coating conditions in water ballast tank, void space and cargo oil tank … · 2018-01-18 ·...

Shipbuilding Technology ISST 2007, Osaka, 2007

© 2007: JASNAOE-RINA 51

COATING CONDITIONS IN WATER BALLAST TANK, VOID SPACE AND CARGO OIL TANK OF AGED SHIPS AND REQUIRED PERFORMANCE STANDARD OF PROTECTIVE COATINGS FOR NEW SHIPS Takanobu Murakami, Shin Kurushima Dockyard Co., Ltd. Takayuki Sasaki, IHI Marine United Inc. Masahiro Kuwajima, Mitsui Engineering & Shipbuilding Co., Ltd. Masanobu Koori, Mitsubishi Heavy Industries, Ltd.

SUMMARY PSPC (Performance Standard for Protective Coatings) for water ballast tanks and double hull spaces of bulk carrier was adopted at MSC82 as resolution MSC.215(82) in last December, and protective coatings for void spaces was discussed at DE50 in March this year. Furthermore, protective coatings for cargo oil tanks have been discussed at JWG (Joint Working Group) of IACS, and the proposal of JWG will be submitted to IMO. We, members of SAJ (the Shipbuilders’ Association of Japan) participated in all discussions and introduced the actual situation of ship’s coating through the results of several investigations. In this paper, we would introduce the coating conditions of the ships aged more than 10 years in water ballast tanks, void spaces and cargo oil tanks with some photos, and express our considerations regarding the relation between tank coating at new building stage and the coating conditions of aged ships. 1. INTRODUCTION

In these couple of years, coating standard including surface preparation and coating application has been discussed for the purpose of enhancing the safety of ships. It has been expanding from double hull space of bulk carrier to water ballast tanks and void spaces of all kinds of ships, and further to cargo tanks of oil tankers.

Discussion in IMO on the coating standard for water ballast tanks was started based on TSCF15 (15 years specification issued by Tanker Structure Co-operative Forum). During the discussions at IMO meetings and in corresponding group, we have repeatedly express our view on the effectiveness and practicability of the standard. With regard to the expansion of the standard to void spaces and cargo oil tanks, NMRI (National Maritime Research Institute) and SAJ carried out the inspection of ships to clarify the actual coating conditions of aged ships in order to know the necessary specification and application of coating for 15 years target life. In this connection, we would show our considerations on the necessary standard for each spaces of ship, i.e. ballast water tanks, void spaces and cargo oil tanks. 2. NEW REGULATIONS FOR PAINTING 2.1 WATER BALLAST TANKS As for water ballast tanks, new regulation was adopted as resolution MSC.215(82) in last December.

The summary of the resolution is as follows; a) The resolution shall apply to ships of not less than 500

gross tonnage: for which the building contract is placed on or after 1 July 2008; or in the absence of a building contract, the keels of which are laid or which are at a similar stage of construction on or after 1 January 2009; or the delivery of which is on or 1 July 2012.

b) The resolution shall apply to all dedicated seawater ballast tanks arranged in ships and double side skin spaces arranged in bulk carriers of 150 m in length and upwards.

c) CTF (Coating Technical File) shall be kept on board. d) Inspection work shall be done by qualified inspectors

certified to FROSIO LevelⅢ or NACE Level 2 or equivalent.

e) Epoxy type multi-coat system with stripe coats shall be applied.

f) Coating system shall pass pre-qualification test. g) NDFT (nominal dry film thickness) of 320μm with

90/10 rule shall be applied. h) Free edges shall be treated to rounded radius of 2 mm,

or by three pass grinding or equivalent process. i) Damaged shop primer and welds shall be blasted to Sa

21/2. j) After erection, butts shall be treated to St 3 or better or

Sa 2 where practicable. Small damages up to 2% of total area shall be treated to St 3, and contiguous damages over 25 m2 or over 2% of the total area of the tank shall be treated to Sa 21/2 respectively.

k) Requirements of surface cleanliness such as oil contamination, dust, water soluble salts are prescribed



Guideline for implementation of MSC.215(82) is being discussed in IACS/JWG for practical and consistent application. 2.2 VOID SPACES PSPC for void space was discussed at DE50 in March this year. As the output of DE50, the draft resolution will be submitted to MSC83. While the meeting in DE50, we proposed the practical standard based on the inspection results for void spaces of aged ships. The summary of the draft resolution is as follows; a) The draft resolution shall apply to bulk carriers and

oil tankers as recommendation basis until the SOLAS amendments to make it mandatory will be adopted.

b) Definition of void spaces is clarified. c) Epoxy based paint and NDFT of 200μm with 90/10

rule shall be applied. d) Free Edges shall be treated by one pass grinding or

equivalent. e) Damaged shop primer shall be treated to Sa 2 or St 3. f) After erection, butts shall be treated to St 3 or better

or Sa 2 where practicable. g) One stripe coat shall be applied to thermally cut free

edges and small holes only.

h) Requirements for dust quantity and soluble salts limit are relaxed compared with those for water ballast tanks.

2.3 CARGO OIL TANKS European countries and shipowners’ and oil companies’ associations submitted their proposal of new SOLAS regulation to MSC82 which make PSPC for cargo oil tanks mandatory. In this connection, Japan submitted the proposal of using corrosion resistance steel in the cargo oil tanks as an alternative. DE50 instructed the correspondence group to develop the draft new SOLAS regulation regarding cargo oil tank protection for the discussion at DE51. The development of PSPC for cargo oil tanks will be further considered at DE51. 3. REPORT ON THE COATING CONDITION OF ACTUAL SHIPS 3.1 INSPECTED SHIPS In order to investigate appropriate coating standard, three (3) aged ships were inspected. Outline of the inspected ships are shown on Table 1.

Table 1. Inspected ships Ship A Ship B Ship C Type of Ship Tanker

(VLCC) Tanker

(VLCC) Bulk Carrier

(PANAMAX) Age of Ship 15 years old 12 years old 11 years old Shipyard Japanese Japanese Japanese Operator Japanese company Japanese company Japanese company Major Sea Route East Asia – Middle East East Asia – Middle East East Asia – Oceania



3.2 WATER BALLAST TANKS 3.2.1 COATING SPECIFICATIONS IN WATER

BALLAST TANKS

Coating specifications in water ballast tanks of inspected three (3) ships are shown on Table 2.

Table 2. Coating Specifications in Water Ballast Tanks Ship A Ship B Ship C Type of Paint Tar Epoxy paint Tar Epoxy Paint Tar Epoxy paint Dry Film Thickness 200μm

(1spray) 200μm (1spray)

220μm (1spray)

Stripe coat Not applied Holes and narrow spaces Not applied Primary surface preparation Sa2.5 (shot blast)

IZP Sa2.5 (shot blast)


IZP Free edge Removed burrs 1 pass grinding 1 pass grinding Steel

condition Weld bead No treatment No treatment No treatment Surface treatment St 3 St 3 Sa2.5 (Partially St3) 3.2.2 OVERVIEW IN THE WATER BALLAST

TANKS Ship A) Photo-A-W-1

Photo-A-W-2

Photo-A-W-3

These photos show deck head areas under upper deck, and these areas are considered to be in severest condition for corrosion. There were some areas of which condition was worse than of these photos and deck plates of such areas had cut off for renewal work.



Ship B) Photo B-W-1

Photo B-W-2

Photo-B-W-3

These photos show middle areas in height. Some rust was initiated from edges, welds, small fittings and small holes.

Deck head areas of this ship had already recoated at previous docking and kept good condition. Ship C) Photo C-W-1

Photo C-W-2

These photos show middle areas in height. Rust was initiated from edges and welds and spread to surrounding. 3.3 VOID SPACES 3.3.1 COATING SPECIFICATIONS IN VOID

SPACES Coating specifications in void spaces of inspected three (3) ships are shown on Table 3.



Table 3. Coating Specifications in Void spaces Ship A Ship B Ship C Coating type Alkyd based Tar epoxy Surface-tolerant epoxy Dry film thickness 70μm

(2 spray) 125μm (1spray)

100μm (1spray)

Stripe coat Not applied Not applied Not applied Primary surface treatment Sa 2.5 (Shot blast)

IZP Sa 2.5 (Shot blast)

IZP Sa 2.5 (Shot blast)

IZP Free edge No treatment No treatment No treatment Weld bead No treatment No treatment No treatment

Steel condition

Weld spatter Loose spatter to be removed by scraper

Loose spatter to be removed by scraper

Loose spatter to be removed by scraper

Grade St 2 (By disk sander and/or

power brush)

Between St 2 and St 3 (By disk sander and/or

power brush)

Loose rust to be brushed off.

Surface treatment

Treated area Damaged shop primer, welds and rusted areas

Damaged shop primer, welds and rusted areas

Damaged shop primer, welds and rusted areas

Water soluble salt Removed to the extent invisible to the naked eye. Oil contamination Removed. The traces may be visible. 3.3.2 OVERVIEW IN THE VOID SPACES Ship A) Photo-A-V-1

Photo-A-V-2

Photo-A-V-3

Almost all areas were in quite good condition. Slight rust was found on the welds in Photo-A-V-2 and at the edge of manhole in Photo-A-V-3, but did not spread further.



Ship B) Photo-B-V-1

Photo-B-V-2

Photo-B-V-3

All areas including edges and welds were in perfect condition. Photo-B-V-3 shows a part where main coating was not applied and shop-primer was exposed. Slight rust was found on the shop primer damaged during construction, but good condition was kept where shop-primer was intact even without main coatings.

Ship C) Photo C-V-1

Photo-C-V-2

Photo-C-V-3

Almost all areas were in quite good condition. There were small mechanical damages at the edge of opening in Photo-C-V-2, but the rust did not spread further. Some rusted areas caused by mechanical damages were appeared on the floor in Photo-C-V-3, but the rust also did not spread further.



3.4 CARGO TANKS 3.4.1 COATING SPECIFICATIONS IN CARGO

TANKS

Coating specifications in cargo oil tank (slop tank) of inspected two (2) ships are shown on Table 4. Slop tanks were inspected because ordinary cargo tanks were not coated.

Table 4. Coating Specification in Cargo tanks Ship A Ship B Ship C Type of Paint Tar Epoxy paint Tar Epoxy Paint - Dry Film Thickness 200μm

(1spary) 200μm (1spray)

-

Stripe coat Not applied Holes and narrow spaces - Primary surface preparation Sa2.5 (shot blast)


IZP -

Free edge Removed burrs 1 pass grinding - Steel condition Weld bead No treatment No treatment - Surface treatment St 3 St 3 - 3.4.2 OVERVIEW IN THE CARGO TANKS Ship A) Photo A-C-1

Photo A-C-2

Photo-A-C-3

These photos show rusted areas of deck head under upper deck.A lot of rust was found but the condition was much better than in water ballast tanks of this ship, and plate thickness loss was quite small. Ship B) Photo B-C-1



Photo B-C-2

Photo B-C-3

Overall coating was still in good condition. Coating damages were observed mainly on upper deck plate and on fillet welds of upper deck longitudinal.

4. CONCLUSION From the results of the inspection, it is considered as follows; 4.1.1 WATER BALLAST TANKS ・ Deck head area under upper deck seems to be in quite

severe environmental condition, while other regions are comparatively in mild condition.

・ In general, rust is initiated from edges and welds, and good treatment on edges and welds will prevent rust initiating.

・ Apparently, coating specifications of the ships for water ballast tanks at new building don’t satisfy 15 years coating life.

4.1.2 VOID SPACES ・ Although all inspected ships had been in use for 10 to

15 years, coatings in void spaces were still almost perfect condition.

・ Very small local corrosions were observed in the areas prone to be damaged mechanically. (estimated to be smaller than 0.1% of the total area)

・ Coating specifications of the ships in the void spaces at new building are sufficient for 15 years coating life.

4.1.3 CARGO TANKS ・ Coatings in the cargo tanks were comparatively in

better condition than those in water ballast tanks. ・ Though some corrosions were observed in deck head

areas, plate thickness loss was quite small, while recoating or plate renewal was necessary for some of deck head areas in water ballast tanks of the same ship.

・ Therefore, PSPC for cargo tanks could be relaxed compared with those required by PSPC for water ballast tanks.

coating conditions in water ballast tank, void space and cargo oil tank … · 2018-01-18 ·...

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