JPS5877550A - Steel pipe with high collapse strength - Google Patents

Abstract

PURPOSE:To enhance the collapse strength of a steel pipe while keeping the intrinsic corrosion resistance by providing residual tensile strength to the inside of the pipe in the peripheral direction within a certain limit. CONSTITUTION:By suitably regulating the amount of cooling water used during hardening and tempering in a stage for manufacturing a steel pipe such as an oil well pipe, <=0.15 time as much residual tensile stress as the yield stress of the pipe is provided to the inside of the pipe. Thus, the colapse strength (strength to squeezing rupture) is enhanced without deteriorating the corrosion resistance. When this method is applied to an oil well pipe for a deep well used under severe conditions, a significant effect of enhancing the durability is produced.

Description

【発明の詳細な説明】 本発明は、コラプス強度（圧潰破壊に対する強さ）Ｋす
ぐれた鋼管に関する。DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a steel pipe with excellent collapse strength (strength against crushing fracture) K.

近時、石油・天然ガス事情の逼迫から、油井・天然ガス
井は深井戸化の傾向が著しく、加えて産出ガス中に湿潤
な硫化水素の含まれる場合が多くなってきたが、このよ
うな苛酷な環境下で使用される油井管には、高耐食性と
ともに優れたコラン。In recent years, due to the tightening of the oil and natural gas situation, there has been a marked trend toward deeper oil and natural gas wells, and in addition, the produced gas is increasingly containing wet hydrogen sulfide. Coran has excellent corrosion resistance and is suitable for oil country tubular goods used in harsh environments.

ス強度が要求される。strength is required.

しかるに、耐食性とコラプス強度は一般に相反するもの
として位１１９うけられる。すなわち、コラプス強度の
向上は、材′ａそのものの改良によって降伏強度の上昇
を図ることで実現用能であるが、降伏強度を高めること
はとりも直さす引張強度を上昇させるということを意味
し、との引張強度σ）上昇は耐食性θ）劣化に直結する
のである。したがって、油井管の場合、利質面での操作
によるコラプス強度の向上（ｔｊ−限度があり、有効々
７１策と１はなり得ない。However, corrosion resistance and collapse strength are generally considered to be contradictory. In other words, improving the collapse strength can be achieved by increasing the yield strength by improving the material 'a' itself, but increasing the yield strength also means increasing the tensile strength. , the increase in tensile strength σ) is directly connected to the deterioration of corrosion resistance θ). Therefore, in the case of oil country tubular goods, there is a limit to improving the collapse strength (tj) by operating on the profit side, and it cannot be effectively 71 measures or 1.

本発明の目的は、鋼管本来の耐食性を生かしつつコラプ
ス強度の向上を得ることを可能にすることにある。An object of the present invention is to make it possible to improve the collapse strength while taking advantage of the inherent corrosion resistance of steel pipes.

すなわち本発明の要旨とするところは、事前内周面に当
該鋼管の降伏応力のｏ、ｉｓ倍以下の管周方向への引張
残留応力を付ケしたことを特徴とする高コラプス強度鋼
管、にある。That is, the gist of the present invention is to provide a high collapse strength steel pipe, characterized in that a tensile residual stress in the circumferential direction of the pipe is preliminarily applied to the inner circumferential surface, which is equal to or less than o,is times the yield stress of the steel pipe. be.

従来、１１ｒｌ管に残留する応力かそのコラプス強度に
与える影響についてはその十分な解明がなされてい々か
った。残留応力がコラプス強度に影響するであろうこと
は、例えば次のような事例から予１７４は容易である。In the past, the residual stress in the 11rl tube and its influence on the collapse strength have not been sufficiently elucidated. It is easy to predict from the following example that residual stress will affect the collapse strength.

油井管の製造工程においては、焼入れ一焼戻し処理後、
曲がり矯正を目的として、冷間にてストレートナ加工が
実施されるが、このヌ１−レー１−す加工によシ鋼管は
、周方向の降伏強度が低下し、丑だ同時に管内面局方向
に圧縮の残留応力が発生し、このとき、コラプス強度が
低下するという現象が起こる。しかしながら、このよう
な事例では、つねに残留応力の変化と同時に月利の降伏
特性および管の断面性能（楕円度、偏肉度）の変化が起
こるため、残留応力だけσ）影響だけをみようとしても
容易Ｋｕいかず、このために残留応力の影響の解明は従
来、殆んどなされていなかった訳である。いま丑で一般
には、圧縮・引張の何れであっても、とにかく残留応力
の存在はコラプス強度にとって好捷しくないとする見方
が主流であり、残留応力についてＱｊこれを（１γ力排
除する方向に努力が払われていたのが実状である。In the manufacturing process of oil country tubular goods, after quenching and tempering,
Cold straightener processing is performed for the purpose of straightening bends, but steel pipes subjected to this neck straightening process have a lower yield strength in the circumferential direction, and at the same time, the yield strength in the inner direction of the tube decreases. Compressive residual stress is generated, and at this time a phenomenon occurs in which the collapse strength decreases. However, in such cases, changes in the yield characteristics of the monthly yield and the pipe's cross-sectional properties (ovality, thickness unevenness) always occur at the same time as changes in the residual stress, so even if we try to look only at the effects of the residual stress (σ), Therefore, the effect of residual stress has not been clarified in the past. Currently, the prevailing view is that the presence of residual stress, whether compressive or tensile, is not good for collapse strength. The reality is that efforts have been made.

残留応力のコラプス強度に対する影憎稍＝考慮した技術
もないではない。特開昭５１−３３’１２’１号は、そ
うした技術の提案であるが、これば管内周面に周方向の
引張残留応力（２０％〜１（午伏点）をＨ４してコラプ
ス強度の向上を図るというものである。しかるにかかる
手法は、残留応力とコラプス強度の１７１５に存する関
係を正確に把握したというものではなく、油井管の場合
のようにコラプス強度のみならず耐食性も同時に要求さ
れる鋼管に対しては、実際」二全く役に立たないもので
ある。There is no technology that considers the influence of residual stress on collapse strength. JP-A No. 51-33'12'1 proposes such a technique, which increases the collapse strength by applying circumferential tensile residual stress (20% to 1 (node point) H4 on the inner circumferential surface of the pipe). However, such methods do not accurately grasp the 1715 relationship between residual stress and collapse strength, and as in the case of oil country tubular goods, not only collapse strength but also corrosion resistance is required at the same time. In fact, it is completely useless for steel pipes.

すなわち、上記の技術において、コラプス強度は管内周
面への引張残留応力を高めれば高めるほど向上するとい
うことになっているが、これは誤識である。そもそも」
−記のものは、鋼管のコラプスは何れのときにも管内面
側から発生するという前提に立っているが、この条件は
必ずしも事実とは一致しない。鋼管に外圧が作用して生
じる管周方向への圧縮応力は、管内面において最大とな
るのは確かである。しかしながら、管そのものに予め残
留応力が与えられている場合は、外圧負荷時の管周方向
への圧縮応力は必ずしも管内面で最大になるとは限らな
い。つ捷り、肉厚方向の残留応力分布としては、管内面
側に引張応力がかかるときはそれに見合う圧縮応力が管
外面側に作用することになるので、内面側で引張残留応
力が大きくなると、それにつれ外圧負荷時の管周方向圧
縮応力は管内面側では減少するが、反面管外面側では増
大する傾向となり、遂には管外面での圧縮応力が内面で
のそれを上廻ることとなる。このような場合には、管外
面から先に降伏が開始されることとなシ、このためコラ
プスの形態は全く変化してし−まう。すなわち、管内面
局方向への引張残留応力もある限度をこえるとそれ以上
付与しても、コラプス強度の向上は決してあろう筈がな
いのである。That is, in the above technology, the collapse strength is said to improve as the tensile residual stress on the inner circumferential surface of the tube increases, but this is a misconception. in the first place"
The article described above is based on the premise that the collapse of a steel pipe always occurs from the inner surface of the pipe, but this condition does not necessarily match the reality. It is true that compressive stress in the circumferential direction of a steel pipe, which is generated by external pressure acting on the steel pipe, is at its maximum on the inner surface of the pipe. However, if residual stress is previously applied to the tube itself, the compressive stress in the circumferential direction of the tube when external pressure is applied does not necessarily reach its maximum on the inner surface of the tube. Regarding the residual stress distribution in the wall thickness direction, when tensile stress is applied to the inner surface of the tube, a commensurate compressive stress will act on the outer surface of the tube, so if the tensile residual stress increases on the inner surface, As a result, the compressive stress in the circumferential direction when external pressure is applied decreases on the inner surface of the tube, but on the other hand tends to increase on the outer surface of the tube, and eventually the compressive stress on the outer surface of the tube exceeds that on the inner surface. In such a case, yielding begins from the outer surface of the tube first, and the form of collapse changes completely. In other words, if the tensile residual stress in the local direction of the inner surface of the tube exceeds a certain limit, the collapse strength will never be improved even if more than that is applied.

先述の如く、管内面への周方向の残留引張応力を増せば
増すほどコラプス強度が改善されるというのは恐らく、
降伏応力の上昇によるコラプス強度向上の効果までも残
留応力付与によるものとして捉えているからであろうと
判断される。降伏応力の上昇が、耐食性の劣化に直結す
ることは、頭記したとおりであり、したがって特開昭９
．−．３３グ１≠号に係る手法は、油井管に対しては実
月月−全く役に立ち得るものでないのである。As mentioned earlier, the collapse strength is probably improved as the residual tensile stress in the circumferential direction on the inner surface of the tube increases.
This is probably because the effect of improving collapse strength due to an increase in yield stress is also considered to be due to the application of residual stress. As mentioned above, an increase in yield stress is directly linked to deterioration of corrosion resistance, and therefore,
．． −． The method according to No. 33G1≠ is completely useless for oil country tubular goods.

このように従来、残留応力のコラプス強度へのｔＷにつ
いて、その詳細を知らしめるに足る事例の存在は全くな
かったものである。As described above, in the past, there have been no cases that are sufficient to provide details regarding the influence of residual stress on collapse strength tW.

しかるに本発明者の詳細ｆｊ：笑験、検討の結果、上記
両者間の関係は、第１図に示す如く〔管内面の残留応カ
ニσＲ〕／〔降伏応カニσｙ〕と〔コラフ。However, as a result of the inventor's detailed experience and study, the relationship between the two is as shown in FIG.

ヌ圧：Ｐｃｒ〕／（残留応力のないときのコラプス圧：
　Ｐｃｒｏ）との関係をもって知ることができ、引張の
残留応力の値がσｙの０．／、ｆ倍以下の範囲にあると
き従来品（残留応力がない鋼管）を上廻るコラプス強度
が得られることが判明した。すなわち、ｆＶｆｙとは、
管内面の残留応力σＲをそのときの降伏応力σｙで除し
て無次元化したもの、Ｐｃｒ／／ＰＣｒＯとは上記残留
応力付加時のコラプス圧ＰＣｒをそのときの降伏応力σ
ｙ下での残留応力無付加時のコラプス圧Ｐ（Ｍ）で無次
元化したもの、をそれぞれ指し、したがって第１図の関
係は材質によらずあらゆる鋼管に共通して成立つもので
ある。コラプス強度の最大値は、σＲがθ０６σｙのと
き得られ、残留応力のない従来品の／θｒ倍となる。Collapse pressure: Pcr]/(Collapse pressure when there is no residual stress:
It can be known from the relationship with Pcro) that the value of tensile residual stress is 0.0 of σy. It has been found that a collapse strength exceeding that of conventional products (steel pipes with no residual stress) can be obtained in the range of /, f times or less. In other words, fVfy is
The residual stress σR on the inner surface of the tube is divided by the yield stress σy at that time to make it dimensionless, and Pcr//PCrO is the collapse pressure PCr when the above residual stress is applied to the yield stress σy at that time.
y, which is made dimensionless by the collapse pressure P (M) when no residual stress is applied. Therefore, the relationship shown in FIG. 1 holds true for all steel pipes regardless of the material. The maximum value of collapse strength is obtained when σR is θ06σy, which is /θr times that of the conventional product without residual stress.

なお、鋼管に付与する残留応力の制御は、鋼管製造工程
の焼入れ一焼戻し段階で、冷却水の使用量を適当に調節
することにより、きわめて容易に行い得るものである。Note that the residual stress imparted to the steel pipe can be extremely easily controlled by appropriately adjusting the amount of cooling water used during the quenching and tempering stages of the steel pipe manufacturing process.

因みに第２図は、前出第１図の関係（ｌ＼）と、先述の
特開昭、５’　Ａ　−、−３３≠、２≠号公報に記載の
実施例に基いて書き改めだ関係（１３）とを比較して示
しだものであるが、両者は全く異なるもθ）ＶＣなって
いる。熱論、付−リする残留応力の範囲についても、大
巾にかけ＋；ｒ＋ｒれているのが判る２、 次に、本発明の実施効果について説明する。Incidentally, Figure 2 is a rewritten relationship based on the relationship (l\) in Figure 1 above and the example described in the aforementioned Japanese Patent Application Publication No. 5'A-, -33≠, 2≠. (13) and θ)VC, which are completely different. It can be seen that the range of residual stress applied in thermal theory also varies widely.2 Next, the effects of implementing the present invention will be explained.

外径ｊ−Δ−１肉厚ｇ７間のれ１１１Ｆ亡（０）３％Ｃ
−θノ３％Ｓｊ−−／、グど％Ｍｎ−θ１０％ｊ七糸）
を供ｄ代した。Outer diameter j-Δ-1 wall thickness g7 gap 111F (0) 3%C
-θノ3%Sj--/, Gudo%Mn-θ10%j Nanite)
I made a donation.

この鋼管は、周方向残留応力の肉１′２方向分在しｊ′
第３図に示す如くであって、管内面にＱま３０　”ｆ′
／Ｊ程度の圧縮残留応力がイτｊ与されている。降伏応
力σｙとしては７７　”／Ｉ＋ｚ’であった。This steel pipe has residual stress in the circumferential direction distributed in two directions.
As shown in Fig. 3, there is a
A compressive residual stress of approximately /J is applied. The yield stress σy was 77''/I+z'.

このような鋼管を再び、ｊθ０七以−１−に加熱し、種
々の冷却速度にて管外面から水冷して管内面に種々な大
きさの残留応力をトＩ与した。このときの冷却水量密度
と管内面の残留応力値との関係は第グ図の如くであった
。管内面の残留応力１］ｔ″は、加熱後の冷却条件の変
更によって３θ〜’／ｙｒｍ’　（１）圧縮応力から３
０崩ンｉの引張応力丑での範囲の任意値に調節可能であ
った。Such a steel pipe was again heated to jθ07-1-, and water-cooled from the outside of the pipe at various cooling rates to impart residual stress of various magnitudes to the inside of the pipe. At this time, the relationship between the cooling water flow density and the residual stress value on the inner surface of the tube was as shown in Fig. The residual stress 1]t'' on the inner surface of the tube can be changed from 3θ~'/yrm' (1) to 3 from compressive stress by changing the cooling conditions after heating.
It was possible to adjust the tensile stress to any value within the range of 0 collapse i.

得られた鋼管の各々について、コラプス試験を実施した
。結果は第５図（ハ）如くであった。冷却条件の変化に
より、管周方向の降伏応力が若干変わってくるだめ、縦
軸については先に説明したＰｃ］／Ｐｃｒｏの値をとっ
て示した。A collapse test was conducted on each of the obtained steel pipes. The results were as shown in Figure 5 (c). Since the yield stress in the circumferential direction of the tube changes slightly due to changes in cooling conditions, the value of Pc]/Pcro as described above is taken for the vertical axis.

第３図から明かな如く、管内面に付与する残留応力値が
本発明に基くＯ，ｔｊ倍σｙ以下の圧縮応力になってい
る場合は、残留応力が０の従来品に較べよシ高いコラプ
ス圧が確保されている。As is clear from Fig. 3, when the residual stress value applied to the inner surface of the tube is a compressive stress equal to or less than O, tj times σy based on the present invention, the collapse is higher than that of the conventional product with residual stress of 0. pressure is ensured.

以上の説明から明かなとおり本発明は、鋼管のコラプヌ
強度改善に有効々対策であり、しかもその適用により鋼
管本来の耐食性が損われるというよりなＩＶ念がなく、
したかつて本発明はとくに使用条件力苛酷な深井戸用油
井管に実施してその耐久性向上に大なる効を奏するもの
である。As is clear from the above explanation, the present invention is an effective measure for improving the collapsing strength of steel pipes, and moreover, there is no risk that the inherent corrosion resistance of steel pipes will be impaired by its application.
The present invention is particularly effective in improving the durability of oil country tubular goods for deep wells, which are subject to severe operating conditions.

【図面の簡単な説明】[Brief explanation of drawings]

第１図は、′ｒシσｙとＰ０シＰＣ］Ｔｏとの間の関係
および本発明範囲を示す図、第２図は前出第１図の関係
と先行発明に基く同上関係とを比１咬して示した図、第
３図は実施例に用いた鋼管の尚初の管周方向残留応力の
肉厚方向分布を表わす図、第弘図は実施例における冷却
水量密度と管内面の残留応力ｆ］Ｈとの間の関係を示す
図、第５図は実施例における実験結果を示す図である。 特開昭５８−７７５５０（４） ン ■−「−刀一−−］ （−％４１）［４・浦碧明副如条 Ｈ へ　　１ だ ＼ 区　　　ｋ：１　　９巴FIG. 1 is a diagram showing the relationship between 'r σy and P0 PC]To and the scope of the present invention, and FIG. 2 is a comparison of the relationship shown in FIG. 1 and the above relationship based on the prior invention. Figure 3 is a diagram showing the thickness direction distribution of residual stress in the circumferential direction of the steel pipe used in the example, and Figure 3 is a diagram showing the distribution of the cooling water amount density and residual stress on the inner surface of the pipe in the example. FIG. 5 is a diagram showing the relationship between stress f]H and FIG. 5 is a diagram showing experimental results in Examples. JP-A-58-77550 (4) N■-“-Toichi--] (-%41) [4. Ura Aoiaki Vice Jojo H to 1 da\ Ward k: 1 9 Tomoe

Claims (1)

【特許請求の範囲】[Claims] （１）　　鋼管内周面に当該布１１管の降伏応力の０．
１３倍以下の管周方向への引張残留応力をト１与したこ
とを！ｉ！１′徴とする高コラブヌ強度鋼管。(1) 0.0% of the yield stress of the fabric 11 pipe on the inner peripheral surface of the steel pipe.
A tensile residual stress of 13 times or less in the pipe circumferential direction was applied! i! High strength steel pipe with 1' characteristic.