FR2610008A1 - AMAGNETIC MANGANESE AND CHROMIUM STEEL AND TUBULAR ELEMENT OF A BOREHOLE MADE IN THIS STEEL - Google Patents

Abstract

1. A non-magnetic manganese and chromium steel resistant to corrosion under stress in a chlorinated medium, characterized in that it comprises by weight at the most 0.06% carbon, 19-26% manganese, 7-13% chromium, about 0.3% nitrogen and 0.6% silicon and residual nickel and molybdenum contents lower than 0.2% and 0.1% respectively, the remainder being formed by iron, apart from the unavoidable impurities.

Description

26 10008

  The invention relates to a non-magnetic manganese and chromium steel, resistant to stress corrosion in a chloride medium and a tubular element

  a drilling column made with this steel.

  Tubular elements of a co-

  boreholes, such as drill collars, stabilizers

  or other measuring or measuring equipment

  which are made of non-magnetic steel. These

  must be resistant to corrosion

  under stress in the drilling muds which contain

  high proportions of chloride.

  It is quite common to use

  cations in the field of oil drilling,

  nickel-chromium or chromium non-magnetic steels

  nickel-manganese. However, the elements made of these steels which are stressed on the one hand in fatigue and on the other hand in corrosion by drilling muds

  do not have sufficient resistance to

  erosion under stress, so that breaks in these parts occur after use of more or less long duration in the well. These breaks lead to shutdowns and require

  extremely expensive repairs.

  The operation of measuring and control equipment in the drill string requires other

  the use of non-magnetic steels

  must not exceed 1,005 for the elements

  tubulars supporting these materials. The steels used

  the above-mentioned elements of the drill string must therefore

an austenitic structure.

  When such austenitic steels are subjected to stress corrosion, that is to say to stresses in a corrosive medium such as drilling mud heavily loaded with chloride, their resistance to this form of corrosion is mainly obtained by the that these steels develop on their surface a passivation layer whose composition results from the interaction of the corrosive medium with the surface of the steel element whose composition is chosen

  in order to obtain a passive satlsfai-

  health. However, the micro-deformations caused in the steel element by mechanical stresses

  even relatively small, translates into

  which lead to the surface and cause a mechanical break in the passive layer, so that areas of the surface where the metal is

  bare. The region thus depassivated becomes active and

  feels anodic potential vis-à-vis the rest of the

surface that has remained passive.

  As a result of this depassivat: one localized,

  three cases may arise, depending on the

  of the material constituting the element

stress corrosion.

  If the rate of repassivation of the material is very slow and in particular much slower than the rate of anodic dissolution, the sliding step having revealed an overshot zone is the starting point of a corrosion which extends

  quickly, step by step, to the whole surface.

  Corrosion is no longer localized and the material

  is subject to generalized corrosion.

  If the re-saturation speed of the exposed metal is very fast, and in particular greater than the active anodic dissolution rate, the passive layer is reformed immediately and no cracking occurs.

  can not happen. However, a meal speed-

  sufficient sivation can only be obtained by using

  alloys with very high nickel contents of at least 35%. Such alloys are insensitive to stress corrosion, in most

  corrosive environments but can not be used

  commonly used, for elements of a drill column, the dimensions of which are generally

  because of their high cost price.

  Vee. Finally, if the anodic dissolution rate

  and the rate of repassivation of the material are similar

  As a result, the depassivated area remains localized and thus stabilized. The crack that originated in this area may, however, spread and lead to a break. Non-magnetic nickel-chromium steels

  chromium-nickel-manganese used for the

  components of a drill string are gener-

  destroyed by this process.

  In particular, for certain elements of a drill string, a chromium-nickel-manganese steel whose composition is as follows (in% by weight) is commonly used: carbon <0.07, manganese-18, chromium 12 , nickel 2, molybdenum. 0.5, nitrogen, 0.3, silicon - 0.6, sulfur <0.005, phosphorus <0.035. The

  The structure of such steel is austere and its

  Minimum mechanical characteristics obtained after hot work-hardening at around 700 'are the following: - yield strength = 730 N / mm, tensile strength - 880 N / mm 2, - elongation at break: 23%, stress & fracture = 50%

KCV = 50 J.

  The drill string elements made of this steel, whose corrosion behavior under

  constraint is similar to the third type described above.

  above, tend to undergo cracking up to complete failure under the effect of stress corrosion under conditions that are

  those of drilling in a chloride medium.

  The object of the invention is therefore to provide a manganese and chromium nonmagnetic steel resistant to corrosion under stress in a chlorinated medium which makes it possible to produce tubular elements for

  drilling columns whose susceptibility to cracking

  ration and rupture is clearly limited.

  For this purpose, the steel according to the invention comprises (en masse):

  - not more than 0,06% of carbon, from 19 to 26% of manganese

  from 7 to 13% of chromium, approximately 0.3% of nitrogen and 0.6% of silicon and residual contents of nickel and molybdenum, less than 0.2% for nickel and 0, 1% for molybdenum, the rest, with the exception of unavoidable impurities,

being made of iron.

  The invention also relates to a tubular element of a drill string made of a steel

according to the invention.

  In order to fully understand the invention,

  we will now describe, as examples not

  two types of alloys according to the invention, as well as the tests carried out on samples made of these steels and a mode of elaboration of elements for

  column made of steel according to the invention

  tion. The single figure is a diagram giving the stress at break in chloride medium of steels

  according to the invention and steel according to the prior art

laughing.

Example 1

  A steel has been developed with the following composition (in mass%):

  carbon <0.06, manganese '19.20, chromium 2 12, nitrogen--

  0.3, silicon-0.6, sulfur <0.005, phosphorus <0.035 nickel <0.2, molybdenum <0.1, the balance to arrive at

  % being constituted, with the exception of inert impurities

  vitable, by iron. The structure of such a steel is austenitic and its mechanical characteristics after hot work hardening around 700'C are equivalent to those

  steel according to the prior art described above.

  The magnetic permeability of steel, inferred

  than 1005, also meets the requirements for its use for measurement and control device holders for drill columns. The steel according to the invention, quite surprisingly, has a very good performance

  stress corrosion, as it will be

  much further, although it does not contain any elements

  passivating agents such as nickel and molybdenum.

significant levels.

  So far, to increase the resistance to

  stress-free erosion of such manganese and chromium non-magnetic steels, the aim was to increase the content of passivating elements such as nickel, molybdenum and chromium, within permissible limits.

  function of an acceptable selling price of steel.

  In the case of the steel according to the invention, the passivating elements nickel and molybdenum have been completely removed, and the chromium passivating element

  has been maintained at a value close to its usual value

tual.

Example 2

  A second steel was developed whose composition

  sition is the following (in mass%): carbon <0.06, manganese 25, chromium 28, nitrogen, 0.3, silicon - 0.70, sulfur <0.005, phosphorus

0.035.

  As in the steel of Example 1, nickel and molybdenum are maintained as residual elements. In the case of this steel according to Example 2,

  not only the passivating elements nickel and molyb-

  dene have been removed but still the chrome has been

  reduced to a level much lower than the usual level

  tual. To obtain a satisfactory structure and therefore suitable magnetic properties of

  steel, it is necessary to respect certain

  between these main alloying elements.

  In the case of the steels according to the invention, the contents of carbon, nitrogen, silicon, manganese and chromium (in mass%) must satisfy the following relations: A = 497 - 462 (C + N) - 9.2 Si - 8 , 1 Mn - 13.7 Cr,

with A <15.

  Corrosion tests Stress corrosion tests were carried out on steel specimens according to the prior art, the composition of which is given above, in

  steel according to example 1 and steel according to the example

2 of the invention.

  The corrosion tests were carried out in a solution whose composition is close to

  that of the most corrosive drilling mud encountered

tred and used in drilling.

  The chloride contents of such a drilling mud are as follows: MgCl2 310 g / l

Nacl 110 g / l.

  oxygenated by bubbling air so as not to block

the cathodic process.

  Three types of tests were performed.

  - 1 '/ constant load tests.

- 2 '/ slow tensile tests.

  - 3 '/ fatigue corrosion tests.

  1V / Constant load tests: For each of the grades of steel

  the purpose of the tests, a test piece of trac-

  according to NACE TM 01-77 and this test piece is immersed in the corrosive solution maintained at 110 ° C. A load corresponding to 90, 75 and 50% of the yield strength is applied successively to these test pieces and the breaking time is recorded under these conditions. The results of the test are presented

in Table I below.

TABLE I

  NUANCE CHARGE according to NUANCE NUANCE the prior art Ex. 1 Ex. 2

% 10 H> 1000 H> 1000 H

TIME

75% 6 H> 100 H> 1000 H

BREAKING

% 1 H 500 H> 1000 H

  It therefore appears that the steel grades according to the invention quite unexpectedly have a resistance to stress corrosion which is much greater than that of the grade according to the invention.

the prior art.

  Even more unexpectedly, the shade corresponding to the low chromium example 2 has the best characteristics of corrosion resistance. 2 '/ Slow tensile tests: The strain rate during the test is maintained at a value equal to: 1 x 10-7 L / L sec-, with J L / L = relative elongation of the specimen during

of the test.

  the test results for the grade

  according to the art and for the nuances according to the

  Examples 1 and 2 are given in the accompanying figure, in the form of a histogram representing, in a comparative manner, the breaking stresses in

slow pulling of test pieces.

  We see that the shades according to the invention have comparable withstand characteristics, under the conditions of the test, these characteristics being much higher than those of the shade according to

the prior art.

  In addition, the test makes it possible to quantitatively determine the action of stress corrosion by comparing the tensile strength in the corrosive medium and in the air, this resistance in the air being obtained by means of test of

usual traction.

  The tensile strength in the medium

  corrosive can be considered as a parameter

  is representative of the corrosion resistance.

  3 '/ Fatigue-corrosion test: The test consists of subjecting a test specimen to a rotary bending in the chloride solution mentioned above. The speed of rotation is

  Rotations per minute. In a first series of

  that is, a load equal to 75% of the yield strength of the material is applied and, in a second series of tests, a load equal to 50% of this elastic limit. We note each time the number of cycles to

breaking.

  The test results for each of the

  for the nuance according to the prior art and the two shades according to the invention are given

  in Tables II and III, respectively.

TABLE II

A C I E R NUMBER OF CYCLES

  Nuance according to the prior art 76 000 Nuance n '1 according to the invention 250 000 Nuance n' 2 according to the invention 375 000

TABLE III

A C I E R NUMBER OF CYCLES

  Nuance according to the prior art 21 000 Nuance No. 1 according to the invention 30 000 Nuance No. 2 according to the invention 31 000 The tests show that the grades according to the invention have a very superior behavior to the grade

  according to the prior art, for a solicitation in

  corrosion, in a chlorinated environment.

  The tests also show that the second grade of the invention, low chromium, has characteristics a little higher than those of the first hue with higher chromium, during the tests.

fatigue corrosion.

  4 '/ Processing and formatting of parts

tubular for drill string.

  The two shades according to the invention have been used for the production of tubular parts for

  drilling columns and in particular for the manufacture of

  rods. These tubular pieces have a

  length (9 to 10 meters) and have

  connection markings at each of their ends.

  Mechanical characteristics of steels

  according to the invention at least equivalent to the characteristics

  mechanical properties of steels according to the prior art

  are obtained by hot work hardening at a temperature of

  between 700 and 800 ° C, with a rate of

  hardening of 20 to 30%. The forging temperature of the tubular products is chosen so as to be situated, with respect to the precipitation curve in

  steel in an area corresponding to the Precision Onez

  pity. "This avoids a coarse precipitation

  carbonitrides at the grain boundaries which could

  drag an intergranular cracking mechanism.

  During the tests, in sludge

  Since the pH is between 6 and 8, this type of cracking has not been observed. In addition, drilling muds are generally at pHs between 10 and 12.

  The conditions for the forging of tubular

  as defined above correspond to a forging temperature of 680 to

650 °.

  It was impossible to maintain the product temperature at 680 ° C during any operation

  forging and maintain this constant temperature

  te throughout the length of the product.

  We have therefore developed a technique originally

  forging for tubular pieces of great lengths of steel according to the invention. This technique involves forging first the middle of the bar to

  a temperature corresponding to a point

  above the precipitation zone; this temperature

  is greater than 830 ° C. The rate of hardening

  It is wise to obtain the required mechanical characteristics at this forging temperature, then the bar is forged at its ends (over a length of about 1.5 meters) at a temperature corresponding to

  a point below the precipitation zone.

  The forging operation is thus regulated by

  function of the air cooling curve am-

  binder of steel, to avoid forging in the area

precipitation criticism.

  This results in a tubular element of great length for a drill string having satisfactory mechanical characteristics, good resistance to intergranular cracking, and

  Generally speaking, very good resistance to

  erosion in chlorinated drilling muds.

  The invention is not limited to the two

  those which have been described above and, in particular,

  the manganese and chromium contents of the steel

  the invention may be different from the levels mentioned above. However, to obtain satisfactory properties of the steel, the manganese content must be greater than or equal to 19% and less than or equal to 26%; likewise, the content

  chromium must be greater than or equal to 7% and

  13% or more. For chromium contents

  situated towards the lower limit of the

  localized corrosion, for example under the influence of

  fet of alternating solicitations, no longer appears and only the generalized corrosion of steel can be

observed.

Claims (7)

  1. Non-magnetic manganese and chromium steel resistant to corrosion under stress in a chlorinated medium, characterized in that it comprises (by mass), at most 0.06% of carbon, from 19 to 26% of   manganese, 7 to 13% chromium, approximately 0.3% azo-   te and 0.6% silicon and residual contents in   nickel and molybdenum less than 0.2 and 0.1% respectively   the rest, with the exception of unavoidable impurities, being made of iron.   2.- Non-magnetic steel according to the claim   characterized by the fact that it contains (in   se) about 19.2% manganese and 12% chromium.   3.- Non-magnetic steel according to the claim   characterized by the fact that it contains (in   se) about 25% manganese and 8% chromium.   4.- Non-magnetic steel according to any one   that claims 2 and 3 characterized by the fact   it contains less than 0.005% sulfur and 0.035% of phosphorus.   5. Non-magnetic steel according to the claim   characterized by the fact that its   C, nitrogen N, silicon Si, manganese Mn and   in Cr chromium are such that they respect the relationship following statement:   497 - 462 (C + N) - 9.2 Si - 8.1 Mn - 13.7 Cr <15.   6.- tubular element for drill string characterized in that it is made of a steel comprising (en masse), at most 0.06% of carbon, 19 to 26% of manganese, 7 to 13% of chrome, about   0.3% nitrogen and 0.6% silicon and   nickel and molybdenum alloys less than 0.2% and 0.1% respectively, the rest, with the exception of unavoidable impurities, being made of iron.   7.- Tubular element according to the claim   tion 6, of great length, of the order of 10   characterized in that it is obtained by a forging operation of a bar of forging, initially, the central portion of the bar   at a temperature above the pre-   in the steel and then forging the ends of the bar at a temperature below the precipitation zone in the steel.