NDT under harsh conditions

NDT technicians have to mobilise their technology into hazardous locations. One such location is a hydrofluoric acid (HF) alkylation unit in a refinery. According to Federal Energy information, there are 135 petroleum refineries operating in the USA. Of these, about 50 have ‘alkylation units’, which use hydrofluoric acid as a catalyst. There are two such units in the Greater Los Angeles area.

My earliest memory of working in a HF alkylation plant was in the early 1970s, taking ultrasonic thickness measurements. At that time we were not issued with special personal protective equipment (PPE), but simply warned: “Don’t get any hydrofluoric acid on you because it can cause severe burns and will penetrate to attack the bones!” Fortunately, I never did get any on me!

We have come a long way from these early days and there are now stringent requirements in place concerning the PPE that is required to enter the HF alkylation unit.

Prevention is indeed the best medicine when working with a chemical as hazardous as hydrofluoric acid. The following personal protection garments should be utilised when working within this environment:

Gloves – polyvinyl chloride (PVC) or neoprene gloves – gauntlet style
Shoes – closed toe, leather or durable non-porous material with overboots
Vinyl jacket, with the sleeves taped to the gloves
Vinyl trousers, with the trousers taped to the neoprene overboots
Eyewear – chemical splash goggles at all times, worn over safety glasses
Ventilation – fume hood use is always advised.

Prior to leaving the HFD alkylation unit and removing the outer PPE, the technician is required to undergo a complete shower.

It should be abundantly clear that ‘suiting up’ and removing the extra PPE is time-consuming, access to the inspection area by way of ladders and manlifts is tedious and conducting NDT processes under these conditions is extremely complex. The difficulty of manipulation of instrument controls and the application of transducers is multiplied tenfold by the conditions.

Oh, and did I mention that in Southern California the temperatures in the summer range from 26°C (80°F) to 33°C (90°F)? Add to this the weight and hermetically sealed nature of the PPE and you can visualise the physical nature of the conditions. Strap on the additional weight of the NDT equipment and the technician emerges from the unit several pounds lighter at the end of the day.

The large quantity of piping, flanges, valves, pressure vessels, tower and tanks in the HF alkylation unit calls for extensive NDT coverage. Such is the nature and severity of leaks and failure that extensive NDT must be conducted while ‘on stream’. Guided wave testing (GWT) provides the ability to examine long sections of piping, ultrasonic thickness testing supports the findings from GWT, radiography has specific applications and damage to a flange face requires a special phased array ultrasonic application.

This type of petrochemical unit and the harsh conditions facing the NDT technicians require strength, stamina and dedication in order to provide the ongoing information that allows the refinery to maintain a safe and productive environment.

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