Quality Assurance As a testimony to our commitment to be the best, Markinhas achieved ISO/TS 16949:2002, ISO 9001:2000 and ISO 1401 registrations.
At Markin there is a dynamic commitment to quality and Customer satisfaction that transcends from our President to every individual in our organization. We're committed to meeting your tubing requirements while exceeding your expectations.
Our commitment means meeting and exceeding your supplier metrics with our first delivery and every time thereafter. It means continually improving our internal operations and processes so we can pass cost savings solutions onto you in the form of very competitively priced low carbon welded steel tubes.
A dynamic commitment to quality is an all-encompassing attitude that is found company wide in everything we do, from engineering and tube manufacturing to fabrication and delivery. Quality products, superior Customer service, and finding solutions to your tubing related issues are our commitments to you!
As testament to exceeding Customer quality metrics and Customer satisfaction, the testing described below is performed throughout our manufacturing process.
Tube Dimensional Tests
Outside diameter - Is checked at the end of the line using micrometers. Many readings are taken along a 3' piece of tubing. The high, low and average readings are recorded. Each micrometer is checked on a daily basis against a stepped block of known dimensions. Any micrometer that does not measure correctly is replaced. The old micrometer is calibrated before being placed back in service.
Wall thickness - Is checked by orienting the weld at 12:00, cutting the tube in half lengthwise at the 3:00 and 9:00 position and measuring the wall thickness with pointed micrometers at the 6:00 position.
Wall next to weld - Is checked using pointed micrometers and checking for the minimum wall thickness on each side of the weld flash. There should be no more than .001" difference from side to side.
Weld flash height - Is checked using pointed micrometers. The wall thickness over the weld flash is measured at several points, as is the wall thickness on either side of the flash, just away from the weld (not the same a wall next to weld). The difference between the readings of the wall and one the flash determines the weld flash height. These values are compared with the max and min values specified, if any. Also verified on the optical comparator. See Optical Comparator below (under Weld Tests).
Tube Integrity Testing
Eddy Current Testing - Is performed inline on the tube mill and is a 100% check of the tubing. Its biggest limitation is the size of the smallest hole or opening that is detected and that is typically in the .013" to .015" range. It works by inducing a magnetic flux in the tubing and then looking for changes in the flux field. Some surface imperfections can also be found. Defects found by the eddy testers are marked at the start and end of the defect with a paint marker.
Pressure Test - Coiled tubing is pressurized at 500psi and submerged under water. The coiler operator visually inspects the tubing for any sign of leaks. This method will find smaller leaks than can be found with eddy current testing. The disadvantage is that small leaks can be sealed by Galfan® on the coating lines and may not be found in the pressure test. Every coil of tubing is pressure tested. Cut lengths are not pressure tested under water.
Weld Tests
Flatten Test - Tubing is flattened in a hydraulic press with the weld on the outside edge after flattening. This tests the outside of the weld in tension.
Reverse Flatten Test - A sample of tubing is cut in half lengthwise through the 3:00 and 9:00 with the weld located at the 12:00 position. The sample is then flattened in a hydraulic press. This tests the inside of the weld in tension. Generally only performed on larger diameter tubing.
Cup Test - Unless otherwise specified, tubing is expanded so the outside diameter fits in the expanded inside diameter. This test is common for refrigeration applications but is sometimes used for automotive as well.
Bead Test - Samples (typically five pieces) of tubing is cut to the appropriate length using a band saw. The samples have a bead formed using appropriate tooling in a hydraulic press.
Flare Test - Samples (typically five pieces) of tubing is cut to the appropriate length using a band saw. The samples have a single flare formed using appropriate tooling in a hydraulic press. Depending on the tubing diameter, the flare may be formed at the same time as the bead.
Expansion Test - A sample of tubing is expanded in a hydraulic press using a punch with a 10:1 taper to 125% minimum of the original outside diameter.
Optical Comparator Checks - A sample of tubing is cut in half with the weld at the 12:00 position and the saw cut running through the 3:00 and 9:00 positions. The sample is formed in a fixture and placed in a vice on the optical comparator. The profile of the weld is examined at 50x magnification to check the weld for edge alignment and to verify the weld bead height.
Hardness Testing
Rockwell 30T Hardness - Rockwell 30T scale is a superficial hardness test that uses a ball indentor and a 30-kilogram load. The test is conducted on the inside of the tubing at 180° from the weld. To determine the true hardness value correction factors that take into account the curvature of the tubing should be applied. Five readings are taken on each sample and the median value recorded.
Vickers Microhardness - Microhardness is checked on an exception basis for problem solving or evaluation of the tubing on special circumstances. A sample is cut from the tubing and the cross-section ground and polished. A diamond-shaped indentor is pressed into the cross-section of the tubing at one or more locations with a specific load. The length and width of the impression left by the indentor is measured. Those values are compared to values in a table that determines the Vickers microhardness. Note, there is little or no actual correlation between Vickers microhardness and Rockwell R30T superficial hardness in spite of conversion tables existing.
Visual Inspections
Visual inspections are made primarily for surface defects such as scratches, roll pickup, roll marks, superficial oxidation on the inside and outside of the tubing, luder lines or stretcher strains and other potential surface conditions. Accept/reject criteria are defined in the Visual Standards Manual.
Galfan® Tests (Internal Lab)
MEK rub test - Methyl Ethyl Ketone (MEK) is used to check that the epoxy paint is cured to the Galfan®. MEK is applied to a cheesecloth pad, the pad then surrounds the tubing and the tubing rubbed, using enough pressure so that the pad slides on the tubing surface, 50 times back and forth otherwise known as double rubs. Very little paint should come off on the pad and no bare spots should appear on the tubing. Curing is a fine balance between having sufficient cure to pass the test without being over cured and losing flexibility.
Mandrel Bend Test - Tubing is tested for coating adhesion by wrapping the tubing around a 1" diameter mandrel for approximately three full wraps. There should not be any flaking or peeling of either coating.
Tape Test - Tubing is also tested for coating adhesion by applying a 3M tape to the surface and pulling it off the surface. The tape should not remove any coating from the surface. The tape is applied to a white sheet of paper for evaluation.
Thickness Testing - the coating thickness is checked for each coating using a Fisher Permascope. A sample of the tubing approximately 18" long is check in five places along eight longitudinal axis. The Permascope measures both coating thicknesses and provides the average, high, low and standard deviation for each coating.
Galfan® Tests (External Lab)
As part of the PPAP process, samples of tubing are subjected to accelerated corrosion testing. Tests are performed to the specified requirements for each Customer. Typical specifications for Galfan® include:
- GM-124M
- Ford WSA-M21P26-A
- Chrysler PS-8688.
Tests include 3000-hour salt spray, 1000-hour creep back salt spray test, long-term cyclic corrosion testing and gravelometer testing.
Internal Laboratory Testing
Galfan® and epoxy paint coated tubing samples are subjected to fluids testing. Tests are conducted per the Customer requirements to the fluids used. Fluids include gasoline (monthly), diesel fuel (monthly), brake fluid (weekly), oxidized gasoline (monthly), E85 low pH (monthly) and bio-diesel (monthly). The tubing must pass 24-hour immersion with no softening or flaking of the coatings.
Other internal lab tests include testing the concentration of cleaners, paint prep (Bonderite) and test and dip tanks.
Additionally we can perform metallurgical checks by cross sectioning the tubing and polishing the tubing for microscopic examination of the weld and subsequent etching for grain structure analysis. The OGP Smartscope can also be used for full measurement of a tubing cross section (OD, wall, wall next to weld, bead height) but due to the samples preparation time it is not practical for process control.
External Laboratory Testing
In addition to the Galfan® corrosion testing described above, samples are sent to outside laboratories for tensile, yield and elongation (TYE) testing and hydrostatic pressure tests as part of annual verifications, chemistry analysis of the steel (as necessary) and failure analysis (as necessary). External labs used are A2LA certified.
Fabrication Testing
Length - A checking fixtures is setup with gage blocks or a nominal length standard with a stop at one end and a dial indicator set to "0". Five pieces are checked at prescribed intervals and the deviation from nominal recorded on a Control Chart.
Straightness - Tubing is supported in two Vee blocks at a specific distance apart, typically a multiple of 12". A dial indicator is placed on the tubing midway between the two Vee blocks and the tubing is rotated. The total indicator runout (TIR) per foot is recorded. Customers may specify straightness as a maximum bow dimension. In that case the tubing ends would be placed against a straight edge and the maximum gap determined with gage pins.
Dimensional Checks of End Forms - End forms are checked using a variety of measurement techniques including dial calipers, micrometers, and go - no go gages. Other checks may be performed on an optical comparator.
Bent Parts - Profile gages are used to check that bent parts are properly formed.
ID Mandrel Requirements - When a customer uses a mandrel in their process, the inspection may be performed in several ways, depending on the requirement. If there is a minimum inside diameter requirement for the full length of the tubing, a ball of the specified diameter will be passed through the full length of the tubing. If the inside diameter requirement is restricted to a specific distance at the end(s) of the tubing and gauge pin check is performed.
Additionally, OD and hardness will be checked after fabrication as well as visual inspection for surface defects.
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