Zhao Zhifeng

(Yiyang Vocational and Technical College,Yiyang City of Hunan Province 413049)

Abstract: With the rapid development of science and technology,ship transportation has become one of the main modes of transportation for human being;hence people pay increasing attention on the safety of shipping.The welding inspection and quality control plays an important role in ensuring the safety of the ship's structure.It is necessary to make an objective and accurate evaluation on the quality of the welded joints,and control the welding defects of the ship in a certain range so as to ensure the safety of the ship's navigation.This paper mainly focuses on the shipbuilding welding inspection and quality control,analyzes the problems existing in the quality control of ship's welding inspection,and probes into its control measures to provide scientific reference for ensuring the safety of ship's navigation.

Keywords:ship;welding inspection;control

With the 40 years of Reform and Opening-up,China's economy is in an important period of high-speed development.And it is impossible to achieve the steady development of the economy without the active contribution of the transportation industry,during which shipping plays a significant role and more cargo is carried out by shipping,especially with the application of containers.The basic requirements for safe navigation of a ship on a sea or river are strong and safe ships.Welding technology is widely used in shipbuilding industry,for which the shipbuilding industry of China can be developed rapidly,to a great extent,depends on whether we have a qualified welding technology.As the welding inspection and quality control of the ship are of great importance to the safety,reliability and service life of the ship,it is necessary to have strict control of ship welding inspection and quality control.That is why we need to analyze the core value of ship welding technology from the technical view of welding, take positive and effective measures to ensure the quality of ship,so as to promote the healthy development of China's shipbuilding industry.

I.An Overview of Ship Welding Quality Inspection

With the rapid development of science and technology,welding technology is more and more widely used in the process of ship building and connection and the previous riveting connection method has been gradually phased out.With the emerging of various styles and structures of ships,the welding connection technology is increasingly widely applied in the ship building and welding.Therefore,the quality of the ship greatly hinges on that of the welding,and if quality problems occur in the welding process,the safety of the ship will not be guaranteed,which makes it indispensible for the quality inspectors to work meticulously, attach more importance to the inspection,according to the actual situation,work carefully on the daily inspections of welding,safeguarding the quality of ship.At present,the inspection of the ship's welding quality mainly includes the following aspects:testing and testing the welding materials; choosing suitable welding technology;supervision of welding personnel's work;supervising the welding of the whole structure of the ship;inspecting welding of related facilities at sea;checking submarine pipeline welding and so on.The most important work is to inspect and supervise the whole structure of the ship welding,and there are some discussions on how to do the welding inspection of it well.The inspection of welding quality in the overall ship structure includes:firstly,to inspect the welding seams before welding begins;then to check the surface quality of the weld and the specific specification,and finally to check the internal quality of the weld[1].

II.Analysis on the Current Situation of Ship Welding Inspection and Quality Control

With the social development,we have achieved great progress in the welding technology,which plays a vital role in improving safety of ships.However,there are still some defects of welding inspection and quality control in ship welding technology in China,which not only seriously affects the cost of manufacturing, but also increases the amount of funding for follow-up repairs,but also brings great challenge to the safety operation of the ship.So it is imperative to arouse enough attention to this issue.There are many kinds of welding defects,which are divided into internal and external defects according to their position in welds.There are some common internal defects,such as pores,slags,incomplete penetration defects,welding cracks,and etc,and the external defects,such as the dimensions and shapes of welding seams being unable to meet the requirements,arc craters,welding beading,welding undercuts,slags,surface pores and welding cracks,etc.[2].These defects are mainly caused by low quality of steel, improper selection of welding materials,poor cleaning conditions of groove surface,low assembly precision,poor performance of welding equipment,improper selection of process parameters,improper technical regulations and poor weather conditions,etc.

(i)Incapability or insufficient knowledge of the quality control of ship welding of the welding technicians

Now the shipbuilding industry is going mechanized and streamlined operations, which requires the welding technicians to possess the corresponding professional quality,skills as well as the professional knowledge.With the backward conception, some of the welding technicians are unwilling to learn the new welding knowledge,which makes them strange to the new welding equipment imported by some enterprises.In addition,there are some other technicians with bad behaviors,such as non-compliance the welding procedure,dereliction of duty or corner-cut.Hence without qualified techniques,it is extremely easy to cause various defects to these technicians.

(ii)Problems of parameter adjustment of welding equipment and material selection

Although the progress of welding technology has promoted the rapid development of ship building,we are still confronted a great deal of problems,such as the upgrade of welding equipment and materials being unable to keep up with the pace of the times,and some fund-intensive,technology-intensive and relatively special materials still being unable to be widely available,which makes that the selection of welding material remains in the ordinary material unrenewed.For example, the welding wires with strong rust resistance,used for the welding seams of the hull longitudinal fillet welding on plain board with plenty of electrodes and huge current,are not in a timely supply,the wires and flux used in multi-wire submerged arc welding for large ships are still not widely available,and the flux-cored wires used to prevent cracks at hull roots and with relatively high requirements on thickness,are not well applied.As a result,there is still a lot of work to do to further popularize these specialized welding equipment and welding materials.

(iii)Problems Existing in the Structural Design of Ship Welding

In the structural design of ship welding,the welding material should follow the principle of equal strength and hardness,that is,the welding material should be identical to the base material in strength and hardness,so that the solidity and reliability of welding can be ensured.But in the actual welding operation,the metal materials are mostly chosen,which is not in accordance with the welding seams in strength.Especially the low-alloy high-strength steel material is widely used now,of which,the strength is much higher than that of the metal of welding seams.This is actually contrary to the principle of equal strength and hardness,which undoubtedly causes huge potential danger to the welded joints.

III.Measures on Welding Inspection and Quality Control of Ships

The welding defects mainly include pores,incomplete penetration, slags, cracks and burn-through and etc.This paper puts forward some measures for welding inspection and quality control in the procedure of welding:

(i) Inspection and Quality Control of Seams before Welding

As a necessary measure to ensure welding quality, the pre-weld inspection on seams could provide the weld groove to meet the requirement of quality.It is important for inspectors to observe the relevant requirements of welding technology,based on the actual situation and according to the relevant standards and regulations,to carry on the detailed examination,to consult the documents,to understand the seams assembly accuracy and the requirements on positioned welding for plane block production line, curved block production line and three dimensional block production line,to know,from the segmented work diagram,the welding groove shape and the corresponding welding method of the different parts of the ship after studying block diagram the working drawing of developing the hull plate and the process files of ship cradle welding,and inspect meticulously on the shape of the welding groove is inspected carefully so that the inspectors can know very well about the accuracy of the welding groove shapes in different parts.

(ii)Welding Specification and Surface Quality Inspection of Welding Seams

The welding specification and surface quality inspection of the welds require inspectors to know the professional knowledge and have a basic knowledge of relevant materials and equipment so as to ensure the welding seams in compliance with the specifications and a high surface quality.During the inspection,it is essential to know the type of the welding seams and how it is tagged.The specification of seams mainly refers to the relevant regulations of the size and the style of welding seams,of which,the style mainly includes butt weld,lap weld,fillet weld,plug weld and so on.Besides,the fillet weld seams can be divided into fillet welding on both sides,full penetration fillet welding on both sides,staggered intermittent fillet welding and chain intermittent fillet welding and so on.In addition,the inspectors also need to have a very good knowledge of the process documentation about ship welding.

(iii) Inspection on Internal Quality of the Welding Seams

The internal quality inspection of the welds shall be carried out after the defects repaired in the specification dimension of the seams and surface quality inspection.During inspection,strictly abide by the relevant codes of operation,the inspectors involved shall be responsible for the standardization of the process and specific plans.The internal quality of the weld seams can be detected by radiographic,ultrasonic beam sweep and penetration testing or other appropriate means.

At present,most shipbuilding or repair yards adopt radiographic and ultrasonic method to carry out internal quality inspection,and have achieved good results[3].The detection above is employed to produce and form reflection lines or beams on the defects or the bottom surface by using ray emission or ultrasonic beam, so as to determine the corresponding specification and type of the defects on a basis of impulse waveform.In small and medium-sized shipyards,it is usually easy to ignore the internal quality inspection of the welds seams,which requires the inspectors to develop the corresponding defects detection experience, repair in time for the unqualified seams,and control the repair process at the same time.In addition,it is vital to prepare additional inspection for the seams with the qualified rate below 80%, take good charge of the non destructive testing,and do a good estimation of the seams position to be detected.

(iv)Continuous Improvement of the Welding Technology and Professional Operation Level of Ship Welding

It is crucial to achieve a fundamental breakthrough in welding technology for China's welding to integrate with the rest of the world.In order to accelerate the upgrade and progress of welding technology, it is necessary to take new technology application as prerequisite,accord with the ship-design philosophy and make appropriate adjustment on a basis of the development of the ship design technology.At the same time, it is also important to improve the professionalism of the welding technicians,through training management,assessment management and etc,to strengthen the comprehensive technical level and quality of them,so as to ensure the quality of the welding and the stable operation of welding process[4].

(v) Promoting the Improvement of Welding Quality based on the Improvement of Ship Welding Management System

Modern ship enterprises should build welding process characteristics based on their own advantages, through continuous reform and innovation,improve the quality management system's capability of the welding,and make use of modern ship building theory to carry out welding management,on a basis of the characteristics of welding and manufacturing technology.Hence,they should make improvement on the welding management system featured by their own characteristics of ship design,based on their own management structure.In this way,the ship's welding management system is more in line with the requirements of ship building,in compliance with the characteristics of enterprise management so that the management of welding can be done more effectively.

IV.Conclusion

To sum up,the hull welding is an essential part of shipbuilding which will greatly affects ship's basic function.Hence any defects or welding related problems is never neglected.Therefore, in the process of welding, the professional technicians should adopt scientific methods to detect the defects of welding seams in time, and put forward corresponding improvement measures for different types of defects,and better improve the quality of welding,so as to ensure that the ship built satisfies the requirements and further strive to make contribution to the development of ship industry in China[5].