Marine Structural Failures and Ship Design Assessment

Marine Structural Failures and Ship Design Assessment
Evaluating prescribed coatings for ship design and hull integrity management Allan T Larsen. MIMarEST, MRINA Head of Section , Damage Repair and Offshore (DNS) Bureau Veritas - Paris

Introduction by Allan Larsen

Introduction The title of this presentation is quite long and detailed so what will be included ? Coatings in the modern era of shipping. Latest rules and regulations to deal with the causes of corrosion. The challenge of delivering new coatings in today’s shipping climate. Interface of owners, charterers and suppliers on developing products. Coatings in Sea Water Ballast Tanks . Crude oil tanker corrosion.

Coatings in the ‘Modern Era’
Introduction by Allan Larsen Coatings in the ‘Modern Era’

The “modern era” is a demanding era.
What is ‘the modern era’? Ships remaining in service longer than previously anticipated. Ships operators have a need to reduce operational downtime. Quick port turn around times are common place. New rules and regulations require to be complied with. Increased number of surveys required . Increased period between dry dockings ( up to 7.5years ). Class and Statutory bodies requiring longer periods of time onboard. Strong shipping competition in a difficult economic climate. Ships staff performing onboard inspections. Ships operating with smaller crew numbers onboard (often at minimum safe manning levels). The “modern era” is a demanding era.

Coatings in the modern era.
The marine industry has seen many developments over the years: Engines have become more economical and cleaner to run. Navigation has become simpler with GPS and ECDIS etc Safety has improved with GMDSS, VDR, AIS and LRIT. and coatings along with the means of preparation and application have developed and improved . Something to consider : The ships coating for external hull, internal hull, tanks, voids, cargo holds/tanks etc. is the largest single component onboard most vessels.

Coatings are of course critical in ensuring the protection of steelwork from corrosion caused by the aggressive climates in which ships operate. Failing to protect the steelwork can and does lead to loss of strength in the vessels structure and in severe cases loss of water and weather tightness also. (and for the commercially inclined – great cost to rectify). The coatings must therefore be correct for the application and correctly applied in order to ensure protection of the vessel. It is for this reason that regulations have been developed with regards to ships coatings. With this ‘modern era’ in mind it is clear that the coatings being applied must be carefully selected to comply with rules and regulations but also which can be successfully applied in short time periods, easily repaired with the vessel in service and remain effective for long periods of time.

Today’s coatings are best understood by specialist companies as this ‘technology’ is complicated and advanced. It is not, as it may appear to the lay-man, simply “painting” the ship. Many coating types are now available on the market at varying costs and with varying effectiveness when applied. Until recently the choice of coating and it’s condition were of no interest to Classification Societies or Statutory Bodies. It was however of interest to Owners and Vetting Agents. In the modern era the coating is subjected to inspection at Class Survey,Statutory Survey and where used Condition Assessment Surveys (CAP). And in the modern era the demand for coatings to be more effective and to remain so for many years is high. (up to seven years for external hull coatings and fifteen years in ballast tanks, voids etc.). Coatings are therefore now a major consideration for the vessel.

Regulations

PSPC regulations. Background
In 1991 the IMO expressed concerns over the continuing loss of ships carrying bulk cargoes. The MSC were therefore requested to develop requirements for the “design, construction, operation, maintenance and survey of bulk carriers.” In 1997 the contracting governments of SOLAS adopted SOLAS Ch XII on additional safety measures for bulk carriers . This entered into force on 01 July In May MSC 75 approved a list of recommendations following a number of Formal Safety Assessments. This included “Improved coating: Controls and/or performance standards for protective coatings, in relation to compatibility with cargoes.” In December 2002 MSC 76 made the coating of dedicated Sea Water Ballast Tanks mandatory for Oil Tankers and Bulk Carriers. In 2006 MSC 79 adopted revisions of SOLAS XII which entered into force on 01 July 2006. Following adoption at MSC 82 in December 2006 the performance standards were set to enter into force for ships >500gt for which contracts were placed on or after 01 July 2008.

PSPC regulations. Background
Many organisations assisted in the development of the regulations to be applied including : BIMCO IACS Intercargo Intertanko Following debate the sub committee made the following stipulations: The coating performance standards should apply to all ballast and void spaces on all ship types . Target coating life should be 15 years. A Coating Technical File should be included as a requirement. Verification and Inspection aspects and requirements for steel primers needed to be clarified.

PSPC Date line. Contract for construction ≥ 8.12.2006 NR 530:
24/03/2006 PSPC Date line. 1st July 2008 PSPC enter into force Dec. 2006 Adoption of IMO PSPC June 2008 IACS PR34: IACS PR 34 (Rev. 3) CSR WBT of DH Oil Tankers ≥ 150 M WBT of Bulk Carriers ≥ 90 M DSVS of Bulk Carriers ≥ 150 M Contract for construction ≥ NR 530: Class Notation CPS (WBT) CLASSIFICATION RULES IMO Res. MSC.215 (82) UI SC 223 WBT All Ships ≥ 500 G.T. DSSS Bulk Carriers ≥ 150 M Building contract ≥ Keel laying or at similar stage of construction ≥ Delivery date ≥ IMO Res. MSC.215 (82) applies STATUTORY REGULATIONS MSC.216(82) BV references are: Development Department

PSPC – SOLAS SOLAS (2009) Part A-1 Regulation 3.2 concerns :
Protective coatings of dedicated seawater ballast tanks in all types of ships and double skin spaces of bulk carriers. Part 2 of the above regulation reads as follows : All dedicated sea water ballast tanks arranged in ships and double-side skin spaces arranged in bulk carriers of 150m in length and upwards shall be coated during construction in accordance with the performance standard for protective coatings for dedicated seawater ballast tanks in all types of ships and double-sided skin spaces of bulk carriers, adopted by the Maritime Safety Committee by resolution MSC.215(82), as may be amended by the Organisation, provided that such amendments are adopted, brought into force and take effect in accordance with the provisions of article VIII of the present Convention concerning the amendment procedures applicable to the Annex other than Chapter I.

PSPC – Resolution MSC.215(82)
The resolution is long and complex but in summary covers : Section 1 Purpose Section 2 Definitions Section 3 General Principles Section 4 Coating Standard Section 5 Coating System Approval Section 6 Coating Inspection Requirements Section 7 Verification Requirements Section 8 Alternative Systems

The resolution as adopted on 08 December 2008 is entitled: Annex 1 Resolution MSC.215(82) Performance standard for protective coatings for dedicated seawater ballast tanks in all types of ships and double-side skin spaces of bulk carriers .

Administration / Class Coating Inspector Shipyard /
24/03/2006 PSPC – Resolution MSC.215(82) Verification of compliance to PSPC / PR34 Is responsible to implement step by step the compliance of Coatings to PSPC / PR34 Are responsible to produce a Coating complying to PSPC / PR34 Administration / Class Coating Inspector Shipyard / Coating Manufacturer PSPC General Principles Development Department

The resolution is supported by guidelines including : Guidelines for the Information to be included in a Ship Construction file Ref MSC.1/Circ.1343 dated 02 June 2010. Guidelines for maintenance and repair of protective coatings Ref MSC.1/Circ.1330 dated 11 June 2009. There is also a very useful ‘overview’ of the PSPC matter entitled ‘Development of Mandatory IMO Performance Standards for Protective Coatings on Ships’. This document was produced by Heike Hoppe – Senior Technical Officer, Maritime Safety Division at IMO.

Resolution MSC.215(82) – what are the requirements?
Application of coatings : The shipowner , shipyard and coating specialists shall decide and agree upon a process for inspection of surface preparation and coating process. The process for inspection of surface preparation and coating process shall be submitted to the administration (or RO) for review. The inspections concerned shall be recorded in a Coating Technical File.

Resolution MSC.215(82) – NC Technical File
A Coating Technical File shall be produced and will contain details on at least the following items : Part One Copy of statement of compliance or type approval certificate. Part Two – Technical Data Sheet Product name and identification mark / number. Materials,components and composition of the coating system, colours. Minimum and Maximum dry film thickness. Application methods, tools and/or machines: Condition of surface to be coated (de-rusting grade, cleanliness, profile, etc.) Environmental limitations (temperature and humidity)

Part 3 Shipyard work records of coating application, Applied actual space and area (m2) of each compartment. Applied coating system. Time of coating, thickness, number of layers etc. Ambient condition during coating Method of surface preparation. Part 4 Procedures for inspection and repair of coating system during ship construction.

Part 5 Coating log issued by the coating inspector. Statement from supplier that coating was applied in accordance with specifications. Details of deviations from specification. Part 6 Shipyards verified inspection report . Completion date of inspection Result of inspection Remarks Inspectors signature.

Resolution MSC.215(82) – Technical File
Part 7 Procedures for in-service maintenance and repair of coating system. In-service maintenance of coating systems shall also be included in the Coating Technical File. (reference should be made to the relevant guidelines.). Where full recoating is performed the same information as detailed for New Construction shall be entered into the Coating Technical File.

Resolution MSC.215(82) – Coating Standard
Coatings should remain in ‘good’ condition for a period of 15 years . Note: the definition from IMO Resolution A.744(18) (Guidelines on the Enhanced Programme of Inspections during Surveys of Bulk Carriers and Oil Tankers) for “good” is as follows : “ condition with only minor spot rusting”.

Resolution MSC.215(82) – Coating Standard
The resolution relates to the ships steel structure however it is “recommended” within the document that the coating of independent items within the spaces such as hand rails , ladders etc are coated to the same standard as the structure.

Resolution MSC.215(82) – Design of Coating System
Selection of the coating system This shall be considered by all parties with knowledge of the service conditions and planned maintenance aspects of the vessel. Coating manufacturers shall have products with documented performance records and technical data sheets. Coatings should be suitable for the area of the vessel to which they are applied (ie where temperature variations etc exist).

Coating type Coatings should be Epoxy based systems or Other coating types with proven performance to meet the requirements. It is “recommended” that multi coat systems each coating is of a contrasting colour to the previous. The final top coat shall be of a light colour.

Coating pre qualification test The resolution provides in Appendix 1 details for ‘test on simulated ballast tank conditions’ and acceptance criteria for coatings subjected to this. Epoxy type coatings applied prior to the date of entry of the resolution which have remained in ‘good’ condition for a period of five years or more can be condisdered to comply with the standard. All other coating types must be tested as per the Resolution Appendix 1 requirments.

Resolution MSC.215(82) - Design of the Coating System
24/03/2006 Resolution MSC.215(82) - Design of the Coating System Coating pre-qualification tests (UI SC 223/ IACS PR 34 / NR 530) Development Department

Job Specification The Resolution specifies the following : There shall be a minimum of two stripe coats applied. The second stripe coat may be reduced in scope in way of weld seams if NDTF can be achieved – details to be included in CTF. There shall be a minimum of two spray coats applied. Stripe coats shall be applied by brush or roller. Curing times must be observed. Contaminants must be removed. Job specifications must contain dry-to-recoat times. Job specifications must contain walk-on-times.

NDFT – Nominal total dry film thickness This shall be 320 microns minimum. Manufacturer shall advise maximum NDFT. Wet film thickness has to be monitored during application.

Resolution MSC.215(82) – Primary Surface Preparation
Blasting and profile To be to SA 2.5 Shall not be performed where relative humidity is above 85% Shall not be performed where surface temperature of steel is less than 30C above the dew point. Water soluble salt limit equivalent to NaCl (ISO /2:1988) Not more than 50mg/m2 Shop primer Coating manufacturer to confirm compatibility with main system. Primer to be free Zinc Silicate based or equivalent.

Resolution MSC.215(82) – Secondary Surface Preparation
Steel condition Prepared to allow even coating distribution at NDFT. Edges of components to have rounded radius of 2mm . Surface treatment SA 2.5 Remove 70% of any shop primer which has not passed a pre-qual test. Surface treatment after erection SA 2.5 where practicable Coatings in overlaps shall be fearthered. Profile requirements Blasted to microns or as recommended by manufacturer.

Resolution MSC.215(82) – Secondary Surface Preparation
Dust Dust quantity rating “1” for dust size class ‘3’,’4’ or ‘5’. Lower dust size classes to be removed if visible without magnification. Water soluble salts limit equivalent to NaCl after preparation. Not more than 50mg/m2 of Sodium Chloride. Oil contamination There shall be no oil contamination.

Resolution MSC.215(82) – Miscellaneous
The Resolution also includes : Ventilation Adequate to allow curing and drying . Environmental conditions Coating to be applied under controlled humidity and surface conditions. Testing of coatings Destructive testing shall be avoided. Repairs Any defects in the coating shall be repaired appropriately and details of repairs shall be documented.

Coating inspections

Resolution MSC.215(82) – Coating Inspections
Coating inspections shall be performed by personnel qualified to one of the following levels. NACE Coating Inspector Level 2 FROSIO Inspector Level III Othe qualification deemed eqivalent to those above. Results from inspections shall be contained in the CTF.

Resolution MSC.215(82) – Coating Inspections
Inspections items shall include Primary surface preparation Coating thickness Block assembly Erection

Resolution MSC.215(82) – Verification requirements
The administration or RO shall perform the following checks prior to review of the Coating Technical File. Technical Data Sheet , Statement of Compliance or Type Approval Certificate comply with the standard. Coating identification is as shown on documentation. Inspectors qualifications are as required. Inspectors reports indicate compliance with the documentation.

Challenges of coating delivery
Introduction by Allan Larsen Challenges of coating delivery

Challenges of coating delivery.
The world economic climate has affected many areas of the maritime industry resulting in a need for companies and service suppliers to reconsiders earlier plans for vessels. Many ship owners with an ageing fleet were comfortable to place orders for new construction vessels at which time two distinct ship management techniques would be used . To identify future trade patterns,routes and markets. and to design and construct a suitable vessel or vessels for those trades. To simultaneously either offer existing vessels for sale or to use asset integrity management techniques to reduce maintenance costs but ensure the vessel condition remains satisfactory until delivery of replacement vessel.

Unfortunately, unforseen by most of the world, the global economy collapsed and the situation for ship owners with NC orders could not be sustained . New construction orders were cancelled and owners decided to continue to operate existing shipping. This resulted in many cases in ships undertaking repairs and maintenance which had not been planned for nor expected. In many cases repair and maintenance had in fact been programmed out of existing ships as companies expected to be disposing of these in a relatively short period as new construction tonnage entered service.

Now, in many cases the owner has an unexpected ‘challenge’ . To return existing shipping to a satisfactory condition to continue to operate. To protect the vessel against further corrosion damage for the extended life time of the vessel.

The new challenge for existing and ageing ships : Steel work repairs required (sometimes extensive). Unplanned Class and Statutory Surveys of the vessel. Removal of existing coatings (including blasting back antifouling) Preparation of new steel for coating application. Preparation of existing but corroded steel for coating application. Hydrostatic (wet) testing of tanks following repairs. All in the shortest possible operational downtime of the vessel !

Future applications

Coatings – future applications.
In order for future applied coatings to be effective it would be prudent for various parties to interface and discuss forthcoming needs and the following could be considered : The owner has an asset which he wishes to protect in the most suitable way. The charterer holds information on the requirements for carriage of cargoes such as cargo type, aggressive components of cargo, abrasivness of cargoes, frequency of carriage etc. The coating supplier has information on the suitability of various coatings for the protection of the vessel from the natural environment and the cargoes carried.

Coatings – future developments.
Technology will continue to advance and this includes Coating Technology. As discussed there are various parties who can influence these developments including Owners, Charterers and Coating Suppliers. Interfacing of these parties along with Chemical Engineers, Marine Engineers, Naval Architects and both Class and Statutory bodies will ensure the correct products are availabel to suit future requirments.

Evaluating existing coatings in ballast tanks
Introduction by Allan Larsen Evaluating existing coatings in ballast tanks

Coatings for sea water ballast tanks
There are several coating types available on the market however for acceptance by Classification Societies only tanks with hard coatings are considered to be ‘coated’. Hard coating – a coating that chemically converts during it’s curing process or a non-convertible air drying coating which may be used for maintenance purposes . It can be either inorganic or organic. (Res MSC215(82)) The following slides demonstrate how to evaluate ballast tank coatings. There are six basic descriptions for coating condition : Good Transition Good to Fair Fair Transition Fair to Poor Poor Not coated ( or coating completely depleted )

Evaluating Ballast tank coating in good condition
Resolution A.744(18) IACS Condition with only minor spot rusting. Condition with spot rusting on less than 3% of the area under consideration without visible failure of the coating. Rusting at edges or welds must be on less than 20% of edges or weld lines in the area under consideration.

Ballast tank coating. Transition Good to Fair condition

Ballast tank coating. Fair condition
Resolution A.744(18) IACS Condition with local breakdown of coating at edges of stiffeners and weld connections and / or…. Condition with breakdown of coating or rust penetration on less than 20% of the area under consideration . .. light rusting over 20% or more of areas under consideration, but less than as defined for poor. Hard rust scale must be less than 10% of the area under consideration. Rusting at edges or welds must be on less than 50% of edges or weld lines in the area under consideration.

Ballast tank coating. Fair transition to Poor condition
Transition Fair to Poor.

Ballast tank coating. Poor condition
Resolution A.744(18) IACS Condition with general breakdown of coating over 20% or more or .. Condition with breakdown of coating or rust penetration on more than 20% or … Hard scale at 10% or more, of areas under consideration. hard rust scale on more than 10% of the area under consideration or local breakdown concentrated at edges or welds on more than 50% of edges or weld lines in the area under consideration.

Coating Failure Courtesy of IACS.

Coating Condition Cracking Blistering

The consequence of poor coatings in ballast tanks
Severe structural corrosion and failure following coating breakdown inside wing ballast tanks.

The consequence of cargo interaction
Cargo inter action with coating. Five year old vessel. Cargo : Caustic Soda.

Crude oil tanker ballast tank corrosion
Introduction by Allan Larsen Crude oil tanker ballast tank corrosion

Crude oil tanker corrosion
Like all vessels Crude Oil Tankers can experience corrosion problems associated with the natural environment in which it operates . However , for these vessels there are other considerations affecting the rate of corrosion : Sulphur content of cargo. Sulphur content of Inert Gas. Frequency of tank cleaning. Medium used for tank cleaning. Heated cargo tank shared boundaries with ballast tanks. Alternate loaded and ballast condition voyages (non segregated tanks). On larger vessels fatigue and stress corrosion.

Crude oil tanker corrosion
Crude oil tanker water ballast tanks can be particularly susceptible to corrosion including those tanks which are used for alternate Cargo / Ballast Operations. (these are however being phased out). The segregated / dedicated ballast tanks on these vessels tend to be of a side wing, hopper and inner bottom section arrangement.

Crude oil tanker corrosion – water ballast tanks
It is generally accepted that ballast tanks corrode more quickly in upper areas due to the presence of an air space . Sloshing of sea water in the upper area adds to the aggressive environment within the tanks. Where the ballast tank is adjacent to a heated cargo tank the atmosphere between the water surface and the tank top boundary becomes a warm salt water spray in heavy seas– ideal to cause corrosion. Where ballast tanks adjacent to heated cargo (and bunker) tanks remain empty following ballast voyages the rate of corrosion can be accelerated in areas of coating breakdown.

Necking occurs at the junction of long’l bulkhead plating and long’ls, The deflection of the bulkhead plating and long’ls due to reverse, cyclic loading from cargo oil and ballast plus the accumulated mixtures of water, mud and scale at their junctures accelerates the corrosion rate. The similar necking could also occur in the transverse bulkhead plating and stiffeners, or in the inner bottom plating and long’ls inside the double bottom space. In uncoated ballast tanks, the long’ls are the most affected. Corrosion rates can reach 0.33 mm/year for non protected steel But, in coated ballast tanks, the plating is the principally affected area due to local corrosion i.w.o. coating failure. Corrosion reduces not only the strength capability, but also the stiffness of the structural components.

Remember , each boundary of the ballast tanks can corrode from either side . In the case of the wing tank inner longitudinal bulkheads corrosion from the cargo tank side can have severe effects on the component. This is also true for the double bottom section tank top being affected. The process of corrosion here can be accelerated by the prescence of sulphur and moisture combined . In order to reduce the corrosion process the cargo tanks of crude oil tankers tend to have the lower areas (and underdeck areas) coated – usually extending about one meter above the tank bottom and below the tank top. This however offers no protection to the uncoated areas. In uncoated areas it is often possible to see lines of corrosion where automatic tank cleaning has been performed.

The extent of corrosion affecting the ballast tank inner longitudinal bulkhead and double bottom tank top caused by cargo tank cleaning is affeted by the cleaning medium. In order of decreasing effect, the mediums affecting tank corrosion are: Hot Sea Water Ambient Sea Water Crude Oil Washing All washing mediums however can remove protective oily films residual from crude oil carriage.

In closing the message is simple. The correct choice of coatings along with good application processes will meet with the rules & regulations and protect the ship from corrosion. Good through life maintenance of the coatings is essential in ensuring that the level of protection remains sufficient to continue to protect the ship. Cooperation between various parties is of great importance to avoid initial application problems or problems when the coating is in service.

Marine Structural Failures and Ship Design Assessment

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