What are Seamless Hydraulic Pipes
Seamless hydraulic pipes are those rigid pipes made from Carbon Steel (Generally low carbon Steel) that are used to transfer fluid, usually oil, under high pressure in the range of 100 bars to 500 bars.
The hydraulic pipe or tube line assembly is generally made by using the hydraulic pipes along with Carbon Steel hydraulic ferrule type fittings made as per DIN 2353 standard and consist of a cutting ring or Ferrule which bites onto the tube or pipe and hold the pipe firmly into place in the fitting assembly.
The hydraulic pipes come in the size range of 6mm OD upto 42mm OD and come in various wall thickness to withstand various pressure ratings that may be prevalent in the high pressure hydraulic line. These tubes are made as per DIN 2391 standards or A 179 standards and are made toughened steel. These are available in mainly two varieties : ST 37.4 and ST 52.4
The key features of the hydraulic pipes are their precision workmanship and strength.
The tubes are manufactured using a specialized process, called the Cold drawn process or Drawn on Mandrel method. Here the heated solid rod is first pierced from the centre by the billet which forms a solid void. This is again redrawn a number of times until the tube of desired outer and inner diameter is formed.
A number of tests are performed on the finished tube samples to find their physical characteristics.
Tests performed on a Seamless Hydraulic Pipe and tube
Tensile test – This is a test performed to find out the physical resistant property of the material against tension and the workability of the material. A sample of the tube is fixed into a Universal Testing Machine and the tube is subjected to pulling or elongation force until the tube elongates and finally breaks. The force at which the hydraulic pipe started to elongate and the force at which it failed are noted and from this the tensile strength of the tube is determined .
Hydrostatic pressure Test – here a sample of the pipe is taken and subjected to high pressure using a hydrostatic testing device until the sample fails. The pressure at which the tube fails is taken as the burst or failure pressure and from this the working pressure is calculated using a suitable factory of safety
Eddy Current Test – here an electric alternating current is passed through the tube material and depending on the resistance to the current flow observed, defects in the tube material are detected
Test for Surface smoothness : This is a test used to find the roughness of the tube surface. An instrument called a PROFILOMETER is used and this determines if there is undesired roughness on the surface of the tube which needs further treatment or process to bring about the desired smoothness.
Flaring, Flattening and Bending Test : These are mechanical test used to study the workability and formability of the material of the hydraulic pipe or tube. Here the end of the hydraulic pipe is flared at the end to check the flaring capacity of the tube. The end of the tube is flattened by applying a hammering force of the tube is bent using a tube bending machine. The force applied in each of the above three methods are measured and made note of and from this the flaring, flattending and bending properties of the hydraulic pipe are determined
Salt Spray test or test to check plating or phosphating : In this test a sample of the pipe is exposed to a simulated salt water condition and the time taken for the tube to resist the salt water environment against corrosion and surface deterioration is made note of and the corrosion resistant properties of the hydraulic tube or pipe is determined.
Chemical composition test : This test is done to find out the elemental chemical composition of the material used in the tube and finds out the elements present in the metal along with their percentage composition.
Metallurgical and Stero Microscopy test : In this test the metallurgical and microscopic structure of the material of the hydraulic pipe is determined and the methods used are microscopy or metallography
