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Ian Nash discusses…

Crop and Renew Steel Repairs:
Time to Change the Record

Replace 2,000 sqm of tank top in 36 days not 60 days. Saving 24 days of off hire rates at $75K USD per day translates as a saving of $1.8M USD.

As reported in Splash247.com  (06 Oct 2021) bulk carrier rates have rocketed with “Extreme coal shortages” in ChinaIndia and Europe and “firm iron ore export volumes out of Brazil and Australia and mineral exports in the Pacific. A lack of tonnage is also driving freight rates due to port congestion in China along with other Covid-related delays. Nearly 6% of all bulk carriers are currently tied up in port congestion off China, according to data from Braemar ACM.”

Global raw material steel prices across USA, China, and Western Europe in 2021 have increased month on month and were over $2,000/MT. Docking availability will influence the price of repairs as owners and operators plan their Classification Society approved permanent repairs due to steel corrosion or impact damage.

There is enough evidence in the above statements to demand thinking outside the box, with charter rates climbing to decade high numbers. The vessel is not earning unless it is sailing, so how can we reduce the shipyard steel repair schedules?

Ref: Aqualis Braemar LOC

The current costs for repairs can be intimidating. The cost of ship steel as a raw material is always a factor but it is not the only factor shipowners should be considering. The ship steel used in shipbuilding and ship repair must be Class approved and of a specific grade depending on the application. The price of steel repairs is made up of several factors including raw material, labour, engineering, preparation of existing structure, overhead and profit.

Although the same scantlings and the same grade material are generally used when replacing corroded material with new steel (plates, sections) in crop and renew repair, the quality of the “renewed” structure is never the same as the existing structure was. The crop and renew process requires all steel cut edges to be prepared by flame cutting, involves arc gouging and grinding, kilometres of welding between the new plates and the existing structure that include full penetration double-welded butt welds and double-side fillet welds. In addition, crop and renew repair always involves less favourable welding conditions than for new construction. The excessive root gaps between the replacement steel plate and the existing structure are always too irregular to permit satisfactory weld preparation or are located so that access is insufficient for producing sound, full penetration welds. All the above not only affects the quality – reducing strength – but also affects speed of installation and increase demand on installation labour.

Overall, removing large areas of plate steel can have an effect on the vessel, which then needs to be rectified before the vessel goes back to sea.

Common after effects of large-scale ship steel repair by removing substantial portions of the existing corroded hull structure:

  • Transferring high stresses from one location to another;
  • Overloading neighbouring structures;
  • Hull distortion including twisting, buckling and deformation of the hatch cover coamings. These distortions can effect machinery and shaft alignments that may lead to noise and vibration problems.

This is where SPS comes into its own. It is a Classification Society-approved permanent repair designed to last the lifetime of the vessel. SPS utilises the existing stiffened plating of the structure as one of the SPS faceplates. This provides a permanent repair with enhanced strength of the original structure, additional corrosion protection and increased fatigue resistance for the design loads.  SPS effectively contributes to the global strength of the vessel. In areas where SPS is fitted, it is regarded as reinstating the structure for both local and global longitudinal strength aspects.

Ultimately, it’s clear that in this current global environment, cost savings must be found. Choosing SPS over traditional crop and renew can mean the difference between days spent in a shipyard and days spent at sea. In today’s buoyant chartering market, this choice should clearly be embraced.

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