THRESHOLD CRITERIA FOR DETERMINING FRACTURE REPAIR PROCEDURES

1. THRESHOLD CRITERIA FOR DETERMINING FRACTURE REPAIR PROCEDURES SSC Project Recommendation for FY-2008

2. BACKGROUND • Steel Repair NVIC 7-68 explains how to properly insert hull plating, but lacks guidance as to when • Critical Length and brittle mode of fracture are difficult to relate to actual ship hull plating situations • Modern welding technology has improved quality of gouge & re-weld repairs, including a smaller heat-affected zone • Loss of West Coast repair drydock capacity has caused increased use of in-water dry habitat technique (i.e., welder in an evacuated box) for below-the-waterline fracture repairs

3. CASE HISTORY 1 • Travelers attended an ACP-enrolled TAPS tanker on drydock in Singapore • MISLE history revealed 4 previous amidships in-line transverse bottom shell fatigue fractures, all repaired in-water (over several years) by gouge & re-weld • Longest = 62” and running into an erection butt • Fractures caused by a design detail problem that had been corrected

4. CASE HISTORY 1 • In the past, these kind of repairs would have been considered temporary, but class now accepting them as permanent • Travelers recommended:- ABS improve weld procedure;- Notation to re-examine at the next drydocking; • Owner’s steel superintendent opted to crop out a 2.5m wide band from bilge to bilge because he felt he could not guarantee against re-fracturing

5. CASE HISTORY 2 • Travelers asked to consult on a side shell fracture found in way of a deep tank on an ACP enrolled operating container ship in service • Question specifically was:- whether a gouge and re-weld job as proposed by the company was an acceptable repair- if so, would it be considered a temporary repair and for how long- if not, what would be the basis for considering the repair permanent

6. CASE HISTORY 2 - Longitudinal fracture - 2-3 inches in length- 3/4 inch high tensile steel plate- Below the loaded waterline -Next scheduled drydocking in 1 year

7. CASE HISTORY 2 - 2-3 inches from longitudinal weld seam

8. CASE HISTORY 2 • Because deep tank emptied and fracture above the waterline after cargo discharge, local CG preferred permanent repair by insert IAW limited guidance in Steel Repair NVIC 7-68. • Travelers and ABS recommended:- NDT and safe-ending of fracture;- Gouge and re-weld;- Operate with deep tank empty;- Regular visual exam by crew and report any change;- Condition of Class to re-examine at the next drydocking; • Owners conducted repairs per the above. Repair inspected by CG and after voyage from West Coast to China and return • Final disposition of repair referred to Class

9. NEED FOR PROPOSED STUDY • Field needs a reference that provides a review of the sum total of factors to be considered when deciding whether to gouge & re-weld or to insert hull plating including, where appropriate, threshold criteria • Factors would include location, orientation, relation to previous repairs, plate material & condition, inset damage, upset internal structure, vessel service, etc., etc. • Establishment of post-repair policy also needed (e.g., appropriate NDT, scheduled re-examination, etc.)

10. NEED FOR PROPOSED STUDY • This guidance would mitigate the overall lessening of experience levels among CG marine inspectors and other maritime professionals due to:- the decline in the size of the U.S. flag fleet; - the advent of the ACP program; - the decrease in stateside deep draft hull repair availabilities; and - continued advances in welding/repair technologies