Activity_15263_Letter_Report_-_64_ANB_Corrosion_Survey_Analysis_(WI-4).pdf

US COAST GUARD – Surface Forces Logistics Center

ESD Naval Architecture Section

To: MKC Joseph Barratt, Small Boat Product Line

From: Benjamin Brainard, Naval Architect

Approved: Tim McAllister, Chief, Naval Architecture Section

Date: 15 April, 2016

Subject: 64 ANB (643502) Hull Corrosion Survey Analysis

Activity: 15263

Summary

The majority of the contractor’s recommended repairs are acceptable. In two instances, the NAV

ARCH recommendation for repairs is significantly less than the contractor’s recommendation.

Smaller localized repairs or replacements can alleviate having to remove whole panels and can help avoid excessive removals or interferences. In addition, there are a few areas where it may be easier and cheaper to clad weld the small pits, if they are accessible. Possible alternate renewal plans are presented for large removal sections, as well. Also, it is recommended that contractor-identified caution or warning areas adjacent to plate sections recommended to be removed are renewed. Using these recommendations reduces the area of repair by at least 100-ft

Background

A 64-ft ANB (hull 643502) is currently in dry dock at Horizon Shipbuilding in Bayou La Batre, Alabama. A complete side scan ultrasonic test (UT) inspection of the hull showed significant pitting in the shell plating in various areas. Based off these results, the contractor (Gladd

Solutions) recommended replacing 881-ft of hull plating

. Figure 1 provides a key plan of the shell plate, as provided by the contractor. Table 1 and Table 2 provide a summary of the contractor repair recommendations. Given that the recommended replacement would require significant work, the SFLC-ESD-NAME-Naval Architecture Section (NAV ARCH) was tasked with reviewing the data provided by the contractor and providing a recommendation on the amount of plate renewal and repair work required.

Gladd Solutions, “Ultrasonic Corrosion Inspection Report: USCG ANB 643502,” 12 March, 2016

15 April, 2016

Surface Forces Logistics Center

Figure 1 – Port Side Shell Plate Key Plan (Starboard Side Similar)

Table 1 – Port Side Plate Summary (Gladd Solutions recommendation)

PORT SIDE

Plate

ID

Defect

ID

Lower Left

Coordinates

(x,y)

Size

Square

Feet of

Repair

Description of Defect

TOTAL X Y 432

1p 1p1 158, 0 74 71 37 Interior Corrosion

1p2 107, 0 26 71 13 Interior Corrosion

2p 2p1 0, 0 234 72 117 Interior Corrosion

3p 3p1 129, 0 230 96 153 Interior Corrosion

4p 4p1 129, 0 230 46 74 Interior Corrosion

6p 6p1 67, 23 20 23 4 Exterior Grind Divot

7p 7p1 0, 0 74 37 20 Interior Corrosion

8p 8p1 207, 0 60 14 6 Interior Corrosion

8p2 110, 0 33 10 3 Interior Corrosion

TR TR1 0, 0 67 10 5 Interior Corrosion

Table 2 – Starboard Side Plate Summary (Gladd Solutions recommendation)

STARBOARD SIDE

Plate

ID

Defect

ID

Lower Left

Coordinates

(x,y)

Size

Square

Feet of

Repair

Description of Defect

TOTAL 449

1s 1s1 0, 0 234 71 116 Interior Corrosion

2s 2s1 0, 0 234 72 117 Interior Corrosion

3s 3s1 0, 0 185 96 123 Interior Corrosion

3s2 343, 30 15 65 7 Interior Corrosion

4s 4s1 79, 0 19 47 7 Interior Corrosion

5s 5s1 0, 0 98 71 48 Interior Corrosion

6s 6s1 0, 0 44 69 22 Interior Corrosion

7s 7s1 155, 24 55 8 4 Interior Corrosion

TR TRs1 65, 0 67 10 5 Interior Corrosion

Discussion

First, the inspection report, contractor recommendations, and boat drawings were all reviewed.

The location of structural members, interferences, and equipment was identified for each of the recommended repair areas. The recommendation by the contractor to renew the majority of the aft plating (Plate ID’s 1p, 2p, 1s, and 2s) was of particular concern, due to the numerous exterior interferences and structures present and the location of significant machinery and equipment above these plates (in the Lazarette/Steering Gear Compartment and Engine Room). However, the corrosion of these plates is so severe and widespread that little of the current plating can be retained. It is recommended that these plates be renewed in smaller sections to limit the potential for damage to or need to remove exterior structures, interior structures, machinery, and equipment.

In addition, it was found that several of the repair areas are near or above docking blocks.

Special consideration should be given to these areas to ensure that the boat remains properly supported while making these repairs.

In most cases, the corrosion has occurred to the plating at locations near frames and longitudinal stiffeners. Given this pattern, the corrosion is likely due to water collecting at these locations. An on-site investigation of these areas would be required to confirm this assertion.

Given the way boat structures are designed with frames and longitudinal stiffeners or girders, interior pockets are formed between structural members where water can accumulate on the shell plating. Typically, drain holes (also called rat holes or limber holes) are provided at strategic locations that will allow water to drain into the bilge in areas where bilge pumps are installed. If standing water is found, the presence of drain holes needs to be investigated. If drain holes are not present, they should be created, unless part of an oily water containment pocket. It is also common for existing drain holes to get clogged by debris. All drain holes should be created by a hole with a radius of 1/2-inch, at the bottom of the structural member in the lowest lying areas, and should be cleaned regularly. Drain holes should be located at least 3-inches from frames or bulkheads.

If standing water is found, the underlying paint system should be inspected, properly cleaned, and touched up with paint as needed to prevent corrosion to the shell plating and structural members.

Transverse frames and longitudinal girders in contact with damaged hull plating should be inspected for corrosion damage. If the structural members are significantly damaged, they should be repaired, cleaned, and painted as necessary.

Recommendations

The recommendations of the contractor were used as a starting point. The NAV ARCH recommendations are provided in Table 3 and Table 4 with NAV ARCH concurrence or non-concurrence provided in the “NAV ARCH Opinion” column for each original Repair ID.

Comments are provided for each repair. If the “NAV ARCH Opinion” states “CONCUR”, repair the areas per the contractor’s recommendation. If the “NAV ARCH Opinion” states “CONCUR, WITH COMMENT”, additional information is provided.

For Plate ID 2s, where complete replacement was recommended, and Repair ID 3p1, where two-thirds of the existing panel was recommended to be replaced, the NAV ARCH recommendation

DOES NOT CONCUR with the contractor’s recommendation. Smaller localized repairs or replacements can alleviate having to remove large sections of panels and can help avoid excessive removals or interferences. Table 5 provides the NAV ARCH recommendation to break down Plate ID 2s where necessary repairs are required and Table 6 provides the same information for Plate ID 3p. By using these recommendations, approximately 37-ft (32%) of the original plating for Plate ID 2s and approximately 63-ft (41%) of the original plating for Repair

ID 3p1 would be retained. Figure 11 and Figure 12 provide updated sketches of the differing repairs recommended by NAV ARCH. The repairs necessary for the other Plate ID’s can be taken from the sketches originally provided by Gladd Solutions. NAV ARCH comments on these sketches are illustrated in Figure 2 through Figure 10.

In most cases, the best option is to crop out and renew plating. However, there are a few areas where it may be easier and cheaper to clad weld. Alternate renewal plans for Repair ID’s 3s1 and

4p1 that reduce the amount of plate renewed by clad welding small areas of corrosion are presented in Figure 2 and Figure 7, respectively. Clad welding is also a possible repair option for

Repair ID 6s1 in lieu of replacing the current plate insert. In addition, it is recommended that various small pits outside of the recommended renewal areas be clad welded for Plate ID’s 1p, 7p, and TRp. However, if these areas are inaccessible, require a significant amount of clad welding (more than a 2-inch diameter hole), or require the removal of interferences, removing the damaged plating and installing a local plate insert may be the best option for repair.

Repair ID’s 4p1 and 5s1 include half-inch thick insert plates. These inserts should not be removed when the surrounding thinner plating is renewed, as the inserts have not significantly corroded.

In two locations, it is recommended that warning areas are renewed as part of renewals occurring on adjacent plates. For Plate ID 4s, it is recommended that the forward section be renewed to consolidate the renewal of Repair ID’s 3s2, 5s1, and 6s1. This recommended renewal is illustrated in Figure 4. For Plate ID 8p, it is recommended that the warning area above the cooler at the aft end of the plate (aft of frame 20) be included in Repair ID 7p1 as a proactive measure to reduce the probability of future damage. This recommended insert is shown in Figure 8 and

Figure 9.

The ½” thick plate insert surrounding the spudwell has several individual locations with deep pitting. These pits, shown in Figure 3, should be repaired by clad weld or the plate should be removed and a new ½” insert should be installed in its place.

When renewing large sections of plates, existing seams or butts should be followed whenever possible.

Appendix A provides the typical requirements for cutting patches in shell plating as well as some basic criteria for drain holes in structural members. Procedures on how to repair holes in plating via clad welding are also included.

Table 3 – NAV ARCH Opinion for Starboard Side

STARBOARD SIDE

Plate

ID

Repair

ID

NAV

ARCH

Opinion

Defect

Type

Defect

Cause Comment(s)

1s 1s1

CONCUR,

WITH

COMMENT

Interior

Corrosion

Interior

Pockets

- Recommend renewing plate in sections due to presence of interferences/structure

(cooler, transducer, etc.) and important machinery/equipment above

- Relocate or modify block as required

2s 2s1

DO NOT

CONCUR

Interior

Corrosion

Interior

Pockets

- See Table 5 for NAV ARCH recommendation

3s 3s1

CONCUR,

WITH

COMMENT

Interior

Corrosion

Interior

Pockets

- Relocate or modify blocks as required

- See Figure 2 for alternate renewal plan that minimizes required block relocation

3s2 CONCUR Interior

Corrosion

Interior

Pockets

4s 4s1

CONCUR,

WITH

COMMENT

Interior

Corrosion

Interior

Pockets

- Forward section may be included with repairs 3s2, 5s1, and 6s1 to consolidate repairs (see Figure 4)

- Relocate or modify block as required

- Clad weld to repair ½” plate insert surrounding spudwell or renew insert (see

Figure 3)

5s 5s1

CONCUR,

WITH

COMMENT

Interior

Corrosion

Interior

Pockets

- Do not remove ½” insert aft of FR 5 at

CL (see Figure 5)

- Relocate or modify block as required

6s 6s1

CONCUR,

WITH

COMMENT

Interior

Corrosion

Interior

Pockets

- Relocate or modify block as required

7s 7s1 CONCUR Interior

Corrosion

Interior

Pockets

TR TRs1 CONCUR Interior

Corrosion

Table 4 – NAV ARCH Opinion for Port Side

PORT SIDE

Plate

ID

Repair

ID

NAV

ARCH

Opinion

Defect

Type

Defect

Cause Comment(s)

1p 1p1 CONCUR Interior

Corrosion

1p2

WITH

COMMENT

Interior

Corrosion

Interior

Pockets

- Clad weld pit outboard of cooler at FR

21 (see Figure 6)

- Relocate or modify block as required

2p 2p1

CONCUR,

WITH

COMMENT

Interior

Corrosion

Interior

Pockets

- Recommend renewing plate in sections due to presence of interferences/structure

(rudder, shaft, struts, etc.) and important machinery/equipment above

3p 3p1

DO NOT

CONCUR

Interior

Corrosion

Interior

Pockets

- See Table 6 for NAV ARCH recommendation

4p 4p1

CONCUR,

WITH

COMMENT

Interior

Corrosion

Interior

Pockets

- ½” plate insert surrounding spudwell does not need to be replaced (see Figure

7)

- Relocate or modify block as required

- Alternate renewal recommendation to reduce amount of plate removed provided

(see Figure 7)

6p 6p1

CONCUR,

WITH

COMMENT

Exterior

Grind

Divot

- Clad weld if possible

7p 7p1

CONCUR,

WITH

COMMENT

Interior

Corrosion

Interior

Pockets

- Extend cut above cooler opening forward to FR 20 to renew plating in

“warning area” on plate 8p (see Figure 8)

8p 8p1

CONCUR,

WITH

COMMENT

Interior

Corrosion

Interior

Pockets

- Clad weld pits aft of FR 18 near turn of bilge (see Figure 9)

- Clad weld pit at FR 16 near WL

8p2 CONCUR Interior

Corrosion

TR TRp1

WITH

COMMENT

Interior

Corrosion

Interior

Pockets

- Clad weld pits in caution area on CL at

WL (see Figure 10)

Table 5 – NAV ARCH Recommendation for Starboard Side Plate ID 2s

STBD SIDE

Plate

ID

Repair

ID

Defect

Type

Defect

Cause Comment(s)

2s* 2s1 Interior

Corrosion

Interior

Pockets

- Recommend renewing plate in sections due to presence of interferences/structure

(rudder, shaft, struts, etc.) and important machinery/equipment above

2s2

Corrosion

Notes:

* See Figure 11 for Plate ID 2s

Table 6 – NAV ARCH Recommendation for Port Side Plate ID 3p

PORT SIDE

Plate

ID

Repair

ID

Defect

Type

Defect

Cause Comment(s)

3p* Misc Interior

Corrosion

Interior

- Clad weld pits at FR 19 and FR 20

3p1

Corrosion

Interior

Pockets

- Renew plating from just forward of FR

11 to just aft FR 14 for entire width of plate

- Relocate or modify block as required

3p2 Interior

Corrosion

Interior

Pockets

- Renew plating around block (just aft FR

14 to just aft FR 17, just inboard of longitudinal 6 ft off CL to outboard edge of plate)

- Relocate or modify block as required

Notes:

* See Figure 12 for Plate ID 3p

Figure 2 – Alternate Renewal Plan, Plate ID 3s (red shapes highlight NAV ARCH additions)

Figure 3 – Starboard Spudwell ½” Plate Insert (adjusted scale on Plate ID 4s, red shapes highlight NAV ARCH additions)

Figure 4 – Intersection of Plate ID’s 3s, 4s, 5s, and 6s (red shapes highlight NAV ARCH additions)

Figure 5 – Plate ID 5s (red shapes highlight NAV ARCH additions)

Figure 6 – Plate ID 1p (red shapes highlight NAV ARCH additions)

Figure 7 – Alternate Renewal Plan, Plate ID 4p (red shapes highlight NAV ARCH additions)

Figure 8 – Intersection of Plate ID’s 7p and 8p (red shapes highlight NAV ARCH additions)

Figure 9 – Plate ID 8p (red shapes highlight NAV ARCH additions)

Figure 10 – Plate ID TRp (red shapes highlight NAV ARCH additions)

Figure 11 – Plate ID 2s (red shapes highlight NAV ARCH additions)

Figure 12 – Plate ID 3p (red shapes highlight NAV ARCH additions)

Appendix A: Repair Requirements

In accordance with paragraph 3.5.3 of SFLC Technical Standard 100 “Hull Structures”, when material deterioration due to corrosion is limited to areas less than 2-ft , repairs may be accomplished by welding in lieu of replacement. In addition, scattered pits with depths at least

25%, but not greater than 45%, of the original thickness may be repaired by shielded metal arc welding (SMAW). See Figure 13 for procedures to repair pitting corrosion by welding.

Figure 13 – Procedures for Welding of Pitting Corrosion (Taken from IACS Rec. 47)

Figure 14 through Figure 18 provide the typical patch requirements as taken from MIL-STD-

1689A.

Figure 14 – Patch Requirements from MIL-STD-1689A

Figure 15 – Inserts, Patches and Small Access Plate Requirements (taken from MIL-STD-1689A)

Figure 16 – Relationship of Inserts, Patche s and Small Access Plates to Existing Butt Welds (taken from MIL-STD-

1689A)

Figure 17 – Typical Drain Hole (taken from MIL-STD-1689A)

Figure 18 – Alternative Drain Holes (taken from MIL-STD-1689A)