Hull Inspection, Damage & Repair - Part III

Hull Inspection, Damage and Repair ( Reporting and Assessing Structural Defects )  Part III

Stress Concentrations

Stress concentrations occur at any discontinuity in the structure with an intensity related to the abruptness of the change. For convenience, areas of stress can be divided into the following seven types.

Hard Point (more than 80mm from the structure)

The hard spot (or hard area) can be defined as:

• a point (or area) locally rigid in a flexible or less rigid structural element.
• also as a point (or area) where the deflection curve of a plate is
• abruptly interrupted by the effect of a very rigid member supported by the plate.
• as a point (or area) where there is an abrupt change in rigidity.

These abrupt changes in the deflection lines induce high local stresses. In those points (or areas) there is a great possibility to find cracks.

There are 3 types of hardpoints:

Hardpoint Nº 1. 

Bracket welded to a plate. Distance to the nearest stiffener >= 80 mm Consequences > Crack perpendicular to the bracket in the plate. Also, it can be caused by a “doubler”.

Hardpoint Nº 2. 

End of a face flat in a bracket Consequences > Crack in the bracket plating

Hardpoint Nº 3. 

Different deformation, under the same loads = Change of rigidity = Hardpoint 

The brackets should not end on unsupported plating.

The corners of trunks should not end on unsupported plating

SOLUTIONS:

The solution, although it may sound trivial, is to avoid or eliminate the hard points or to make a gradual change of rigidity

1) To place a small pad under the bracket toe. 

2) To extend the bracket to the next support.  

3) To place longitudinal support underneath the bracket.

4) To place transverse support underneath the bracket toe.

In other cases, we have to make the change of rigidity more gradual. Among the many possible solutions, we have to elect the best under the quality/cost criteria.

End of Bracket

The ends of brackets and of stiffeners are prone to fractures and therefore, should be examined carefully. 

We can consider three types of more frequent failures:

End of bracket Nº 1) - In this case, the welding connection of bracket or stiffener with the plating is fractured

End of bracket Nº 2) 

In this case, the bracket or stiffener breaks the support element

End of bracket Nº 3) 

In this case, the bracket or stiffener breaks the support plate.

In addition to three listed above there is also, Bracket Nº4) 

In this case, the bracket itself is broken.

SOLUTIONS for End of Bracket 

Change of Section

No1

No2

No3

In general, the solution is to modify the shape of the bracket (or to add a new one), although, sometimes, it is necessary to increase the size of the bracket.

In other cases, it will be necessary to extend the bracket to the adjacent stiffener or to incorporate a new stiffener to fix end the bracket.

Change of Section

Change of Section –Solution –Fit bracket

Change of Thickness

Solution – Insert an intermediate thickness 

Diminish the thickness difference and make the transition as gradual as possible, in the order of 3:1 or 4:1. 

Insert an intermediate thickness plate when the difference in thickness is more than about 1.5-2 times. Otherwise, improve the transition to 4-5: 1 by chamfering *

*A chamfer is a transitional edge between two faces of an object. A form of a bevel, it is created at 45° angle to two adjoining right-angled faces. A lark's tongue is a chamfer which ends short of a piece in a gradual upward curve, leaving the balance as a right angle.

Openings

Case 1

The solution for the photo above is to close the opening.

Case 2

The solution for case 2 – Increase the radius

If a flange is present on the opening ( as above) increasing the flange thickness in addition to increasing the radius will also reduce the stress.

Misalignments

Solution 1- Full penetration weld

Changing the fillet weld to a full penetration weld ( allows better continuity of the stresses through the misalignment.

Solution 2- Thicker insert

A thicker insert will also allow for better continuity of the stresses through the misalignment. Care should be taken to chamfer the ticker plate

to minimise the effect of the change of thickness.

Solution 3 Re –align

Re-alignment of structure in existing ships is never recommended as it will require a great deal of work to disconnect adjoining structure, and will induce other misalignments in the vicinity

Full penetration weld and a thicker insert will always be easier and cheaper.

Three Planes

(crack always on fillet weld)

When the three planes meet, such as at the intersection of a longitudinal and transverse bulkhead with a platform /stringer deck, there is always the possibility of the stress concentration arising at the point where they intersect. This can lead to fractures, although the type of damage depends on the size and type of the ship.

Solution 1 – Fit bracket (no scallop) in line with the plane on the other side

Solution 2 – Close scallops ( where the bracket is already fitted)

Difference Between Hard Points and End of Brackets

References :

1. Bureau Veritas (2006). Mini Survey Handbook Part A - Ships in Service. (First ed.). France: Marine Division Ships in Service Management ( DNS).
2. Gutierrez, M. – Retired Senior Surveyor LR, 2018. Conversation/Lecture to/with Aleksandar Pudar from 18 to 21/9/2018.
3. Lloyd's Register Marine (2014). Hull Inspection, Damage and Repair. (Third Edition ed.). United Kingdom: First published by Lloyd's Register ,2009. 
4. Lloyd's register marine (2015). Hull Inspection, Damage and Repair. (First ed.). United Kingdom: Lloyds Register.
5. Researchgate.net. 2018. “ Pitting intensity diagrams” www.ResearchGate.com [Online]. Available from: <https://www.researchgate.net/figure/Pitting-intensity-diagrams-Figure-taken-from-2_fig4_320716318 > [Accessed on : 2 October 2018]. 
6. Marchant , T, Dr.Lomas, J & Dr.Callow, L (2009). WHITE PAPER:THE FEASIBILITY OF A CORROSION RESISTANT SHIP. [Online]. (1 ed.). United Kingdom: © BMT Defence Services Limited 2009 © Amtec Consultants Ltd 2009. Available from: <https://www.bmtdsl.co.uk/media/6098421/BMTDSL-Corrosion-Resistant-Ship-Whitepaper.pdf >[Accessed on : 2 October 2018]. 
7. Tanker Structure Co-operative Forum (1995). GUIDELINES FOR THE INSPECTION AND MAINTENANCE OF DOUBLE HULL TANKER STRUCTURES. (1st  ed.). England: Witherby & Co.Ltd.
8. Tanker Structure Co-operative forum (2014). Guidance Manual for Tanker Structures - Consolidated Edition 2014. (2nd ed.). Great Britain: Witherby Seamanship International.
9. Tanker Structure Co-operative forum (1986). Guidance Manual for the Inspection and Condition Assessment of Tanker Structures. (1st  ed.). England: Witherby Marine Publishing.
10. Tanker structure co-operative forum (1992). Condition Evaluation and Maintenance of Tanker Structures . (1st ed.). England: Witherby & Co.Ltd.

Hull Inspection, Damage & Repair Part II

Hull Inspection, Damage and Repair ( Reporting and Assessing Structural Defects )  Part II

Considerations When Dealing With Damages

Fatigue

1. Alternate or cyclic loading
2. Loads lower than breaking load and yield stress

The material fatigue can be defined as the failure under alternating fatigue load or the propagation of a fracture due to a load of a cyclic nature.

Items of structure that form part of a ship may fail due to service loads and associated stresses, which are much smaller than the maximum breaking loads and stresses they were designed to withstand.

Fatigue

These loads are either cyclical or alternating in action.

In all types of fatigue fracture, crack start because of the concentration of localized stress in the component of the structure.

The fatigue curve

The fatigue curve shows the number of fatigue cycles at given stress before an item fails.

By reducing the stress in a location below the fatigue limit it should not fail again in the service life of the ship.

If a fatigue failure occurs early in the life of a ship the remedial action must be comprehensive in order to reduce the actual stresses to blow the fatigue limit.

If a fatigue failure occurs in a location late in the ship life it may be appropriate simply to repair as per the original design.

Corrosion Under Stress

 Accelerated corrosion will occur where there are high levels of stress. Even within the same space on a ship, corrosion rates at locations of stress concentration will be greater than in those locations where the stresses are lower. This can be seen particularly where sea water is present, such as inside ballast tanks where coatings have broken down.

The “stress cycle”

The acceleration of corrosion is cyclical and self-perpetuating; it occurs because wastage from corrosion leads to more stress on the area and in turn corrosion.

An area suffering from corrosion can rapidly deteriorate if coatings are not repaired or modifications are not carried out on the structure, which will reduce the stresses present.

The stress cycle often produces fracture lines at the point of the highest initial stress. In other cases, the area around the initial stress concentration becomes corroded.

Corrosion Under Stress

Progress(ive) of Corrosion

Inspections would be simple if the rate of corrosion was linear, however, the real rate of corrosion tends to accelerate over time.

Progressive corrosion

The stress cycle applies here too and once corrosion is established, it will become progressively worse unless preventive action is taken. 

Corrosion will continue to develop when:

The coating is not in good condition

The load that the structure is carrying is high; and

There is greater humidity and or higher surrounding temperatures

Solving stress and progressive corrosion :

Recoat protective coatings to stop corrosion

Increase thickness of structural members to reduce stress

Increase the radius of openings to reduce stress

Increase the thickness of flanges used at the opening to reduce stress

Close opening to reduce stress.

Humidity and Heat

In general heat and humidity affects the tanks mostly above the load line. 

The only solution to prevent this corrosion is the adequate maintenance of the coating

Higher temperatures and humidity will increase corrosion rates in unprotected environments. 

If they are both present, the effect is compounded and the rate of corrosion accelerates rapidly.

Areas on the ship that are most prone to increased heat and humidity  ( and therefore to accelerated corrosion) are the tanks above the waterline and those next to heated spaces.

Within a tank, particular attention should be paid to its uppermost part, especially where the tank boundary is exposed to direct sunlight.

Vulnerable tanks:

• Fore and aft peak tanks
• Deep Tanks 
• Side tanks
• Tween deck tanks
• Topside tanks
• Tanks adjacent to heated fuel oil tanks
• Ballast tanks adjacent to heated cargo tanks.

Age of Ship

The age of the ship is one of the most important factors to be considered when selecting a suitable repair. The same defect may have different treatment depending on the ship’s age.

The age of a ship and how much longer a ship is excepted to stay in service, are factors that must sensibly be taken into account when assessing the seriousness of a defect and establishing an appropriate repair.

When defects are due to fatigue, then the age of the ship gives an indication of the actual levels of stress. 

Remember the fatigue curve; fewer cycles to failure usually indicate higher stresses are present in the area of the defect.

Fatigue curve occurring on a new or young ship most probably indicate that significantly higher levels of stress than were expected at the time of design are actually present.

This could possibly be due to poor workmanship at the time of build or because of poor design. 

Correcting poor workmanship, if that is established as the cause, might include correcting the misaligned structure, fitting missing brackets, or inserting the correct grade and thickness of the material.

If, however, stress concentration has occurred due to poor design, then significant modifications to arrangements may be needed such as fitting much larger and softer bracket, closing openings by fitting lugs or collars, increasing grades and thickness of the material used.

Fatigue defects occurring for the first time in an older ship, say after 20 years of service, show that although the structure has eventually failed ( such as a crack developing) there was a little wrong with either the initial design or workmanship.

The most appropriate action in such a case would probably be to repair as per the original design condition; in the case of a defect that took 20 years to develop, such repair per should ensure another 20 years of service.

When there is the damage to a ship the ship’s age gives us information about the actual levels of stress that has contributed to the failure.

Stress Concentration Factor

The stress concentration factor in a given area is measured by the ratio ( SCF) between the maximum stress and the nominal stress and the nominal stress in the surrounding structure. 

A WELD MUST NEVER BE LOCATED ON A

 PLACE OF STRESS CONCENTRATION

References :

1. Bureau Veritas (2006). Mini Survey Handbook Part A - Ships in Service. (First ed.). France: Marine Division Ships in Service Management ( DNS).
2. Gutierrez, M. – Retired Senior Surveyor LR, 2018. Conversation/Lecture to/with Aleksandar Pudar from 18 to 21/9/2018.
3. Lloyd's Register Marine (2014). Hull Inspection, Damage and Repair. (Third Edition ed.). United Kingdom: First published by Lloyd's Register ,2009. 
4. Lloyd's register marine (2015). Hull Inspection, Damage and Repair. (First ed.). United Kingdom: Lloyds Register.
5. Researchgate.net. 2018. “ Pitting intensity diagrams” www.ResearchGate.com [Online]. Available from: <https://www.researchgate.net/figure/Pitting-intensity-diagrams-Figure-taken-from-2_fig4_320716318 > [Accessed on : 2 October 2018]. 
6. Marchant , T, Dr.Lomas, J & Dr.Callow, L (2009). WHITE PAPER:THE FEASIBILITY OF A CORROSION RESISTANT SHIP. [Online]. (1 ed.). United Kingdom: © BMT Defence Services Limited 2009 © Amtec Consultants Ltd 2009. Available from: <https://www.bmtdsl.co.uk/media/6098421/BMTDSL-Corrosion-Resistant-Ship-Whitepaper.pdf >[Accessed on : 2 October 2018]. 
7. Tanker Structure Co-operative Forum (1995). GUIDELINES FOR THE INSPECTION AND MAINTENANCE OF DOUBLE HULL TANKER STRUCTURES. (1st  ed.). England: Witherby & Co.Ltd.
8. Tanker Structure Co-operative forum (2014). Guidance Manual for Tanker Structures - Consolidated Edition 2014. (2nd ed.). Great Britain: Witherby Seamanship International.
9. Tanker Structure Co-operative forum (1986). Guidance Manual for the Inspection and Condition Assessment of Tanker Structures. (1st  ed.). England: Witherby Marine Publishing.
10. Tanker structure co-operative forum (1992). Condition Evaluation and Maintenance of Tanker Structures . (1st ed.). England: Witherby & Co.Ltd.

IMPROVING LIVING CONDITIONS ON BOARD: PART 2 : PROPOSED SOLUTION

LIVING CONDITIONS, ENTERTAINMENT, TRAINING AND VR/AR PROJECT

PROPOSED SOLUTION 

Subject: LIVING CONDITIONS, ENTERTAINMENT, TRAINING AND VR/AR PROJECT

PART II

PROPOSED SOLUTION 

5. Solution for upgrade

5.1 Solution for upgrade Training/gymnasium facilities

The ideal facelift of the vessel gyms would involve the following:

●     Replace the flooring with Polymax Rubber Flooring; non-slip and easily replaceable. Customisable to contain logo and to be in company colors. Alternately, the use of a lighter colour will improve floor reflectance with the result of increasing the illuminance in the room.

●     Mount Acrylic Mirrors on one wall. Easily installable and shatter proof. Applied on 18mm plywood to avoid distortion

●     Posters (Darebee.com) can be displayed which provide some inspiration as well as informative charts that can assist in more efficient workouts.

●     To provide full body workout, a climbing rack and pull up rack would be beneficial.

●     To save space and reduce the risk of weights moving during rolling, it would be advisable to replace free weights with Powerblock Adjustable Dumbbells (see Snapshot below). Current dumbbells are free-weight type i.e. very hazardous

●     A Hi-Fi system which enables crew to listen to music from their personal device or from CD to keep them motivated.

●     Mini fridge to keep chilled water or protein bars.

For each vessel, separate plan will be created at later stages, pending approval.

Proposal for Panamax

5.7m*3.8m 21.66m2

 (Inspired by Gymmarine web page, designed by Ms Bond)

Gym Flooring - Polymax

Power Block Sport 5.0 Adj. Dumbbells Set 2-22.5 kg                       

Alternative is to create a “Standard List of Equipment” for current gym equipment, which may mean supplying some items to different vessels.

Once vessels have all equipment, it is maintained from the office, sports fund should be used for any additional items/fridge stock or for excursions.

5.2 Solution for Upgrade Crew and Officers TV/Smoke Room and Libraries

While most vessels in the fleet have TV, they do not have TV with USB connection or Digital TV. Without access to Digital TV, they have no access to live TV whilst in port. An ideal upgrade is to provide these vessels with Digital TV with USB connection.

Another solution is to provide Marine grade satellite antenna.

(http://www.inmarsat.com/service/tvro/ or http://www.kvh.com/MarineSat/ ) The crew want the ability to watch TV while at open sea. We have TV lines in each cabin so setting up TV while ashore

To be able to have TV on board, the above solutions are viable only for a vessel that has Fleet Xpress Inmarsat Internet on board. (Aframax 1 is in test phase)

Also recommend to replace all supplier calendars and have only company calendars hanging in all communal areas.

5.2.1 Solution for Upgrade of Chemical vessels Crew/Officers Mess /Smoking /TV room

Proposal for an upgrade on Chemical vessel Crew/Officers Mess /smoking /TV room is to install a partition between mess area and smoking/tv area.

Either shelves or plants can be used, both options are multi-purpose.

5.3 Solution for upgrade of the Internet on board

The most viable solution for the upgrade of the internet on board is Inmarsat FleetXpress. This is currently being tested by IT on MT Aframax 1.

Price: 4500 USD initial cost + 2100 monthly cost.

Time: From delivery seven days for installation +1 day for commissioning in suitable port

The rest of the fleet will be upgraded if testing on Aframax 1 returns good results.

5.4 Solution for upgrade of Communal spaces /Galley / Mess room

In the past, our vessels had many plants. This is no longer the case. Provide plants in communal spaces, can be beneficial in providing cleaner air and better moral. A standardised list of plants must be kept on board vessels and those plant must be supplied during vessel delivery and resupplied at every dry-dock.

NASA’s Clean Air Study found the plants below are effective at removing benzene, formaldehyde, trichloroethylene, xylene, and ammonia from the air—chemicals that have been linked to health effects like headaches and eye irritation.

Symbols in the picture under each plant demonstrate what kind chemicals that plant filters/remove from the air.

With a fairly small investment, a lot can be done just by introducing these plants into on board life; a good moral booster being one of the benefits.

There are other benefits to having these plants around; the graphic shows at a glance the plants that make the best natural air filters. NASA research suggests having at least one plant per 10 m2 of home or office space.

This may become the official company list of plants that should be on board the vessel Numbers and locations will vary on case-by case basis depending on vessel size and type. Vessels that are visiting ARA could be easily supplied from IKEA; same goes for new deliveries.

An example is this ‘Simple Indoor Herb Garden With Adjustable Grow Light’ for a vessel that has a galley with no windows; the lamp can be excluded for galleys with windows. As can be seen below, set up is simple and can be supplied on board with four monthly stores with a small guide for the cook and steward.

5.5 Solution for Upgrade of Curtains

The only solution to update any of the curtains on any vessel is to take sizes of windows, number of windows and outsource this to a company’s whose core business is Marine Upholstery and Curtains. This is a very expensive and time-consuming project, as customs curtains can take considerable time. To give an example from what can be found online without going into too much detail is the starting price of 15 USD per Meter. An option could be to focus on replacing the curtains in communal/recreational areas as well as crew quarters.

5.6 Solution for Upgrade of Bonded Stores (working)

Bonded stores is currently maintained by Master or whomever he appoints. Normal practise currently is, inventory of bonded stores is sold to reliever, which in some cases means that stock is not replenished in the month prior to sign off and the month following reliever joining.

The proposal is for Bonded stores to be under an “Approved Order List”, with inventory sent at the end of each month.

5.7 Solution for Upgrade E-Publications / E-magazine / Distance Learning(working)

We should be maintaining a library of e-books, e-magazines and e-publications that can be accessed by office and vessels at any time.

Both educational and leisurely publications can be supplied weekly/monthly.

Crew survey needs to be carried out initially to ensure supply at least one publication which is in each their mother tongue and national news.

A Vessel Survey to get feedback and supply what meets vessel needs should be carried out three-monthly.