The International Maritime Organization (IMO) regulated that ships must cut their sulphur oxide emissions by 2020. As a result of this, shipping companies have turned to scrubber systems, which reduce the amount of sulphur emitted from burning fuels. Scrubber systems allow a ship to continue using cheaper bunker fuel than low sulphur fuel which reduces the switching cost to an entirely new fuel system. The sulphur in exhaust gas is neutralised in the scrubber tower by the absorbent used such as sea water and passed out from the discharge pipe.

Unfortunately, scrubber systems come with their own issues. The piping in the scrubber system is very prone to corrosion, particularly in the discharge valve. This is due to the elevated temperatures of the exhaust gas scrubber discharge which creates a very corrosive environment. The risk is that a reduction in wall thickness would mean that corrosion is present.

Therefore, DNV GL has introduced a requirement whereby piping in scrubber systems should be annually checked for their thickness.

As stated in 2017 by DNV GL: “Newer SOx scrubber systems often are equipped with diffusers inside the distance piece. These diffusers themselves are vulnerable to corrosion attacks, but more important, their fixation to the distance piece, either welded or bolted, often forms a weak spot in the corrosion protection of the distance piece. For the safety of the crew and the vessel, we believe it is necessary that the condition of the distance piece be confirmed on a yearly basis.”

DNV, GL – Survey requirements for fleet in service Part 7, Chapter 1, Section 2, 3.1.9:“The wall thickness of distance piece(s) for SOx scrubber system discharge valve(s) shall be verified to be undiminished.”

The recommended solution is UTM (ultrasonic thickness measurement). Ultrasonics is the simple and effective solution for testing for corrosion, required by DNV GL. Coltraco Ultrasonics are proud industry experts in ultrasonic technology. Coltraco manufacture two industry leading ultrasonic thickness gauges, ideal for the regular testing of scrubber systems.

Portagauge® 3 is a low cost single-echo portable thickness gauge. The quick, simple and hardy Portagauge® 3 allows accuracy of ±0.1mm even on corroded, challenging and some plastic surfaces. With a 50 hour battery life, measuring thickness ranges between 1.5mm to 99.9mm and a variety of verified testing materials such as steel, quartz and glass PVC, the Portagauge® 3 provides the versatility to suit a range of safety needs. This easy to use ,highly dependable handheld unit is ideal for scrubber systems.

For more advanced requirements – identifying the metal only thickness – Coltraco Ultrasonics also have the Portagauge® 4 which is an advanced thickness gauge. Offering unparalleled accuracy, the Portagauge® 4 uses triple echo technology which allows operators to inspect the underlying metal thickness, independent of any surface coatings such as paint. For applications where true metal readings and a higher degree of accuracy is required, the Portagauge® 4 is the ideal solution. With a variety of sensor options available and underwater variants, this range of units can easily be adapted to a variety of different roles and requirements.