JP2001124638A - Method for diagnosing stress on steel pipe - Google Patents
Method for diagnosing stress on steel pipeInfo
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- JP2001124638A JP2001124638A JP30858499A JP30858499A JP2001124638A JP 2001124638 A JP2001124638 A JP 2001124638A JP 30858499 A JP30858499 A JP 30858499A JP 30858499 A JP30858499 A JP 30858499A JP 2001124638 A JP2001124638 A JP 2001124638A
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- stress
- steel pipe
- barkhausen noise
- pipe
- value
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- Investigating Or Analyzing Materials By The Use Of Magnetic Means (AREA)
Abstract
Description
【０００１】[0001]
【発明の属する技術分野】本発明は、地中に埋設された
鋼管に地盤沈下や地層変動等によって発生した応力を、
鋼管から発生するバルクハウゼンノイズを利用して、非
破壊的に診断する方法に関する。BACKGROUND OF THE INVENTION The present invention relates to a steel pipe buried in the ground which is subjected to stress caused by land subsidence or geological deformation.
The present invention relates to a non-destructive diagnosis method using Barkhausen noise generated from a steel pipe.
【０００２】[0002]
【従来の技術】ガス供給管、水道管等の鋼管は地中に埋
設されているため、地盤沈下などが発生すると、沈下量
の異なる鋼管部位の間に曲げ応力が発生する。その応力
が鋼管に長期間に渡って作用すると応力腐食割れが発生
する危険が生じ、また、その応力が過大になると鋼管が
破損してしまう場合が出てくる。特に、ガス供給管でこ
のようなことが起こらないように埋設管に作用している
応力を監視し、安全性を確認しなければならない。2. Description of the Related Art Steel pipes such as gas supply pipes and water pipes are buried in the ground, and when land subsidence occurs, bending stress is generated between steel pipe portions having different settlement amounts. If the stress acts on the steel pipe for a long period of time, there is a risk that stress corrosion cracking will occur, and if the stress is excessive, the steel pipe may be damaged. In particular, it is necessary to monitor the stress acting on the buried pipe so as to prevent this from occurring in the gas supply pipe and to confirm the safety.
【０００３】このために、地表から鋼管表面へ細い抗を
開けて、その抗に沈下棒と呼ばれる棒を差込み、その棒
の沈下量から地中で生じている鋼管の変形を推定して曲
げ応力を求める方法が従来から実施されている。しか
し、この方法では鋼管の水平方向の変位を測定できない
こと、沈下棒の数が制限されているために鋼管の変形量
の推定精度が不十分なこと、の理由から、応力診断の精
度に問題があった。[0003] For this purpose, a thin bolt is opened from the ground surface to the surface of the steel pipe, a rod called a sinking rod is inserted into the steel pipe, and the deformation of the steel pipe generated in the ground is estimated from the amount of sinking of the rod to determine the bending stress. Has been conventionally implemented. However, this method cannot measure the displacement of the steel pipe in the horizontal direction, and the accuracy of estimating the amount of deformation of the steel pipe is insufficient due to the limited number of sinking rods. was there.
【０００４】そこで、磁歪を利用した磁歪センサ（磁気
異方性センサ）を鋼管表面に直接あてて、その出力値か
ら鋼管に作用している応力を求める方法が提案されてい
る。この測定原理は、鉄などの鋼材では磁歪は正である
ため、鋼管表面に応力が作用すると、引っ張り応力方向
では透磁率が増加し、圧縮応力方向ではそれが減少する
ことを用いたものである。例えば、鋼管周囲で測定した
磁歪センサ出力をサイン曲線で近似して算出した値が保
安上の基準値を越えない値、または、最小値となるよう
に調整する応力解放方法（特開平３−１７６６３０号公
報）、２ヶ所の応力中立部近傍の磁歪センサ出力の角度
依存性を直線近似し、両者の傾きの平均値から曲げ応力
を推定する方法（特開平３−１７６６２６号公報）、磁
歪センサ出力とＳＩＮθ近似との差をＳＩＮ２θで近似
し、その振幅値から偏平応力を推定する方法（特開平３
−１７６６２７号公報）、電縫管を磁歪センサで測定す
る際に溶接部の測定値を除去してＣＯＳθ、ＣＯＳ２θ
で補正する方法（特開平５−２８１０５８号公報）、磁
歪センサ出力が最大となる位置、及びそこから９０°ず
れた位置の外径を実測して偏平率を求めて、軸方向最大
応力値を補正する方法（特開平６−２８８８４２公
報）、磁歪センサ等で部分的に測定した応力を沈下量測
定によるシミュレーションに取り入れて埋設管全体の中
の最大応力を求めて基準値を越えないようにする管理方
法（特開平９−２４２９３３号公報）、等が開示されて
いる。Therefore, a method has been proposed in which a magnetostrictive sensor (magnetic anisotropic sensor) utilizing magnetostriction is directly applied to the surface of a steel pipe, and the stress acting on the steel pipe is determined from the output value. This measurement principle is based on the fact that magnetostriction is positive in steel materials such as iron, so that when a stress acts on the surface of a steel pipe, the permeability increases in the tensile stress direction and decreases in the compressive stress direction. . For example, a stress release method for adjusting a value obtained by approximating a magnetostriction sensor output measured around a steel pipe with a sine curve to a value not exceeding a security reference value or a minimum value (Japanese Patent Laid-Open No. 3-176630). Japanese Patent Application Laid-Open No. 3-176626 discloses a method of linearly approximating the angle dependence of the output of a magnetostrictive sensor near two stress-neutral portions and estimating a bending stress from an average value of the inclinations of the two. A method of approximating the difference between the approximation and SINθ approximation by SIN2θ and estimating the flat stress from the amplitude value
176627), when the ERW pipe is measured by a magnetostrictive sensor, the measured value of the welded portion is removed and COSθ, COS2θ
(Japanese Unexamined Patent Publication No. 5-28158), a flattening rate is obtained by actually measuring the outer diameter at a position where the output of the magnetostrictive sensor is maximized and at a position shifted by 90 ° from the position, and determine the maximum stress value in the axial direction. Correction method (Japanese Patent Application Laid-Open No. Hei 6-288842), the stress partially measured by a magnetostrictive sensor or the like is incorporated into a simulation based on the measurement of the amount of settlement to determine the maximum stress in the entire buried pipe so as not to exceed a reference value. A management method (JP-A-9-242933) and the like are disclosed.
【０００５】しかしながら、これらの方法を既埋設管に
適用する場合には、管を埋設する前、すなわち、外部応
力が負荷されていない状態での所定の測定部位における
出力値（初期値）がわかっていれば問題ないが、それが
不明の場合には初期値は場所によってばらつくために埋
設後に測定した出力値から直接的に応力を求めることは
できない。したがって、種々の補正方法を用いて応力を
求めなければならなかった。However, when these methods are applied to an already buried pipe, the output value (initial value) at a predetermined measurement site before the pipe is buried, that is, in a state where no external stress is applied, is known. There is no problem if it is not clear, but if it is unknown, the initial value varies depending on the location, so that the stress cannot be directly obtained from the output value measured after embedding. Therefore, the stress has to be obtained using various correction methods.
【０００６】[0006]
【発明が解決しようとする課題】以上の如く、従来の方
法では、測定部位の初期値が不明の鋼管の各部位に作用
している外部応力を求めようとする場合には、ある程度
の仮定的判断を必要とするため、測定精度の低下は避け
られなかった。As described above, in the conventional method, when it is attempted to obtain the external stress acting on each part of the steel pipe whose initial value of the measurement part is unknown, a certain degree of hypothesis is required. Decision of measurement was inevitable due to the need for judgment.
【０００７】そこで本発明は、表面に制御された圧縮残
留応力が付与された鋼管を用いることにより、埋設前の
初期値が不明の場合であっても十分な精度で応力診断を
可能にする方法を提供することを目的とする。Accordingly, the present invention provides a method for enabling stress diagnosis with sufficient accuracy even when the initial value before embedding is unknown by using a steel pipe to which a controlled compressive residual stress is applied to the surface. The purpose is to provide.
【０００８】[0008]
【課題を解決するための手段】本発明の要旨とするとこ
ろは、下記の通りである。 （１）鋼管を診断対象とし、励磁ヘッドと検出ヘッドか
ら構成される磁気ヘッドを用いて前記励磁ヘッドにより
鋼管の測定部位を交流励磁し、前記検出ヘッドに誘起さ
れる電圧信号を周波数分離してバルクハウゼンノイズを
検出し、前記鋼管に負荷された応力値を診断する鋼管の
応力診断方法であって、予め前記鋼管表面に所定の圧縮
残留応力を付与しておき、前記鋼管表面の所定の測定部
位において、前記鋼管の軸方向に励磁して測定したバル
クハウゼンノイズの実効値電圧をＶL 、周方向に励磁し
て測定したバルクハウゼンノイズの実効値電圧をＶC と
した場合、（ＶL −ＶC ）の値から、前記鋼管と同一の
部材を使って予め求めておいた外部応力とバルクハウゼ
ンノイズの実効値電圧との関係を表す検量線を用い、前
記測定部位に作用している軸方向の前記応力値を求める
ことを特徴とする鋼管の応力診断方法。The gist of the present invention is as follows. (1) A steel pipe is to be diagnosed, and a measurement part of the steel pipe is AC-excited by the excitation head using a magnetic head including an excitation head and a detection head, and a voltage signal induced in the detection head is frequency-separated. A method for diagnosing stress in a steel pipe, which detects Barkhausen noise and diagnoses a stress value applied to the steel pipe, wherein a predetermined compressive residual stress is applied in advance to the steel pipe surface, and a predetermined measurement of the steel pipe surface is performed. When the effective value voltage of Barkhausen noise measured by exciting in the axial direction of the steel pipe at a portion is V L , and the effective value voltage of Barkhausen noise measured by exciting in the circumferential direction is V C , (V L from the value of -V C), using a calibration curve showing the relationship between the effective voltage of the steel pipe external stress and previously obtained using the same members as Barkhausen noise, acting on the measuring site Stress diagnostic method of the steel pipe, characterized in that determining the stress value in the axial direction is.
【０００９】（２）現場設置前における前記鋼管表面の
測定部位の軸方向と周方向にそれぞれ励磁して測定した
バルクハウゼンノイズの実効値電圧を均一にするよう
に、前記測定部位の面内方向に前記圧縮残留応力を付与
した前記鋼管を用いることを特徴とする前項１に記載の
鋼管の応力診断方法。(2) The in-plane direction of the measurement site so that the effective value voltage of the Barkhausen noise measured by excitation in the axial direction and the circumferential direction of the measurement site on the surface of the steel pipe before installation on the site is uniform. 2. The method for diagnosing stress in a steel pipe according to the above item 1, wherein the steel pipe having the compressive residual stress applied thereto is used.
【００１０】（３）前記測定部位の面内方向に等方的に
均一に前記圧縮残留応力を付与した前記鋼管を用いるこ
とを特徴とする前項２に記載の鋼管の応力診断方法。(3) The method for diagnosing stress in a steel pipe according to the above (2), wherein the steel pipe to which the compressive residual stress is uniformly applied isotropically in an in-plane direction of the measurement site is used.
【００１１】[0011]
【発明の実施の形態】鋼材のバルクハウゼンノイズは、
外部応力及び結晶粒径、析出物や転位等の組織に応じて
変化するため、外部応力を診断するためには組織を変化
させないことが必須であった。すなわち、鋼材に外部応
力が作用しても、それが弾性範囲内にあるときには、組
織変化がないためバルクハウゼンノイズは応力のみに依
存し、かつ、応力に対して可逆的に変化する。しかし、
鋼材に降伏応力以上の外部応力が作用し、それが塑性領
域に入ってしまうと転位の増殖や結晶回転などが起こり
組織が変わってしまうため、もはや外部応力のみを診断
をすることが不可能になってしまう。DETAILED DESCRIPTION OF THE INVENTION Barkhausen noise of steel
Since it changes according to the external stress, the crystal grain size, the structure such as precipitates and dislocations, it is essential that the structure is not changed in order to diagnose the external stress. That is, even when an external stress is applied to the steel material, when the external stress is within the elastic range, there is no structural change, so that the Barkhausen noise depends only on the stress and changes reversibly with respect to the stress. But,
When an external stress greater than the yield stress acts on the steel material and enters the plastic region, dislocation multiplication and crystal rotation occur, and the structure changes, so it is no longer possible to diagnose only the external stress. turn into.
【００１２】本発明者らは、外部応力の大きさが降伏応
力より大きくなった場合においても組織変化をほとんど
生じさせなくするように、測定部位の残留応力の初期状
態を制御することを可能にし、さらに、そのような状態
において、応力とバルクハウゼンノイズの関係を詳細に
調べた結果、本発明に至ったものである。すなわち、本
発明者らは、弾性領域から塑性領域に至るまで、さら
に、塑性領域においては種々の歪みの大きさまで塑性変
形させた場合における、応力あるいは歪みと軸方向及び
周方向に励磁して測定したバルクハウゼンノイズの大き
さ、の関係を詳細に測定した。その結果、一端、測定部
位を塑性変形させて、その部位の面内方向に圧縮残留応
力を付与した試料に引っ張り応力を新たに負荷した場合
には、応力あるいは歪みとバルクハウゼンノイズの実効
値電圧の直線相関が成り立つ応力あるいは歪み範囲が、
圧縮残留応力が無い場合に比べて格段に広くなることを
見出した。さらに、軸方向に励磁して測定したバルクハ
ウゼンノイズの実効値電圧（ＶL ）は引っ張り応力ある
いは引っ張り歪みに応じて非常に敏感に変化するのに対
して、圧縮側ではほとんど変化しないこと、また、周方
向に励磁して測定したバルクハウゼンノイズの実効値電
圧（ＶC ）は、引っ張り側及び圧縮側の両方において、
応力あるいは歪みが変化してもほとんど変化しないか、
変化しても僅かであることを見出した。The present inventors have made it possible to control the initial state of the residual stress at the measurement site so that even when the magnitude of the external stress becomes larger than the yield stress, the structural change hardly occurs. Further, in such a state, a detailed investigation of the relationship between stress and Barkhausen noise resulted in the present invention. In other words, the present inventors measured the stress or strain in the axial and circumferential directions when the plastic deformation was performed from the elastic region to the plastic region, and further in the plastic region to the magnitude of various strains. The relationship between the magnitude of the Barkhausen noise thus obtained was measured in detail. As a result, when a tensile stress is newly applied to a sample to which a compressive residual stress is applied in the in-plane direction by plastically deforming the measurement site at one end, the effective value voltage of the stress or strain and Barkhausen noise is obtained. The stress or strain range where the linear correlation of
It has been found that it is much wider than in the case where there is no residual compressive stress. Furthermore, the effective value voltage (V L ) of Barkhausen noise measured by being excited in the axial direction changes very sensitively according to tensile stress or tensile strain, but hardly changes on the compression side. , The effective value voltage (V C ) of the Barkhausen noise measured while being excited in the circumferential direction is expressed in both the tension side and the compression side.
Little change in stress or strain,
It was found that even if it changed, it was slight.
【００１３】通常の電縫管やシームレス管では鋼管表面
の各部位ごとに組織や残留応力が異なるために、実際に
バルクハウゼンノイズを測定してみると同じ鋼管でも測
定部位が数ｃｍ異なるだけでその実効値電圧は大きく異
なってしまう。したがって、各測定部位ごとの初期値の
管理が必要になり、管理する上で煩雑になってしまう。
本発明者らは、電縫管やシームレス管表面の面内方向に
ほぼ同じ大きさの圧縮残留応力を付与することによって
鋼管表面のどの測定部位でバルクハウゼンノイズを測定
しても同じ大きさの実効値電圧が得られることを見出し
た。この圧縮残留応力を面内に等方的に付与することに
よって、初期値の値も等方的になって、どの方向から外
部応力が負荷されても応力の診断精度の低下を防ぐこと
が可能になる。しかし、鋼管周囲に渡る所定の測定部位
でバルクハウゼンノイズを測定する場合、それらの全て
の測定部位に均一な大きさの圧縮残留応力を付与するこ
とは可能であっても、製造工程の省力化や生産性を考慮
した場合、残留応力を付与する工程は出来るだけ簡略化
することが望ましい。[0013] Since the structure and residual stress of a normal electric resistance welded pipe and a seamless pipe are different for each part on the surface of the steel pipe, when the Barkhausen noise is actually measured, even the same steel pipe differs only by a few centimeters. The effective value voltage is greatly different. Therefore, it is necessary to manage the initial values for each measurement site, and the management becomes complicated.
The present inventors have applied the same level of compressive residual stress in the in-plane direction of the surface of an ERW pipe or a seamless pipe to measure the Barkhausen noise at any measurement site on the steel pipe surface. It has been found that an effective value voltage can be obtained. By applying this compressive residual stress isotropically in the plane, the initial value is also isotropic, and it is possible to prevent the accuracy of stress diagnosis from lowering even if external stress is applied from any direction. become. However, when measuring Barkhausen noise at predetermined measurement sites around the steel pipe, even if compressive residual stress of a uniform size can be applied to all of those measurement sites, labor saving in the manufacturing process is achieved. When considering the productivity and productivity, it is desirable to simplify the process of applying the residual stress as much as possible.
【００１４】本発明者らは、例えば、エアーブラスト、
ショットブラストなどの小さな鋼球やセラミックス粒子
を試料表面に高速で衝突させる方法、サンダーによる研
磨、等、を用いて鋼管に導入される圧縮残留応力の大き
さを評価した。その結果、これらの処理を何度か繰り返
せば、鋼管周囲の測定部位の全てにほぼ均一な圧縮残留
応力が付与されるが、処理の程度を軽くしていくと、測
定部位によって圧縮残留応力の大きさが異なってくるこ
とがわかった。しかし、測定部位によって圧縮残留応力
の大きさが異なる場合においても、同じ測定部位である
ならば、軸方向と周方向の圧縮残留応力の大きさはほぼ
同じであることも新たに判明した。The present inventors have proposed, for example, air blast,
The magnitude of the compressive residual stress introduced into the steel pipe was evaluated using a method in which small steel balls such as shot blast and ceramic particles collide with the sample surface at high speed, sanding, and the like. As a result, if these treatments are repeated several times, almost uniform compressive residual stress is given to all the measurement sites around the steel pipe. It turned out that the size was different. However, it has been newly found that even when the magnitude of the compressive residual stress differs depending on the measurement site, the magnitude of the compressive residual stress in the axial direction and the magnitude of the compressive residual stress in the circumferential direction are substantially the same if the measurement site is the same.
【００１５】上記のような方法で圧縮残留応力を付与し
た鋼管のある一個所の測定部位に注目した場合、現場設
置前の外部応力が無付加の状態では、軸方向と周方向の
それぞれの方向に励磁して測定したバルクハウゼンノイ
ズの実効値電圧は均一（ＶL〜ＶC 、外部応力なし）で
あるが、そこに外部曲げ応力が負荷されると、軸方向に
励磁して測定したバルクハウゼンノイズ（ＶL ）は応力
に応じて変化するが、周方向に励磁して測定したバルク
ハウゼンノイズ（ＶC ）はほとんど変化しない。したが
って、ＶL −ＶC を求めれば、測定部位の場所によら
ず、外部応力によって生じた実効値電圧のみを抽出でき
ることになる。なお、実際のバルクハウゼンノイズの実
効値電圧を検出する場合の測定誤差などを考慮すると、
現場設置前の外部応力が無付加の状態において、軸方向
と周方向のそれぞれの方向に励磁して測定したバルクハ
ウゼンノイズの実効値電圧の差（ＶL −ＶC ）が２ｍＶ
〜３ｍＶ程度以下であるなら、ＶL とＶC は均一と見な
せる。Attention is paid to one measurement site of a steel pipe to which a compressive residual stress is applied by the above-described method. In a state where no external stress is applied before the installation at the site, the axial direction and the circumferential direction are different. bulk effective voltage of the Barkhausen noise measured with the excitation uniform (V L ~V C, no external stress), but when there external bending stress is loaded, as measured by excitation in the axial direction The Hausen noise (V L ) changes according to the stress, but the Barkhausen noise (V C ) measured by exciting in the circumferential direction hardly changes. Therefore, if V L −V C is obtained, it is possible to extract only the effective value voltage generated by the external stress regardless of the location of the measurement site. Considering the measurement error when detecting the actual effective voltage of Barkhausen noise, etc.,
In a state where no external stress is applied before installation in the field, the difference (V L −V C ) between the effective value voltages of Barkhausen noise measured by exciting in both the axial direction and the circumferential direction is 2 mV.
If it is more than about ~3mV, V L and V C can be regarded as uniform.
【００１６】通常のガス導管などでは、鋼管に内圧がか
かっている状態で測定することになるが、内圧は既知で
あるため、内圧によって鋼管表面に生じている応力は力
学的に計算可能である。したがって、この場合、外部応
力を求めたい場合には、測定値からこの内圧による応力
増加分を差し引けば良い。In a normal gas pipe or the like, the measurement is performed in a state where an internal pressure is applied to the steel pipe. However, since the internal pressure is known, the stress generated on the steel pipe surface by the internal pressure can be calculated dynamically. . Therefore, in this case, when it is desired to obtain the external stress, it is sufficient to subtract the stress increase due to the internal pressure from the measured value.
【００１７】次に測定手順について説明する。各測定部
位において制御された圧縮残留応力が付与された鋼管表
面上の周囲に渡って複数の所定の場所で軸方向及び周方
向にそれぞれ励磁してバルクハウゼンノイズの実効値電
圧ＶL 及びＶC を測定する。その際、鋼管の管軸中心線
を含み鋼管表面の所定の測定部位と交わる平面を考え、
各平面の内の一枚を基準面として、各測定部位をその基
準面と各測定部位を含む平面とのなす角度で表示する。
どの面を基準面としても良い。それらの角度と（ＶL −
ＶC ）との関係をグラフまたは表に表す。ここで、通常
の測定点数は数点から数十点程度である。Next, the measurement procedure will be described. The effective value voltages V L and V C of Barkhausen noise are excited respectively at a plurality of predetermined locations in the axial direction and the circumferential direction at a plurality of predetermined locations around the circumference of the steel pipe surface to which the controlled compressive residual stress is applied at each measurement site. Is measured. At that time, consider a plane that includes the pipe axis center line of the steel pipe and intersects with a predetermined measurement site on the steel pipe surface,
One of the planes is used as a reference plane, and each measurement site is displayed at an angle between the reference plane and a plane including each measurement site.
Any surface may be used as the reference surface. Those angles and (V L −
V C ) is shown in a graph or table. Here, the usual number of measurement points is about several to several tens.
【００１８】次に、このグラフまたは表から（ＶL −Ｖ
C ）の最大値を求める。この部位は軸方向に作用してい
る引っ張り応力が最大となるところである。実効値電圧
の最大値から予め同じ鋼種を使って求めておいた検量線
を用いて軸方向の最大引っ張り応力値を求めることがで
きる。ここで、応力とバルクハウゼンノイズの関係を表
す検量線は、歪みゲージを貼り付けた同じ鋼種の部材に
応力を負荷していきながら、バルクハウゼンノイズを同
時に測定することによって、容易に求めることができ
る。Next, from this graph or table, (V L -V
C ) Find the maximum value of. This portion is where the tensile stress acting in the axial direction is maximized. The maximum tensile stress value in the axial direction can be obtained from the maximum value of the effective value voltage using a calibration curve previously obtained using the same steel type. Here, the calibration curve representing the relationship between stress and Barkhausen noise can be easily obtained by simultaneously measuring Barkhausen noise while applying stress to the same steel type member to which the strain gauge is attached. it can.
【００１９】さらに、この最大引っ張り応力値をσmax
とすると、Ｍ＝Ｚ×σmax、（ただし、Ｚは断面係数）
から曲げモーメントＭを求めることができる。降伏応力
に相当する圧縮残留応力を鋼管表面に付与した場合、降
伏応力の約２倍に相当する外部引っ張り応力までバルク
ハウゼンノイズで診断が可能になる。Further, this maximum tensile stress value is defined as σ max
Then, M = Z × σ max (where Z is the section modulus)
From the bending moment M. When a compressive residual stress corresponding to the yield stress is applied to the surface of the steel pipe, it is possible to diagnose by Barkhausen noise up to an external tensile stress corresponding to about twice the yield stress.
【００２０】電縫管では溶接部、及びその両側に熱影響
部があるが、これらの部位ではバルクハゼンノイズが大
きく変化してしまう場合がある。被覆や塗装が施されて
いない場合には目視でそれらの部位を確認できるため、
予め測定部位から除くことができるが、被覆や塗装があ
って目視で確認できない場合には、測定値からこれらの
部位に相当する値を除外すればよい。溶接部や熱影響部
では，測定部位の角度とバルクハウゼンノイズの実効値
電圧との関係を表したグラフにおいて、実効値電圧が不
連続的に変化するため、それらの部位を容易に見つける
ことができる。公知の非接触式磁気ヘッド（特開平７−
１７４７３０号公報）を用いれば被覆材の上からでも測
定が可能となる。In an electric resistance welded pipe, there are a weld zone and heat affected zones on both sides thereof. However, in these zones, the Barkhausen noise may greatly change. If the coating or coating is not applied, you can visually check those parts,
Although it can be removed from the measurement site in advance, if there is a coating or a coating that cannot be visually confirmed, the values corresponding to these sites may be excluded from the measurement values. In the graph showing the relationship between the angle of the measured part and the RMS voltage of Barkhausen noise in the weld and heat affected zone, the RMS voltage changes discontinuously, so it is easy to find those parts. it can. Known non-contact type magnetic heads (Japanese Unexamined Patent Publication No.
174730) enables measurement even from above the coating material.
【００２１】試料のより深い部位から発生するバルクハ
ウゼンノイズほど減衰が大きくなるため、検出コイルに
発生する電圧は小さくなる。これはskin depth効果と呼
ばれ、定量的に示すと次にようになる。試料表面におい
てバルクハウゼンノイズが１／ｅに減衰する発生源の深
さをｄとすると、ｄ＝（ρ／πｆμ）1/2、（ρは電気
抵抗、ｆはバルクハウゼンノイズの検出周波数、μは透
磁率）で表される。残留応力を付与する深さは、検出深
さをｄとした場合、少なくとも０．５ｄ以上であること
が好ましい。それが０．５ｄより少ない場合には、バル
クハウゼンノイズと応力あるいは歪みとの関係におい
て、両者の直線相関が成り立つ応力範囲が低下するから
である。Since the attenuation increases as the Barkhausen noise generated from a deeper portion of the sample decreases, the voltage generated in the detection coil decreases. This is called the skin depth effect. Assuming that the depth of the source at which the Barkhausen noise attenuates to 1 / e on the sample surface is d, d = (ρ / πfμ) 1/2 , (ρ is the electric resistance, f is the detection frequency of Barkhausen noise, μ Is represented by magnetic permeability). The depth at which the residual stress is applied is preferably at least 0.5d or more, where the detected depth is d. If it is less than 0.5 d, the stress range in which a linear correlation between the Barkhausen noise and the stress or the strain is satisfied is reduced.
【００２２】本発明を実際に使う場合には、被測定部材
における外部応力とバルクハウゼンノイズの実効値電圧
との関係を示す検量線を予め測定しておき、この検量線
を用いて実際に測定した実効値電圧差（ＶL −ＶC ）を
応力へ換算すればよい。When the present invention is actually used, a calibration curve indicating the relationship between the external stress in the member to be measured and the effective voltage of Barkhausen noise is measured in advance, and the actual measurement is performed using the calibration curve. effective voltage difference (V L -V C) may be converted to the stresses.
【００２３】[0023]
【実施例】以下、実施例をもって本発明を具体的に説明
する。外径３１８ｍｍ、肉厚６．９ｍｍ、長さ６０００
ｍｍのＳＧＰ３００Ａ鋼管表面の全面に渡ってスチール
系研掃材を用いたショットブラスト処理を施すことによ
って圧縮残留応力を付与した。但し、部位によってショ
ットブラスト処理の強さを積極的に変えて、圧縮残留応
力の大きさを場所によって変化させた。この鋼管を曲げ
て任意量の外部応力を負荷した状態でバルクハウゼンノ
イズを測定し、本発明によって外部応力が診断できるか
否かを調べた。The present invention will be specifically described below with reference to examples. Outer diameter 318mm, wall thickness 6.9mm, length 6000
Compressive residual stress was given by performing shot blasting using a steel-based abrasive material over the entire surface of the SGP300A steel pipe having a thickness of 2 mm. However, the strength of the shot blasting process was positively changed depending on the site, and the magnitude of the compressive residual stress was changed depending on the location. Barkhausen noise was measured in a state where the steel pipe was bent and an arbitrary amount of external stress was applied, and it was examined whether or not the external stress could be diagnosed by the present invention.
【００２４】バルクハウゼンノイズの測定は、以下のよ
うにして行った。珪素鋼板を積層したＵ字型励磁コアに
１０００ターンのエナメル線を巻いた励磁ヘッド、及び
断面積が２ｍｍ×８ｍｍのアクリル製ボビンに５００タ
ーンのエナメル線を巻いた検出ヘッドからなる磁気ヘッ
ドを用いて軸方向及び周方向の二つの方向に励磁して各
測定部位の実効値電圧ＶL 及びＶC をそれぞれ測定し
た。励磁周波数は１００Ｈｚ、検出周波数は１０ｋＨｚ
〜１００ｋＨｚである。同一鋼種を使って予め求めてお
いた検量線を用いて、（ＶL −ＶC ）を応力に換算した
場合、及び比較例としてＶL を応力に換算した場合につ
いて検討した。The measurement of Barkhausen noise was performed as follows. A magnetic head consisting of a U-shaped excitation core laminated with a silicon steel sheet and having an enameled wire of 1000 turns wound thereon and a detection head having an engraved wire of 500 turns wound on an acrylic bobbin having a cross-sectional area of 2 mm × 8 mm is used. The magnets were excited in two directions, an axial direction and a circumferential direction, to measure the effective value voltages V L and V C at each measurement site, respectively. Excitation frequency is 100Hz, detection frequency is 10kHz
１００100 kHz. Using a calibration curve previously obtained using the same steel species, it was investigated when converted to V L to stress as if converted to (V L -V C) stress, and Comparative Examples.
【００２５】鋼管の測定部位は管軸中心線を含み鋼管表
面の所定の測定部位と交わる平面を考え、その内の一枚
の平面を基準面とし、測定部位をその基準面と各測定部
位を含む平面とのなす角度で表示した。実際には、任意
の面を基準面として、２２．５°の間隔で１６ヶ所を鋼
管周囲にわたって一周分測定した。The measurement site of the steel pipe includes a plane including the center line of the pipe axis and intersecting with a predetermined measurement site on the surface of the steel pipe. One of the planes is used as a reference plane, and the measurement site is defined by the reference plane and each measurement site. Indicated by the angle between the plane and the plane. Actually, measurement was performed for one round around the steel pipe at 16 locations at an interval of 22.5 ° with an arbitrary plane as a reference plane.
【００２６】ショットブラスト処理後の鋼管表面の残留
応力の大きさの深さ方向の分布は、表面から板厚方向へ
所定厚さだけエッチングした後、Ｘ線残留応力測定法に
よって求めた。その結果、各測定部位では、表面から約
１５０μｍの深さまではほぼ同じ大きさの圧縮残留応力
が面内で等方的に均一に入っているが、圧縮残留応力の
絶対値は、各測定部位で異なっていることを確認した。The distribution of the magnitude of the residual stress on the surface of the steel pipe after the shot blasting in the depth direction was determined by an X-ray residual stress measurement method after etching a predetermined thickness from the surface in the thickness direction. As a result, at each measurement site, a compressive residual stress of approximately the same magnitude enters isotropically uniformly in the plane at a depth of about 150 μm from the surface, but the absolute value of the compressive residual stress is Was different.
【００２７】図１は、各測定部位において、軸方向及び
周方向に励磁して測定したバルクハウゼンノイズの実効
値電圧ＶL 及びＶC を示す特性図である。各測定部位の
圧縮残留応力の大きさが異なっているために、実効値電
圧はばらついている。このグラフからでは、鋼管のどの
部位に最大引っ張り応力が負荷されているのかを求める
ことは困難である。FIG. 1 is a characteristic diagram showing the effective value voltages V L and V C of Barkhausen noise measured at each measurement site while being excited in the axial and circumferential directions. Since the magnitude of the compressive residual stress at each measurement site is different, the effective value voltage varies. From this graph, it is difficult to determine which part of the steel pipe is subjected to the maximum tensile stress.
【００２８】図２は、本発明に従ってＶL −ＶC を求め
た特性図である。この図から、明らかに２３°の部位と
２１０°部位の間に軸方向に引っ張り応力が作用してい
ることがわかり、約１１０°部位に最大引っ張り応力が
作用していることがわかる。[0028] FIG. 2 is a characteristic diagram of obtaining the V L -V C in accordance with the present invention. From this figure, it is apparent that a tensile stress is acting in the axial direction between the 23 ° portion and the 210 ° portion, and that a maximum tensile stress is acting on the approximately 110 ° portion.
【００２９】図２では最大で４．５ｍＶ増加している
が、これを予め求めておいた検量線を用いて応力に換算
すると、２１０ＭＰａとなる。この値は、曲げた鋼管の
曲率を精度良く測定して計算によって求めた歪みの値を
応力に換算した値とほぼ一致した。In FIG. 2, the maximum value is increased by 4.5 mV, but it is 210 MPa when converted into a stress using a previously obtained calibration curve. This value almost coincided with the value obtained by measuring the curvature of the bent steel pipe with high accuracy and converting the value of strain obtained by calculation into stress.
【００３０】したがって、本発明によって、各測定部位
の圧縮残留応力の大きさが異なっている場合においても
応力の診断が可能であることがわかる。Therefore, according to the present invention, it can be understood that stress can be diagnosed even when the magnitude of the compressive residual stress at each measurement site is different.
【００３１】[0031]
【発明の効果】本発明によれば、表面に予め圧縮残留応
力が付与された鋼管のバルクハウゼンノイズを鋼管の周
囲に渡って所定の部位で測定することによって、鋼管に
作用している応力を精度良く診断することが可能とな
る。本発明は弾性域のみならず、塑性域においても適用
することか可能であるため、本発明を用いることによっ
て、埋設してある鋼管に対して、本来最も注意して監視
し、場合によっては直ちに応力解放工事を実施しなけれ
ばならないような塑性領域にある応力の診断精度も格段
に向上する。According to the present invention, the stress acting on the steel pipe is measured by measuring the Barkhausen noise of the steel pipe having a compressive residual stress applied to its surface in a predetermined area around the circumference of the steel pipe. Diagnosis can be made with high accuracy. Since the present invention can be applied not only to the elastic region but also to the plastic region, by using the present invention, the embedded steel pipe should be monitored with the utmost care, and in some cases immediately The accuracy of diagnosing stress in a plastic region where stress release work must be performed is also greatly improved.
【図１】バルクハウゼンノイズの実効値電圧のプロファ
イルを表す（実測値）特性図である。FIG. 1 is a (measured value) characteristic diagram showing a profile of an effective value voltage of Barkhausen noise.
【図２】バルクハウゼンノイズの実効値電圧のプロファ
イルを表す（本発明による計算結果）特性図である。FIG. 2 is a characteristic diagram showing a profile of an effective value voltage of Barkhausen noise (calculation result according to the present invention).
───────────────────────────────────────────────────── フロントページの続き (72)発明者 山名 成彦 東京都千代田区大手町２−６−３ 新日本 製鐵株式会社内 (72)発明者 佐々木 孝雄 東京都千代田区大手町２−６−３ 新日本 製鐵株式会社内 (72)発明者 辻本 潤 東京都千代田区大手町２−６−３ 新日本 製鐵株式会社内 Ｆターム(参考） 2G053 AA19 AB20 BA12 BA26 BC02 BC14 CA03 CC02 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shigehiko Yamana 2-6-3 Otemachi, Chiyoda-ku, Tokyo Inside Nippon Steel Corporation (72) Inventor Takao Sasaki 2-6-3, Otemachi, Chiyoda-ku, Tokyo Within Nippon Steel Corporation (72) Inventor Jun Tsujimoto 2-6-3 Otemachi, Chiyoda-ku, Tokyo F-term within Nippon Steel Corporation (reference) 2G053 AA19 AB20 BA12 BA26 BC02 BC14 CA03 CC02
Claims (3)
ヘッドから構成される磁気ヘッドを用いて前記励磁ヘッ
ドにより鋼管の測定部位を交流励磁し、前記検出ヘッド
に誘起される電圧信号を周波数分離してバルクハウゼン
ノイズを検出し、前記鋼管に負荷された応力値を診断す
る鋼管の応力診断方法であって、 予め前記鋼管表面に所定の圧縮残留応力を付与してお
き、 前記鋼管表面の所定の測定部位において、前記鋼管の軸
方向に励磁して測定したバルクハウゼンノイズの実効値
電圧をＶL 、周方向に励磁して測定したバルクハウゼン
ノイズの実効値電圧をＶC とした場合、（ＶL −ＶC ）
の値から、前記鋼管と同一の部材を使って予め求めてお
いた外部応力とバルクハウゼンノイズの実効値電圧との
関係を表す検量線を用い、前記測定部位に作用している
軸方向の前記応力値を求めることを特徴とする鋼管の応
力診断方法。1. A steel pipe is to be diagnosed, a measuring part of the steel pipe is AC-excited by a magnetic head including an excitation head and a detection head by the excitation head, and a voltage signal induced in the detection head is frequency-separated. A method for diagnosing the stress value applied to the steel pipe by detecting Barkhausen noise and applying a predetermined compressive residual stress to the surface of the steel pipe in advance; When the effective value voltage of Barkhausen noise measured by exciting in the axial direction of the steel pipe is V L , and the effective value voltage of Barkhausen noise measured by exciting in the circumferential direction is V C V L -V C)
From the value of the above, using a calibration curve representing the relationship between the external stress previously determined using the same member as the steel pipe and the effective value voltage of Barkhausen noise, the axial direction acting on the measurement site A method for diagnosing stress in a steel pipe, comprising determining a stress value.
部位の軸方向と周方向にそれぞれ励磁して測定したバル
クハウゼンノイズの実効値電圧を均一にするように、前
記測定部位の面内方向に前記圧縮残留応力を付与した前
記鋼管を用いることを特徴とする請求項１に記載の鋼管
の応力診断方法。2. An in-plane direction of the measurement site so that the effective value voltage of the Barkhausen noise measured by exciting each in the axial direction and the circumferential direction of the measurement site on the surface of the steel pipe before installation in the field is uniform. The method for diagnosing stress in a steel pipe according to claim 1, wherein the steel pipe to which the compressive residual stress is applied is used.
に前記圧縮残留応力を付与した前記鋼管を用いることを
特徴とする請求項２に記載の鋼管の応力診断方法。3. The method for diagnosing stress in a steel pipe according to claim 2, wherein the steel pipe to which the compressive residual stress is uniformly and isotropically applied in an in-plane direction of the measurement site is used.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP30858499A JP4029119B2 (en) | 1999-10-29 | 1999-10-29 | Steel pipe stress diagnosis method |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP30858499A JP4029119B2 (en) | 1999-10-29 | 1999-10-29 | Steel pipe stress diagnosis method |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JP2001124638A true JP2001124638A (en) | 2001-05-11 |
| JP4029119B2 JP4029119B2 (en) | 2008-01-09 |
Family
ID=17982801
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP30858499A Expired - Fee Related JP4029119B2 (en) | 1999-10-29 | 1999-10-29 | Steel pipe stress diagnosis method |
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| Country | Link |
|---|---|
| JP (1) | JP4029119B2 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104316238A (en) * | 2014-11-21 | 2015-01-28 | 国家电网公司 | Stress measurement device and method for inner wall of steel penstock |
-
1999
- 1999-10-29 JP JP30858499A patent/JP4029119B2/en not_active Expired - Fee Related
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104316238A (en) * | 2014-11-21 | 2015-01-28 | 国家电网公司 | Stress measurement device and method for inner wall of steel penstock |
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| Publication number | Publication date |
|---|---|
| JP4029119B2 (en) | 2008-01-09 |
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