All high-performing steel tubing and piping must undergo a variety of testing in order to determine their levels of strength and reliability. These tests evaluate numerous qualities of the tested specimen, including its yield strength, tensile strength, resistance to penetration and ductility. Below are some quality control testing procedures used to determine the durability of pipes and tubes before they reach end users.
One test used to determine a steel pipe’s yield strength, tensile strength and ductility is the Tension Test. During tension testing, continuous force is applied to the tested pipe or tube. The goal of tension testing to identify at which point the test specimen elongates or fractures.
The hardness test is used to approximate a steel product’s tensile strength. Hardness testing involves measuring a tube or pipe’s resistance to penetration. Commonly used hardness testing methods include the Rockwell test and the Brinnell test. The specification for these tests are defined in ASTM A370.
Charpy Impact Test
The Charpy Impact Test is an effective, scientific method for identifying a metal’s resistance to impact. This test is used to measure the amount of energy absorbed by a metal during fracture. It can also help define a specimen’s level of toughness, notch sensitivity and impact toughness.
The Charpy Impact Test is widely used because it is fairly easy to conduct and inexpensive. During this test, a heavy pendulum hammer is used to strike and fracture the specimen. The impact of the strike causes elastic deformation. The height at which the hammer swings is used to assess the impact energy.
Another quality assessment method is the flattening test. This test gauges the ductility, or the plastic deformation ability, of seamless steel pipes under specified conditions, without crack defects. In this test, a sample is taken from a seamless steel pipe that has passed the initial visual inspection. The length of the sample must be at least 10mm, but no more than 100mm. When testing the pipe end of a full-length pipe, the specimen is cut longitudinally, with the cut depth being at least 80 percent of the outside diameter.
The flattening test can be done on a universal testing machine, as well as a pressure testing machine. The machine is equipped with two parallel platens. The width of the parallel platens should exceed the width of the flattened sample. The length of the platen is different than that of the specimen, and it should have the right amount of rigidity.
Reverse Flattening Test
Reverse flattening test is performed on electric welded tubing, about four inches long. The specimen is first divided 90 degrees longitudinally. It is then opened and flattened, with the weld reaching the point of maximum bend. The reverse flattening test helps detect flash overlaps and the lack of weld penetration.
During the crush test, the specimen is a ring, sectioned from a tube. It is typically 2 ½” long. In instances where the steel tube’s outside diameter is ¾” or less, the specimen is approximately 2 ½ times the actual outside diameter of the tested tube. The tested tube is placed on its end and crushed either by pressing or hammering. The crush test is used to assess ductility.
The flange test is designed to measure the ductility of pressure tubes and assess their ability to withstand beading operations. A ring, at least 4 inches long, is cut from the tube specimen. The flange test is conducted on this ring.
The flaring test is designed to determine whether specific types of pressure tubes are ductile enough and ideal for flare type fittings. During flaring testing, a tapered mandrel is inserted into the tube until the diameter of the tube expands to the extent designated by the application specification.
The bend test involves a tubular specimen being bent at room temperature to an inside diameter and extent defined by the associated specification. The bending speed is not typically a factor, and the outside portion should not display any major cracking.
Reverse Bend Test
Designed specifically for electric welded tubing, the reverse bend test is used to detect flash overlaps and lack of weld penetration. The test is performed on a 4-inch long section of annealed tubing, larger than NPS ½. The specimen is divided 90 degrees longitudinally then opened and bent around a mandrel. The mandrel is parallel to and on the outside of the tube, with the weld being held at the maximum point of deformation.
Drifting is a method of testing steel pipe. It measures the interior diameter of the entire length of pipe to prepare for the successful insertion of other smaller pipes or pumps.
Holiday detection pertains to the equipment and method used to identify holidays in pipeline type coatings.
A millage gauge is a tool designed to measure the thickness of applied coatings.
Engineered to measure thickness, a micrometer is an instrument available in two basic types: 1) flat tip, and 2) ball tip. The latter is used to measure the thickness of steel pipe walls.