The Importance of NDT Technology Application in the Plant Engineering

Abstract

The Non-Destructive Testing (NDT) technology is a new, comprehensive,and rapiadly-developing engineering science after the second world war. It is extensively applying to numerous science & technology sphere, particularly industry. From the author’s practical experience that engaged in NDT technology work up to more 20 years, the article introduces the feature and advantage of the NDT technology, explained the importance of NDT technology application as a very effective technology of the fault diagnosis in the plant maintenance by many typical example, and introduces the application methods, testing technique and applicable devices by the actual example. It attempts to give plant maintenance personnel a better understanding about NDT technology, representative of the present advanced industry level in the world. It expects to draw the attention of the plant maintenance personnel to NDT technology application in the plant engineering, in order to go a step further to raise the plant maintenance level for ensuring the plant’s safe-runing and service life, so that to meet the needs of the economic development and to obtain better economic benefit.

1. Introduction

The NDT technology has been a comprehensive and rapidly developing engineering technology after the second world war , it is mainly based on the various changes of the physics character in the material, to make non-destructing the operation performance and shape of inspected workpiece as condition, to carry inspection by a hundred percent, then to determine the quality state of inspected workpiece. Thereby, its application is attained highly attentiemphasizing and speedly developing in industry , physics research and bioengineering and etc. Its development fully recognised and was given a conspicuous position. It became a very important technology means for controlling quality of products, assuring the plant safe-runing and etc. That is not all, it is already developed to Non-Destructive Evalution technology from the pure testing technology, it does not only includ the non-destructive testing and inspecting, but also is concerned with the damage-allowance design based on fracture mechanics for evaluation the safe operating-life of products and plants. So even if the NDT itself is not a production technique, but its technique level can represent the industrial technique level of these departments, trades, zone and even the country. Now, it occupies a very important status in the machinebuilding and military industry, and brings into play important function in the safe-ensuring system of many important heavy plants. But it has not yet attained enough attention and wide application in the plant diagnosing and maintenance engineering of the general equipments or ordinary civil-equipments. The article will expound some view of author in this aspect.

2. How was the question raised

Except the aviation industry, space industry, nuclear industry and many military industry and etc. Where NDT is already widely applied , in the safety ensuring system of some civil industry, e.g, the boiler and pressure vessel, heavy generating equipment, and some heavy high-load mechanical equipments and etc. NDT technology is also applied on required by the administrative departments concerned in the country. But the NDT technology often has not been considered in the safety ensuring system of numerous common civil, public and amusement equipment which is closely related to the human safety. In these equipment’s check at present, technicians still mostly rely on visual check and monitor abnormal sound by human ears during runing or strip inspection in fixed term that is very backward inspecting methods for the safety inspection of service equpments. So the result often turns out that they can not early and effectly find the hidden danger. Take for example,several important safety accidents that happened in GUANGDONG province ., the axle bolt break off due to fatigue crack of the trainlike high-speed inertial vehicle for amusement in GUANGZHOU East amusement park, the chain hoist break off of suspending bridge on TIANHU lake in CONGHUA city, the suspending cable break off due to corrosion of HAIYIN bridge on pearl river in GUANGZHOU city, and the lazy arm break off due to crack of tower crane in GUANGZHOU XIJI harbour and etc.,in addition, in a machine work that is the author was worked, because of the fastening bolts break off due to fatigue crack on the oil hydraulic cylinder of the punch & shear machine with four column, result in the cylinder cover fly-out....and so on. If the NDT technology was employed to inspect in fixed term that is defined by the maintenance specification of the equipment, and the NDT technology was carried out based on non-strip ( call as in situ inspecting ), then it will be early found the omen of accident, therefore avoid the accidents. But because of many plant managers don’t know the NDT technology , they don’t know the applying range and the feature of the NDT technology, so often don’t consider the application about the NDT technology when enacting the maintenance and management rule of plant. Therefore we can say that it is lack of a advanced, effective and strong means for quality safety in the plant engineering system. As far as I know , the lift-hanger and hoist cable of crane, the press rolls of sugarcane mill up to the concrete structure or road-surface of the high-way and overpass, the component bearing high-load in the thrilling amusement equipment and so on, that not yet the relevant NDT method and acceptance specification are defined. Thereby, how is take these advanced NDT technology introduced into these area, is a very important topic.

3. The function of NDT technology in the plant engineering

For ensuring the safe running of the service plant, the NDT technology is enough to exert its speciality about non-destruction and reliability, and that can employ testing on situ in many case ( i.e don’t need to dismantle the component ). As all know, the NDT & Evaluation technology is a new engineering science which possesses the speciality about multi-science comprehensive application and close-combination between the theory and practice, it is need higher requirement whether the theoretical or systematical or technolotical. It is involved with multiaspect content, e.g, the physics, material science, electronics technology, measuring techique and informatics technology and etc. So we can say that each feature of material almost all is applicable as basis of certain NDT method, and almost all formal energy can be utilized to define the physical character of the material or to detect flaw in the material. As for the NDT technical method applied at present, it has already up to several ten kinds. In these methods, the concerned physical basis is included acoustics, optics, heat, electricity, magnetics, machine, radiology, physicochemistry, electromagnetics, particle beam, or combined application by certain character. At present, the main NDT method that is more widely applying is Ultrasonic Testing ( UT ), Magnetic Testing ( MT ), Eddy-current Testing ( ET ), Radiographic Testing ( RT ) and Penetrant Tseting ( PT ) ( they are called as five-kinds conventional methods ), in addition, the Acoustic emission Testing ( AT ) and Leak Testing ( LT ) is obtained more and more application as well. Of course, various NDT method possesses various character and own testing technological requirement, suitable testing object and testing range.
The fatigue crack is commonly encountered and more dangerous in the important high-load component of service plant, and specially the early fatigue crack can hardly find by means of visual inspecting, but if properly applying the PT ( it has certain requirement for the surface roughness of inspected workpiece ), MT ( it must be ferromagnetic material ), ET ( it must be conducting medium ), UT and RT ( it basically don’t influenced by the kinds of material ), then these conventional NDT method can to inspect out the defect effectly. As the author’s background of practical experience which is engaged in NDT technology which works up to more than 20 years, the following are some examples about applying NDT method in service inspecting for some common equipment or component of plant:

The service steel-cable for bearing load: At present it is already available to commercial portable electromagnetic ( eddy-current ) detector for detecting breakage or break-point of the cable, and it can test in situ.

The fastening bolt or axlelike part or case and etc. on machine equipment, it only provided that one end or one side is exposed out, then can be to detect the fatigue crack in situ with UT method but don’t need to take apart for inspection. In practice, because the part or component is situated under the action of tension or bending stress, so the crack’s slotness is often more than the state after load-off, thereby, the effect of using in-situ NDT method is often taking precedence of taking apart for inspection.

It can be employed to the MT, ET, PT and etc. for testing that is all exposed out component ( e.g, lazy-arm and lift-hanger of crane, rail and clamp, axel or hub and so on ).

Bearing load spring: it can be employed to the ultrasonic surface wave or magnetic particle method for detecting.

Bearing pressure vessel or barrel-type workpiece and etc.: it can be employed the UT, MT, PT and RT method and so on, in addition, it can be employed the AT method for dynamic monitoring together with the pressure-tight test by means of water.

In addition, the using of hot-infrared testing for monitoring the abnormal hot-point of high-speed runing component, the using of remote-control AT for monitoring the abnormality in runing equipment, and the using of the endoscope technology for detecting surface-defect in the inner hole, and so on. These examples are enough and can’t all be to given here.

4. That needs pay attention to some problem about the popularization and application of the NDT technology in plant engineering

When popularizing and applying the NDT technology in plant engineering, the following problems ought to be noticed:

[1] At first, the plant engineering manager ought to possess more and better knowledge about the method and principle of NDT technology, applying object and range, suitable testing device, the development of new technique and detecting equipment, and right established the concept about application of NDT technology in the work of plant management.

[2] The NDT technologist ought to construct well communication and the cooperating relationship with the plant manager in order to carry out the NDT technology and establishing suitable inspection technics and acceptance specification of inspecting quality about the work of service plant.

[3] The NDT technology self had strict requirement about technique qualification level for the NDT personnel. In my country, as same to each country, it already carries out the qualification and certification rule for technique level of NDT personnel in fixed term. It takes the NDT personnel classed to three level, i.e, elementary (Ⅰ), middle (Ⅱ) and high (Ⅲ). The NDT personnel must be to possess corresponding technique qualification level and working in the limits authorized by the qualification level. Thereby, it must pay attention the qualification level and its effective time of NDT personnel when applying NDT technology in plant engineering.

5. Conclusion

The NDT technology belongs to special testing technology over scope of high-new science & technology. When combining with the safety evaluation technology, e.g, fracture mechanics, damage-allowance design, it will not only effectively to detect out the dangerous defects, but to evaluate the security, service life and etc. of service plant for continuing run according to various factor about size, quantity, length, density, placement , property and etc. of defects evaluated by detecting. Therefore, if the NDT technology is obtained wide popularization and application in the plant engineering, then we can believe that will give very useful contribution and to obtain well economic benefit.

1997.11 in Guangzhou