Annex 4 - Requirements for extent of thickness measurements at areas of substantial corrosion of double hull oil tankers
Clasification Society 2024 - Version 9.40
Statutory Documents - IMO Publications and Documents - Resolutions - Assembly - IMO Resolution A.744(18) – Guidelines on the Enhanced Programme of Inspections During Surveys for Bulk Carriers and Oil Tankers – (Adopted on 4 November 1993) - Annex B - Guidelines on the Enhanced Programme of Inspection During Surveys for Oil Tankers - Part A - Guidelines on the Enhanced Programme of Inspections During Surveys of Double Hull Oil Tankers - Annex 4 - Requirements for extent of thickness measurements at areas of substantial corrosion of double hull oil tankers

Annex 4 - Requirements for extent of thickness measurements at areas of substantial corrosion of double hull oil tankers

Parent topic: Part A - Guidelines on the Enhanced Programme of Inspections During Surveys of Double Hull Oil Tankers

Sheet 1 - Requirements for Extent of Thickness Measurements at Areas of Substantial Corrosion Renewal Survey of Double Hull Oil Tankers

BOTTOM, INNER BOTTOM AND HOPPER STRUCTURE
Structural member Extent of measurement Pattern of measurement
Bottom, inner bottom and hopper structure plating Minimum of three bays across double bottom tank, including aft bay Measurements around and under all suction bell mouths 5-point pattern for each panel between longitudinals and floors
Bottom, inner bottom and hopper structure longitudinals Minimum of three longitudinals in each bay where bottom plating measured Three measurements in line across flange and three measurements on vertical web
Bottom girders, including the watertight ones At fore and aft watertight floors and in centre of tanks Vertical line of single measurements on girder plating with one measurement between each panel stiffener, or a minimum of three measurements
Bottom floors, including the watertight ones Three floors in bays where bottom plating measured, with measurements at both ends and middle 5-point pattern over two square metre area
Hopper structure web frame ring Three floors in bays where bottom plating measured 5-point pattern over one square metre of plating. Single measurements on flange
Hopper structure transverse watertight bulkhead or swash bulkhead
  • lower 1/3 of bulkhead
 5-point pattern over one square metre of plating
  • upper 2/3 of bulkhead
 5-point pattern over two square metre of plating
  • stiffeners (minimum of three)
 For web, 5-point pattern over span (two measurements across web at each end and one at centre of span). For flange, single measurements at each end and centre of span
Panel stiffening Where applicable Single measurements

Sheet 2 - Requirements for Extent of Thickness Measurements at Areas of Substantial Corrosion Renewal Survey of Double Hull Oil Tankers within the Cargo Area Length

DECK STRUCTURE
Structural member Extent of measurement Pattern of measurement
Deck plating Two transverse bands across tank Minimum of three measurements per plate per band
Deck longitudinals Every third longitudinal in each of two bands with a minimum of one longitudinal Three measurements in line vertically on webs and two measurements on flange (if fitted)
Deck girders and brackets (usually in cargo tanks only) At fore and aft transverse bulkhead, bracket toes and in centre of tanks Vertical line of single measurements on web plating with one measurement between each panel stiffener, or a minimum of three measurements.

Two measurements across flange. 5-point pattern on girder/bulkhead brackets

Deck transverse webs Minimum of two webs, with measurements at both ends and middle of span 5-point pattern over one square metre area.

Single measurements on flange

Vertical web and transverse bulkhead in wing ballast tank (two metres from deck) Minimum of two webs, and both transverse bulkheads 5-point pattern over one square metre area
Panel stiffening Where applicable Single measurements

Sheet 3 - Requirements for Extent of Thickness Measurements at Areas of Substantial Corrosion Renewal Survey of Double Hull Oil Tankers within The Cargo Area Length

STRUCTURE IN WING BALLAST TANKS
Structural member Extent of measurement Pattern of measurement
Side shell and longitudinal bulkhead plating:   Single measurement
  • upper strake and strakes in way of horizontal girders
Plating between each pair of longitudinals in a minimum of three bays (along the tank)  
  • all other strakes
 Plating between every third pair of longitudinals in same three bays Single measurement
Side shell and longitudinal bulkhead longitudinals on: Each longitudinal in same three bays
Every third longitudinal in same three bays 		3 measurements across web and 1 measurement on flange
3 measurements across web and 1 measurement on flange
  • upper strake
  • all other strakes
Longitudinals - brackets Minimum of three at top, middle and bottom of tank in same three bays 5-point pattern over area of bracket
Vertical web and transverse bulkheads (excluding deckhead area): Minimum of two webs and both transverse bulkheads
Minimum of two webs and both transverse bulkheads 		5-point pattern over approx. two square metre area
two measurements between each pair of vertical stiffeners
  • strakes in way of horizontal girders
  • other strakes
Horizontal girders Plating on each girder in a minimum of three bays Two measurements between each pair of longitudinal girder stiffeners
Panel stiffening Where applicable Single measurements

Sheet 4 - Requirements for Extent of Thickness Measurements at Areas of Substantial Corrosion Renewal Survey of Double Hull Oil Tankers within the Cargo Area Length

LONGITUDINAL BULKHEADS IN CARGO TANKS
Structural member Extent of measurement Pattern of measurement
Deckhead and bottom strakes, and strakes in way of the horizontal stringers of transverse bulkheads Plating between each pair of longitudinals in a minimum of three bays Single measurement
All other strakes Plating between every third pair of longitudinals in same three bays Single measurement
Longitudinals on deckhead and bottom strakes Each longitudinal in same three bays Three measurements across web and one measurement on flange
All other longitudinals Every third longitudinal in same three bays Three measurements across web and one measurement on flange
Longitudinals - brackets Minimum of three at top, middle and bottom of tank in same three bays 5-point pattern over area of bracket
Web frames and cross ties Three webs with minimum of three locations on each web, including in way of cross tie connections 5-point pattern over approximately two square metre area of webs, plus single measurements on flanges of web frame and cross ties
Lower end brackets (opposite side of web frame) Minimum of three brackets 5-point pattern over approximately two square metre area of brackets, plus single measurements on bracket flanges

Sheet 5 - Requirements for Extent of Thickness Measurements at Areas of Substantial Corrosion Renewal Survey of Double Hull Oil Tankers within the Cargo Area Length

TRANSVERSE WATERTIGHT AND SWASH BULKHEADS IN CARGO TANKS
Structural member Extent of measurement Pattern of measurement
Upper and lower stool, where fitted Transverse band within 25 mm of welded connection to inner bottom/deck plating

Transverse band within 25 mm of welded connection to shelf plate

5-point pattern between stiffeners over one metre length
Deckhead and bottom strakes, and strakes in way of horizontal stringers Plating between pair of stiffeners at three locations:

approximately 1/4, 1/2 and 3/4 width of tank

5-point pattern between stiffeners over one metre length
All other strakes Plating between pair of stiffeners at middle location Single measurement
Strakes in corrugated bulkheads Plating for each change of scantling at centre of panel and at flange of fabricated connection 5-point pattern over about one square metre of plating
Stiffeners Minimum of three typical stiffeners For web, 5-point pattern over span between bracket connections (two measurements across web at each bracket connection and one at centre of span).


For flange, single measurements at each bracket toe and at centre of span

Brackets Minimum of three at top, middle and bottom of tank 5-point pattern over area of bracket
Horizontal stringers All stringers with measurements at both ends and middle 5-point pattern over one square metre area, plus single measurements near bracket toes and on flanges
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