Tanks hydrotest

The destructive hydraulic forces of mild-mannered water were displayed in a classic style on a summer evening in 1996. A Gulf Coast chemical plant had just rejuvenated a recovery tank and started a hydrotest when things went wrong. The poorly executed test added 35,000 to the repair costs. Other than embarrassment, no one was injured. In the previous three weeks this tank had received repairs consisting of a new floor and new walls in the lower section. 

Figure 3-2 A closer look at the slightly leaning tank and the walkway that was torn off during the hydrotest.

At this section of the plant in the past, chemical process operators (not maintenance mechanics) handled the tank-filling step in the hydrotest process. Operators would typically drape a fire hose into an oversize roof nozzle and fill the tank from the nearest hydrant. In this case, it was reported the two mechanics asked their maintenance supervisor if they could connect the hose to a flanged lower-valved nozzle on the tank. The supervisor remembers requesting the mechanics to roll a blind flange at the top for venting purposes if they used the lower nozzle for filling. There must have been a miscommunication. Obviously the mechanics failed to understand the dynamics of the filling operation when they chose to open only the two 1/2-inch top vents. 

Figure 3-3 Tank bottom is bulged during a hydrotest. 

The mechanics in this area wanted to do a good job and this incident occurred. How can you impress upon the craftsmen the weaknesses of low-pressure tanks The maintenance superintendent in this area wanted practical training to reduce the probability of a repeat. Concerned supervision scheduled 100 mechanics in this section of the plant to a tender tank presentation patterned after the Institution of Chemical Engineers Hazard Workshop Module The Hazards of Under and Over-Pressurizing Vessels. [4] Procedural changes for hydrotests were also made. 

Figure 5-1 Residual, undetected water from a hydrotest explosively vaporizes and ruptures a surge tank. Courtesy of Trevor A. Kletz.

At this section of the plant in the past, chemical process operators (not maintenance mechanics) handled the tank-filling step in the hydrotest process. Operators would... 

Nuclear power generation Carbon and stainless steel piping and tanks copper-nickel, stainless, brass, and aluminum-bronze cooling water pipes and tubes, especially during construction, hydrotest, and outage periods... 

The corrosion action of sulfate-reducing bacteria (SRB) is well known in the oil industry, especially in cooling water systems, fire water loops, after hydrotesting of tanks and vessels, and in mothballed or water-flooded systems. 

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