Avoiding Tank Failure

Q. What advice do you have for selecting process tanks?

It begins with design. The most critical joint in a welded tank — whether metal or polymer — is the weld between the bottom channel and the vertical. The entire design is based around that interface. Software developed specifically for that purpose can predict the structural integrity based on the material and the solution it will hold. It then defines the construction members needed for the tank, along with piping/plumbing systems, hatches and cleanouts, access platforms, lifting and grounding lugs and other requirements. The result is a design that improves strength, resilience and service life.

Q. What are some best practices for avoiding tank failure?

Regular inspections are critical, with corrosion the most important thing to watch for with steel tanks. Spark testers are effective in identifying weaknesses and pinpointing leaks in polymer tanks.

Failures in poly tanks are rare. If they occur, it’s usually due to mechanical damage from forklifts or cranes. Failures caused by chemical attack can occur when the chemistry changes from when the tank was first installed, or when a line is run outside process guidelines.

With polypropylene tanks, repair is easily achieved in the field. Portable extrusion or hot air welders can fix leaks. Issues with steel tanks are best solved with a polypro or PVC liner. Flexible drop-in or rigid sheet liners are welded to fit, providing an excellent temporary or semi-permanent fix.

For extremely corrosive chemicals such as bright dip, steel tanks can be supplied with a liner as part of the original build.

One problem we’ve been surprised to see is bright dip tanks made from 316, rather than 316 L (low carbon) steel. Bright dip solution is 85% phosphoric, with nitric and sulfuric. Carbon precipitation forms around the welds, and that cocktail of chemistry attacks the carbon precipitation, resulting in leaks.

Bright dip tanks are serious business — critical to every anodizing line. They should always be manufactured from 316L. (Polypro is not recommended, due to its expansion/contraction characteristics.)

Process tanks are an investment. It’s important to review how materials differ and do your research when selecting a vendor.

There’s value to working with a company that has the construction, software and people resources required for your job. Its important to find a partner who can assist you in working through any peripheral issues, such as power conversion and pollution control, that can accompany a project.