Making Waves - industrial marine work in full sail

TWI Bulletin, July - August 1996

Derek Russell, Manager of Power Beam Processes, is currently Chairman of TWI's Ship Industry Panel. He takes overall responsibility for technical developments and projects concerning the ship industry sector at TWI.

Chris Woodley joined TWI in 1960. He is currently in the Industrial Membership Department with responsibility for recruitment in the UK, focusing on the shipbuilding, base metals and railway industrial sectors.

TWI is dedicated to serving the main industrial manufacturing sectors worldwide. Derek Russell and Chris Woodley summarise TWI involvement with the ship industry sector.

The ship industry has many facets, these include shipbuilding, repair, operations, ownership, classification societies and equipment suppliers. All of these are covered by the interests of the TWI Ship Industry Panel.

Ship industry panel

The Panel has a broad remit to ensure that TWI activities are directed towards the needs of industries associated with ships and shipping, achieved through pro-active discussions between Industrial Member Companies in the sector and TWI. Its objectives are:

• To define trends in the industry leading to particular needs in production, methods, equipment, materials, design and operation of ships.
• To promote adoption of projects in TWI's Core Research Programme (CRP) which address this sector.
• To develop collaborative projects within various national and international initiatives and to identify relevant topics for group projects.
• To identify training needs and help TWI develop programmes to meet those needs.
• To formulate the special requirements of industry in areas of standards, quality control and safety, and help to satisfy them.

Scheduled meetings are run twice a year (three have been held so far) attended by an average of 35 people, mostly from the shipbuilding and equipment supply sectors. The main technical topics discussed at these meetings have covered the following:

• distortion and inaccuracy arising during fabrication and means of improving overall accuracy
• jigging and faring developments
• advances in welding and cutting processes
• benchmarking of fabrication practices.
• managing innovation and new technology
• development in panel line and production systems

Panel members have been involved in a number of national and international collaborative developments of relevance to the ship industry sector. These have included:

• development and application of friction stir welding of Al alloys
• classification society approval of laser welding for ship construction and the associated materials and welding procedure validation work
• in-service monitoring of ship structures
• technology transfer of best practice arc welding methods for ship construction
• feasibility studies of the exploitation of laser cutting in the shipbuilding and structural steel industries

Work and activities of the panel are supported internally at TWI by a Ship Industry Team, which meets at regular intervals. Members are taken from relevant TWI departments covering welding processes, materials, structural integrity, NDT, health and safety and information services. The team is currently planning the next panel meeting whose main theme is 'developments in joining technology for future ship production', with emphasis on new processes and refinements of existing processes.

Topics of interest to the ship industry

Productivity involvement

TWI helps Industrial Member companies plan their move towards use of best practice in fabrication processes and increased mechanisation. By commissioning a brain-storming session via TWI's consultancy services, a company can assess changes needed in production. For the ship industry this could mean:

• full production/construction analysis to identify activities where most savings can be made, and development of a productivity improvement strategy
• reducing labour-intensive processes eg use of semi-automatic and fully mechanised equipment and robots to replace manual cutting, assembly and welding
• reorganisation of workstations: stockyard, transport and handling; piece part preparation; sub-assembly; assembly and erection; pipeshop and outfitting - to optimise material and information flow and identify mechanisation needs
• increased attention to quality, health and safety and environmental requirements

Distortion control and rework

Many shipyards still accept unnecessarily high levels of rework caused by inaccuracies in fabrication and inadequate attention to distortion from cutting and welding. Working with industrial members specialists in the ship industry sector can help you to:

• assess potential savings from improved accuracy
• devise and help implement cost-effective distortion control methods
• recommend and justify alternative processes - such as laser, electron beam, plasma, friction and adhesives - which could have a very significant impact on productivity and quality.

Corrosion and fatigue

Fatigue and corrosion are the most common causes of failure in the industry. Backed by over 40 years of research, TWI is an authority on analysis and avoidance of such failures in marine fabrications, and has been a major contributor to the drafting of National and International Standards for design and assessment of structures to resist fatigue in both steel and aluminium. Using accumulated experience and knowhow technical experts can:

• predict life expectancy and recommend economically viable joint design
• advise on cost-effective surface treatments to enhance corrosion and fatigue resistance
• run special fatigue tests

In addition to supporting the Marine Corrosion Club, members of staff have published in excess of a hundred papers over 30 years addressing corrosion cracking of stainless steels.

Materials and fabrication

TWI has world-leading knowledge of the materials and the optimum cutting, forming and welding processes used in marine fabrication. This knowhow coupled with expertise in specialised materials, provides an unparalleled resource for the progressive shipbuilder and designer. TWI advises on stainless and nickel steels for LNG ships; duplex stainless steels for high performance applications; structural high tensile and high toughness steels; aluminium alloys; and the joining of non-metallic materials such as engineering plastics and composites which are increasingly used for marine applications.

Consultancy services available are broad ranging and cover not only selection of the most appropriate materials for designers, and selection of cutting and welding processes and procedures for the shipbuilder but also advice on inspection and repair techniques for the ship owner.

As an independent authority, TWI liaises with classification societies, ship owners, designers and builders to achieve agreement in areas where traditional specifications are inappropriate.

New technologies

TWI is playing a leading role in developing many new technologies relevant to shipbuilding. Among them laser welding, the friction processes of welding and surfacing, and applications of adhesives have played large parts in recent TWI work.

Laser welding

The need for shipyards to increase productivity and reduce fabrication costs led to a search for methods of improving the accuracy of fabrication. The need for a reduction in distortion, and ability to predict precisely distortion due to welding follows from this, and created an interest in the possibility of applying deep penetration, laser welding for butt and T-joints. Although many shipyards identified the benefit of laser welding, the difficulties in obtaining classification society approval to existing rules was found to be a serious obstacle to its implementation. A development programme has been carried out to produce relevant technical information and evidence, to allow the classification societies to define rules and guidelines for laser welding technology in ship fabrication. Applications proposed are:

• plate butt welds
• full penetration T-butt joints for stiffener attachment
• partial penetration T-butt joints for stiffener attachment
• fabrication of T-stiffeners

The main advantages for laser welding, which lead to reduced manufacturing costs in comparison to arc welding, are considered to be:

• reduced structural distortion leading to reduced re-work
• faster joint completion rates
• more accurate structures permitting easier subsequent assembly of modules
• advanced welding process mechanisation and automation

These benefits can only be realised if laser welds, having the quality and properties required by the classification societies, can be produced in appropriate steel grades in a shipyard environment. Also, from a shipbuilder's and operator's point of view, the tolerances on materials and procedures must not have an adverse effect on the cost reduction gains to be obtained by improved accuracy and productivity.

A project to answer these questions was co-ordinated and managed by TWI, and the work carried out by a group of 11 research institutes on behalf of 41 industrial organisations representing shipbuilders and their suppliers. In addition, all the European classification societies were actively involved in guiding and evaluating the work. The objective of this work was to define the operational envelope in which laser welding could be satisfactorily carried out in ship construction.

Results have been transferred to the participating companies and classification societies. This has enabled the societies to produce draft guidelines to be used in laser welding of ship structures. The work identified problem areas and proposed solutions by defining operational envelopes for materials and welding procedures for producing sound welds with acceptable properties. The data generated, together with proposals from the classification societies, should encourage laser welding to be used in shipyards.

Friction processes

Advantages of using friction processes in construction include low distortion and thermal disruption, and the ability to join dissimilar materials. Techniques of interest to shipbuilders and owners include:

• friction stir welding for distortion free welds in aluminium plate and sections
• friction hydro-pillar processing for repairing defects in thick sections
• friction surfacing for depositing corrosion or abrasion resistant materials on new or worn components
• friction welding for high quality attachment of studs

Adhesives

Adhesives are playing an increasing role in an ever widening range of manufacturing industries including shipbuilding and marine. TWI advises Member Companies on the following:

• applications where adhesives can be used in place of traditional joining methods
• selection of adhesives for specific materials
• joint design for optimum quality and productivity
• bonding procedures and quality assurance

Conclusion

TWI has a long association with shipbuilding and ship operation. In order to enhance this relationship the Shipbuilding Panel was set up. It meets regularly to examine current trends and needs and to communicate technical development between TWI and industry.