To achieve the system reliability of the linear part (LP) of main gas pipelines (MG), effective methods of their inspection are needed, which, first of all, include in-line inspection (ILI). During planning maintenance and repair of LP MG with account of the technogenic risk of accidents, it is required to process a large amount of data both for the defects identified on the pipes during the ILI, and for the geoinformation data on the objects of the MG environment. In the report discusses the problems dealing with accounting the results of ILI in assessing the frequency of accidents for the LP MG and shows how the usage of modern information technologies allows to support the adoption of rational management decisions when identifying priority selective repair potentially dangerous sections LP MG.
Such decrease in accident rate, first of all, dealing with thes introduction of ILI on MG of Russia. If to accept quite
authentic assumption that in recent years increase in a share of sites of LP MG of the surveyed ILI happened in all gas
transmission companies approximately identical rates and to impose the schedule of decrease by years of percent of sites
of LP MG of uninspected ILI on one of gas transportation subsidiaries (GTO) of PJSC «Gazprom» on statistical points of
values of relative frequency of accidents on 1000 km per year according to annual reports ROSTEKHNAZOR [
The methodology for assessing the technogenic risks of accidents on main gas pipelines
Normative documents of PJSC «Gazprom» on the quantitative assessment and the analysis of risk
The System of Management of Technical Condition and Integrity (SUTSC) of LP MG [
According to ND [
According to statistical data ROSTEKHNAZOR [
It is quite apparent that at identical probability (frequency) of accident, the priority of repair should be given to that site for which destruction or elimination of objects of an environment (buildings, processing equipment, roads, forests, agricultural grounds etc), in case of accident can result in the greatest damage.
According to ND [
According to statistical data ROSTEKHNAZOR [
According to ND [
In the presence of estimates of probability (expected frequency) of accidents for the considered site of LP MG which
can be received on ND [
- definition of calculated scenarios of accidents (the fire in a ditch, struyevy it is ardent, a dispelling of a low-speed loop of gas and a dispelling of two streams gas);
- assessment of the conditional probabilities of implementation of calculated scenarios of accidents on a tree of events; - calculation of intensity, totals and duration of emissions of natural gas; - calculation of distribution of the striking factors of accidents (chips of the destroyed MG, an air wave of compression, gas contamination and thermal radiation from the fire); - calculation of number of victims among the population and personnel from accidents; - calculation of the number of destroyed and damaged property and the natural environment from accidents; - calculation of damage from accidents; - calculation of potential, individual, collective and social risks from accidents; - calculation of the expected annual damage and technogenic risk taking into account frequencies of emergence of accidents.
To assess the above-described algorithm of technogenic risk asessment in the SUTSC of LP MG, it is necessary to process a colossally large amount of initial data, an approximate list of which is given in the ND [8, Annex A].
This list includes more than seventy tables reflecting the technological characteristics of the LP MG section, the actual layout of the pipes, the location of compressor stations, information on gas pipeline crossings through water barriers, railways, roads, information about parallel gas pipelines, roads and Railways, a list of gas pipeline sections passing near industrial facilities, settlements, information about the climatic region, data of operational documentation, etc. Moreover, each of the above tables contains several dozen columns and, in some cases, several hundred rows, and besides all the tables should be compiled for each pipeline section.
Besides it is necessary to have detailed topographical and cartographical information including a flow diagram of MG, plans of routes of the main gas pipelines and the description of objects of a social, economic and production and natural environment.
Collecting and formalization of all listed above input data is rather laborious task, but following ND [
However with results of ILI many questions arise with assessment of probability (expected frequency) of accidents for the considered site of LP MG. 2.2
The methodology for assessing the expected frequency of accidents, taking into account the results of the ILI
At assessment of probability (expected frequency) of accidents ND [
The Central postulate of MEHOCHAGaz is that for the considered n-th section of the gas pipeline the value of the total coefficient of influence of kvl is determined, showing how many times the expected specific frequency of accidents in this section λn differs from the average specific frequency of accidents λsr.
According to MEHOCHAGaz, the expected relative frequency of accidents (per 1000 km per year) on the n-th section of the route is determined by the formula:
I J i ¦ ¦ i j pi qij Bij (1) O n O sr k O vl sr k reg kvozr kkat
,
Bsr const где kvl, kreg, kvozr, и kkat - the nondimensional coefficients of influence, respectively: common, regional, "age" and "category".
Bsr - mark assessment of the hypothetical average section of the pipeline in which accident rate corresponds λsr; 0 d Bij d 10 - mark assessment observed on the analyzed site of MG of "natural" value of a factor of influence of Fij in a 10-mark scale, defined by the corresponding mark and factor function Bij = M ij (Fij); pi и qij - shares (weights) of the i-th group of factors and the j-th factor in the i-th group, respectively; I и J(i) - accordingly: the number of calculated groups of factors of influence and the number of factors of influence in the i-th group.
Results of ILI in MEHOCHAGaz are considered through such factors of influence as: a Stress Corrosion Cracking (SCC), external corrosion (without SCC), quality of production of pipes, installation and construction works and natural influences (results of ILI regarding defects of geometry, joint welds and mechanical damage). Possible mechanical influence of the third parties and level of technical operation is also considered.
Average relative frequency of accidents λsr for the onshore section of the gas pipeline with results of ILI according to
ND [
O n where O ij O ¦ ¦ i sr expresses the relative specific frequency of accidents (per 1000 km per year) on the n-th section of the route associated with each individual factor of influence Fij.
Representation of dependence (1) in the form of (2) gives the opportunity to simplify a problem of splitting the LP MG into certain calculated sites as allows to determine λn by each of factors of influence of Fij separately, taking into account its significance and the changing along the MG.
Changes along the MG of numerical values of the factors of influence considering possible mechanical influence of the third parties and level of technical operation have the fixed discrete character or are the monotonic. Therefore, for calculation of the expected specific frequency of accidents for these factors of influence there is enough splitting LP MG into calculated sites within which their natural values remain constants, and at assessment of the expected specific frequency of accidents on them within MEHOCHAGaz there are no questions.
I J i Provided that according to MEHOCHAGaz the sum of all weight coefficients ¦ ¦ pi qij 1, 00 , the influence i j factors considering results of VTD are most significant as the sum of their weight coefficients is equal 0,81 (p3 = 0,37 and q31 = 1,00 for SCC, p2 = 0,06 и q21 = 1,00 for external corrosion, p456 = 0,38 и q456 = 1,00 for defects of geometry, joint welds and mechanical damage), i.e. results of ILI more than for 80% determine the size of the expected relative frequency of accidents.
And with the influence factors considering results of ILI within MEHOCHAGaz there is a number of problems which reason that circumstance that any defect identified during ILI has strictly particular coordinate but its length is only several millimeters, or it is not specified in the report on ILI at all (the value zero registers).
The fact, first of all, that any score according to the ND [
O 31 O sr kreg kvozr kkat p3 1,q9317 10 0, 2 0,8 1 1,5 0, 9 0, 371,19,70 10 0, 41 , that is the accident rate of the considered PHA is twice higher than average.
With a length of PHA of L expressed in km assessment of probability (expected frequency) of accidents the bound to each separate factor of influence of Fij, is defined as
L Pij O ij 1000 . (4) Then, for the considered situation we receive
L 1 P31 O 31 1000 0, 41 1 000
At damage from one accident in 30 million rubles assessment of specific technogenic risk for such site of LP MG will
make 12,3 thousand rubles on one km per year that according to ND [
Now we decompose the above-considered kilometer segment into ten 100-meter PHA and try to calculate the specific frequency of the accident on each of them. Since only one defect has been identified in the entire 1 km section during the inline inspection, it is obvious that it will only occur in one 100 m PHA and there will be no defects in the other nine PHA. Thus, for nine PHA score B31 = 0 (there is not a single defect KRN), and one of the ten 100 meter PHA get B31 = 10. The expected specific frequency of accidents (per 1000 km per year) at this site will still be 0.41, but the probability (expected frequency) of accidents according to the ratio (4) will decrease tenfold (proportional to the reduction in the length of the analyzed area L from 1 km to 100 m).
Since there are no defects on nine 100-meter PHA, the probability of an accident on the KRN factor is zero. Since
POU is a defect with the assessment of the probability (expected frequency) of accidents according to Madagas decreased
ten times, and for the initial analyzed kilometre stretch, it will drop exactly the same amount. Then at damage from one
accident in 30 million rubles assessment of relative technogenic risk will make about one thousand rubles on km per
year, and such risk according to ND [
Finally, if we consider that length of the defect identified during VTD is only several millimeters, and there are no defects on the site of one km, then we will receive that though on several millimeters the expected specific frequency of accidents (on 1000 km a year) is rather high, and still makes 0,41, but the probability (expected frequency) of accidents both on a piece with defect, and for all initial analyzed site will be almost equal to zero.
It would seem, from the created problem situation it is possible to offer rather simple exit. If on MEHOCHAGaz on the PHA ball assessment already exceeds the maximal value in 10 points, then it is not necessary to divide it into more shallow calculated pieces, and on all length of the site to accept identical assessment of probability (expected frequency) of accidents. However such approach at the subsequent assessment of technogenic risk is hardly rational as it is necessary to consider an arrangement of objects of an environment of MG. So, if the defect of SCC is located in immediate a bliza to an object of an environment which destruction at accident, can be bound to extensive damage, then the averagings received in the way apart to 1 km of assessment of probability (expected frequency) of accidents will give significantly the underestimated estimates of technogenic risk and vice versa when the defect of SCC is on removal almost in 1 km, estimates of technogenic risk will be unreasonably overestimated.
Thus, it is desirable to consider the actual coordinate of the defect identified during ILI, at least to within one pipe what there would be an opportunity to range all defect tubes on a priority of selective repair taking into account technogenic risk.
Within MEHOCHAGaz for this purpose it is possible to suggest to refuse a tight restriction on the maximal values of score estimates (10 points) concerning the factors of influence considering results of ILI.
If on the considered site of LP MG with L km long, by results of VTD only one defect of SCC is identified, then according to MEHOCHAGaz ball and factor function has to be written down in a look B31 5, 33 Isc , where Isc expressly injected complex called an indicator of intensity of a stress corrosion which is calculated through average density found a stress - corrosion defects and with only one defect with the relative depth of dsc-i (% of wall thickness of a pipe) equal Isc dsc i / L .
And, if Isc > 1,875, then ball assessment of B13 has to be limited to the maximal value – 10 points. Then from a ratio B31 5, 33 Isc 5, 33 d sc i / L 10 it is possible to define that if one defect of SCC on the site 1 km long gives B31 = 10, then its relative depth is only 2% of wall thickness of a pipe. But if to consider that length of this defect not of 1 km, and only several millimeters (or zero), then for an index of intensity of a stress corrosion at dsc-i → 0 we will receive indeterminacy in a look Isc 2% / dsc i o f
, unambiguously larger, than 1,875.
If in MEHOCHAGaz for the factors of influence considering results of ILI to refuse a tight restriction on the maximal values of ball estimates (10 points), and to substitute the ball and factor function B31 for defect of SCC with the relative depth of dsc-i in a ratio (4) for assessment of probability (expected frequency) of accidents, we will receive P31 O 31 10L00 O sr k reg kvozr kkat p1 q31 5, 33 dsc i (5)
1, 97 1000
Using the ratio of (5) probability (expected frequency) of accident is defined for any defect of SCC regardless of
length of the analyzed site of LP MG. Having assessment of an accident risk and having information on environment
objects in a defect coordinate point on ND [
According to MEHOCHAGaz score and factor functions for external corrosion (without SCC) defects and defects of geometry, joint welds and mechanical damage, have an appearance similar to defects of SCC, respectively B21 0,00565 Ic 0,00565 d c i / L и B456 0,11 Imech 0,11 d mech i / L , and therefore for all of the factors considering results of ILI it is possible to use ratios of type (5).
Thus, degree of danger of the defects identified during ILI is considered in MEHOCHAGaz only through one
equivalent indicator – the relative depth of defect (or the relative length for sites of joint welds). Therefore, for example,
for external corrosion defects (except SCC), than more their relative depth, that high probability (expected frequency) of
accident. However, if to analyze ILI reports at whom degree of danger of anomalies according to ND [
So specialists of the same specialized organization which was carrying out ILI in 2016 on one of MKU with category pipes I for defect like CORR (corrosion) at wall thickness of a pipe of 9 mm and absolute depth of defect of 1,35 mm (the relative depth of 15%) appropriated category (A), and on other MKU with pipes all the III to category, appropriated to the same type of defect of CORR at wall thickness of a pipe of 8 mm and absolute depth of defect of 6,4 mm (the relative depth of 80%) only category (C). It would seem, according to MEHOCHAGaz, everything has to be exactly the opposite, but the matter is that in case of the former absolute lengths of defect made nearly a meter (851 mm), and in the second it was only 29 mm, but the most important, the defect with the relative depth of 15% was identified on a pipe with external diameter of 1020 mm, and defect with the relative depth of 80% - on a tuba with a diameter only 530 mm.
For elimination of that contradictory situations at assessment of probability (expected frequency) of accidents in MEHOCHAGaz it is possible to suggest to consider not only the relative depth of defect, but also other its parameters (defect length, external diameter and wall thickness of a pipe etc), or at least to limit calculated values of the relative depth of defects, for example, for category of danger (A) to values more than 30%, for category (B) – from 15% to 29%, and for category (C) – less than 14%.
From the analysis of the coefficients standing in expressions for score and factor functions (5,33 for SCC, 0,00565 for
external corrosion and 0,11 for defects of geometry, joint welds and mechanical damage) and corresponding to them to
weight coefficients (p3 = 0,37, p2 = 0,06 and p456 = 0,38), it is possible to estimate that according to MEHOCHAGaz with
the same relative depth degree of danger of defects of SCC in 6 thousand times more, than defects of external corrosion
as (5,33 0,37)/(0,00565 0,06) = 5 817, and defects of geometry, joint welds and bruises it is more dangerous than external
corrosion more than by 100 times - (0,11 0,38)/(0,00565 0,06) = 123. The given ratios demand separate detailed
discussion as it agrees, for example, ND [
And on ND [
Besides, according to ND [
In reports on ILI the revealed defects - anomalies (ANOM), fall into to particular type which total makes nearly three tens. Most often (more than 80% of defects) are identified as anomalies like CORR (corrosion), further there are GWAN (girth weld anomaly), MIAN (pipe mill anomaly), DENT (dent), TECH (technological defect), TMTM (metal outside), ARTD (artificial defect) etc.
But MEHOCHAGaz does not contain the answer to a question, what types of anomalies according to reports of ILI it is necessary to fall into to the least dangerous defects – external corrosion (without SCC) and what to the most dangerous – SCC. It is clear, that all other types of anomalies have to define the influence factor considering quality of production of pipes, installation and construction works and natural influences.
At the same time it is quite apparent that to external corrosion (without SCC), it is necessary to refer, first of all, anomalies like CORR (corrosion) and COCL (corrosion cluster). It is possible to include in the same group GRIN (grinding).
The anomaly like SCC (stress corrosion cracking) belongs to the most dangerous defects of SCC, but considering ND
[
Approbation the methodology for assessing the technogenic risks
The Risk calculated and analytical module (RAM) was developed for approbation of the methodology for assessing
the technogenic risks of accidents and definition of a priority of maintenance and selective repair of LP MG [
After digitization (vectorization) of topographical and cartographical information, input data about objects of an environment and objects of LP MG are published on the ArcGis Desktop geographical portal, due to formation of their list and the main characteristics with the indication of geographical coordinates of objects and arrangements concerning a gas pipeline axis. Then the cost of objects of an environment of MG is determined. Further information about technical condition of sites of LP MG is added and calculation of estimates of technogenic risk, both for all GTO and for each its linear production division (LPU), MKU and on each separate defect pipe is made.
For support of adoption of rational administrative decisions when determining precedence of selective repair of potentially dangerous sites LP MG, results of calculations of RAM "Risk" are presented in the form of the schedules and histograms reflecting dynamics of change of estimates of specific technogenic risk on the analyzed sites and priority of their repair.
So figure 2 shows the dynamics of changes in estimates of specific anthropogenic risk for the entire (surveyed ILI)
length of LP MG for one of GTO from which it is visible that these estimates do not exceed the established ND [
Realization of methodology of ND [
During the testing and practical application of ND [
All regulated changes in MEHOCHAGaz should be considered in the subsequent releases of RAM "Risk" then on its basis it will be possible to create the informational and analytical system of the class BI (Business intelligence) the realizing OLAP technology (Online analytical processing) for support of adoption of rational and reasonable administrative decisions when scheduling technical tinning and selective repair of LP MG. The estimates of technogenic risk calculated in RAM "Risk" will accumulate in tables of the relational database (OLAP cubes) with a binding to LPU, MKU, the defect pipe and each separate defect taking into account type of its anomaly identified at ILI. All these data will be defined on a timeline taking into account terms of carrying out ILI and repair of pipes, when fixing once a month, taking into account an interval of scheduling and adoption of administrative decisions. The users who got the authorized access to this information system will be able to carry out via the web interface the analysis of estimates of technogenic risk on LP MG in any cuts interesting them and in any point of Internet access or to internal network of gas transmission company.
Except display of information in the form of tables, schedules or charts (as it, for example, is shown in the figure 1), in this analytical system it is expedient to realize service like "Yandex traffic". Against the background of topographical information to estimate the most dangerous sites of LP MG with unacceptable technogenic risk at 10 points and to display in red color, sites with acceptable risk from 1 to 9 points – yellow, and sites with slight (admissible) risk of 0 points – green.
Such figurative submission of information will give the chance to users at the viewing scale most shallowly quickly to assess the common situation for all gas transmission company, and at increase in scale to detail information on LPU or MKU. It will allow to define, quickly enough, the most problem sites also will be reduced by time for adoption of rational administrative decisions when scheduling diagnostics and selective repair of LP MG taking into account technogenic risk. avtomatizacii v obrazovanii nauke i proizvodstve AS’2017 = The systems of automation in education, science and production AS’2017, SibGIU, 2017, pp. 78–81 (In Russ.).