A certified ANST inspector prepares to test for discontinuities. Pressure vessels often need to meet ASME, Section VIII, Division One and Section I codes.

Mark Demchak prepares for a magnetic particle machine test.

Fabricators need to understand inspection requirements and have a firm grasp of how nondestructive examinations (NDE) work to determine material integrity. The field of nondestructive material characterization is concerned with material identification and microstructural characteristics — such as resin curing, case hardening, and stress — factors that have a direct influence on the service life of parts, according to the American Society for Nondestructive Testing, Inc. (ASNT).

NDE, sometimes called nondestructive testing or inspection, examines the performance of test pieces to see how long they can be used on the job and how often they need to be checked. It detects cracks and identifies discontinuities in casting, forming, and parts in service. Since most end users today require inspections, NDE specialists, physicists, metallurgists, chemists, electrical engineers, and mechanical engineers continually look for ways increase the accuracy of NDE tests and procedures.

Competition drives the demand for NDE
As materials costs rise, design engineers try to reduce weight and size whenever possible, often by substituting aluminum or magnesium alloys for steel or iron. However, switching to a light alloy may require changing a part's size or shape thereby subjecting it to increased stress.

Because engineers work with known loads and understand that materials and workmanship are never perfect, they typically add a safety factor to their designs. This safety factor reflects the relative importance of using lighter weight materials, costs, and perceived risks for the end user.

Today's competitive demands encourage increased use of materials with a limited record of operating characteristics and performance creating potentially dangerous problems. Yet when bridges, buildings, or aircraft fail due to faulty welds, who takes the blame? In one instance an aircraft was built from an alloy whose work hardening, notch resistance, and fatigue life were not well known. Some models experienced disastrous failures after a short service life. Performing nondestructive tests can therefore help increase product safety and save lives.

Avoid an unpleasant surprise
Shop owners can save time, money, and increase their reputation for quality workmanship by thoroughly checking new specifications for inspection requirements. That information is normally a part of the bid package, the codes, and the drawings.

"If a shop quotes a job and forgets to factor in the cost of required inspections, those dollars will eventually come out of the fabricator's pocket," explains Mark Demchak, co-owner of Total Quality Testing, Inc., Cleveland, Ohio.

"In one case, a firm had a building project that called for them to inspect of 10% the welds on pilings to meet American Welding Society D1.1, Structural welding code — steel. The firm had placed almost 90% of the pilings without weld inspection. He had to have all the remaining welds checked by a fulltime onsite inspector and was lucky he didn't have to pull out the installed pilings for inspection."

"On the other hand, another shop welding a complex pipe configuation brought in table top-sized welded sections for X-ray inspection as they completed the components," recalls Demchak, who started Total Quality Testing with his partners in 1993.

"Some components were small enough to have two or three on one film. That shop saved money by inspecting as fabrication progressed. They minimized rework and reduced testing fees."

Don't low ball the bid
"Some firms try to 'low bid' to get the work, so they minimize inspections or other costs," says Demchak. Customers may contribute to the problem by allowing their purchasing department to write specs for inspection services rather than the firm's maintenance or engineering department.

These moves often backfire creating product loss, downtime, rework, reinspection, accidents, or environmental impact.

Demchak cites an example. "On one job welds were made on an 8-in.-thick cylinder. We found a crack in the weld and asked if they wanted the inspector to wait an hour to make sure the defect was removed. The firm said 'no' to the extra $50.

"They ground out the filler metal on the 45°-bevel. With only a visual inspection they left a small part of the crack, and rewelded the joint. That remaining defect caused additional failure.

"We made two return trips for inspection," says Demchak, "each time we found more flaws. The workpiece was finally scraped."

Many times when a firm spends hundreds of dollars for either in-house or outside NDE services, it offsets the thousands of dollars in financial or accident risks of poor service of the part or component. "Firms may test a raw material such as a casting, a welded fabrication, selected finished parts, or completed fabrication," says Demchak.

To improve production flow, design engineers and NDE engineers should work together early in the design process so that NDE technicians can make timely inspections. Using concurrent engineering that includes NDE minimizes delays resulting from rework.

Reassure me
Customers also drive requirements for test reliability. "As a result, emphasis has shifted from concern about the size of discontinuity that can be found to the size of discontinuity that can be missed," says J. Steve Cargill, in an article "How Well Does Your NDE Work?", Materials Evaluation magazine, July 2001. While the difference between the two questions sounds subtle, radically different approaches are required to answer both questions.

Some jobs call for progressive inspections of the base metal, first weld pass, final pass, then magnetic or X-ray inspections. "At the fabrication level more shops have their welders check on welds using magnetic particle and liquid penetration methods," says Demchak.

"This works well to catch and correct flaws early, but a certified inspector is still required to meet the code requirements. While some shops just read the back of the can and go, others ask a test lab to train their welders."

Inspections on the rise
More fabrication specifications require inspections of some type compared to 10 yr ago and most code requirements now include NDE. Customers, pushed by architects and design engineers, are also establishing more inspection requirements from quality issues, such as ISO 9000, as well as liability concerns.

" There are outside certifying agencies like A2LA and NADCAP for automotive work, and auditors that check on test labs. They look for traceability of workpieces that come into the shop, personnel certifications, and equipment calibrationmethods," says Demchak. "After several decades of application, the welding industry has completely accepted standard nondestructive testing as an inevitable and invaluable part of the production and maintenance of components," says F. H. Dijkstra and J. A. de Raad, in an update of a plenary lecture given by Frits H. Dijkstra at the Seventh European Conference on Non-Destructive Testing, Copenhagen, Denmark, May 1998.

"Its application has been well regulated, acceptance criteria for weld discontinuities exist, good schemes for personnel qualification are in place, and equipment has evolved to a standard approaching perfection."

Adding value
According to Dijkstra, NDE can be seen as an added value by end users. "However, this requires presenting NDE to them as a solution that improves safety, enhances quality, and saves money."

"It especially adds value when a customer wants to monitor a field erection," explains Demchak.

Demchak's firm was hired by the Cleveland Orchestra when the Severance Center was renovated. "We were asked to monitor the NDE inspections of contractors. The reputation of the orchestra required maintaining acoustic excellence in the hall so the construction had to be accurate in every dimension."

The firm inspected structural steel components, dimensions, bolt hole locations, and welds — at the steel fabrication shops and at the Severance Center during the project. "Initially, our inspections were seen as interruptions that slowed production," recalls Demchak, "but soon managers realized that we were catching errors they could fix in the shop rather at the job site at a much higher cost."

For more information call: Total Quality Testing, Inc., Cleveland, OH, (216) 676-6900. The American Society for Nondestructive Testing, Inc., Columbus, OH, (800) 222-2768, www.asnt.org, Fischer Technology Inc., Windsor, CT, 800-243-8417, Fischer-Technology.com

 

Check the checkers Fab shop owners need to do some homework before calling a lab for the first time. Here's what to ask: Find out if the lab and its inspectors are certified by ASNT SNT-TC-1A for training and testing. Ask for a certification package and a list of inspectors certified to ASNT. Request inspector certifications with the paperwork for the inspection work. Ask about specialization. Most labs have equipment for certain types of tests, such as Navy nuclear. Ask for references of work in geographic areas and for contacts at these firms. Ask your customer who did their last inspections. Sometime a change of a fabrication or heat-treat shop dictates changing the inspection lab to minimize moving heavy workpieces. Ask the prime contractor for preferences on labs. Ask the prime contractor for inspection specifications rather than adding the cost of searching for the correct spec. Finally ask the lab about inspection costs. "We estimate welds per hour, the number of days required, and normally add one repair cycle," says Demchak. Most firms know the quality of welds from their welders so they can estimate the number of re-welds. Total Quality Testing checks itself with other labs by having them inspect one of its jobs and then compares results. "Labs will compete in the morning, then help each other out in the afternoon because most of us have specialized areas of expertise that we share," explains Demchak.

 

Nondestructive examination techniques The six major categories of NDE are mechanical and optical, penetrating radiation, electro-magnetic and electronic, sonic and ultrasonic, thermal and infrared, and chemical and analytical. Here is a summary of what each test detects. Mechanical and optical: Color, cracks, dimensions, film thickness, gaging, reflectivity, strain distribution and magnitude, surface finish, surface flaws, and through-cracks. Penetrating radiation: Cracks, density and chemistry variations, elemental distribution, foreign objects, inclusions, microporosity, misalignment, missing parts, segregation, service degradation, shrinkage, thickness, and voids. Electromagnetic and electronic: Alloy content, anisotropy, cavities, cold work, local strain, hardness, composition, contamination, corrosion, cracks, crack depth, crystal structure, electrical and thermal conductivities, flakes, heat treatment, hot tears, inclusions, ion concentrations, laps, lattice strain, layer thickness, moisture content, polarization, seams, segregation, shrinkage, state of cure, tensile strength, thickness, and disbonds. Sonic and ultrasonic: Crack initiation and propagation, cracks, voids, damping factor, degree of cure, degree of impregnation, degree of sintering, delaminations, density, dimensions, elastic moduli, grain size, inclusions, mechanical degradation, misalignment, porosity, radiation degradation, structure of composites, surface stress, tensile, shear and compressive strength, disbonds, and wear. Thermal and infrared: Bonding, composition, emissivity, heat contours, plating thickness, porosity, reflectivity, stress, thermal conductivity, thickness, and voids. Chemical and analytical: Alloy identification, composition, cracks, elemental analysis and distribution, grain size, inclusions, macrostructure, porosity, segregation, and surface anomalies. Information provided by: The American Society for Nondestructive Testing, Inc. asnt.org