Hanwha Ocean designed and built several 3,100-ton (t) destroyers, where defects causing cracks in the piping were discovered. The destroyers with defects are now operating normally after repairs. The Navy and the Defense Acquisition Program Administration (DAPA) are reviewing the piping and structure changes since the unaffected destroyers used the same piping.
According to the defense industry on the 20th, the first occurrence of piping defects was reported in one Daegu-class destroyer in 2022. This piping is a passage for ballast water (water filled into a ship to stabilize its center of gravity), designed to penetrate the fuel tank. It is reported that as a large amount of seawater passed through the piping, holes were formed, leading to issues when seawater leaked into the fuel tank.
This Daegu-class destroyer (FFG·Frigate Guided Missile) is part of the Batch-II program initiated to replace the Ulsan-class (1,000t) destroyer, the first destroyer project. 'Batch' refers to a group of vessels built of the same type, with performance improvements made from Batch I to III.
Batch-I is the Incheon-class (2,500t), which is smaller than the Daegu-class. A total of eight Daegu-class destroyers were constructed from 2016 to 2023 at a cost of about 3 trillion won. Hanwha Ocean (then Daewoo Shipbuilding & Marine Engineering) provided the basic design in 2011, and Hanwha Ocean and HD Hyundai Heavy Industries constructed them in parts.
It has been confirmed that more than half of the eight vessels, including the first destroyer to experience issues, encountered similar problems. According to DAPA, at the time Hanwha Ocean created the basic design in 2011, the piping was made of a copper-nickel alloy, but it was later changed to stainless steel.
Changing the material of the piping during the design process did not require the approval of DAPA or the Defense Technology Quality Agency, so Hanwha Ocean made the change independently. The destroyer with the initial defect used an unapproved type of stainless steel (SUS304L) instead of the changed stainless steel (SUS316L).
The unapproved stainless steel was used in only about 1.6 meters of the total 131 meters of piping. Hanwha Ocean said that a subcontractor mistakenly used another stainless steel piping. A Hanwha Ocean official stated, "We supply in 6-meter units, and during the processing of the piping, the subcontractor used different piping."
Regarding the decision not to use corrosion-resistant copper-nickel piping, they remarked that "using copper-nickel piping could lead to fuel contamination and sediment problems, and at that time, stainless steel was the best choice."
Only one vessel used the different material piping, but other destroyers were found to have holes in their stainless steel piping, allowing seawater to enter the fuel tanks. The piping of this destroyer used SUS316L.
A military official stated, "Holes have also formed in other destroyers that used corrosion-resistant stainless steel (SUS316L). Currently, other unaffected destroyers are changing their piping structure to bypass the fuel tanks."
The Navy repaired one of the affected destroyers independently. They rerouted the piping to ensure it did not penetrate the fuel tank. Another vessel was repaired jointly by Hanwha Ocean and the Navy, and Hanwha Ocean plans to repair the other affected destroyers for free in July and October.
The military, DAPA, and each company are conducting technical reviews to determine the circumstances surrounding the use of stainless steel and assign responsibility. Understanding the exact circumstances is necessary to decide who will bear the repair expenses for the destroyers. Hanwha Ocean has agreed to cover the costs for the destroyers it built, but it is reported that the expenses for the repair of the destroyers constructed by HD Hyundai Heavy Industries have yet to be determined. The total cost for replacing the piping for all eight vessels is estimated to be in the hundreds of millions of won.
The circumstances around the use of stainless steel differ between Hanwha Ocean and DAPA. Hanwha Ocean maintains that it followed reporting protocols when making changes to the design, while DAPA believes the evidence is insufficient. Although the change in piping material does not require approval from DAPA or the Defense Technology Quality Agency, whether proper oversight was conducted remains an issue. It is understood that HD Hyundai Heavy Industries claims it bears no responsibility as it built the destroyers according to the design.
A DAPA official noted, "We are continuing legal reviews regarding repair expenses and liability. This is part of the discussions to resolve the issue."