Understand the latest alloy verification technologies for the production and fabrication of tubes and pipes
Advances in technology are making many tools smaller, faster, and easier to use, and so are materials identification instruments used in the production and fabrication of tubes and pipes. Mobile optical emission spectroscopy (OES), portable X-ray fluorescence (XRF), and portable laser-induced breakdown spectroscopy (LIBS) are all examples of portable instruments with the power to perform laboratory analyzes on field. . Portable elemental analyzers allow users to test materials on the shop floor in seconds to determine their elemental composition, verifying that the metal used in production meets required specifications.
Positive Material Identification (PMI) capability helps mitigate risk and improve productivity, but it can be difficult to determine which of these three analytical techniques is best for tube and pipe producers and fabricators. . An overview of how OES, XRF, and LIBS systems work, and the benefits they offer tube and pipe manufacturers, can go a long way in making a sound investment in equipment.
How they work
A non-destructive test, XRF irradiates the test sample with high-energy X-rays produced by a miniaturized X-ray tube in the instrument. This causes the atoms in the sample to emit secondary (or fluorescent) X-rays specific to the elements present in the sample. The instrument’s detector measures and analyzes these characteristic secondary X-rays to determine their chemical identity and concentration in the metal being tested. This capability makes XRF useful for qualitative and quantitative analysis of the composition of materials.
Rather than emitting X-rays like an XRF analyzer, OES instruments send out a high voltage electrical pulse to excite atoms in a sample. The sample then discharges an arc spark which can be measured and analyzed by a spectrometer in the OES unit. From there, the OES system determines the chemical composition of the sample being tested.
LIBS analyzers ablate the surface of the sample with a highly focused laser, which produces a plasma composed of electronically excited atoms and ions. These atoms begin to decay in their ground states and emit wavelengths of light, unique to each element, which are analyzed by a spectrometer in the LIBS device. As with XRF, LIBS analysis can be used for both quantitative and qualitative measurements.
Of the three, XRF is the only one classified as non-destructive; OES and LIBS are minimally destructive in that they leave a scorch mark on the sample.
Considerations to keep in mind when choosing a basic analyzer include portability, measurement speed, and ease of use.
Portability can have a substantial impact on productivity. Both LIBS and XRF are available as lightweight portable analyzers, with some LIBS units weighing as little as 6 pounds. This means that analysis can be performed anywhere in the factory or warehouse, as well as in hard-to-reach areas in the field. A mobile OES can weigh up to 80 pounds and requires a cart.
Factors that contribute to speed and ease of use include:
• Sample preparation – Mobile OES and LIBS generally require sample preparation as even traces of contaminants such as grease, paint and oxidation can lead to unreliable results. Sample preparation involves cleaning and grinding a square inch of test area on the metal. XRF rarely requires sample preparation.
• Instrument configuration – XRF is point-and-shoot technology that does not require daily setup. Daily setup of LIBS is relatively minimal, requiring a two-step process that takes approximately 10 minutes. Daily setup of the OES requires several steps and 15-20 minutes, and both instruments require regular cleaning.
• Analysis speed – Depending on the material tested, the advanced LIBS and OES analyzers can test most samples in about 10 seconds. This includes materials in which the carbon content is of interest. An XRF analyzer, for most materials, can identify and provide the chemistry of many types of alloys in 3-5 seconds. However, this does not include carbon analysis, and the analysis time may increase slightly if other light elements are present in the alloy. A few seconds may not seem like a lot of time, but seconds add up quickly in situations that may require multiple average readings or when multiple samples need to be analyzed. Therefore, choosing the right technology is important for any application where higher throughput is the goal.
Tube and pipe producers and manufacturers need to consider more than just productivity when choosing an elemental analyzer. The three technologies differ in their analytical capabilities, so it is important to match the capabilities to the materials to be tested.
LIBS and OES are both useful for differentiating alloys and quantifying carbon concentrations in low alloy steels, carbon steels, and stainless steels. This includes the low carbon content of L grade stainless steels.
XRF provides rapid chemistry and quality verification of incoming raw materials and final products, and it can be used for composition analysis and to measure the thickness of alloy coatings. In the case of steel pipes, for example, a coating can be applied to prevent oxidation during storage and transport or to facilitate the application of paint. The ability to analyze coating layers helps ensure quality control and reduce coating waste.
Often, XRF and LIBS may be required to perform extensive quality control of end products. These complementary devices can be used throughout the production process, from testing of incoming materials to outgoing quality assurance or quality control of finished tubes, pipes and assemblies.
Trust but verify
As the industry continues to globalize, many tube and pipe producers and manufacturers increasingly purchase materials from overseas, and these may include new suppliers that they have not worked with before. . Unfortunately, material test reports may not always be accurate. A trust but verification approach is therefore necessary to confirm the composition of the material sent by the supplier. This is where analytical technology comes in.
Inexperienced or unreliable vendors may try to keep costs down by not performing PMI in-house, or they may not use an outside testing lab to verify the equipment they ship. The consequences of mixing materials can range from end user rejection to catastrophic failure that can result in injury or even death. For example, using an inferior material in a critical application, such as an aircraft engine, puts the safety of everyone on board at risk. By exercising due diligence in performing the PMI on site, pipe and tube producers and manufacturers can go a long way in protecting their reputation and their business. Using elemental analysis to quickly spot problems avoids the costly problem of determining that products have been developed out of specification after adding value during the production process. Often the manufactured part or assembly must be completely scrapped.
Checking materials does not stop at entry control. Supervisors and those responsible for quality control must ensure that the right materials are used throughout the production process, so best practices require PMI at every stage of production. Highest compliance uses a testing protocol that follows the part, assembly, or equipment through the production process until final validation.
For critical components, a PMI should be the first step upon receipt of shipment, and inspections should continue to the point of installation. For facilities prior to the inspection process (for example, a 30-year-old refinery), performing a thorough validation may require a shutdown to verify the integrity of components and assemblies that were not submitted. to adequate tests before installation. Full use of PMI technology today may prevent such drastic action in the future.
James Stachowiak is Technical Sales Director of Thermo Fisher Scientific, 168 Third Ave., Waltham, MA 02451, 800-678-5599.