- Extending Tank Life. A regular inspection program can help minimize lifetime cost
- Electrolysis. When electrolytic damage is spotted, corrective actions is taken. The cure is often simple: better grounding or sacrificial zincs.
- Biological corrosion. A coating system and/or the use of biocides can be instituted. Just like antibiotics, the biocide must be matched to the specific organisms you have--we can do that.
How long until this collapses entirely? Ordinarily the shell carries only its own weight, but on a cone bottom tank such as this, it supports the entire mass of the tank.
- Sour water. Sometimes the bottoms water is simply corrosive, due to salt or acidity. Coatings, process changes and chemical inhibition are all practical. We can provide corrosion testing services.
A lining can be an economical solution to pitting.
- Improper repairs. Tanks have been ruined by well meaning but poorly implemented repairs. Square (not rounded) corners, improper weld placement (too near an older weld), incorrect materials or plate thickness, and welded patches when what is really needed is an epoxy lining that can stop corrosion are just a few examples. An experienced inspector can suggest best long-term solution.
This tombstone patch was installed over a small leak while the tank remained in-service. The cause? Grounding was disrupted when ground cables were stolen for the copper scrap and a stay current began eating the tank. Without routine inspection, the tank would have been lost within a few years.
- Reducing Pollution Risk. Tanks subject to regular inspection have much lower failure rates.
- Catastrophic failures. This risk can be virtually eliminated. Brittle fracture analysis (included standard inspections) can spot metallurgy and design problems. Thickness testing can catch corrosion-based thinning before it becomes serious. Vent inspection protects against tank collapse; we've seen too many easily avoided losses. (Isolated internal pitting is very difficult to identify during external inspections--pin hole leaks soon after a formal inspection are always possible. Structural failure is the focus on formal inspections.)
Severe chime corrosion can lead to catastrophic failures of large tanks. Minute flexing of the shell/chime interface during fill/drain cycles leads to early paint failure. In this case, concrete was poured around this tank with poor grading, directing water against the tank rather than away. Better grading, sealing the tank to the slab, and better paint maintenance would have avoided an expensive repair. The tank shell and floor were fine.
- Pin-holes. While it is impossible to be certain a tank will not develop a hole soon after inspection, the conditions that lead to this type of corrosion (electrolytic, biological, chemical) can be identified and corrected.
- Safety. Even a small gasoline leak can have devastating affects. Improperly located vents (flash fires and explosions) and defective catwalks are just a few of the items commonly uncovered during inspections. Inspections include more than just the structural integrity of the tank; they investigate the safety of the entire tank system.
Improper venting can collapse tanks and cause devastating explosions. These vents were led to the ground to reduce the mess of accidental overfills. Unfortunately, they also provide a place for volatile components to condense and concentrate, and leading them to the floor places them too close to potential ignition sources. I was called in to investigate a tank that had rocketed into the air after grinding sparks ignited the concentrated vapors accumulated in the ground level vent of a used oil tank.
Improper construction or repair. This sharp corner (should have been 6-inch radius) has buckled the plate and may cause tearing in the future. I've seen tanks ruined by tears. We can provide simple guidance to contractors; usually there is no cost difference between correct and incorrect repair.
More improper repairs. The chine was not prepared before painting and thus continued to rot out. The internal epoxy lining lasted only 6 years (pin holes on the shell and manway) because it was prepped by water blasting and pits were not repaired before coating. No surprise that there is also a square-cornered patch. They wasted their money and lost the tank.
- Liability and Fines. Spills are expensive. Even if the spill is not tank integrity related, regulators will ask for the files and documented inspections and training can persuade them that you have done all that is reasonable.
Some tanks really need inspections. How these remain in service without containment escapes me. A leak would be devastating both the environment and to the business. Because they are 100% accessible (on saddles), external UT testing will be very economical, without the need for tank cleaning or entry.
