Of the many different nondestructive evaluation (NDE) techniques, ultrasonic inspection continues to be the leading nondestructive method for inspecting composite materials, because measurements can be quantitative and the typical defect geometries and orientations lend themselves to detection and characterization. This article focuses on the three common methods for ultrasonic nondestructive inspection of plastics, namely pitch-catch, through-transmission, and pulse-echo, as well as the three basic types of ultrasonic NDE scans: the A-scan, B-scan, and C-scan. The discussion includes the linear and phased array systems that are sometimes used for large-scale inspection tasks to reduce scan times, the various gating and image processing techniques, and how ultrasonic data are interpreted and presented. A brief section on future trends in ultrasonic inspection is presented at the end of the article.

In a shaft subjected to reversed torsional stresses, failure resulted from the gradual development of fatigue cracks from opposite sides of the shaft. These broke out from origins located adjacent to the fillets at the start of the square section. The remaining uncracked material which fractured at the time of the mishap was in the form of a narrow strip, situated slightly to one side of the center of the shaft. The material was a mild steel in the normalized or annealed condition, having a carbon content of approximately 0.3%. The cracking was characteristic of that resulting from torsional fatigue. Because it occurred on two different planes at 45 deg to the axis of the shaft it was due to reversals of torsional stress rather than fluctuations of unidirectional torque. Following this failure, the shafts of six other similar cranes were tested ultrasonically. Cracks to varying degree were found in all the shafts. Timely replacement was possible and the likelihood of serious accidents removed.

The large steel ring produced for a nuclear application from a billet of 8822 steel was inspected. The large billet was first forged into a doughnut preform in a large press, and then formed into the ring by ring rolling. A straight-beam ultrasonic inspection was instituted and calibrated using the back-surface-reflection method to determine whether adequate ultrasonic penetration was available. Areas of indications were noted at approximately midheight and adjacent to the bore area. An axial angle-beam inspection from the outside was performed, mainly in the area of indications to reveal detectable indications. The indications were not considered serious enough to reject the forgings. A few small indications in the areas tested were revealed by magnetic particle inspection. The area was conditioned by grinding and polishing to obtain an additional inspection at a greater depth from the inside surface. A much more severe condition was revealed after the test. The indications were classified as areas of chemical segregation and nonmetallic inclusions. The ring was considered unsatisfactory for the application and replacement of the defective ring from an acceptable billet was the most economical solution.

Octagonal cast ingots weighing 6.5 tons and made of unalloyed heat treated steel CK 45 according to DIN 17200, and crankshafts forged from these ingots showed internal separations during ultrasonic testing. To determine the cause of defect, an ingot slice and a crank arm were examined metallographically. Investigation showed this was a case where flaky forgings were made from cast ingots with primary grain boundary cracks. This parallelity supports the often expressed opinion that both occurrences have the same origin, i.e. that hydrogen precipitation was the driving force in the formation of primary grain boundary cracks in cast ingots.

The gun mount used in two types of self-propelled artillery consists of an oil-filled recoil cylinder and a sand-cast (MIL-I-11466, grade D7003) ductile-iron piston that connects to the gun tube through a threaded rod. The piston contains several orifices through which oil is forced as a means of absorbing recoil energy. During operation, the piston is stressed in tension, pulled by oil pressure on one end and the opposing force of the gun tube on the other. The casting specification stipulated that the graphite be substantially nodular and that metallographic test results be provided for each lot. Investigation (visual inspection, fatigue testing, 0.25x/0.35x/50x magnifications, 2% nital etched 60x/65x magnifications, and SEM views) showed that most of the service fractures occurred in pistons containing vermicular graphite. Recommendations included ultrasonic testing of pistons already in the field to identify and reject those containing vermicular graphite. In addition, metallographic control standards were suggested for future production lots.

An LNG tanker experienced a fracture of the solid tail shaft, which is a section of the main drive shaft. The tail shaft was made of a forged low-carbon steel. In spite of two ultrasonic inspections, a large defect the size of a football in the center of the shaft was missed. During heat treating following forging, it was surmised that the defect led to the propagation of an internal brittle crack, or clink. A fatigue crack propagated from this origin to the outer surface of the shaft after about a year of service. Finally a last ligament of a few square inches held the shaft together and broke, leading to the separation of the shaft. The cause of failure was fatigue crack initiation and crack growth under reverse bending cyclic stresses. There was no indication that misalignment existed because there was no indication of fretting at the bolt holes in the flange at the end of the shaft. In the case of this shaft, a solution would have been to machine the core of the shaft to remove the brittle material or to use a tubular shaft.

Cracking occurred in an ASME SB166 Inconel 600 safe-end forging on a nuclear reactor coolant water recirculation nozzle while it was in service. The safe-end was welded to a stainless-steel-clad carbon steel nozzle and a type 316 stainless steel transition metal pipe segment. An Inconel 600 thermal sleeve was welded to the safe-end, and a repair weld had obviously been made on the outside surface of the safe-end to correct a machining error. Initial visual examination of the safe-end disclosed that the cracking extended over approximately 85 deg of the circular circumference of the piece. Investigation (visual inspection, on-site radiographic inspection, limited ultrasonic inspection, chemical analysis, 53x metallographic cross sections and SEM images etched in 8:1 phosphoric acid) supported the conclusion that the cracking mechanism was intergranular SCC. No recommendations were made.

This paper describes the remote ultrasonic (UT) examinations of a high-level radioactive waste storage tank at the Savannah River Site in South Carolina. The inspections, carried out by E.R. Holland, R.W. Vande Kamp, and J.B. Elder, were performed from the contaminated, annular space of the 46 year old, inactive, 1.03 million gallon waste storage tank. A steerable, magnetic wheel wall crawler was inserted into the annular space through small (6 in., or 150 mm, diam) holes/risers in the tank top. The crawler carried the equipment used to simultaneously collect data with up to four UT transducers and two cameras. The purpose of this inspection was to verify corrosion models and to investigate the possibility of previously unidentified corrosion sites or mechanisms. The inspections included evaluation of previously identified leak sites, thickness mapping, and crack detection scans on specified areas of the tank. No indications of reportable wall loss or pitting were detected. All thickness readings were above minimum design tank-wall thickness, although several small indications of thinning were noted. The crack detection and sizing examinations revealed five previously undetected indications, four of which were only partially through-wall. The cracks that were examined were found to be slightly longer than expected but still well within the flaw size criteria used to evaluate tank structural integrity.

This paper reviews several fatigue failures from the waterwall, superheater, and economizer portions of the boiler, their causes and how they were mitigated and monitored. Some cases required simple field modifications by cutting or welding, repair of existing controls, and/or changes in maintenance. Nondestructive inspections by visual, magnetic particle, ultrasonic, and radiographic methods for detecting and monitoring damage are discussed. These failures are presented to provide hindsight that will help others in increasing the success rate for anticipating and analyzing the remaining life of other units.

A 150 mm (6 in.) schedule 80S type 304 stainless steel pipe (11 mm, or 0.432 in., wall thickness), which had served as an equalizer line in the primary loop of a pressurized-water reactor, was found to contain several circumferential cracks 50 to 100 mm (2 to 4 in.) long. Two of these cracks, which had penetrated the pipe wall, were responsible for leaks detected in a hydrostatic test performed during a general inspection after seven years of service. Investigation (visual inspection, visual and ultrasonic weld examination, water analysis, and chemical analysis) supported the conclusion that the failure was caused by SCC due to stress, sensitization, and environment. Recommendations included replacing all pipe sections and installing them using low-heat-input, multiple-pass welding procedures.

The purpose of this investigation was to determine the cause of the ultrasonic signal attenuation noted during an inspection of a composite aircraft component. Although ultrasonics was able to identify the location of the defective areas, destructive analysis had to be utilized to determine the exact nature of the defect. The investigation describes how cross-sectioning, fractography, and chemical analysis were utilized to determine the type of defect responsible for the signal attenuation.

Field failures, traced to internal cracks that were initiated from gross nonmetallics, were encountered in the upset portion of forged 4118 steel shafts. Ultrasonic inspection was thought to be the best method for detection from the location of these cracks, their orientation, and the size of the shaft. A longitudinal beam was sent in from the end of the shaft. The shaft was observed to have a radially drilled oil hole 9 mm in diam. Since there was a variation in flaw orientation, testing of the shaft was desired from both the long and short end. The rejection level was set at 20% of full screen and was based on the size of flaws observed when the shafts were cut up. The inclusions were considered to be rejectable if the size was larger than 20 mm diam. Similar flaws were observed in larger shafts, but no flaws were observed once the shafts were sectioned. It was interpreted that the flaw signals were false and had happened when a portion of the beam struck the oily surface of the longitudinal oil hole. The problem was solved by removing the oil film from the longitudinal oil hole.

One of the coils in the radiant section of a primary reformer furnace used in an ammonia plant was found leaking. The bottom of one of seven outlet headers (made of ASME SA-452, grade TP316H, stainless steel) was revealed during examination to be ruptured. It was revealed by metallurgical examination that it had failed as a result of intergranular fissuring and oxidation (creep rupture). The ruptured area revealed that the header had failed by conventional long-time creep rupture as a result of exposure to operating temperatures probably between 900 and 955 deg C. Three samples from different sections (ruptured area, slightly bulged but nonruptured area and visually sound metal) were inspected. The presence of pinhead-size intergranular fissures throughout the cross sections of the latter two samples was observed. An ultrasonic attenuation method was employed to investigate the remaining headers. All headers were revealed by ultrasonic readings to be in an advanced stage of creep rupture and no areas were found to be fissured to a degree that they needed immediate replacement. As a conclusion, the furnace was deemed serviceable and it was established that in the absence of local hot spots, the headers would survive for a reasonable period of time.

A 2 ft. diam 20 ft. long cylinder with a wall thickness of 1 in. used for the transportation of a compressed gas failed by cracking. The cylinder was forged in a low ally steel. The working pressure was 3000 psi and it had been in service for about seven years. A longitudinal crack, about 2 in. long, developed at the approximate mid-length of the vessel, and allowed slow de-pressurization. Subsequent examination by radiography and ultrasonic means indicated the crack was associated with an irregularly shaped, laminar type of defect located within the wall of the vessel. It was concluded that failure of this vessel resulted from the development of a radial crack orientated in the axial direction. This appeared to have originated on the bore surface in a region where the laminar defect closely approached this surface. The defect was introduced during the manufacture of the vessel, probably originating as a secondary pipe in the ingot which was subsequently displaced and forced into the wall of the vessel during the piercing operation.