^ Titanium could be an interesting material for marine scrubbers, particularly for luxury cruise liners. Image Wikimedia Commons, Rapidfire
Article by Michael C. Gabriele, ITA Freelance Writer

Rob Henson of VSMPO Tirus US, chairman of the ITA committee, explained that this opportunity for titanium initially unfolded due to global regulations established by the International Maritime Organization (IMO). Effective on Jan. 1, 2020, this regulation restricts the amount of sulfur in marine fuel in order to reduce the sulfur oxide (SOx) exhaust gases leaving a ship’s smokestacks. The regulation, originally unveiled several years ago, extends to an estimated 40,000 to 60,000 ocean-going vessels, representing a large and potentially lucrative market for utilizing titanium in marine scrubber construction.
These ocean-going vessels are a critical link in the global supply chain and the fuel costs they incur are a key factor in remaining competitive. The global mandate by the IMO is significant as fuel is a major expense for ocean-going ships, which generally utilize marinegrade “bunker” diesel fuel that has a high sulfur content (3.5%). The IMO regulation calls for a lower fuel oil sulfur content of 0.5 % if the ships desire to sail along most global shipping routes. The heavy fuel oil with its higher sulfur content is less expensive, but pollutes more and the smokestack emissions must be reduced through the use of scrubbers.

Scrubber technology

Design and production of marine scrubbers
Design and production of marine scrubbers

A marine scrubber is a metal cylinder typically measuring 35 feet in length and 6 to 8 feet in diameter. In addition to the cylinder, the scrubber system includes other industrial components such as pipes, tubes, valves and a high-volume water supply system. Specialty stainless steels and nickel alloys have historically been widely used for marine scrubbers, but these metals have a limited service life. By contrast, titanium offers lifecycle advantages in its superior resistance to the sulfur laden exhaust gases, high operating temperatures (660 degrees F and higher) and the corrosive seawater spray used to cool the scrubber system. Henson said titanium Grade 2 and possibly Grade 12 are well suited for marine scrubber fabrications.

There is an extensive service history for titanium in elevated temperature seawater environments as well as in land-based flue-gas desulfurization (FGD) exhaust systems, including petrochemical, refining and power generating services. Additionally, laboratory work conducted in 2008 and presented in the paper “Corrosion resistant material selection for the manufacturing of marine diesel exhaust scrubbers” (see Reference 1) found titanium fully resistant to corrosion in the post-quench environments of the scrubber.

Long service life

While titanium has a higher up-front installation cost for a marine scrubber compared with Super Austenitic stainless steel (SASS), the increased investment for titanium can be shown to provide a considerably longer service life and a lower “total cost of ownership” based on the aforementioned FGD and seawater environment. Henson pointed out that, unlike specialty stainless steel or nickel alloys, titanium—when properly welded and assembled— maintains an overall corrosion resistance level comparable to the base metal without the requirement for postweld heat treatment.
Alberto Di Cecio, director, marine department, for Ecospray Technologies Srl, Alzano Scrivia, Italy, said his company, during the last 10-plus years, has installed over 400 marine scrubbers on a variety of vessels, mostly cruise ships. Di Cecio estimated his company has a back order of 300 marine scrubbers. SASS and nickel alloys represent Ecospray’s materials of choice for the vast majority of installations to date. (The popular Carnival cruise line company holds a majority ownership stake in Ecospray. According to a report in the April 8 edition of The New York Times, it’s estimated that Carnival Corp. serves half of the global cruise market, about 11.5 million travelers a year.)

“Titanium can be shown to provide a longer service life and a lower total cost of ownership”

Di Cecio, during a long-distance telephone interview, acknowledged that ship builders, especially luxury cruise liners, have expressed interest in using titanium for marine scrubbers, in light of the requirements to conform to the IMO pollution regulations. “Yes, titanium could be an interesting material for this application,” he said, revealing that Ecospray is currently involved in a study with an Ohio-based fabricator. He said that, on paper, titanium could prove to be an improvement over nickel-based or stainless steel alloys, given titanium’s long-term, life-cycle advantages and corrosion resistance properties.
“I’m interested in exploring this. I like the challenge,” he said. For the near term, titanium might be specified for applications on cruise ships or ferries, but cargo ships and oil tankers would most likely have little interest, given titanium’s perceived cost premium, according to Di Cecio.

Challenges remain

Despite titanium’s promise and superior properties, Di Cecio said fabricator acceptance, in-port or in-transit repairs, and supply chain questions all pose major hurdles for titanium use in marine scrubbers. On a larger manufacturing scale, it would be very complicated to change the supply chain and part specifications in order to accommodate titanium, he said. He also considered the time, effort and cost needed to do repairs on board ships.

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“The production techniques, welding and machining would all be different for titanium,” he said, anticipating resistance from fabricators to implement such changes. Ecospray and its fabricators also would have to reconsider the handling of internal scrubber components such as pipes, nozzles and valves. Ecospray utilizes 22 fabricators throughout Europe, North America and Asia to build its scrubbers. It sources SASS from several mills.
Another source, a marine professional engaged in IMO compliance technologies, concurred with Di Cecio’s assessment. “Titanium may be the answer (as an enhanced material for marine scrubbers), but without one in operation it’s a bit hard to tell.
People see (titanium) as an exotic and expensive material, and you need to overcome this perception.”
The concerns expressed by Di Cecio are not new challenges to industrial application development for titanium and make it clear that the ITA must continue its mission to connect those interested in titanium with industry experts to assure accurate perception of the global titanium supply chain.

Henson argues that when taking a “high-altitude” look at the real total cost of ownership for a titanium scrubber, the units actually cost the vessel owner considerably less over the expected 25-year life of the vessel.

Titanium supply chain

Addressing concerns about the titanium supply chain, Kevin Cain, president of Uniti Titanium, said his company “supplies a global network of industrial market participants including engineering companies, equipment fabricators, distributors and OEMs. Uniti’s global supply chain of titanium mill products supports a variety of industrial processes including purified terephthalic acid, chlorine, thermal desalination, gold and nickel hydrometallurgical plants as well as refinery equipment for the production of low-sulfur fuels. Our supply chain is well stocked and up to the challenge of supporting new business. We have participated in titanium supply to the largest thermal desalination plant, which required 6,000 metric tons of titanium welded tubes and have supplied titanium alloy plate for the fabrication of a titanium clad-steel autoclave for gold ore processing with a final equipment weight of 980 metric tons.”
The overarching reason for considering titanium for scrubber construction is that it’s anticipated to last much longer than the SASS materials currently being used around the world, according to Henson.
One source working in scrubber installation and maintenance reports that “the SASS materials don’t hold up in the high temperature, highly acidic environment of a marine scrubber. The high internal temperatures, the reality of interruptions to the sea water flow and the acid generation mechanism of sulfur and water all make for a very tough operating environment. Add to this the cyclic heating and cooling of the scrubber shell and you have a very hostile environment for SASS materials.
Cracks (up to 3 feet long) have been witnessed in the scrubber shell, which allows acids to leak out of the scrubber and downhill onto machinery, steel decks and framing, with a resulting loss of supporting structures.”

Total cost of ownership

Additional technical information on corrosion in marine exhaust gas cleaning systems (scrubbers) had been slated to be presented at the Corrosion 2020 conference (on March 14 in Houston, sponsored by NACE International). Unfortunately, this forum was postponed due to concerns regarding the coronavirus. The presentation, which was to have been delivered by a fellow ITA committee member, argued that “total cost of ownership” for titanium scrubbers is much less than that for SASS units, and can eliminate the 5-7 year replacement cycle that is just now beginning to manifest in ships outfitted early in the IMO 2020 compliance cycle. “We have discussed this replacement cycle with professionals in the cruise line community and it points to the recurring need to remove and replace scrubbers on the order of 5-7 years.” The cost to transport the new units, and remove/ replace the old units is considerable, the ITA committee member said.
On cruise ships, repairs and replacement are difficult to do without disruption to the passenger experience and loss of revenue generating bed space to the company, the ITA committee member pointed out. “If one compares the CAPEX (capital expenditure) between SASS and titanium, the titanium scrubber costs about 35% more at construction.
But over time, this cost is eclipsed by the replacement expenses associated with changing out a SASS scrubber three to four times over 25 years, while the titanium unit continues to operate. The delta in OPEX (operational expenditure) over 25 years is quite large, to say nothing of the interruption to vessel operations and loss of revenue.”

A final corrosion concern/titanium opportunity involves the discharge of sea water based effluent from marine scrubbers in “open-loop” operation. The scrubber overboard sea water flow is discharged into the surrounding sea water, while the vessel is at sea and sometimes in port. This effluent will have a low pH, meaning that it is a strong acid. This acid can, over time, attack the external skin of the steel ship with resulting corrosion. Titanium can have a positive impact on preventing this corrosion if placed around the effluent ‘overboard discharge’ area.

About the author

Michael C. Gabriele

A former American Metal Market editor, Michael C. Gabriele, based in New Jersey, has been a freelance writer developing editorial content for the International Titanium Association [titanium.org] for more than 15 years.

1. “Corrosion resistant material selection for the manufacturing of marine diesel exhaust scrubbers, E. Aragon, J. Woillez, C. Perice, F. Tabaries and M. Sitz” (posted online by Science Direct, Elsevier, Materials & Design, Volume 30, Issue 5, May 2009): www.sciencedirect.com]
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