Comparative Economic Efficiency of Radiation Methods for Quality Control of Welded Joints
Abstract Generated abstract
This paper compares the economic efficiency of radiation methods for nondestructive quality control of welded vessel seams with wall thicknesses from 10 to 400 mm. It evaluates X-radiography, gammagraphy, betatron radiography, radiometry, and combined inspection schemes using calculated productivity, inspection cost, capital investment, and reduced cost per linear meter under specified operating assumptions. The analysis shows that the preferred method depends strongly on wall thickness, source type, mechanization, batch size, auxiliary time, and the share of selective radiographic verification. Radiometry with SID-1 is advantageous up to about 47 to 48 mm, GUP-Co-60 gives the lowest reduced costs from 50 to 100 mm, PMB-6 with fluorescent screens is most favorable from 100 to 240 mm, and BD-3 radiometry becomes most economical above roughly 200 to 240 mm.
Full Text
COMPARATIVE ECONOMIC EFFICIENCY OF RADIATION METHODS FOR QUALITY CONTROL OF WELDED SEAMS
V. A. BERDONOSOV, L. M. DOBNER, Yu. S. PROKOF’EV, G. T. SHKARINA
(Presented by the scientific seminar of the Department of Industrial Economics)
At present, in various branches of industry, welded vessels with wall thicknesses from 10 to 400 mm are widely used. Various methods of nondestructive testing are used to check the quality of the welded seams of such products; among these, radiation methods have the greatest relative share. These methods are based on the use of various sources—X-ray apparatuses, isotopes, or betatrons.
In practical application, in accordance with the technical conditions for inspection, it is always necessary to decide which of the existing methods is the most suitable. At the same time, experience in flaw-detection work shows that it is often expedient to use not any one method, but an entire set of them.
In this case, the choice of the inspection method must be made not only from the point of view of technical feasibility, but also with regard to its economic expediency.
The degree of economy of one or another inspection method is determined by a whole series of factors.
As studies conducted at NIIEĖ have shown, when using different sources and at different wall thicknesses of the vessels being radiographed, the degree of influence of individual factors on the amount of expenditures for carrying out inspection changes substantially.
In the proposed work, the following factors determining the amount of reduced costs for quality control of welded seams have been taken into account:
1) the type of source used;
2) the wall thickness of the products being radiographed;
3) the level of mechanization of auxiliary work;
4) the size of the batch of products inspected with one readjustment of the radiation source;
5) different cassette-loading schemes, etc.
The investigated inspection variants are given in Table 1.
Taking as a basis the optimal inspection conditions (optimal focal distance, standard RT-1 film, speed of radiometric inspection when using the SID-1 installation 0.2–1 linear m/min, for the BD-3 flaw detector—1.5 linear m/min, as well as comparatively simple access to the welded seams), we obtain dependences of the time norm, inspection cost, specific capital investments, and reduced costs per 1 linear m on the thickness of the products.
As calculations of the productivity of various inspection methods have shown, in the thickness interval up to 50 mm scintillation inspection is the most productive; moreover, as the batch of items being radiographed increases, the time expenditures for carrying out the inspected operations decrease. If the RUP-200-5 and RID-21 units are compared, it is obvious that at thicknesses up to 8 mm X-radiography is more productive, while at greater thicknesses better results are given by the RID-21 unit with the isotope Ir\(^ {192}\).
Table 1
Range of thicknesses controlled by the unit
| Inspection method | Name of unit | Thickness, mm | Thickness, mm | Thickness, mm | Thickness, mm |
|---|---|---|---|---|---|
| 10÷50 | 50÷100 | 100÷200 | 200÷400 | ||
| Gammagraphy | RID-21 | + | − | − | − |
| X-radiography | RUP-200-5-1 | + | − | − | − |
| Radiometry | SID-1 | + | − | − | − |
| Gammagraphy | GUP-Co-60 | − | + | + | − |
| Radiography | PMB-6 | − | + | + | − |
| Radiography | B-35 | − | − | + | + |
| Radiometry | BD-35 | − | − | + | + |
When comparing betatron defectoscopy (based on the PMB-6 unit) and gamma-defectoscopy (using the GUP-Co-60 unit), it turned out that in the thickness interval 50÷200 mm betatron defectoscopy in combination with fluorescent screens is significantly more productive. When the PMB-6 unit is used with lead screens, a gain in time in comparison with gammagraphy is obtained for products with a wall thickness above 120 mm.
The time expenditures for inspection when using the BD-3 scintillation defectoscope depend substantially on the size of the batch of products inspected with one readjustment. When the batch is reduced from 200 to 10 linear meters, the piece-calculation time increases by more than a factor of two.
Analysis of the productivity of inspection using the B-35 unit makes it possible to conclude that auxiliary time has a determining influence. Thus, when the auxiliary time is doubled, the piece-calculation time increases twofold at a thickness of 200 mm and by a factor of 1.5 at a thickness of 400 mm.
As for combined methods of inspection (scintillation inspection in combination with X- or gammagraphy on the basis of different sources), in this case the percentage of selective inspection of defects on X-ray film has a major influence on productivity. The productivity of one or another inspection method reflects only the expenditures of direct labor for carrying out inspection operations.
A generalized evaluation of the inspection methods being compared is given by the indicator of reduced costs \(C_{\text{p}}\), which takes into account the cost of inspection operations and the capital investments necessary for carrying them out.
The index of reduced costs by inspection variants was calculated by the formula
\[ C_{\mathrm{p}}= \frac{t_{\mathrm{shk}}}{60} \left[ C_{\mathrm{zch}}\cdot P\cdot k_{\mathrm{d}} + N\cdot k_{\mathrm{n}}\cdot k_{\mathrm{vr}}\cdot C_{\mathrm{ep}} + \frac{\sum_{d=1}^{h} K_{\mathrm{d}}\left(a+\mathrm{v}+\varepsilon_{\mathrm{n}}\right)} {F_{\mathrm{d}}\cdot k_{\mathrm{z}}} \right] + \]
\[ + C_{\mathrm{p}} + C_{\mathrm{x}}\cdot p^{m}\ \text{rubles/linear m}, \tag{1} \]
where \(t_{\mathrm{shk}}\) is the piece-calculation time for inspecting one linear meter of welds;
\(C_{\mathrm{zch}}\) is the hourly wage rate of inspectors;
\(P\) is the number of inspectors servicing the installation;
\(k_{\mathrm{d}}\) is the coefficient taking into account additional payments, bonuses, and contributions to the social insurance fund;
\(N\) is the total power of electric motors and radiation sources;
\(k_{\mathrm{N}}\) is the average coefficient of utilization of sources and electric motors by power;
\(k_{\mathrm{vr}}\) is the same with respect to time;
\(C_{\mathrm{ep}}\) is the cost of 1 kWh of electric energy;
Fig. 1. Graph of the dependence of reduced inspection costs on the vessel wall thickness.
1 — reduced inspection costs in radiometry based on the SID-1 installation; 2 — reduced costs for comprehensive inspection using SID-1 and RUP-200-5-1 installations with an inspection batch size of 200 linear meters; 3 — the same with an inspection batch size of 10 linear meters; 4 — reduced inspection costs based on the RID-21 installation using an \(Ir^{192}\) source; 5 — the same using a \(Cs^{137}\) source; 6 — reduced inspection costs based on the RUP-200-5-1 installation
Fig. 2. Graph of the dependence of reduced inspection costs on the wall thickness of a vessel.
1 — reduced inspection costs based on a PMB-6 betatron with fluorescent screens; 2 — the same using lead screens; 3 — reduced inspection costs based on the GUP-Co-60 installation; 4 — reduced inspection costs based on a B-35 betatron, provided that the auxiliary exposure time is 10 min.; 5 — the same provided that the auxiliary exposure time is 10 min.; 6 — reduced costs for comprehensive inspection with B-35 and BD-3 installations \(auxiliary exposure time 10 min., sampling rate of radiographic inspection 50%, inspection batch size 10 linear meters\); 7 — the same for an inspection batch size of 200 linear meters.
\(h\) — the number of standard sizes of fixed and working-capital assets used in carrying out inspection;
\(K_d\) — the cost of one unit of equipment of the \(d\)-th standard size used in inspection;
\(v\) — coefficient accounting for the costs of current repairs;
\(a\) — coefficient of depreciation deductions;
\(\varepsilon_n\) — normative coefficient of comparative economic efficiency;
\(F_d\) — annual effective operating-time fund of inspection equipment;
\(k_z\) — load factor of inspection equipment;
\(C_p\) — cost of film, including processing and interpretation costs, per one exposure;
\(C_{x.r}\) — cost of chemical reagents per 1 exposure;
\(m\) — number of exposures per 1 meter.
The dependence of the reduced costs per 1 running meter of welded seams is presented in Figs. 1 and 2.
Analyzing the graphs, one can establish the regions in which different methods of radiation flaw detection are expedient to use. Thus, in particular, radiometric inspection based on SID-1, even under the most unfavorable conditions in combination with 50% radiography and with a lot size of inspected products of 10 running m, has advantages over 100% radiography practically over the thickness interval up to 47–48 mm. At a thickness of 50 mm, this method is only slightly inferior to radiography using the isotope \(Jr^{192}\).
As can be seen from the graph presented in Fig. 2, in the thickness interval of 100–240 mm the use of the PMB-6 installation with fluorescent screens is the most advantageous.
In the range from 50 to 100 mm, the lowest reduced costs correspond to the use of the GUP-Co-60 installation. At thicknesses exceeding 200–240 mm, the most economical is the use of radiometry based on the BD-3 installation.