According to a nationwide report conducted in the USA, corrosion costs industry over $276 billion every year. Understanding how to control it is paramount to running a safe, productive and cost-effective operation.
Corrosion is the deterioration of a substance or its properties because of a reaction with its environment. There are various kinds of corrosion, including uniform, galvanic, crevice, pitting, intergranular and stress. Of these, crevice and pitting are among the most prevalent and problematic – particularly for marine-based industries.
This is an electrochemical oxidation reduction process, which occurs within localised volumes of stagnant solution trapped in pockets, corners or beneath a shield (seal, deposit of sand, gasket or fastener, for instance). It is considered much more dangerous than uniform corrosion as its rate can be up to 100 times higher.
Pitting is characterised by a localised attack in the form of deep and narrow holes that can penetrate inwards extremely rapidly while the rest of the surface remains intact. It is most aggressive in solutions containing chloride, bromide or hypchlorite ions. The presence of sulphides and H2S can also promote it. Stainless steels are particularly sensitive to pitting corrosion in seawater environments.
Certain measures, such as avoiding stagnant areas, installing draining systems or using cathodic protection, can help avoid both crevice and pitting corrosion. Perhaps more critical is choosing the best possible components for the given application and environment.
Parker 6Mo Snap-Trap®+ tube clamps have minimal tube contact points, making them a much better solution for avoiding crevice corrosion compared to traditional clamps, particularly in marine environments. Designed by an offshore contractor; Snap-Trap®+ is a field proven solution with over one million installed worldwide. Together with Parker’s 6Mo fittings and tubing, they give you far greater confidence in your long-term corrosion control.
An independent testing house performed a salt spray test of Parker tubing and clamps of different sizes and material combinations. The test was performed according to ASTM B-117 / ISO 9227 which is testing in salt fog containing 5% NaCl and has a temperature of 35°C. The testing time was 312 hours (13 days). This corresponds to about 5 years of vibration on an offshore platform. A second test lasting 1000 hours was also conducted as a comparison. The 6Mo and 316L clamps and tube were attached to a common canal of AISI 316 and exposed to vibrations during the whole testing period. The results clearly show no ill effects on the 6Mo tube from the clamp regardless of time spent under vibration.
Jim Breeze is Product Manager, Instrumentation Connections and Process Valves, Parker Hannifin, Instrumentation Products Division Europe.