3. Trends in improving methods of rationing, calculation, and management of mechanical properties of pipe steels

In the evolution ( ) of pipeline transport in Russia and abroad, three trends have been and are currently dominant (Figure 3) in view of Eqs. (1)–(4) in deterministic formulation [3–7]:


At the first stages (1930–1960) of the development of pipeline systems, carbon (with a carbon content of 0.22–0.35%), unalloyed steels with larger of the abovementioned margins and ,

Figure 3. Basic determinate variations in design parameters of pipelines.

From Eqs. (2) and (3), it follows that margins and in the calculations for the allowed stresses are related to the factors m, K1, K2, and Kн, in Eq. (3) for calculations on the limiting

№. Factor Symbol Value 1. Condition load effect factor m 0.6–0.9 2. Load reliability factor K<sup>1</sup> 1.1–1.5 3. Material resistance factor K<sup>2</sup> 1.34–1.55 4. Design safety factor K<sup>н</sup> 1.0–1.05

In essence, the safety margins and stability according to Eqs. (2)–(4) reflect the role of statistical and probabilistic uncertainties, inaccuracies, ignorance, and responsibility of

Based on strength and stability calculations under Eq. (1) with addition of Eqs. (2) and (3) for the pipeline with given p, N, Mв, Mt, Rв, and D, the wall thickness is chosen to be greater than the minimum ratio of yield strength and strength to margins and with subsequent

Equation (2) defines the area of allowable stresses for deterministic normative calculations of

The values of the factors in the calculations according to the norms [2] are given in Table 2.

3. Trends in improving methods of rationing, calculation, and management

In the evolution ( ) of pipeline transport in Russia and abroad, three trends have been and are currently dominant (Figure 3) in view of Eqs. (1)–(4) in deterministic formulation [3–7]:

• Increase of the diameter of pipelines D (from 250–300 to 1200–1400 mm) and pressures p

• Increase of mechanical properties of pipe steels (yield strength ) (from 200–250 to 600–

At the first stages (1930–1960) of the development of pipeline systems, carbon (with a carbon content of 0.22–0.35%), unalloyed steels with larger of the abovementioned margins and ,

• Decrease in safety margins (from 1.8–3.2 to 1.2–1.5) and (from 2.4–3.5 to 1.6–1.8)

800 MPa) and strength (from 400–450 to 700–900 MPa)

ð4Þ

states at and :

86 Probabilistic Modeling in System Engineering

Table 2. Calculated normative values of factors.

binding of stability with and .

of mechanical properties of pipe steels

(from 2.0–2.5 to 14.0–16.0 MPa)

pipeline strength (Figure 1).

.

pipeline systems.

and lesser p, D, , and were predominantly used. Under these conditions, when determining the thickness of the pipe wall , the margins and yield strength proved to be key factors, because they gave smaller permissible stresses under Eqs. (2) and (3).

The idea that increasing the pipe steels yield strength is crucial in those years led to the desire of metal scientists, technologists, and designers to reduce the material consumption of pipelines by increasing the yield strength by all available methods and means (alloying steels, thermomechanical processing of sheets and pipes while reducing margins ). The same approach was typical for the development of general engineering, energetics, oil and gas chemistry, transport, and construction.

In the process of accelerated development of pipeline systems, low-alloy steels, low-carbon low-alloy steels, and low-alloy thermo-hardened steels have been consistently used since the 1960s.

This aspiration not supported by the necessary scientific justifications led to:


From the generalized statistical analysis of damage and destruction of various objects (including those working under increased pressure), it follows that engineering materials, design, and technological solutions associated with increase of and decrease of are insufficient to prevent large-scale emergency and sometimes catastrophic situations. It became clear that the existing engineering practice of calculation focused on the designation of independent margins and and the basic characteristics of strength and is entailed with the danger of a real and reliable operation of pipeline systems.

One of the main problems was a complex, interrelated deterministic, statistical, and probabilistic analysis of the determining parameters—safety margins , , and and mechanical properties and in Eqs. (1)–(4). According to Eqs. (2) and (3), the minimum allowable stresses give the maximum quantitative coherence between these parameters:

$$n\_\mathbf{y} = n\_u \left\{ \sigma\_\mathbf{y} / \sigma\_u \right\} \tag{5}$$

and substantiation of strength of the vessels and pipelines in nuclear reactors [8–10] and space

Probabilistic Analysis of Transportation Systems for Oil and Natural Gas

http://dx.doi.org/10.5772/intechopen.75078

89

Four strategic tasks are being solved by methods of deterministic, statistical, and probabilistic

• Design and construction of new pipelines for liquid and gaseous hydrocarbons transportation (including marine and harsh climatic conditions of Siberia, the North Sea and the

• Extension of operation of existing pipelines within the limits of modern regulatory

• Resolving the issues of complex technical diagnostics, repair, and restoration works in the damage areas beyond the norms of permissible defects for the prolongation of safe exploi-

• Decommissioning in cases of significant exhaustion and formation of dangerous critical

The tasks of justifying and ensuring industrial safety of pipeline systems in accordance with the criteria of strength, resource, and risks in compliance with the Federal Law No. 116-FZ "On Industrial Safety of Hazardous Production Facilities" are resolved with the coordinating and decisive role of Rostekhnadzor with the participation of the Russian Academy of Sciences, leading oil and gas companies as Transneft, Gazprom, Rosneft, the Russian Union of Oil and Gas Constructors and leading academic and industry institutes

The main directions of scientific research and applied developments in this direction are

The solution of problems of formation and development of industry norms and rules for substantiating the strength, durability, resource, and reliability of pipelines is concentrated in

In normative documents [13] that are governing the industry, the following assumptions were

• Temporary technological heredity is not explicitly taken into account from the processes of obtaining the parent metal and the production of sheets and pipes in factories and enterprises.

• The federal legislation on justification and ensuring industrial safety by risk criteria

• Industry norms and rules for justifying strength, durability, and reliability

reflected in the proceedings of the I and II Forums on industrial safety [12].

the research institutes of Transneft and Gazprom.

4. Modern problems of justifying the strength of pipeline systems

and missile systems [11].

Arctic Sea)

and universities.

made:

modeling and calculation nowadays in Russia:

requirements for strength and durability

The solution of these tasks must meet the modern requirements of:

tation within the assigned terms

and un-repairable defects

Managing safety margins and for the purpose of their reduction should be carried out in accordance with ratio / , which is featuring, as shown on Figure 1, the hardening degree (or module) of tubular steels in the elastoplastic range beyond the yield point . For the majority of actually used pipe steels as they are improved with existing hardening methods, with the growth of and , the ratio / is increased due to preferential growth of (Figure 4).

In the nomenclature and types of the previously used tube carbon steels (Figures 1 and 2) with reduced yield strength (less than 300 MPa) and a ratio / (less than 0.6), the traditional calculations of the yield strength with margins were of primary importance. With a further increase in the yield strength and decrease in the safety margin , the calculations for the ultimate strength with margins have become determinative, in accordance with Eq. (5).

However, in this case, the problem of increasing the danger of stability loss under and an uncontrolled dangerous transition to large plastic deformations according to Eq. (2) remains, in fact, not explicitly reflected in Eq. (5), due to a reduction in the degree of hardening of steels with a simultaneous increase of and the ratio / . Such conclusion in the framework of modern concepts of strength calculations [1, 3–6] required a gradual transition from calculations in stresses to calculations in deformations е. This transition already received not only its scientific justification [6–8] but also its practical implementation in norms

Figure 4. Coherence between strength margins and mechanical properties of pipe steels.

and substantiation of strength of the vessels and pipelines in nuclear reactors [8–10] and space and missile systems [11].
