydraulic tube?

In everyday use, the terms are often used interchangeably. Strictly speaking, tubes are sized by outside diameter and wall thickness and used with compression and flared fittings, while pipes are often sized by nominal bore and schedule and joined by welding, threading, or flanges.

When should I use a pipe instead of a hose?

Use rigid pipes for fixed runs between components that do not move relative to each other. Use hoses where there is movement, where flexibility is needed for routing or servicing, or where vibration would be too much for a rigid line.

How do I measure a hydraulic pipe?

Measure the outside diameter and the wall thickness with calipers. Metric tube is described as outside diameter × wall thickness, for example, 12 × 1.5, which has an inside diameter of 9 mm.

What pressure can a hydraulic pipe handle?

It depends on the outside diameter, wall thickness, material grade, temperature, and safety factor. Always check the manufacturer’s pressure table, and make sure the fittings are rated for the same pressure.

How should I cut and bend hydraulic pipe?

Cut it square using a fine-tooth saw with a guide or a dedicated tube cutting machine, then deburr the inside and outside and clean out any chips. Bend it using a proper tube bender with formers matched to the tube size, as bending without the correct tools can flatten, kink, or weaken the pipe.

Why do hydraulic pipes need clamping?

Unsupported pipes vibrate, which can cause fatigue cracks, loose fittings, and leaks. Clamping along the run and near bends and fittings keeps pipes secure and reduces noise.

When should I use stainless steel pipe?

Use stainless steel in marine, offshore, chemical, food-processing, and other corrosive environments, or where cleanliness and long-term corrosion resistance are important.

How long do hydraulic pipes last?

Properly selected, supported, and protected steel pipes can last for the life of the machine. Inspect them regularly for corrosion, cracks, dents, vibration damage, and leaking fittings.ad.