With the aim of determining the possible use of dismountable assembled pipes after prolonged storage for

the construction of a pipeline between industries under extreme north conditions, studies are made of their

engineering condition and full-scale tests.

A feature of dismountable assembled pipeline constructions (PMTB-2) is not only that they are predominantly laid

overground, but also the possibility of carrying out rapid assembly and repair of a pipeline without the use of welding. They

are used in oil recovery fields as both product carriers between and within industries, and as main oil pipelines extending sev-

eral hundreds of kilometers, where burying pipelines in trenches is economically undesirable.

Dismountable assembled pipelines are objects of increased danger, the method of laying them is predominantly over

ground and burying into soil is only carried out in overcoming natural or artificial barriers, in critically hot areas, and in

bypassing population areas and industrial objects.

Within the territory of Western Siberia field main pipelines are used with a total extent of more than 500 kilometers,

and in view of opening up new oil deposits there is an increase in the demand for use of this construction.

The object of our studies is pipes and dismountable assembled joints of field main pipelines of considerable pro-

ductivity with a nominal diameter of 200 mm, intended for transporting oil and oil products over a considerable distance

under natural climatic conditions in the temperature range from –60 to +50°C.

In order to ascertain the operating safety and reliability of a pipeline subject to prolonged conservation, it is neces-

sary to carry out comprehensive full-scale studies of the pipe and joint quality.

Main tasks of the research:

1) general and detailed visual and measurement monitoring (VMM), monitoring by non-destructive methods of the

basic metal and welded pipe joints, manufactured at a different time;

2) determination of the mechanical properties and chemical composition of pipe material and pipeline joint assem-

blies in order to reveal possible degradation of welded joints and the heat-affected zone (HAZ);

3) performance in experimental units of research with action on an object of various constant and variable force deform-

ing factors and their probable combination at normal and lowered temperature, i.e., simulation of extreme operating conditions.

The study for evaluating the actual state of a pipe included eight stages.

The main study method is simulation of all possible main actions on a pipeline: tension, compression, bending,

impact (dynamic) loads at normal and lowered (down to –58°C) temperature, and internal pressure.

Chemical and Petroleum Engineering, Vol. 47, Nos. 9–10, January, 2012 (Russian Original Nos. 9–10, Sept.–Oct., 2011)

STUDY OF THE SUPPORTING CAPACITY

OF DISMOUNTABLE ASSEMBLED PIPELINE

COMPONENTS FOR EXTREME NORTH

CONDITIONS

V. V. Klimov, A. P. Korchagin,K. A. Kuznetsov, Ya. Yu. Shlenskii,G. Yu. Rozhemberskaya, and V. V. Antipin

Irkutsk Research and Design Institute of Chemical and Petrochemical Engineering (IrkutskNIIkhimmash), Russia.

Translated from Khimicheskoe i Neftegazovoe Mashinostroenie, No. 10, pp. 19–22, October, 2011.

0009-2355/12/0910-0674 ©2012 Springer Science+Business Media, Inc.674

Pipes intended for research, designated for operation within the composition of pipelines with closing joints and rub-

ber sealing sleeves representing a pipe construction (Fig. 1), consist of a main electrically welded straight-seamed pipe with

specially shaped components welded to it (joint construction according to GOST 20772–81 [1]), i.e., a sleeve and a socket

joint. Pipes 219 × 3.5 mm in diameter were prepared according to TU 44-479–87 [2] with coiled steel grade 08G2SF.

In the course of studies, chemical composition and mechanical properties were determined, and macro- and

microstructure of the pipe material and joint assemblies were studied. Overall and detailed VMM were carried out, wall thick-

ness and hardness were measured, and radiographic (RG), ultrasonic (UST) and magnetic powder (MPD) monitoring of the

basic metal and welded 218 joints, selected by random collection of pipes manufactured in different years, were performed.

Nondestructive Monitoring. From the results of VMM, it was established that storage of pipes in the absence of

sheds led to a different degree of surface corrosion damage of their inner surface. In all the pipes studied, local corrosion

damage was discovered to a different extent with a maximum depth of 0.15–0.3 mm, and for some pipes over the lower gen-

erating line uniform corrosion with a width of up to 130 mm was present. On the inner surface of some pipes breakdown

of the paint coating was revealed, and uniform corrosion along all of the surface up to a width of half of the perimeter was

detected. In monitoring the internal surface, it was revealed that in pipes of 1990–1991 output there were no internal circu-

lar joints for welded sleeves and socket joints.

From the results of measuring geometrical dimensions of pipe constructions, it was established that the dimensional

parameters are quite stable and satisfy GOST 20295–85 [3], controlling specifications for pipes used in building pipelines for

the transport of natural gas, oil, and oil products.

In monitoring circular joints by RG and UST methods, defects were revealed in the form of an unwelded root of a

joint over the whole length of a welded joint. In monitoring longitudinal welded joints by VMM, no impermissible defects

were detected.

Pipe wall thickness from the results of measurements equals or is higher than the nominal thickness and varies for

pipes of different manufacturing batches from 3.5 to 4.1 mm.

Study of Chemical Composition and Mechanical Properties. Chemical analysis was carried out for five pipes and

their joint components, i.e., material of all pipes, socket joints and sleeves, and also fused metal of annular joints of welded

socket joints and sleeves corresponded to steel 08G2SF, and support ring material corresponded to steel 50Kh.

Mechanical tests on specimens from pipes showed that strength and ductility properties of the metal of a pipe wall

satisfy the specifications of GOST 20295–85 [3].

The results of testing pipe material and joint components indicate the absence of signs of ageing (and correspond-

ingly a change in mechanical properties) during their prolonged storage.

Mechanical properties of pipe material and joint components at 20°C are provided in Table 1.

Mechanical properties of socket joint and sleeve materials change over quite wide limits, retaining a favorable com-

bination of strength and ductility properties; the yield strength has lower values compared with pipe material.

675

Fig. 1. Pipe connection: 1) sleeve; 2) socket joint; 3) steel support ring;

4) rubber microporous gasket; 5) rubber packing ring; 6) electrically

welded straight-seamed pipe.

Pipes, joining components, and welded joints were tested for impact strength by the Charpy method (in specimens

with a V-shaped notch) at –58°C. From the results of testing materials of five test pipes, they have high impact strength, i.e.,

KCV = 34–80 J/cm2. For socket joint material, the impact strength is low, i.e., the average value from the results of testing

three specimens is 4–17 J/cm2. Sleeve material also has a low impact strength, i.e., 6–13 J/cm2.

In view of the low values of material impact strength for sleeve and socket joint material, additional studied were

carried out at +10, 0, –15, and –30°C. For comparison in the same temperature range similar tests were performed for impact

strength by the Menage method (in specimens with a U-shaped notch) followed by determination of the ductile component

in the transverse section of specimens.

Results of impact strength tests in the temperature range from –58 to +20°C by the Charpy and Menage methods are

presented in Fig. 2. Graphical dependences were plotted for a polynomial approximation. In spite of the scatter determined

for impact value of specimens tested with one temperature value, approximate dependences for the change in KCV and KCU

on temperature have reliability approximation indices exceeding a value of 0.9.

The actual value of impact strength KCU for sleeve material at –58°C is 60–70 J/cm2, compared with KCV equal

to 4–15 J/cm2. Such a marked increase in impact strength with a reduction in stress concentration factor at the tip of a notch,

(with a change-over from a sharp V-shape to a U-shaped notch) indicates that the sleeve material, and possibly for socket

joints, is sensitive to the stress concentration level.

The danger of brittle failure of components in areas of stress concentration at low temperature decreases markedly with

a value of stress concentration factor commensurate with a similar factor at the tip of a U-shaped notch. The temperature of the

ductile-brittle transition for metal in the area of these stress concentrators shifts into a lower temperature region, i.e., below –58°C.

Here it is necessary to bear in mind that the difference in impact strength values obtained in testing specimens with

different types of notches, is connected with a marked increase in energy, required for crack generation at the tip of a U-shaped

notch compared with specimens with a V-shaped notch.

Study object Yield strength σ0.2, MPa Ultimate strength σu, MPa Relative elongation δ5, %

Pipes 484 548.5 27.6

Socket joints 316 512 34.9

Sleeves 340 518 31.1

676

TABLE 1

Fig. 2. Temperature dependence for socket and sleeve material made from steel 08G2SF: a) for

specimens with a V-shaped notch (Charpy); b) for specimens with a U-shaped notch (Menage).

Energy required for further propagation of a generated crack, does not depend on the type of notch, or its initiation.

This is indicated indirectly by the difference in the temperature of ductile-brittle transition according to the B = 50% criterion,

determined in testing specimens with different types of notches (Fig. 3).

Thus, the material of joint components (socket joint and sleeves) at –58°C has low impact strength values, low

resistance to crack formation and development, and correspondingly high sensitivity to stress concentration of production

and construction origin.

Metallographic Studies. Metallographic studies of pipes and welded joints with sockets and sleeves were carried out at

a magnification of ×10 in macrosection templates cut from longitudinal and circular joints, joining pipes with sockets and sleeves.

Studies showed that that microstructure of the basic metal is typical for this type of steel and is a ferrite-pearlite mixture.

In each of the macrosections, hardness measurements of fused metal, heat-affected areas, and areas of sections of

basic metal adjacent to them, were made. Hardness was measured by the Vickers method. No areas of metal with high hard-

ness were revealed.

Cryogenic Studies of Pipe Joints for Maximum Load. In order to estimate the operating capacity of a structure at

negative temperatures in regions of the extreme north cryogenic, studies were carried out for pipe assemblies at –58°C and

the action of external loading factors (tension, bending, impact) and with an internal working pressure (5 MPa).

All the studies were carried out in an experimental unit constructed and manufactured specifically for full-scale

studies of model pipe assemblies 12 m long.

As a result of cryogenic studies, it was established that:

1) With tension under internal pressure for model pipes with two-sided welding they withstood an axial tensile load

with a force of 124.77 to 128.63 tonf without failure and visible deviation from correct geometrical shape of the model com-

ponents. Pipes with one-sided welding did not withstand testing and failed with an axial tensile load of 83.5 tonf and 99.1 tonf

over the ring of a welded joint of a pipe to a sleeve.

2) With bending under internal pressure, a sealed joint of a model with one-sided welding did not lose air-tightness

with a bending force of 3.76 tonf and an internal pressure of 5.49 MPa. One model withstood testing with a bending load of

3.29 tonf and pressure within the model of 5.02 MPa. In two models, there was leakage of the working medium in test joints:

in one due to a concealed defects of the sealing ring, and residues of preserving coating, and in another due to the presence

with a ring grove of residues of preserving coating.

3) Under impact loading, a model of pipes with two-sided welding, under internal pressure, withstood impact test-

ing (dynamic testing) with an energy of 35 kJ without loss of airtightness for a joint assembly, and subsequent loading with

an internal pressure up to 15.0 MPa. In the area of load application (at the surface of a socket) in each model a depression

formed, although there was no leakage of working liquid. Two models of pipes with one-sided welding did not withstand test-

677

Fig. 3. Temperature dependence for proportion of ductile component in a sleeve fracture: a) for

specimens with a V-shaped notch (Charpy); b) for specimens with a U-shaped notch (Menage).

ing with an impact energy of 35 kJ, and they failed over the circular welded joint of the pipe with a sleeve. The joint assem-

bly of one model crumbled, and the area of greatest crumbling in the socket joint from one side parallel to its axis there was

formation of a through crack with an opening width up to 10 mm. The socket of another model deformed insignificantly.

4) Under internal pressure, models with two-sided welding failed with a pressure of 18.06 to 20.72 MPa. Failure of

a model occurred by a classic specimen failure of a thin-walled shell in one of the pipes through basic metal. The opening

dimensions were from 235 × 26 to 390 × 40 mm. The strength reserve factor with respect to the working pressure was

3.61–4.1. Pipes with one-sided welding failed with an internal pressure of 18.89 and 19.91 MPa over a circular welded joint

of a pipe with a sleeve. The strength reserve factor for pressure was 3.78–3.86.

Conclusions. In spite of the fact that the wall material of socket joints and sleeves at –58°C has low impact strength

values (in testing specimens with a V-shaped notch), positive results for full-scale tests on pipes and joints at this tempera-

ture indicate that small stresses arising in joints in an assembled form do not stimulate brittle failure.

Results of comprehensive study of dismountable assembled pipe constructions under low-temperature conditions

and unfavorable external action confirm the possibility of using pipelines of this type to construct temporary on-site intra-

field pipelines and inter-field pipelines.

REFERENCES

1. GOST 20772–81, Joining Devices for Engineering Facilities of Delivery, Pumping, Pouring, Filling, Transporting,

and Storing Oil and Oil Products. Types. Basic Parameters and Dimensions. General Technical Specifications.

2. TU 44-479–87, Electrically Welded Pipes of Low-Alloy Steel.

3. GOST 20295–85, Steel Welded Pipes for Main Gas and Oil Pipelines. Technical Conditions.

678