4. Welding inspection

New words and word combinations.

1. rejection – сортировка, браковка

2. fatique failure – усталостное разрушение

3. ultimatе strength of materials – предел прочности

4. put into service – вводить в действие

5. harmful defects – вредные дефекты

6. to preheat – предварительный нагрев

7. lack of fusion – непровар, отсутствие проплавления

8. clusters of porosity – скопления пористости

9. flaw – трещина, дефект

10. a pulse generator – генератор импульсов

11. to impinge upon – сталкиваться с… / ударяться о…

Inspection in all branches of industry, ranging from textiles to satellites and rockets, is regarded as an essential feature of modern development. In no industry is inspection more rigid than in the sphere of welding.

Inspection aims at the control of quality through the application of established techniques, and involves the rejection of substandard products. Under service conditions most structures are subjected to static or dynаmic loading which could lead to fatique failure. Undersirable defects can affect the ultimatе strength of materials and in consequence contribute to failure. It is of great importance that such defects should be located before equipment is put into service. Therefore inspection should begin at the earliest stage of manufacture.

Metal edges to be welded should be cleaned and magnetically crack detected to reveal the presence of harmful defects in the parent metal. Besides, thе electrodes should be inspected to determine whether they are the required type for the work being done. The parent metal is to be рrеhеаtеd to reduce the rate of cooling during welding and to minimize the tendency for cracking in weld metal. A futher function of inspection should be to determine that the correct preheating temperaturе, proper current and polarity are applied. This is particularly so in connection with welding pressure vessels, boilers and reactors. Welds for this type of service must be free from harmful defects, such as cracks, lack of fusion, excessive slag inclusions or concentrated clusters of porosity.

Destructive tests such as tensile, compressive, bond, fatigue impact etc. have long been used to determine the quality of welds. These tests have their uses, of course, but the method never gave complete satisfaction because it is illogical to destroy a piece in order to determine its quality and approve untested pieces without any real knowledge as to whether or not their composition was the same as that of the tested specimens.

In many cases it is impossible to determine the quality of welds by visual or mechanical examination. To detect the welds economical forms of non-destructive testing, such as X-ray radiography, ultrasonics, magnetic crack detection and dye-penetrants have been developed. It is, can advantage for the inspector to have some knowledge of all methods of testing.

It is of interest to mention about ultrasonics. In contract with expensive X-ray equipment, such as linear accelerators and betatrons, an economical form of non-destructive testing of welds is being used, known as ultrasonic testing.

The Soviet engineer Sokolov appears to have been the first to have used ultrasonic vibrations to detect flaws in metals. And in deed in the last few years, the use of ultrasonics has grown greatly. This method of welding examination has some advantages over other forms of examination.

The equipment is easily portable, it is safe to use, there is no radiation hazard, it has a high sensitivity factor and it is speedy. It can be used by semi-skilled operators in its general application, but the results obtained required to be interpreted by skilled and experienced personnel.

In its simplest form, the ultrasonic equipment consists of a pulse generator which produces ultrasonic pulses of very short duration, usually in a range from about 1 to 3 micro-seconds. These pulses are sent cut from a quartz crystal transducer to the medium under test. When the beam impinges upon any interface or defect, part of the energy will be reflected, received by the instrument, recorded and indicated on the ultrasonic screen. The latest productions of ultrasonic instruments are equipped with a recording device, a manual scanning is being superseded by automatic scanning.

Questions to the text.

1. In what branch of industry is inspection most rigid?

2. What is an inspection?

3. When should all the defects be located?

4. What should an inspector do before welding two sheets of metal?

5. What requirements must the welds of boilers and reactors meet?

6. What destructive methods of testing do you know?

7. Is it logical to destroy a piece to determine its quality?

8. Do the visual and mechanical tests find wide application?

9. What economical forms of non-destructive testing have been developed?

10. Is it an advantage for the inspector to have some knowledge of all methods of testing?

11. What can you say about ultrasonic testing?

12. What Soviet scientist was the first to have used ultrasonics to detect flaws in metals?

13. What is the main feature of ultrasonic equipment?

14. Is there any radiations hazard under ultrrasonic testing?

15. How does the ultrasonic equipment operate?

16. Do you have ultrasonic equipment in your welding laboratory?