ПРОБЛЕМЫ С ОПОРНЫМ ПОДШИПНИКОМ БАЛКИ В СУДОВЫХ ДИЗЕЛЬНЫХ ДВИГАТЕЛЯХ

Бессалов О.В.¹,Дрюков А.П.²,Кочегарова Н.А.³

¹Студент,астраханский государственный технический университет;²студент,астраханский государственный технический университет;³старший преподаватель, астраханский государственный технический университет

ПРОБЛЕМЫ С ОПОРНЫМ ПОДШИПНИКОМ БАЛКИ В СУДОВЫХ ДИЗЕЛЬНЫХ ДВИГАТЕЛЯХ

Аннотация Цель состоит в том, чтобы представить современную методику для структурной прочности судовых дизелей, несущих балок и описать ответственность проектировщиков двигателя, производителей и поставщиков оборудования. Был представлен пример нескольких двигателей того же самого типа, где усталостные трещины возникли в определенных областях их балок опорного подшипника .Обширное исследование показало причину повреждения. Правильность конструкции была доказана должным образом реализована государством в самых современных методах проектирования. Сделан вывод, что причиной повреждения было плохое качество международного изготовления и неподходящей сварки во время изготовления.

Ключевые слова: Судовые дизели; Опорный подшипник балки; Сила усталости; Дизайн; Производство.

Bessalov O.V.¹, Drukov A.P.², Kochegarova N.A.³

¹Sstudent,astrakhan state technical university;²student,astrakhan state technical university;³senior teacher, astrakhan state technical

university

THE PROBLEMS WITH BEARING GIRDERS IN MARINE DIESEL ENGINES

Abstract The aim is to present the state-of-the-art methodology for structural durability evaluation of marine Diesel engines bearing girders and to describe the responsibility of engine designers, manufacturers and system suppliers. An example of several engines of the same type, where fatigue cracks arose in certain areas of their bearing girders, has been presented. The extensive investigation revealed the cause of the damage. The proper design was proved by properly implemented state-of-the-art design methods. Quality and test specifications prescribed by the licensor have been found correct. It is concluded that the damage cause was the impermissible quality of worldwide manufacture and improper production repair welding during manufacture.

Keywords: Marine Diesel engines; Bearing girders; Fatigue strength; Design; Manufacturing.

From the functional and the safety aspect, modern merchant ships are strongly dependent on the prime movers in their propulsion systems, regardless of their concept. The essential propulsion system concept may be based upon marine turbines, or a single- or multi-Diesel engines installation. Diesel engines are commonly used today. It is always important to understand their functional role (class related), as well as the safety aspects of their implementation.

From the designer’s point of view it is necessary to consider the ship in exploitation, operating in heavy seas, rather than nothing more than the floating object during the outfitting phase in the shipyard. Functional problems related to the ship prime mover can usually be solved in the shipyard without further implications to the ship safety. However, any ship during operation may face an extremely difficult situation, when the proper functioning of the propulsion system may be the ship’s crew only hope. So, the designer is to design marine Diesel engines, manufacturer is to manufacture, assemble and test them on the test bed, and finally the shipyard is to mount them and test them onboard during the sea trials. These engines shall be able to withstand all the hazardous situations that may arise later. An important part of the responsibility for the proper functioning of Diesel engines lies also on the ship’s crew, especially the chief engineer, to follow the proper instructions prepared by the engine designers.

Engine designers have to properly deal with the engine as a whole, from its initial specification, to the feedback information obtained from the test bed or onboard, as well as the design of the engine essential parts. From the functional point of view, the most important engine parts are these that transform reciprocating movement of the piston mechanism into rotation of the output flange, such as crankshaft, as well as all the parts taking part in transmission of generated forces to the engine foundation, e.g. the bed plate, the frame box, or the cylinder block. In modern large Diesel engines bedplates usually consist of their outer part made of steel plates, connected together by means of cast steel bearing girders. These bearing girders take over and distribute forces acting on the engine bedplate as a whole, originating from assembly pre-loading by tie rods, cylinder firing loads and bearing reactive loads.

Our article is initiated as a consequence of cracks that developed in several Diesel engine bearing girders in newly built ships and the investigation of the problem cause. The basic aim of the article is to describe the present state-of-the-art methodology, which has to be implemented in design and manufacturing of modern Diesel engine bearing girders. The design of these components shall be based upon a proper structural durability evaluation. The manufacture shall be based upon the proper implementation of quality assurance procedures (production and testing specifications) in general. The final goal of all the mentioned procedures is to avoid any undesirable effects and to prevent initial crack development in similar structures.

The design procedures based upon loading assumptions, selection of suitable materials and the manufacturing procedures, as well as the shaping and dimensioning procedures are described in details. The transition from cylinder loading and tie-rods pre-load to the existing stresses in critical parts of bearing girders is explained. On the other hand, evaluation of structural material properties for cast steel bearing girders in accordance with the international standards, such as ASTM, or FKM-Guideline, dependent also upon the initial and the in-service scope of inspections implemented.

Manufacturer’s responsibility is called for further on. The manufacturers have to keep up to the predefined specifications during manufacture of the components. They are responsible for, quality assurance, component testing, providing proof that the test requirements have been satisfied, as well as for assembly of components into a fully functional system. The point here is upon implementation of proper production repair welding procedures, regularly used to correct unavoidable casting defects, where their improper use may have detrimental consequences to the final behaviour of the bearing girders and engines as a whole.

The mentioned real practical case study example of several engines of the same type, where fatigue cracks arose in certain areas of their bearing girders is presented and analysed. This analysis had the scope to find out the cause of the damage, in order to solve the problems on existing, as well as on engines in future and treat the influence of the design and the manufacturing process to the cracks developed and found on existing engines.

It resulted in conclusion that the cause of the cracks found lies in impermissible quality of world-wide manufacture and improper production repair welding during manufacture. As a consequence of this conclusion, it is recommended that a special attention is to be given by the engine licensors to their manufacture and the implementation of their quality assurance procedures by their licensees world-wide. The proposed approach may, at least in the analysed examples, prevent further problems with cracks in cast steel components exposed to production repair welding.

One of the most common definitions of quality, applied to a machine system component, relies upon its suitability for use. It is not easy to see or determine how many parties took place in its creation, from the design to the final testing prior to delivery. In modern industrial society the parties that may be recognised at a first glance are the designer, the manufacturer and the system supplier.

Design of the component always defines the direction of all further steps to be made in its manufacture and behaviour in exploitation. The designer is responsible for the following:

• full description of the requirements which the components are to satisfy with specified conditions for their use;
• evaluation or estimation of operating loads and component strength;
• constructional shaping and dimensioning;
• selection of suitable materials appropriate to the loading; and
• selection of the manufacturing

On the other hand, the responsibilities of the manufactures are basically related to the fabrication of the component itself. These consist of the following:

• manufacture of the components in accordance with clear and complete specifications for the design and in accordance with standard engineering practice;
• assurance of component quality in accordance with the use-related specifications;
• examination of the components in accordance with prescribed and agreed testing methods;
• proof that the test requirements have been satisfied; and
• assembly with other parts to form a System suppliers are responsible for :
• assembly of all the necessary units and equipment to form plants capable of operation;
• adjusting of plant adjustable parameters if necessary;
• final testing of assembled and built-in plants in accordance with the test specifications;
• proof that all the prescribed and agreed tests have been performed with the results that satisfy the requirements, prior to the delivery of the whole plant.

In modern shipping business all this applies to the bearing girders as the components, marine Diesel engine as the unit and, finally, to the whole ship as a unit. Designers of the two-stroke slow speed large marine Diesel engines, together with all the engine components such as bearing girders, are usually licensors themselves (presently, there remain only three significant international companies in large two-stroke marine Diesel engines business). Manufacturers are their world-wide licensees, i.e., Diesel engine factories around the world. System suppliers are, in this context, the shipyards.

One of the important aspects of a component/unit/plant operational behaviour in practical exploitation further on lies upon the ship operators. These are the shipping companies (ship owners or management companies). Their responsibilities are to always keep up to the operating instructions prescribed by the designers and to avoid any misuse or abuse.

The bearing girders are predominantly manufactured from cast steel. For cast components of the size of bearing girders it is assumed, on the one hand, that an appropriate casting quality is guaranteed, and on the other hand that if casting quality is inadequate, a repair can be effected. Usually, the so-called production repair welding improves the components with casting failures. The requirements for the quality of bearing girders, as well as the procedure for repair welding, must be described in the quality assurance specifications. With the production repair welding the faults caused in production should be removed and the required nature of the casting should be ensured, which should have the characteristics similar to the basic material.

To assure a reliable and economical repair the bearing girder is, depending on the stress distribution divided into individual zones on which the specified casting failures can be accepted or, depending on their shape and position, repaired. These requirements should be specified at the design stage in close cooperation with the engineers being responsible for the manufacturing. If the casting faults are higher than allowable, but possible to improve by repair welding, this could be made if the specified conditions are fulfilled. Depending on the size of the component to be repaired it is necessary to decrease the residual stresses generated by the repair welding.

A repair of the bearing girder is required because of the possible serious damages to the main bearing shell with a potential impact to the crankshaft in case of uncontrolled crack propagation.

The procedure of structural durability validation of bearing girders in large two-stroke marine Diesel engines, is a basis for a reliable lightweight design of modern engines. It is also necessary to prove the cause and the responsibility in the case that the damages (failures) occur at operational usage.

Production repair welding in cast components is a normal practice. This kind of repair of casting defects can not be avoided for economical and practical reasons. Production repair welding is to be performed in accordance with the prescribed quality procedures, based on standards and correctly supervised accordingly by independent bodies.