Non-destructive testing in the nineteen sixties

Some of the more memorable events of the

nineteen sixties include: the assassinations of John F Kennedy and Martin Luther King Jr, the Cuban Missile Crisis, the first moon landing, The Beatles, the introduction of the IBM computer, satellite TV, flower children…

For me it all started in 1960, when I boarded the SS Britannia in Liverpool headed for New York for that venerable vessel’s last Atlantic crossing. By the third day out, rough weather had reduced attendance in the dining room by 75% and the swimming pool was more suitable for surfing. In the bar, our beers would slide off the table, just as the glass neared empty, which would justify a fresh beer.

We landed in New York, where I had some acquaintances and spent Thanksgiving with friends of friends. The elderly grandmother, learning that I was Scottish, asked if I knew Andrew Carnegie! I then headed to Tulsa in Oklahoma. The parents of my college girlfriend lived here and they arranged a job for me. That job, which I had envisioned being a temporary one, was in fact my introduction to NDT and my ongoing immersion into the ‘dark arts of NDT’.

The owner of the company Engineering Test Services (ETS), Dwight Evans, was an electrical engineer recently with Branson Instruments, which was one of the pioneers in the fabrication of ultrasonic instruments. Here, he had been involved in the design of the early ultrasonic instruments. These instruments were the Audigage and the Vidigage, which used the resonance method for obtaining thickness.

Dwight Evans foresaw the application of ultrasonic thickness measurement to ships’ hulls and bulkheads. Prior to the introduction of ultrasonic thickness measurements, the steel hull was measured by drilling a hole and obtaining the thickness with a feeler gauge. Dwight’s company, ETS, was readily accepted as an alternative to the drilling of holes. More than once a ship had been floated off dry dock, only to be re-docked when it was discovered one of the drilled holes had been missed for re-welding!

In the photograph to the left, the technician, without a safety harness, hardhat or scaffold railings and about thirty feet in the air, is using the Audigage to obtain a measurement on a bulkhead. The location was predetermined and ground smooth. My first field opportunity was in a shipyard in Savannah, Georgia, which was still the ‘Deep South’ and integration was not yet a reality. The photograph illustrates that job.

In October 1960, the Dow Chemical Plant in

Freeport, Texas, had an explosion in which five men suffered fatal injuries and 12 others were hurt when a piece of equipment blew up and started a fire. The company said a rupture in a vapour feeder to a distillation column at its No 1 glycerin plant caused the blast and fire, which was localised in the chloride unit of the plant. Corrosion and a resultant loss of wall thickness were factors in the leak of explosive material and the fire that followed.

Dow Chemical instituted an intensive plant-wide programme for thickness measurement of pressure vessels and pressure piping. ETS was contracted to provide crews to meet these requirements using state-of-the-art NDT capabilities. ETS had previous experience of using ultrasonic resonance technology and pulse-echo ultrasonics to provide these services.

The Vidigage is a resonance method instrument that is capable of high accuracy, but requires a clean and smooth surface in order to obtain the multiple signals for interpretation. The Sonoray is a pulse-echo instrument capable of obtaining reflector signals from rough surfaces and through coatings, but with insufficient horizontal linearity to provide the necessary accuracy.

The solution was to combine the two instruments. They were mounted in a van and separate transducers and cables were combined into a 300-foot-long umbilical with sound-powered telephones on either end. The probe operator applied the pulse-echo transducer to the selected test location; the technician noted the approximate wall thickness. The resonance transducer was then applied to the same location and the technician was able to decipher the Vidigage signal, even if only one spike was visible, for an accurate measurement on the Vidigage. Improvement to the linearity of the pulse-echo equipment, development of the echo-to-echo measurements and acceptance of measurements in two decimal places led to abandonment of the resonance instrument.

There were no certification schemes and I was designated ‘technician’ by a combination of on-the-job training and supervisory input!

During the Dow Chemical equipment assessment, Hurricane Carla hit Houston, and especially Freeport, hard. Hurricane Carla was the first Category 5 hurricane of the 1961 Atlantic hurricane season, with wind gusts of over 120 mph. We survived the storm battened down in our apartment complex in Houston. When we returned to the job site we had to beware of the snakes that had taken refuge in the plant!

In combination with the plant inspection,

we were now heavily involved with ship inspection, mostly for tanker ships. The inspection was either in dry dock or on board the ships at sea, when they were on ballast runs. I remember being scheduled on such an on-board trip from Wilmington to Puerto Rico. Unfortunately, I was dispatched to Wilmington, Delaware, only to discover that the ship was waiting for me in Wilmington, North Carolina. With no scheduled flight service between the two Wilmingtons, I chartered a plane and barely caught the ship!

Around 1963, I was transferred to Los Angeles to open a West Coast Branch of ETS. We rented space from Branson Instruments in Van Nuys in the San Fernando Valley. Our immediate client contacts were the shipyards in San Pedro and the refineries in the South Bay, an hour’s journey each way! We relocated to Torrance, California, which was much more convenient.

Oil refineries and chemical plants were now setting up monitoring programmes for projecting life expectancy of piping and pressure vessels. However, the technology of that time did not permit wall thickness measurements to be obtained at temperatures in excess of 200°F. This meant testing during ‘turnarounds’, resulting in maintenance periods when the plants were not operating.
So, the next advance in UT thickness had to be the ability to obtain measurements while the plant was operating, or ‘on-stream’ inspection. Pulse-echo instruments could be used with flowing water that provided the couplant and kept the transducer cool. I was involved in developing high-temperature equipment that did not use flowing water (metallurgists were afraid that it might quench the material or cause thin-wall piping to rupture). The difficulties lay in finding a temperature-resistant diaphragm and an effective adhesive. An early model is shown to the right.

On 20 April 1963, the submarine

USS Thresher sank with all hands. The initial cause was determined to be failure of a silver-brazed joint. There were 3000 silver-brazed joints on the ship and it was estimated that up to 400 may have been improperly made. It was believed that a pipe carrying seawater experienced joint failure and shorted out a main electrical bus board causing loss of power.
The ultrasonic probe is scanned along the brazed joint to determine the percentage of bond. The Navy required technician certification for this inspection and I was one of the few certificated on the West Coast. Later, it was determined that failure of the silver-brazed fitting was not responsible for the loss of USS Thresher.

The development of battery-operated, portable ultrasonic instruments freed the technician from the umbilical cord and allowed inspections involving climbing activities to be carried out. The picture to the left shows a typical uncoated oil tanker shell where the technician had to climb the shell stiffeners and chip off the scale to bare metal in order to obtain a thickness reading.

I left ETS in 1968 and started Ronald Nisbet Associates. In the beginning, I was the only technician. I eventually expanded my workforce to 40 technicians, but that came later, in the nineteen seventies.
Thus endeth the decade of the 60s. Stay tuned for the next episode.

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