JP4088455B2 - Method and apparatus for measuring thickness of multi-layer material - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は、複数層物質の厚さ測定方法および装置に関し、特に、複数層構造をもつ物質の厚さをそれぞれ測定する複数層物質の厚さ測定方法および装置に関する。
【０００２】
【従来の技術】
鋼板等で作られた煙道においては、排ガスによる腐食等によって減肉すると、強度的な問題が生じる。そこで、煙道内に入ることなく外部から保温材などの障害物を介して板厚を検査し、問題個所を特定・補修する必要がある。かかる事情、つまり、外部から板厚を検査して問題個所を特定・補修する必要があることは、煙道の他に、石油やガスタンク、燃焼炉などの立ち入りが困難な構造物についても同様である。
【０００３】
従来の金属板厚さ測定法としては、超音波、渦電流を利用した測定法があるが、このような測定法では、金属板の表面にセンサを接近させて測定する必要がある。かかる従来の測定法で板厚測定をするためには、プラントを停止して煙道内に人が入って内側から測定するか、煙道の外側にある保温材を剥がして測定する必要がある。
【０００４】
また、放射線の透過を利用した測定法では、放射線発生源または、計測器を煙道内に持ち込む必要がある。このため、測定に時間がかかることや保温材の再施工が必要となる等の問題があった。
【０００５】
Ｘ線やガンマ線などの放射線を物質に照射し、散乱する放射線の強度が物質の厚さの関数で示されることを利用して、その物質の厚さを検出する技術が特開平１１−２８１３３９号公報に示されている。
【０００６】
Ｘ線やガンマ線などの波動性放射線を照射して、複数層構造をもつ物質の厚さを測定する従来の技術を、図１１および図１２に示す。鋼板の厚さｔＢを測定しようとすると、腐食層ｔAの影響を受けて散乱量が多くなる。測定対象物質が２層である場合、一方の厚さが既知であることが前提となる。
【０００７】
【発明が解決しようとする課題】
複数層構造をもつ物質の厚さを測定する場合、複数層のうちのいずれかの層の厚さが既知でなくても、各層の厚さを測定できることが望まれている。
【０００８】
本発明の目的は、複数層構造をもつ物質の厚さを測定する場合、複数層のうちのいずれかの層の厚さが既知でなくても、各層の厚さを測定可能な複数層物質の厚さ測定方法および装置を提供することである。
【０００９】
【課題を解決するための手段】
以下に、［発明の実施の形態］で使用する番号・符号を用いて、［課題を解決するための手段］を説明する。これらの番号・符号は、［特許請求の範囲］の記載と［発明の実施の形態］の記載との対応関係を明らかにするために付加されたものであるが、［特許請求の範囲］に記載されている発明の技術的範囲の解釈に用いてはならない。
【００１０】
本発明の複数層物質の厚さ測定方法は、Ｎ（Ｎは２以上の整数）個の層（４０、５０）からなる複数層物質（４０、５０）のそれぞれの前記層（４０、５０）の厚さ（ａ、ｂ）を測定する複数層物質の厚さ測定方法であって、（ａ） 前記Ｎ種類の波長の放射線のそれぞれを前記複数層物質（４０、５０）に照射するステップと、（ｂ） 前記（ａ）にて前記Ｎ種類の波長の放射線が前記複数層物質（４０、５０）にそれぞれ照射されたときの各散乱放射線強度（Ｉ１、Ｉ２）を測定するステップと、（ｃ） 前記（ｂ）にて測定された前記各散乱放射線強度（Ｉ１、Ｉ２）について、前記Ｎ個の層（４０、５０）のそれぞれの厚さ（ａ、ｂ）を未知数とする方程式を立てるステップと、（ｄ） 前記（ｃ）の結果としての前記Ｎ個の前記方程式の連立方程式の解として前記Ｎ個の層（４０、５０）のそれぞれの厚さ（ａ、ｂ）を求めるステップとを備えている。
【００１１】
本発明の複数層物質の厚さ測定方法において、前記Ｎは２であり、前記２種類の波長のうちの第１の前記波長の前記放射線（１１）は、前記２個の層（４０、５０）のうちの第１の層（４０）に入射した後に、前記第１の層（４０）にて散乱した結果、前記複数層物質（４０、５０）の外方に第１の検出放射線として出るとともに、前記第１の層（４０）に入射した前記第１の波長の前記放射線（１１）は、前記第１の層（４０）にて減衰した後に前記２個の層（４０、５０）のうちの第２の層（５０）に入射し、前記第２の層（５０）にて散乱した前記第１の波長の前記放射線（１１）が前記第１の層（４０）で減衰して前記複数層物質（４０、５０）の外方に第２の検出放射線として出て、前記第１の検出放射線と前記第２の検出放射線とが合わせて、第１の前記散乱放射線強度（Ｉ１）として測定され、前記２種類の波長のうちの第２の前記波長の前記放射線（１１）は、前記第１の層（４０）に入射した後に、前記第１の層（４０）にて散乱した結果、前記複数層物質（４０、５０）の外方に第３の検出放射線として出るとともに、前記第１の層（４０）に入射した前記第２の波長の前記放射線（１１）は、前記第１の層（４０）にて減衰した後に前記第２の層（５０）に入射し、前記第２の層（５０）にて散乱した前記第２の波長の前記放射線（１１）が前記第１の層（４０）で減衰して前記複数層物質（４０、５０）の外方に第４の検出放射線として出て、前記第３の検出放射線と前記第４の検出放射線とが合わせて、第２の前記散乱放射線強度（Ｉ２）として測定され、前記測定された前記第１の散乱放射線強度（Ｉ１）をＩ１とし、前記測定された前記第２の散乱放射線強度（Ｉ２）をＩ２とすると、前記連立方程式は、
Ｉ１＝Ｘ１＋Ｙ１．
Ｉ２＝Ｘ２＋Ｙ２．
で表され、
前記第１の検出放射線に対応する前記Ｘ１は、前記第１の層（４０）の厚さ（ａ）の関数であり、前記第３の検出放射線に対応する前記Ｘ２は、前記第１の層（４０）の厚さ（ａ）の関数であり、前記第２の検出放射線に対応する前記Ｙ１は、前記第１および第２の層（４０、５０）のそれぞれの厚さ（ａ、ｂ）の関数であり、前記第４の検出放射線に対応する前記Ｙ２は、前記第１および第２の層（４０、５０）のそれぞれの厚さ（ａ、ｂ）の関数である。
【００１２】
本発明の複数層物質の厚さ測定方法において、前記第１の層（４０）の厚さをａとし、前記第２の層（５０）の厚さをｂとしたとき、
前記連立方程式は、
【数３】
前記Ａ、Ｂは、前記放射線の散乱し易さを示す定数であり、前記μは、前記放射線の減衰係数である。
【００１３】
本発明の複数層物質の厚さ測定方法において、前記放射線は、Ｘ線またはガンマ線である。
【００１４】
本発明の複数層物質の厚さ測定装置は、Ｎ（Ｎは２以上の整数）個の層（４０、５０）からなる複数層物質（４０、５０）のそれぞれの前記層（４０、５０）の厚さ（ａ、ｂ）を測定する複数層物質の厚さ測定装置であって、前記複数層物質（４０、５０）に向けて前記Ｎ種類の波長の放射線のそれぞれを照射可能な放射線発生源と、前記Ｎ種類の波長の放射線が前記複数層物質（４０、５０）にそれぞれ照射されたときの各散乱放射線（Ｉ１、Ｉ２）を検出する放射線検出器と、前記検出された前記Ｎ種類の波長の放射線のそれぞれに対応する前記散乱放射線（Ｉ１、Ｉ２）に基づいて、前記Ｎ個の層（４０、５０）の厚さ（ａ、ｂ）を演算により求める演算部とを備えている。
【００１５】
Ｎ種類の波長の放射線を照射したときの散乱放射線強度の違いは、その波長の違い自体によるものと、その照射対象の複数層物質の物性によるものがある。その両方を利用して、複数層物質の各層の厚さを検出する。
【００１６】
μは、物性定数（Ｘ線の減衰係数）であり、照射するＸ線の波長によって異なり、波長が大きいほど減衰し易い。
Ａ、Ｂは、Ｘ線の散乱のし易さを示す係数であり、Ｘ線が照射される対象物の種類によって異なる。また、Ａ、Ｂは、それぞれ照射するＸ線の波長によって異なり、波長が大きいほど散乱し難い。
【００１７】
【発明の実施の形態】
本発明の複数層物質の厚さ測定方法の一実施形態を説明する。
【００１８】
本実施形態は、複数層構造をもつ物質の各層の厚さをそれぞれ測定する装置に関する。本実施形態では、例えば、外装板や保温材などの障害物が施された鋼板の腐蝕による減肉の検査などを実施することができる。
【００１９】
本実施形態では、照射する放射線の波長を多波長にして、波長毎に散乱放射線を測定して連立方程式を解いて各層の厚さを得る。波長の変更とは、例えばガンマ線の場合はガンマ線波長を変更するし、Ｘ線の場合はＸ線管電圧を変える。
【００２０】
図１に腐食を伴った鋼板に対するＸ線散乱モデルを示す。測定対象物の鋼板５０は腐食しており、腐食層４０が形成されている。図１では、腐食層４０と鋼板５０とからなる２層構造を分かり易くするために、腐食層４０と鋼板５０とを離して図示している。
【００２１】
Ｘ線１１が腐食した鋼板表面に入射すると腐食層４０の厚さaによって散乱（４２）しながら減衰（４５）し、さらに厚さbの鋼板５０に再入射する。ここで散乱したＸ線４７が腐食層４０で減衰（６０）して外部に出て、腐食層４０での散乱（４２）と混ざり合い検出される。
【００２２】
腐食層４０と鋼板５０の厚さをそれぞれａ，ｂとすると、測定される散乱線量は以下の２式の連立方程式で表せる。
【数５】
Ｉ１，Ｉ２：後述する実測値（散乱放射線強度）
Ａ，Ｂ，μ：物性や装置構成で決まる定数
【００２３】
式（１）と式（２）を説明すると、次の通りである。
第１項目は腐食層４０での散乱４２であり、第２項目は鋼板５０による散乱４７に腐食層４０での減衰６０をかけ合わせたものである。未知数であるａ、ｂはＸ線の管電圧を複数レベルに切り換えることで求めることができる。解法は最小２乗法によって集束計算することとした。
【００２４】
次に、図９および図１０を参照して、上記の式（１）と式（２）の導出過程を示す。
【００２５】
１．一枚の板からの散乱Ｘ線
図９に示すような測定系において、板に強度I0のＸ線が入射した場合の散乱Ｘ線強度Iは式(3.1)で表される。
【数７】
式(3.1)は、強度Ｉ０の入射Ｘ線が、板中をＸだけ進む間にｅｘｐ（−μ１ｘ）減衰し，Ｘの点で散乱された後、更に散乱Ｘ線が板を抜けるまでにｅｘｐ（−μ２ｘｓｉｎθ１／ｃｏｓθ２）減衰し、立体角Ωの線量計により検出される過程を示したものである。入射Ｘ線として数百kVのＸ線を用いるので、Ｘ線と板材料との相互作用はコンプトン散乱が支配的である。
【００２７】
従って、散乱断面積ｄｅσ／ｄΩは以下の式で表される。
【数８】
また，n，Ωは以下の式で示される。
【数９】
μ2は散乱X線に対する減衰定数である。散乱X線のエネルギーE2は式(3. 5)で計算される。
【数１１】
板厚tが小さく，式(3.1)の積分範囲内でθ，Ωの変化が十分に小さいと仮定すると，式(3.1)の積分はexpに関する部分だけになる。積分を実行すると式(3.6)のようになる。
【数１２】
図９の様に板に対してX線を垂直{θ1=90(deg)}に照射する場合、sinθ1=1となり、式(3.6)は式(3.7)となる。
【数１３】
２．二枚板の場合
鉄板の表面に腐食層がある場合、図１０に示すように、板Ａ（腐食層）からの散乱X線▲１▼と板Ｂ（健全板）からの散乱X線▲２▼に分けて考える。
【００３３】
▲１▼板A（腐食層）からの散乱X線
上層の板Aから散乱するX線の散乱強度比は式(3.7)で表される。今、板Aと板Bを分けて考えるため、式(3.7)を式(4.1)の様に書き直す。
【数１４】
▲２▼板B（健全板）からの散乱X線
板Bから散乱するX線は式(3.7)を、板Aによる入射X線の減衰と散乱X線の減衰を考慮して修正する必要がある。板Bからの散乱X線強度比は式(4.2)で表される。
【数１５】
以上より、二枚板の場合の観測されるX線の散乱強度比は式(4.1)と式(4.2)を加えたものである。
【数１６】
３．散乱X線からの板厚推測
式(4.1)〜式(4.3)より、
【数１７】
【数１８】
式(5.1)において、板A厚さtaと板B厚さtbの２変数が未知で、他の定数は既知の値である。従って，異なるエネルギーのＸ線を２種類以上照射し、得られる散乱X線強度比測定データをもとに式(5.1)に相当する方程式を２つ以上連立させることにより板厚ta及びtbを求める。
【００３８】
次に、本実施形態の性能評価試験について説明する。
【００３９】
１．１模擬試験
本研究で開発したプログラムについて，システム全体の板厚測定誤差を検討した。
検討条件は以下のとおりである。
(1)腐食錆厚さ 1.4ｍｍ
(2)健全な鋼板の厚さ ６ｍｍ
(3)散乱計測値の指示誤差（測定器自身が有する測定誤差）
指示値は±0.4％で変動するものとし、重み付けとして図２の合計１５通りによるものと仮定する。図２において、「１」〜「３」の各数字は、起こり得る可能性が高いと思われる条件の組合せに対して、より大きな数が割り当てられ、起こり得る可能性が低いと思われる条件の組合せに対して、より小さな数が割り当てられている。
【００４０】
図３から図５に管電圧の組み合わせ別に求めた板厚演算結果を示す。ただし一部条件では現実的でない数値を示したので自動的に評価の対象外とした。
なお、図２から図６において、Ｘ線管電圧というパラメータは、そのＸ線の波長に換算できる物理量である。
【００４１】
図６に総合評価結果を示す。総合的な評価は、図３から図５に図２の頻度に従い重み付けして統計処理を行った。
【００４２】
図６に示した結果は、重み付けして統計処理し、１５回分のデータに対して評価した結果である。例えば１６０ｋVのX線源を用いた場合、１回の測定では±１ｍｍの誤差を含み、１５回の平均値では±0.3ｍｍである。
【００４３】
１．２実機腐食層に対する評価
図７に腐食鋼板の評価結果を示す。腐食鋼板は、裏面からの超音波計測で３．１ｍｍの厚さが測定されたものを使用した。図７において、Ｘ線管電圧組合せの「１１０−１６０」とは、１１０ｋＶのＸ線管電圧に相当する波長のＸ線を照射したときの散乱放射線強度（実測値）を上記式（１）のＩ１とし、１６０ｋＶのＸ線管電圧に相当する波長のＸ線を照射したときの散乱放射線強度（実測値）を上記式（２）のＩ２とし、それらの式（１）および（２）の連立方程式を解いて鋼板５０の厚さｂを求めることを示している。その「１１０−１６０」の組合せのときの鋼板５０の厚さｂは、２．９９３（ｍｍ）として求められた。そのときの超音波計測での実測値３．１（ｍｍ）との差は、−０．１０７（ｍｍ）である。
図７に示すように、その測定結果は２５０ｋVでの値が大き目に現われているが、ほぼ超音波測定の結果と一致している。
【００４４】
図８に実機腐食鋼板の評価結果を示す。図８の見方は、図７と同じである。その切断面の厚さをノギスにより計測した結果が４〜５ｍｍである腐食鋼板を使用した。本結果も２５０ｋVでの値が大き目に現われているが、ほぼノギス測定の結果と一致している。
【００４５】
本実施形態は、鋼板５０とその腐食層４０を例にとって説明したが、複数層構造の測定対象物であれば、何にでも適用可能である。
【００４６】
【発明の効果】
本発明の複数層物質の厚さ測定方法は、複数層構造をもつ物質の厚さを測定する場合、複数層のうちのいずれかの層の厚さが既知でなくても、各層の厚さを測定可能である。
【図面の簡単な説明】
【図１】図１は、本発明の複数層物質の厚さ測定方法の一実施形態において、Ｘ線が照射されたときの腐食層と鋼板の散乱モデルを示す図である。
【図２】図２は、本発明の複数層物質の厚さ測定方法の一実施形態において、線量計測における指示誤差の組合せ頻度（重み付け）を示すグラフである。
【図３】図３は、本発明の複数層物質の厚さ測定方法の一実施形態において、Ｘ線管電圧が１１０ｋＶと１６０ｋＶの組合せでの測定結果を示すグラフである。
【図４】図４は、本発明の複数層物質の厚さ測定方法の一実施形態において、Ｘ線管電圧が１１０ｋＶと２００ｋＶの組合せでの測定結果を示すグラフである。
【図５】図５は、本発明の複数層物質の厚さ測定方法の一実施形態において、Ｘ線管電圧が１１０ｋＶと２５０ｋＶの組合せでの測定結果を示すグラフである。
【図６】図６は、本発明の複数層物質の厚さ測定方法の一実施形態において、図３から図５の組合せでの総合的な評価結果を示すグラフである。
【図７】図７は、本発明の複数層物質の厚さ測定方法の一実施形態において、腐食鋼板による評価結果を示すグラフである。
【図８】図８は、本発明の複数層物質の厚さ測定方法の一実施形態において、実機腐食鋼板による評価結果を示すグラフである。
【図９】図９は、本発明の複数層物質の厚さ測定方法の一実施形態において用いた式の導出過程を説明するに際しての、一枚板からの散乱Ｘ線の測定方法の概略を示す図である。
【図１０】図１０は、本発明の複数層物質の厚さ測定方法の一実施形態において用いた式の導出過程を説明するに際しての、二枚板からの散乱Ｘ線の測定方法の概略を示す図である。
【図１１】図１１は、従来一般の複数層物質の厚さ測定装置の概略構成を示す図である。
【図１２】図１２は、従来一般の複数層物質の厚さ測定方法における散乱放射線強度と板厚との関係を示すグラフである。
【符号の説明】
１１ 照射Ｘ線
４０ 腐食層
４２ 腐食層での散乱
４７ 健全板（鋼板）での散乱
５０ 鋼板
ａ 腐食層の厚さ
ｂ 鋼板の厚さ
ｔＡ 腐食層の厚さ
ｔＢ 鋼板の厚さ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for measuring the thickness of a multi-layer material, and more particularly, to a method and apparatus for measuring the thickness of a multi-layer material, each of which measures the thickness of a material having a multi-layer structure.
[0002]
[Prior art]
In a flue made of a steel plate or the like, a strength problem arises when the thickness is reduced due to corrosion by exhaust gas or the like. Therefore, it is necessary to inspect the thickness from the outside through an obstacle such as a heat insulating material without entering the flue, and to identify and repair the problem part. In this situation, that is, it is necessary to inspect the plate thickness from the outside to identify and repair the problem part, as well as to structures that are difficult to enter, such as oil, gas tanks, and combustion furnaces, in addition to flues. is there.
[0003]
As a conventional metal plate thickness measurement method, there is a measurement method using ultrasonic waves and eddy currents. In such a measurement method, it is necessary to make a measurement by bringing a sensor close to the surface of the metal plate. In order to measure the plate thickness by such a conventional measuring method, it is necessary to stop the plant and measure from the inside when a person enters the flue, or to peel off the heat insulating material outside the flue.
[0004]
In the measurement method using the transmission of radiation, it is necessary to bring a radiation source or a measuring instrument into the flue. For this reason, there existed problems, such as taking time for a measurement and the need of re-construction of a heat insulating material.
[0005]
Japanese Patent Application Laid-Open No. 11-281339 discloses a technique for detecting the thickness of a substance by irradiating the substance with radiation such as X-rays or gamma rays and showing the intensity of the scattered radiation as a function of the thickness of the substance. It is shown in the publication.
[0006]
FIG. 11 and FIG. 12 show conventional techniques for measuring the thickness of a substance having a multi-layer structure by irradiating wave radiation such as X-rays and gamma rays. When the thickness t B of the steel sheet is to be measured, the amount of scattering increases due to the influence of the corrosion layer t A. When the measurement target substance has two layers, it is assumed that one of the thicknesses is known.
[0007]
[Problems to be solved by the invention]
When measuring the thickness of a substance having a multi-layer structure, it is desired that the thickness of each layer can be measured even if the thickness of any one of the multiple layers is not known.
[0008]
An object of the present invention is to measure the thickness of a substance having a multi-layer structure, even if the thickness of any one of the plurality of layers is not known, the multi-layer substance capable of measuring the thickness of each layer It is intended to provide a thickness measuring method and apparatus.
[0009]
[Means for Solving the Problems]
[Means for Solving the Problems] will be described below using the numbers and symbols used in [Embodiments of the Invention]. These numbers and symbols are added to clarify the correspondence between the description of [Claims] and the description of [Mode for carrying out the invention]. It should not be used to interpret the technical scope of the described invention.
[0010]
The method for measuring the thickness of a multi-layer material according to the present invention is the method for measuring each of the layers (40, 50) of the multi-layer material (40, 50) comprising N (N is an integer of 2 or more) layers (40, 50). A method of measuring the thickness (a, b) of a multilayer material, comprising: (a) irradiating the multilayer material (40, 50) with radiation of each of the N types of wavelengths; , (B) measuring each scattered radiation intensity (I 1 , I 2 ) when the multi-layer material (40, 50) is irradiated with the radiation of the N types of wavelengths in (a), respectively; (C) For each of the scattered radiation intensities (I 1 , I 2 ) measured in (b), the thicknesses (a, b) of the N layers (40, 50) are defined as unknowns. And (d) the N number of said methods as a result of (c) And a step of obtaining the thickness of each of the N layers (40, 50) as a solution of the simultaneous equations of equation (a, b).
[0011]
In the method for measuring a thickness of a multilayer material according to the present invention, the N is 2, and the radiation (11) having the first wavelength among the two types of wavelengths is the two layers (40, 50). ) And then scattered as a result of scattering at the first layer (40), and as a first detection radiation outside the multilayer material (40, 50). At the same time, the radiation (11) having the first wavelength incident on the first layer (40) is attenuated by the first layer (40) and then the two layers (40, 50). The radiation (11) of the first wavelength incident on the second layer (50) and scattered by the second layer (50) is attenuated by the first layer (40) and is The first detection radiation and the second detection radiation are emitted to the outside of the multilayer material (40, 50) as the second detection radiation. And is combined, is determined as the first of the scattered radiation intensity (I 1), the radiation of the second of said wavelengths of said two wavelengths (11) is incident on said first layer (40) After that, as a result of scattering in the first layer (40), the multi-layer material (40, 50) is emitted as third detection radiation to the outside and is incident on the first layer (40). The radiation (11) having the second wavelength is attenuated by the first layer (40), then enters the second layer (50), and is scattered by the second layer (50). The radiation (11) of the second wavelength is attenuated in the first layer (40) and exits the multilayer material (40, 50) as a fourth detection radiation, so that the third Together with detected radiation and the fourth detection radiation, measured as the second of the scattered radiation intensity (I 2) Is, when the measured first scattered radiation intensity (I 1) and I 1, the measured second scattered radiation intensity (I 2) and I 2, the simultaneous equations,
I 1 = X1 + Y1.
I 2 = X2 + Y2.
Represented by
The X1 corresponding to the first detection radiation is a function of the thickness (a) of the first layer (40), and the X2 corresponding to the third detection radiation is the first layer. Y1 corresponding to the second detected radiation is a function of the thickness (a) of (40), and the respective thicknesses (a, b) of the first and second layers (40, 50). Y2 corresponding to the fourth detection radiation is a function of the thickness (a, b) of each of the first and second layers (40, 50).
[0012]
In the method for measuring a thickness of a multi-layer material of the present invention, when the thickness of the first layer (40) is a and the thickness of the second layer (50) is b,
The simultaneous equations are
[Equation 3]
The A and B are constants indicating the ease of scattering of the radiation, and the μ is an attenuation coefficient of the radiation.
[0013]
In the method for measuring a thickness of a multi-layer material of the present invention, the radiation is X-rays or gamma rays.
[0014]
The multi-layer material thickness measuring apparatus according to the present invention is configured such that each of the layers (40, 50) of the multi-layer material (40, 50) including N (N is an integer of 2 or more) layers (40, 50). A device for measuring the thickness (a, b) of a multi-layer material, and generating radiation capable of irradiating each of the N types of wavelengths toward the multi-layer material (40, 50) A source, a radiation detector that detects each of the scattered radiation (I 1 , I 2 ) when the multilayer materials (40, 50) are respectively irradiated with radiation of the N types of wavelengths, and the detected A calculation unit for calculating the thickness (a, b) of the N layers (40, 50) based on the scattered radiation (I 1 , I 2 ) corresponding to each of N types of radiation; It has.
[0015]
The difference in scattered radiation intensity when irradiated with radiation of N types of wavelengths is due to the difference in wavelength itself and due to the physical properties of the multilayer material to be irradiated. Both are used to detect the thickness of each layer of the multi-layer material.
[0016]
μ is a physical property constant (X-ray attenuation coefficient), which varies depending on the wavelength of X-rays to be irradiated.
A and B are coefficients indicating the ease of scattering of X-rays, and differ depending on the type of object irradiated with X-rays. A and B differ depending on the wavelength of the X-rays to be irradiated, and the larger the wavelength, the harder to scatter.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the method for measuring the thickness of a multilayer material of the present invention will be described.
[0018]
This embodiment relates to an apparatus for measuring the thickness of each layer of a substance having a multi-layer structure. In the present embodiment, for example, inspection of thinning due to corrosion of a steel plate on which an obstacle such as an exterior plate or a heat insulating material is applied can be performed.
[0019]
In this embodiment, the wavelength of the irradiated radiation is set to multiple wavelengths, the scattered radiation is measured for each wavelength, and the simultaneous equations are solved to obtain the thickness of each layer. The change in wavelength is, for example, changing the wavelength of gamma rays in the case of gamma rays and changing the X-ray tube voltage in the case of X rays.
[0020]
FIG. 1 shows an X-ray scattering model for a steel plate with corrosion. The steel plate 50 to be measured is corroded, and the corrosion layer 40 is formed. In FIG. 1, the corrosion layer 40 and the steel plate 50 are shown separated from each other in order to facilitate understanding of a two-layer structure including the corrosion layer 40 and the steel plate 50.
[0021]
When the X-ray 11 is incident on the corroded steel plate surface, it is attenuated (45) while being scattered (42) by the thickness a of the corroded layer 40, and further reenters the steel plate 50 having the thickness b. Here, the scattered X-rays 47 are attenuated (60) by the corrosive layer 40 and exit to the outside, where they are mixed with the scattered light (42) in the corrosive layer 40 and detected.
[0022]
If the thicknesses of the corrosion layer 40 and the steel plate 50 are a and b, respectively, the measured scattered dose can be expressed by the following two simultaneous equations.
[Equation 5]
I 1 , I 2 : Actual measured values (scattered radiation intensity) to be described later
A, B, μ: Constants determined by physical properties and device configuration [0023]
The equations (1) and (2) will be described as follows.
The first item is the scattering 42 in the corroded layer 40, and the second item is the result of multiplying the scattering 47 by the steel plate 50 and the attenuation 60 in the corroding layer 40. The unknown numbers a and b can be obtained by switching the X-ray tube voltage to a plurality of levels. The solution was calculated by focusing using the least square method.
[0024]
Next, with reference to FIG. 9 and FIG. 10, the derivation process of said Formula (1) and Formula (2) is shown.
[0025]
1. Scattered X-rays from a single plate In a measurement system as shown in FIG. 9, the scattered X-ray intensity I when X-rays having an intensity I 0 are incident on the plate is expressed by equation (3.1).
[Expression 7]
Equation (3.1) shows that incident X-rays with intensity I 0 are attenuated by exp (−μ 1 x) while traveling through the plate by X, and after being scattered at the point of X, further scattered X-rays pass through the plate. FIG. 4 shows a process in which the attenuation is exp (−μ 2 xsin θ 1 / cos θ 2 ) and detected by a dosimeter with a solid angle Ω. Since an X-ray of several hundred kV is used as the incident X-ray, Compton scattering is dominant in the interaction between the X-ray and the plate material.
[0027]
Therefore, the scattering cross section d e σ / dΩ is expressed by the following equation.
[Equation 8]
N and Ω are expressed by the following equations.
[Equation 9]
μ 2 is an attenuation constant for scattered X-rays. Scattered X-ray energy E 2 is calculated by equation (3.5).
[Expression 11]
Assuming that the plate thickness t is small and that changes in θ and Ω are sufficiently small within the integration range of Eq. (3.1), the integration of Eq. (3.1) is limited to exp. When integration is performed, the equation (3.6) is obtained.
[Expression 12]
When X-rays are irradiated perpendicularly to the plate {θ 1 = 90 (deg)} as shown in FIG. 9, sinθ 1 = 1, and equation (3.6) becomes equation (3.7).
[Formula 13]
2. In the case of two plates, when there is a corrosion layer on the surface of the iron plate, as shown in FIG. 10, scattered X-rays from plate A (corrosion layer) 1 and scattered X-rays from plate B (sound plate) 2 Divide into ▼.
[0033]
{Circle around (1)} Scattering intensity ratio of X-rays scattered from the upper plate A scattered X-rays from plate A (corrosion layer) is expressed by equation (3.7). Now, to consider plate A and plate B separately, equation (3.7) is rewritten as equation (4.1).
[Expression 14]
(2) Scattered X-rays from plate B (healthy plate) X-rays scattered from plate B need to be corrected in consideration of attenuation of incident X-rays and scattered X-rays by plate A (3.7). is there. The scattered X-ray intensity ratio from plate B is expressed by equation (4.2).
[Expression 15]
From the above, the observed X-ray scattering intensity ratio in the case of the two plates is obtained by adding the equations (4.1) and (4.2).
[Expression 16]
3. From the thickness estimation formula (4.1) to formula (4.3) from scattered X-rays,
[Expression 17]
[Formula 18]
In equation (5.1), the two variables of the plate A thickness t a and the plate B thickness t b are unknown, and the other constants are known values. Therefore, two or more types of X-rays with different energies are irradiated, and the thicknesses t a and t b are obtained by connecting two or more equations corresponding to equation (5.1) based on the obtained scattered X-ray intensity ratio measurement data. Ask for.
[0038]
Next, the performance evaluation test of this embodiment will be described.
[0039]
1.1 Simulated test The thickness measurement error of the entire system was examined for the program developed in this study.
The examination conditions are as follows.
(1) Corrosion rust thickness 1.4mm
(2) Healthy steel plate thickness 6mm
(3) Scatter measurement value indication error (measurement error of the measuring instrument itself)
It is assumed that the indicated value fluctuates by ± 0.4%, and the weighting is based on the total of 15 patterns in FIG. In FIG. 2, each number of “1” to “3” is assigned a larger number to a combination of conditions that are likely to occur, and is a condition that is unlikely to occur. A smaller number is assigned to the combination.
[0040]
FIG. 3 to FIG. 5 show the plate thickness calculation results obtained for each combination of tube voltages. However, because some values were not realistic under certain conditions, they were automatically excluded from the evaluation.
2 to 6, the parameter called X-ray tube voltage is a physical quantity that can be converted into the wavelength of the X-ray.
[0041]
FIG. 6 shows the comprehensive evaluation results. For the comprehensive evaluation, statistical processing was performed by weighting FIGS. 3 to 5 according to the frequency of FIG.
[0042]
The results shown in FIG. 6 are the results of weighting and statistical processing, and evaluating 15 times of data. For example, when an X-ray source of 160 kV is used, an error of ± 1 mm is included in one measurement, and an average value of 15 times is ± 0.3 mm.
[0043]
1.2 Evaluation for Corrosion Layer on Actual Machine FIG. 7 shows the evaluation results of the corroded steel sheet. As the corroded steel sheet, one having a thickness of 3.1 mm measured by ultrasonic measurement from the back surface was used. In FIG. 7, “110-160” of the X-ray tube voltage combination is the scattered radiation intensity (actually measured value) when irradiated with X-rays having a wavelength corresponding to an X-ray tube voltage of 110 kV in the above equation (1). and I 1, the scattered radiation intensity when irradiated with X-rays having a wavelength corresponding to the X-ray tube voltage of 160kV (the measured value) and I 2 in the formula (2), those of formula (1) and (2) It is shown that the thickness b of the steel plate 50 is obtained by solving the simultaneous equations. The thickness b of the steel plate 50 in the case of the combination “110-160” was determined as 2.993 (mm). The difference from the actually measured value 3.1 (mm) in the ultrasonic measurement at that time is −0.107 (mm).
As shown in FIG. 7, the measurement result shows a large value at 250 kV, but almost coincides with the result of ultrasonic measurement.
[0044]
FIG. 8 shows the evaluation results of the actual corrosion steel sheet. 8 is the same as FIG. The corrosion steel plate whose result of measuring the thickness of the cut surface with calipers is 4 to 5 mm was used. This result also shows a large value at 250 kV, but almost coincides with the result of the caliper measurement.
[0045]
Although this embodiment demonstrated the steel plate 50 and the corrosive layer 40 as an example, if it is a measuring object of a multilayer structure, it is applicable to anything.
[0046]
【The invention's effect】
In the method for measuring the thickness of a multi-layer material according to the present invention, when measuring the thickness of a material having a multi-layer structure, the thickness of each layer is not known even if the thickness of any one of the multiple layers is not known. Can be measured.
[Brief description of the drawings]
FIG. 1 is a diagram showing a scattering model of a corrosion layer and a steel plate when irradiated with X-rays in one embodiment of the method for measuring the thickness of a multilayer material of the present invention.
FIG. 2 is a graph showing a combination frequency (weighting) of instruction errors in dosimetry in an embodiment of the method for measuring a thickness of a multilayer material of the present invention.
FIG. 3 is a graph showing measurement results when the X-ray tube voltage is a combination of 110 kV and 160 kV in one embodiment of the method for measuring the thickness of a multilayer material of the present invention.
FIG. 4 is a graph showing measurement results when the X-ray tube voltage is a combination of 110 kV and 200 kV in an embodiment of the method for measuring the thickness of a multilayer material of the present invention.
FIG. 5 is a graph showing measurement results when the X-ray tube voltage is a combination of 110 kV and 250 kV in an embodiment of the method for measuring the thickness of a multilayer material of the present invention.
FIG. 6 is a graph showing a comprehensive evaluation result in the combination of FIGS. 3 to 5 in an embodiment of the method for measuring the thickness of a multilayer material of the present invention.
FIG. 7 is a graph showing an evaluation result using a corroded steel plate in one embodiment of the method for measuring the thickness of a multilayer material of the present invention.
FIG. 8 is a graph showing an evaluation result using an actual corroded steel sheet in one embodiment of the method for measuring the thickness of a multilayer material of the present invention.
FIG. 9 shows an outline of a method for measuring scattered X-rays from a single plate in explaining the derivation process of the equation used in one embodiment of the method for measuring the thickness of a multilayer material of the present invention. FIG.
FIG. 10 shows an outline of a method for measuring scattered X-rays from two plates when explaining the derivation process of the equation used in one embodiment of the method for measuring the thickness of a multilayer material of the present invention. FIG.
FIG. 11 is a diagram showing a schematic configuration of a conventional general multi-layer material thickness measuring apparatus.
FIG. 12 is a graph showing the relationship between scattered radiation intensity and plate thickness in a conventional general method for measuring the thickness of a multilayer material.
[Explanation of symbols]
11 Irradiation X-ray 40 Corrosion layer 42 Scattering at corrosion layer 47 Scattering at healthy plate (steel plate) 50 Steel plate a Corrosion layer thickness b Steel plate thickness t A Corrosion layer thickness t B Steel plate thickness
Claims (3)
（ａ） 前記２種類の波長の放射線のそれぞれを前記複数層物質に照射するステップと、
（ｂ） 前記（ａ）にて前記２種類の波長の放射線が前記複数層物質にそれぞれ照射されたときの各散乱放射線強度を測定するステップと、
（ｃ） 前記（ｂ）にて測定された前記各散乱放射線強度について、前記２個の層のそれぞれの厚さを未知数とする方程式を立てるステップと、
（ｄ） 前記（ｃ）の結果としての前記２個の前記方程式の連立方程式の解として前記２個の層のそれぞれの厚さを求めるステップとを備え、
前記２種類の波長のうちの第１の前記波長の前記放射線は、前記２個の層のうちの第１の層に入射した後に、前記第１の層にて散乱した結果、前記複数層物質の外方に第１の検出放射線として出るとともに、前記第１の層に入射した前記第１の波長の前記放射線は、前記第１の層にて減衰した後に前記２個の層のうちの第２の層に入射し、前記第２の層にて散乱した前記第１の波長の前記放射線が前記第１の層で減衰して前記複数層物質の外方に第２の検出放射線として出て、前記第１の検出放射線と前記第２の検出放射線とが合わせて、第１の前記散乱放射線強度として測定され、
前記２種類の波長のうちの第２の前記波長の前記放射線は、前記第１の層に入射した後に、前記第１の層にて散乱した結果、前記複数層物質の外方に第３の検出放射線として出るとともに、前記第１の層に入射した前記第２の波長の前記放射線は、前記第１の層にて減衰した後に前記第２の層に入射し、前記第２の層にて散乱した前記第２の波長の前記放射線が前記第１の層で減衰して前記複数層物質の外方に第４の検出放射線として出て、前記第３の検出放射線と前記第４の検出放射線とが合わせて、第２の前記散乱放射線強度として測定され、
前記測定された前記第１の散乱放射線強度をＩ１とし、前記測定された前記第２の散乱放射線強度をＩ２とすると、
前記連立方程式は、
Ｉ１＝Ｘ１＋Ｙ１．
Ｉ２＝Ｘ２＋Ｙ２．
で表され、
前記第１の検出放射線に対応する前記Ｘ１は、前記第１の層の厚さの関数であり、
前記第３の検出放射線に対応する前記Ｘ２は、前記第１の層の厚さの関数であり、
前記第２の検出放射線に対応する前記Ｙ１は、前記第１および第２の層のそれぞれの厚さの関数であり、
前記第４の検出放射線に対応する前記Ｙ２は、前記第１および第２の層のそれぞれの厚さの関数であり、
前記第１の層の厚さをａとし、前記第２の層の厚さをｂとしたとき、
前記連立方程式は、
前記Ａ、Ｂは、前記放射線の散乱し易さを示す定数であり、
前記μは、前記放射線の減衰係数である
複数層物質の厚さ測定方法。 A method for measuring a thickness of a multi-layer material, wherein the thickness of each of the multi-layer materials composed of two layers is measured.
(A) irradiating the multilayer material with each of the two types of wavelengths of radiation;
(B) measuring the intensity of each scattered radiation when the radiation of the two types of wavelengths is irradiated to the multilayer material in (a),
(C) wherein for each scattered radiation intensity measured at (b), the steps to make a equations to unknown respective thickness of the two layers,
(D) a step of obtaining a thickness of each of the two layers as a solution of simultaneous equations of the two said equations as a result of the (c),
The radiation of the first wavelength of the two types of wavelengths is incident on the first layer of the two layers and then scattered by the first layer, resulting in the multilayer material. And the radiation of the first wavelength incident on the first layer is attenuated by the first layer and then the first of the two layers. The radiation having the first wavelength incident on the second layer and scattered by the second layer is attenuated by the first layer and is emitted to the outside of the multi-layer material as the second detection radiation. , The first detection radiation and the second detection radiation are combined and measured as the first scattered radiation intensity,
The radiation of the second wavelength out of the two types of wavelengths is incident on the first layer and then scattered in the first layer. The radiation of the second wavelength incident on the first layer and incident on the first layer is attenuated by the first layer and then incident on the second layer, and is incident on the second layer. The scattered radiation having the second wavelength is attenuated by the first layer and is emitted to the outside of the multi-layer material as fourth detection radiation, and the third detection radiation and the fourth detection radiation. And is measured as the second scattered radiation intensity,
When the measured first scattered radiation intensity is I1, and the measured second scattered radiation intensity is I2,
The simultaneous equations are
I1 = X1 + Y1.
I2 = X2 + Y2.
Represented by
X1 corresponding to the first detected radiation is a function of the thickness of the first layer;
X2 corresponding to the third detected radiation is a function of the thickness of the first layer;
Y1 corresponding to the second detected radiation is a function of the thickness of each of the first and second layers;
Wherein corresponding to the fourth detected radiation Y2 is Ri functions der the respective thicknesses of the first and second layers,
When the thickness of the first layer is a and the thickness of the second layer is b,
The simultaneous equations are
A and B are constants indicating the ease of scattering of the radiation,
The μ is the attenuation coefficient of the radiation.
前記放射線は、Ｘ線またはガンマ線である
複数層物質の厚さ測定方法。The method for measuring a thickness of a multi-layer material according to claim 1 ,
The radiation is an X-ray or a gamma ray.
前記複数層物質に向けて前記２種類の波長の放射線のそれぞれを照射可能な放射線発生源と、
前記２種類の波長の放射線が前記複数層物質にそれぞれ照射されたときの各散乱放射線を検出する放射線検出器と、
前記検出された前記２種類の波長の放射線のそれぞれに対応する前記散乱放射線に基づいて、前記２個の層のそれぞれの厚さを未知数とする方程式を立て、前記２個の前記方程式の連立方程式の解として前記２個の層の厚さを演算により求める演算部とを備え、
前記２種類の波長のうちの第１の前記波長の前記放射線は、前記２個の層のうちの第１の層に入射した後に、前記第１の層にて散乱した結果、前記複数層物質の外方に第１の検出放射線として出るとともに、前記第１の層に入射した前記第１の波長の前記放射線は、前記第１の層にて減衰した後に前記２個の層のうちの第２の層に入射し、前記第２の層にて散乱した前記第１の波長の前記放射線が前記第１の層で減衰して前記複数層物質の外方に第２の検出放射線として出て、前記第１の検出放射線と前記第２の検出放射線とが合わせて、第１の前記散乱放射線強度として測定され、
前記２種類の波長のうちの第２の前記波長の前記放射線は、前記第１の層に入射した後に、前記第１の層にて散乱した結果、前記複数層物質の外方に第３の検出放射線として出るとともに、前記第１の層に入射した前記第２の波長の前記放射線は、前記第１の層にて減衰した後に前記第２の層に入射し、前記第２の層にて散乱した前記第２の波長の前記放射線が前記第１の層で減衰して前記複数層物質の外方に第４の検出放射線として出て、前記第３の検出放射線と前記第４の検出放射線とが合わせて、第２の前記散乱放射線強度として測定され、
前記測定された前記第１の散乱放射線強度をＩ１とし、前記測定された前記第２の散乱放射線強度をＩ２とすると、
前記連立方程式は、
Ｉ１＝Ｘ１＋Ｙ１．
Ｉ２＝Ｘ２＋Ｙ２．
で表され、
前記第１の検出放射線に対応する前記Ｘ１は、前記第１の層の厚さの関数であり、
前記第３の検出放射線に対応する前記Ｘ２は、前記第１の層の厚さの関数であり、
前記第２の検出放射線に対応する前記Ｙ１は、前記第１および第２の層のそれぞれの厚さの関数であり、
前記第４の検出放射線に対応する前記Ｙ２は、前記第１および第２の層のそれぞれの厚さの関数であり、
前記第１の層の厚さをａとし、前記第２の層の厚さをｂとしたとき、
前記連立方程式は、
前記Ａ、Ｂは、前記放射線の散乱し易さを示す定数であり、
前記μは、前記放射線の減衰係数である
複数層物質の厚さ測定装置。A thickness measuring apparatus a plurality of layers substances for measuring the thickness of each of the layers of the multilayer material composed of two layers,
A radiation source capable of irradiating each of the two types of radiation toward the multilayer material;
A radiation detector for detecting each scattered radiation when the radiation of the two types of wavelengths is respectively applied to the multilayer material;
Based on the scattered radiation corresponding to each of the detected two types of wavelengths of radiation, an equation with the respective thicknesses of the two layers as unknowns is established, and simultaneous equations of the two equations and an arithmetic unit which as a solution of obtained by calculating the thickness of the two layers,
The radiation of the first wavelength of the two types of wavelengths is incident on the first layer of the two layers and then scattered by the first layer, resulting in the multilayer material. And the radiation of the first wavelength incident on the first layer is attenuated by the first layer and then the first of the two layers. The radiation having the first wavelength incident on the second layer and scattered by the second layer is attenuated by the first layer and is emitted to the outside of the multi-layer material as the second detection radiation. , The first detection radiation and the second detection radiation are combined and measured as the first scattered radiation intensity,
The radiation of the second wavelength out of the two types of wavelengths is incident on the first layer and then scattered in the first layer. The radiation of the second wavelength incident on the first layer and incident on the first layer is attenuated by the first layer and then incident on the second layer, and is incident on the second layer. The scattered radiation having the second wavelength is attenuated by the first layer and is emitted to the outside of the multi-layer material as fourth detection radiation, and the third detection radiation and the fourth detection radiation. And is measured as the second scattered radiation intensity,
When the measured first scattered radiation intensity is I1, and the measured second scattered radiation intensity is I2,
The simultaneous equations are
I1 = X1 + Y1.
I2 = X2 + Y2.
Represented by
X1 corresponding to the first detected radiation is a function of the thickness of the first layer;
X2 corresponding to the third detected radiation is a function of the thickness of the first layer;
Y1 corresponding to the second detected radiation is a function of the thickness of each of the first and second layers;
Y2 corresponding to the fourth detected radiation is a function of the thickness of each of the first and second layers;
When the thickness of the first layer is a and the thickness of the second layer is b,
The simultaneous equations are
A and B are constants indicating the ease of scattering of the radiation,
Μ is an attenuation coefficient of the radiation
Thickness measuring device of the double several layers material.
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