Waters in turbulent flow, especially those high in dissolved and suspended solids or dissolved and entrained gases, often damage passive oxide films, causing extensive local corrosion. The abrasiveness of the flowing water physically tears metal away from the structure and results in the horseshoe shaped pits characteristic of this attack. The pits are aligned in the manner of a horse walking upstream shown in figure.

In evaluating the effect of entrained gases, the size of the gas bubble often determines the extent of pitting. Larger bubbles destroy the oxide layer, while a small bubble might bounce off the metal surface or actually replenish a passivating oxide film.

The most severe attacks occur at the inlet to heat exchanger tube bundles, points of restricted flow, sharp bends and elbows, etc. Although many materials are subject to impingement, the most serious problems occur in copper and its alloys. In general cooling situations, flow through copper tubes in a heat exchanger should be limited to a velocity of five feet per second. This velocity should be reduced further if total solids or gas concentrations are high.

The corrosion developing at the crevice or pits at the mouth end gradually moves in further and even beyond the tube plate. It may further worsen to upset the water chemistry of your plant.

What will happen next?  
The damaged tube is the source of ingress of cooling water in to the steam space.

What will be your immediate reaction?
Replace the worn out tube with a new one. It is said easily than done. The cost and time for replacement is enormous and how often we can afford downtime to replace each damaged tube.

If this is not right what else?
You think of plugging the damaged tube. It is an easy solution at the cost of the efficiency of your condenser / heat exchanger. 

Really frustrating. How can you avoid this menace?
What is a VALQUASERT?

VALQUASERT is a plastic insert, which can be inserted to the tube mouth end. This Insert is made out of Nylon / Polyethylene according to the requirement and has an excellent wear resistance. The Inserts can be supplied even in Metal or ceramic according to working conditions. Even if it wears down in extreme conditions, it can be easily replaced at miniscule cost comparing to that of replacing the tube and it saves your tube from any mouth end damage.

Whether usage of VALQUASERT will affect my condensers efficiency?

Reduction in area at the mouth end is negligible considering the length of the insert
(average: 6 in) with that of the tube (7 to 10 meters). Even with pessimistic calculations, reduction in efficiency will be negligible considering the fact that generally condensers are over engineered by about 10 to 15 %.