Joint Tanker Project Presentation on New Construction Rules

As previously announced, three classification societies (ABS, DNV and LR) have made a presentation on their final draft new regulations for tanker new building. The presentation covers: (1)  the background/ development framework & systematic review  ; (2) key technical aspects ; and (3) the consequence assessment  & the schedule of industry hearing & implementation.  

The regulations, for oil and product tankers of over 150m length, apply to the entire hull envelope, transverse and longitudinal bulkheads, primary support members and local structure. Fatigue life and sloshing calculations are included.

The regulations, in 12 sections and 4 appendices totalling over 500 pages can be accessed at www.jtp.com. A brief review follows.

Design Basis – these are (a) design parameters (i.e. design life 25 years) (b) external environment conditions (i.e. North Atlantic wave; air temp. – 15˚C; sea temp. 0˚C; (c) internal environment (i.e. cargo spec. gravity min. 1025 kg/m3; ballast sp. gravity. 1025 kg/m3; max. cargo temp. 80˚C; min. cargo temp. 0˚C; corrosion margins for 25 years design life)

Key technical aspects

Loads –   The strength assessment is  based on more severe loading conditions while the fatigue assessment is made for the average expected load. As presented, the rule formula compares well with the wave load calculations done on 9 standard vessels (3 VLCC, suezmax, aframax, product, capesize bulk, panamax bulk, handy bulk).

Gross Thickness – The JTP’s concept of gross thickness is based on the calculation of the net thickness to which is added the necessary (local) corrosion margin. The newbuilding corrosion addition is linked to the ship in service wastage allowance. JTP agreed that the difference between the corrosion addition on a new building and the corrosion allowance for ships in service will be constant of  +  0.5 mm for any structural element. This constant value is called tcorr2.5 because it is expected to represent a sufficient margin of safety for a cycle of 2.5 years of class inspection. In other words, the net tolerance (tnetrequired) + tcorr2.5 will give the value of the renewal thickness on those elements of ships in service.  The net hull girder section (average condition) is calculated by deducting half of the local corrosion allowance. Buckling capacity of items subject to the hull girder stresses are based on net thickness only (no local corrosion allowance is taken into account). This is consistent with IACS UR S11.

Longitudinal Strength – same principles (consistent with IACS UR S11) with a few changes such as increase by 150% of the wave induced shear force Qwave.  Some different coefficient values due to the new concept of deducting a percentage of the corrosion allowance. The JTP permissible stress within 0.4L as compared with the IACS UR S11 are as follows:

 

IACS UR S11

JTP Rules

Bending stress

175k N/mm2

190k N/mm2

Shear stress

110k N/mm2

120k N/mm2

Hull girder ultimate strength (ULS) – This is a new criterion in the mandatory class rules. For the time being, JTP decided to calculate ULS for static load conditions only. The hull girder capacity is limited to deck failure.

Prescriptive regulations – various formulae for longitudinal and local strength calculations of cargo block structure, transverse bulkheads (including corrugated bulkheads), forepeak & forecastle, machinery space, aft section, etc.

Fatigue – 25 years fatigue life for the whole cargo area based on North Atlantic wave loads. Calculations include the longitudinal end connections of the cargo block, hopper knuckle between inner bottom and the frame in midships region. Calibration made with real data from 6 ships.

Finite Element – Load cases for seagoing and static loads in port are presented. JTP might reduce the number of these by eliminating those less critical. Comments requested.

Buckling & Ultimate Strength – Calculated on the net scantling. JTP introduces an advanced buckling analysis for critical elements (i.e. subject to a lifetime of extreme loading). The calculation/verifications are done with a newly-developed software. The advanced buckling analysis assumes a combination of bi-axial compression, share stress and lateral pressure. Comparisons are shown. Calibration made with real data from 6 ships. Worksheets with details of the calculations are on www.jpt.com.

Consequences Assessment – Some preliminary results only. No data of finite element analysis yet. JTP is still working on further refinement and will revert. The consequence assessments are run on 2 VLCCs, 1 suezmax, 1 aframax, 1 product carrier, all current designs from five major shipbuilders in Korea or Japan. Examples are given of a number of physical consequences (increase in plate thickness or increase on the section modulus) and the primary regulation which caused the increase - for instance, the deck plate on an aframax and of a VLCC increases between 0.5 and 1.5 mm due to the hull girder strength criterion.

Industry hearing & Implementation – JTP  suggests that the hearing period  is only up to 1 September. However, good comments would be taken on even if they came late in September. The three Class Societies would follow up in different way with their individual Technical Committees. ABS plans to have an extraordinary meeting of its Technical Committee on late November/early December to adopt the new regulations.   INTERTANKO requested a longer hearing period without the delay of the date of the implementation of these rules.  The arguments for a longer hearing period were: (a) these new regulations are different and more complex than a regular class rule amendment and therefore it a more sophisticated approach is needed than simple one way comments with little possibility of consultation; (b) comments are sought from the three class societies’ technical committees AND from the rest of the industry; this intention is excellent but then the time allocated for the consumption of these new rules, eventual need for clarifications, etc. would certainly be insufficient if limited to July and August only; (c) the process of harmonisation between JTP and JBP would definitely take longer than that and thus the JTP rules would be still open to discussion until November.

One important note: coating is not included among the JTP’s new regulations and criteria.  INTERTANKO made the point that coating life is one of the goal- based criteria brought jointly to the IMO by IACS ,  Greece  and the Bahamas,  and therefore it should have been included it the new JTP regulations.

Attendance at the JTP presentation consisted of up to 60 people including ABS and other Class representatives. INTERTANKO was represented by Nils Kristian Berge of Laurin Maritime and a member of INTERTANKO’s ISTEC technical committee, and INTERTANKO technical and engineering director Dragos Rauta

Next presentation will take place in London on 28 June (see diary). Members are encouraged to register and attend.

Memebers are also encouraged to actively study and comment the rules. Comments could be sent direct to the JTP (the web site has a standard feedback form) and copies to INTERTANKO will be welcomed.

Contact: Dragos Rauta