JP4865741B2 - Damage evaluation method for bent part of steel pipe - Google Patents

Damage evaluation method for bent part of steel pipe Download PDF

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JP4865741B2
JP4865741B2 JP2008019689A JP2008019689A JP4865741B2 JP 4865741 B2 JP4865741 B2 JP 4865741B2 JP 2008019689 A JP2008019689 A JP 2008019689A JP 2008019689 A JP2008019689 A JP 2008019689A JP 4865741 B2 JP4865741 B2 JP 4865741B2
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steel pipe
outer diameter
bending
change rate
flat
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JP2009180610A (en
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伸彦 齋藤
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Mitsubishi Heavy Industries Ltd
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Description

本発明は、オーステナイト系耐熱鋼等の鋼管の曲げ加工を行うに際し、鋼管の曲げ部の状況を、鋼管を破損することなく評価可能にした鋼管の曲げ部の損傷評価方法に関する。   The present invention relates to a method for evaluating damage of a bent portion of a steel pipe, which can evaluate the state of the bent portion of the steel pipe without damaging the steel pipe when bending a steel pipe such as austenitic heat-resistant steel.

火力発電プラント等の高温応力下で用いられているオーステナイト系耐熱鋼のクリープ、クリープ疲労等の高温損傷を評価する方法としては、従来下記の手法が用いられてきた。
１）使用されている材料を抜管し（切り出し）、クリープ破断試験、クリープ疲労試験等の破壊試験を行って、未使用状態からの強度低下度を評価する破壊試験法。
２）使用された温度、応力、時間から未使用材の強度を用いて、損傷度を推定する応力解析法。
３）実際に使用されたオーステナイト系耐熱鋼において、高温探傷と直接関係する粒界析出物及びボイドを定量化して探傷評価する非破壊法（ＳＵＳ材等は、簡易的な寿命評価技術をして、ボイド線密度またはボイド面密度などの非破壊手法が確立されている）。
尚、かかる非破壊手法には、特許文献１（特開平６−３４６２５号公報）および特許文献２（特開平６−５０９６６号公報）等の技術も含まれる。 Conventionally, the following methods have been used as methods for evaluating high temperature damage such as creep and creep fatigue of austenitic heat-resistant steel used under high temperature stress in thermal power plants and the like.
1) A destructive test method in which a material used is extubated (cut out) and subjected to a destructive test such as a creep rupture test and a creep fatigue test to evaluate the degree of strength reduction from an unused state.
2) A stress analysis method that estimates the degree of damage using the strength of unused material from the temperature, stress, and time used.
3) Non-destructive method for quantifying grain boundary precipitates and voids directly related to high-temperature flaw detection and evaluating flaw detection in austenitic heat-resistant steels actually used (SUS materials, etc. have a simple life evaluation technique) Non-destructive techniques such as void line density or void surface density have been established).
Such non-destructive techniques include techniques such as Patent Document 1 (Japanese Patent Laid-Open No. 6-34625) and Patent Document 2 (Japanese Patent Laid-Open No. 6-50966).

前記１）〜３）の方法を、図４のブロック図に示し、前記１）は図４の（１）、前記２）は図４の（２）、前記３）は図４の（３）にそれぞれ対応する。   The method of 1) to 3) is shown in the block diagram of FIG. 4, wherein 1) is (1) in FIG. 4, 2) is (2) in FIG. 4, and 3) is (3) in FIG. Correspond to each.

特開平６−３４６２５号公報JP-A-6-34625 特開平６−５０９６６号公報JP-A-6-50966

しかしながら、前記１）〜３）の手法には、次のような問題がある。
１）の破壊試験法では、使用材を抜管する必要があり、その後の運転のためには、切断工事に加えて、復旧工事の費用、工期がかかってしまう。また、長時間使用された傷を評価するには、運転条件に近い状態で試験を実施する必要があり、評価に時間を要する。また、曲げ部によってはクリープ破断試験片を採取できないという問題もある。
２）の強度評価法では、使用材を抜管する必要はないが、評価に実際に使用された材料ではなく、同じ種類の材料データを用いることから、実際に使用された材料強度データと応力解析の評価に用いた材料強度との差に起因した誤差が生じることがあった。 However, the methods 1) to 3) have the following problems.
In the destructive test method of 1), it is necessary to extrude the material used, and for subsequent operation, in addition to cutting work, cost for restoration work and construction period are required. In addition, in order to evaluate a flaw that has been used for a long time, it is necessary to perform a test in a state close to operating conditions, and it takes time for the evaluation. In addition, there is a problem that a creep rupture test piece cannot be collected depending on a bent portion.
In the strength evaluation method of 2), it is not necessary to extrude the material used, but since the same type of material data is used instead of the material actually used in the evaluation, the actually used material strength data and stress analysis are used. In some cases, an error was caused due to a difference from the material strength used in the evaluation.

３）の非破壊法は比較的有効な手法であるが、ボイド自体のばらつきが大きく、精度が低い。また、曲げ部の挙動がそれと同じかどうかの検証もできていない。
また、前記特許文献１（特開平６−３４６２５号公報）および特許文献２（特開平６−５０９６６号公報）等の技術も同様な問題を有している。 The non-destructive method of 3) is a relatively effective method, but the dispersion of voids is large and the accuracy is low. Moreover, it is not possible to verify whether the behavior of the bent portion is the same.
Further, the techniques of Patent Document 1 (Japanese Patent Laid-Open No. 6-34625) and Patent Document 2 (Japanese Patent Laid-Open No. 6-50966) have similar problems.

本発明はかかる従来技術の課題に鑑み、抜管や精密研磨を必要としない非破壊方法であって、鋼管の曲げ部の外径、管厚、扁平率を計測するだけの簡単な評価方法で以って、高精度の探傷評価が可能な鋼管の曲げ部の損傷評価方法を提供することを目的とする。   In view of the problems of the prior art, the present invention is a non-destructive method that does not require evacuation or precision polishing, and is a simple evaluation method that only measures the outer diameter, tube thickness, and flatness of the bent portion of a steel pipe. Thus, an object of the present invention is to provide a damage evaluation method for a bent portion of a steel pipe capable of highly accurate flaw detection evaluation.

本発明はかかる目的を達成するもので、次の２つの手法を特徴としている。
（１）鋼管の曲げ加工を行うに際し、鋼管の曲げ後における扁平率：Ｓ０（（鋼管の最大外径−鋼管の最小外径）／（公称外径））×１００に設定し、さらに高温応力下で使用中の扁平変化率：Ｓ１（使用中途時の扁平率Ｓ／未使用材の扁平率Ｓ０）×１００に設定し、該扁平変化率Ｓ１が、予め設定された一定値よりも小さくなったとき、前記鋼管に異常が発生したものと判定することを特徴とする（請求項１）。 The present invention achieves such an object and is characterized by the following two methods.
(1) When bending a steel pipe, the flatness after bending of the steel pipe is set to S0 ((maximum outer diameter of the steel pipe−minimum outer diameter of the steel pipe) / (nominal outer diameter)) × 100, and high temperature stress The flat change rate during use is set to S1 (flat rate S during use / flat rate S0 of unused material) × 100, and the flat change rate S1 becomes smaller than a predetermined constant value. When this occurs, it is determined that an abnormality has occurred in the steel pipe (claim 1).

（２）鋼管の曲げ加工を行うに際し、鋼管の曲げ後における扁平率：Ｓ０を（（鋼管の最大外径−鋼管の最小外径）／（公称外径））×１００、扁平変化率：Ｓ１を（使用中途時の扁平率Ｓ／未使用材の扁平率Ｓ０）×１００とし、鋼管の曲げ後における外径変化率：Ｕを（使用中途時の外径／未使用材の外径））×１００に設定し、鋼管の曲げ後における管厚変化率：Ｔを（使用中途時の肉厚／未使用材の肉厚）×１００とし、Ｋ＝Ｔ・Ｓ１／Ｕが予め設定された一定値よりも小さくなったとき、前記鋼管に異常が発生したものと判定することを特徴とする（請求項２）。   (2) When bending steel pipe, flattening ratio after bending of steel pipe: S0 ((maximum outer diameter of steel pipe−minimum outer diameter of steel pipe) / (nominal outer diameter)) × 100, flattening change rate: S1 (The flattening ratio S during use / flattening ratio S0 of unused material) × 100, and the outer diameter change rate after bending of the steel pipe: U ((outside diameter during use / outer diameter of unused material)) X100, tube thickness change rate after bending of steel pipe: T is (thickness during use / thickness of unused material) x100, and K = T · S1 / U is a constant constant When the value is smaller than the value, it is determined that an abnormality has occurred in the steel pipe (claim 2).

本発明によれば、
１）鋼管の扁平変化率：Ｓ１を（使用中途時の扁平率Ｓ／未使用材の扁平率Ｓ０）×１００に設定し、さらに該扁平率：Ｓ０を（（鋼管の最大外径−鋼管の最小外径）／（公称外径））×１００に設定して、かかる扁平変化率：Ｓ１の実績データを、前記鋼管の曲げ部の内圧クリープ中途止め試験により蓄積して、許容の一定値を実績として設定しておく。
そして、任意の試験鋼管で曲げ部の内圧クリープ試験を行い、その試験結果から扁平変化率：Ｓ１を求めて、この扁平変化率：Ｓ１を前記許容の一定値と比較する。そして該扁平変化率：Ｓ１が前記許容の一定値よりも小さくなったとき、前記鋼管に異常が発生したものと判定することができる。 According to the present invention,
1) Flattening rate of steel pipe: S1 is set to (flattening ratio S during use / flattening ratio S0 of unused material) × 100, and further this flattening ratio: S0 is set to ((maximum outer diameter of steel pipe−steel pipe Minimum outer diameter) / (nominal outer diameter)) × 100, and accumulating the actual data of the flat rate of change: S1 by the internal pressure creep interruption test of the bent portion of the steel pipe, and setting the allowable constant value Set as a track record.
Then, an internal pressure creep test of the bending portion is performed with an arbitrary test steel pipe, a flat change rate: S1 is obtained from the test result, and the flat change rate: S1 is compared with the above-described allowable constant value. And when this flat change rate: S1 becomes smaller than the allowable constant value, it can be determined that an abnormality has occurred in the steel pipe.

２）また、係数Ｋ＝Ｔ・Ｓ１／Ｕ、Ｔは管厚変化率（使用中途時の肉厚／未使用材の肉厚）×１００、Ｕは外径変化率（使用中途時の外径／未使用材の外径））×１００）とし、
かかる係数Ｋ＝Ｔ・Ｓ１／Ｕの実績データを、前記鋼管の曲げ部の内圧クリープ中途止め試験により蓄積して、許容の係数Ｋの一定値Ｋ０を実績として設定しておく。
そして、任意の試験鋼管で曲げ部の内圧クリープ試験を行い、その試験結果から前記係数Ｋ＝Ｔ・Ｓ１／Ｕを求めて、この係数Ｋを前記許容の一定値Ｋ０と比較する。そして係数Ｋが前記許容の一定値Ｋ０よりも小さくなったとき、前記鋼管に異常が発生したものと判定することができる。 2) Also, the coefficient K = T · S1 / U, T is the tube thickness change rate (thickness during use / thickness of unused material) × 100, and U is the change rate of outer diameter (outer diameter during use) / Outer diameter of unused material)) × 100)
The actual data of the coefficient K = T · S1 / U is accumulated by an internal pressure creep stoppage test of the bent portion of the steel pipe, and a constant value K0 of the allowable coefficient K is set as the actual result.
Then, an internal pressure creep test of the bending portion is performed with an arbitrary test steel pipe, the coefficient K = T · S1 / U is obtained from the test result, and the coefficient K is compared with the allowable constant value K0. When the coefficient K becomes smaller than the allowable constant value K0, it can be determined that an abnormality has occurred in the steel pipe.

以上の２つの方法により、鋼管の扁平変化率：Ｓ１あるいは係数Ｋ＝Ｔ・Ｓ１／Ｕを求めておき、この、鋼管の扁平変化率：Ｓ１あるいは係数Ｋ＝Ｔ・Ｓ１／Ｕの２つの値のいずれか又は双方が許容の一定値よりも小さくなったとき、鋼管に異常が発生したものと判定するので、抜管や精密研磨を必要としない非破壊方法であって、鋼管の曲げ部の外径、管厚、扁平率を計測するだけの簡単な評価方法で以って、高精度の探傷評価が可能な鋼管の曲げ部の損傷評価方法を得ることができる。   By the above two methods, the flattening change rate of the steel pipe: S1 or the coefficient K = T · S1 / U is obtained, and the flattening change rate of the steel pipe: S1 or the coefficient K = T · S1 / U. When either or both of them are smaller than the allowable constant value, it is determined that an abnormality has occurred in the steel pipe. With a simple evaluation method that only measures the diameter, pipe thickness, and flatness, a damage evaluation method for a bent portion of a steel pipe that enables highly accurate flaw detection evaluation can be obtained.

以下、本発明を図に示した実施例を用いて詳細に説明する。但し、この実施例に記載されている構成部品の寸法、材質、形状、その相対配置などは特に特定的な記載がない限り、この発明の範囲をそれのみに限定する趣旨ではなく、単なる説明例にすぎない。   Hereinafter, the present invention will be described in detail with reference to the embodiments shown in the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the component parts described in this example are not intended to limit the scope of the present invention only to specific examples unless otherwise specified. Only.

図１（Ａ）は本発明の実施例にかかるオーステナイト系耐熱鋼からなる鋼管の曲げ試験時の部分図、（Ｂ）は（Ａ）のＡ―Ａ断面図である。
図１において、鋼管１００を半径Ｒ０で曲げる。ｔは肉厚である。前記半径Ｒ０で曲げたときの、鋼管１００の曲げ後の各寸法から、次の値を算出する。
尚、Ｄｍｘが最大外径、Ｄｍｎが最小外径である。また、１００ａが曲げ後、１００ｂが未使用時である。 FIG. 1A is a partial view during a bending test of a steel pipe made of austenitic heat-resisting steel according to an embodiment of the present invention, and FIG. 1B is a cross-sectional view taken along line AA of FIG.
In FIG. 1, the steel pipe 100 is bent with a radius R0. t is the wall thickness. The following values are calculated from the respective dimensions after bending of the steel pipe 100 when bent at the radius R0.
Note that Dmx is the maximum outer diameter and Dmn is the minimum outer diameter. Also, 100a is after bending and 100b is unused.

まず、前記鋼管１００において、曲げ後の各寸法から、
扁平率：Ｓ０を（（鋼管の最大外径Ｄｍｘ−鋼管の最小外径Ｄｍｎ）／（公称外径））×１００を測定し、さらに、
扁平変化率：Ｓ１を（使用中途時の扁平率Ｓ／未使用材の扁平率Ｓ０）×１００
を測定する。 First, in the steel pipe 100, from each dimension after bending,
Flatness: Measure S0 ((maximum outer diameter Dmx of steel pipe−minimum outer diameter Dmn of steel pipe) / (nominal outer diameter)) × 100,
Flat change rate: S1 (Flat rate S during use / Flat rate S0 of unused material) × 100
Measure.

即ち、鋼管１００の扁平変化率：Ｓ１を（使用中途時の扁平率Ｓ／未使用材の扁平率Ｓ０）×１００に設定し、この扁平率：Ｓ０を（（鋼管の最大外径−鋼管の最小外径）／（公称外径））×１００に設定する。
そして、かかる扁平変化率：Ｓ１の実績データを下記実施例に示すように、前記鋼管１００の曲げ部の内圧クリープ中途止め試験により実績として蓄積しておき、該扁平変化率：Ｓ１の許容の一定値を実績として設定しておく。
次いで、任意の試験鋼管１００の曲げ部の内圧クリープ試験を行い、その試験結果から扁平変化率：Ｓ１を求めて、この扁平変化率：Ｓ１を下記実施例に対応させ、許容の一定値Ｓ１０よりも小さくなったとき、前記鋼管に異常が発生したものと判定することができる。 That is, the flattening change rate S1 of the steel pipe 100 is set to (flattening ratio S during use / flattening ratio S0 of unused material) × 100, and this flatness ratio S0 is set to ((maximum outer diameter of steel pipe−steel pipe Minimum outer diameter) / (nominal outer diameter)) × 100.
Then, as shown in the following examples, the actual data of the flat change rate: S1 is accumulated as a result by an internal pressure creep interruption test of the bending portion of the steel pipe 100, and the flat change rate: S1 is allowed to be constant. Set the value as a record.
Next, an internal pressure creep test of a bent portion of an arbitrary test steel pipe 100 is performed, and a flat change rate: S1 is obtained from the test result. The flat change rate: S1 is made to correspond to the following example, and from an allowable constant value S10 Can be determined that an abnormality has occurred in the steel pipe.

また、前記鋼管１００において、
鋼管の曲げ後における外径変化率：Ｕを（使用中途時の外径Ｄ／未使用材の外径））×１００
及び
鋼管の曲げ後における管厚変化率；Ｔ（使用中途時の肉厚ｔ／未使用材の肉厚）×１００
を測定し、これに、
前記扁平変化率：Ｓ１を（使用中途時の扁平率Ｓ／未使用材の扁平率Ｓ０）×１００
を用いて、
Ｋ＝Ｔ・Ｓ１／Ｕ （１）
を算出する。 In the steel pipe 100,
Rate of change of outer diameter after bending of steel pipe: U (outer diameter D during use / outer diameter of unused material)) × 100
And tube thickness change rate after bending of steel pipe; T (thickness t during use / thickness of unused material) × 100
To this,
Said flat change rate: S1 (flat rate S during use / flat rate S0 of unused material) × 100
Using,
K = T · S1 / U (1)
Is calculated.

この場合は、係数Ｋ＝Ｔ・Ｓ１／Ｕ （１）式は、管厚変化率Ｔ（使用中途時の肉厚／未使用材の肉厚）×１００、外径変化率Ｕ（使用中途時の外径／未使用材の外径））×１００及び
前記扁平変化率：Ｓ１を（使用中途時の扁平率Ｓ／未使用材の扁平率Ｓ０）×１００の関数とする。
そして、かかる係数Ｋ＝Ｔ・Ｓ１／Ｕの実績データを下記実施例に示すように、前記鋼管１００の曲げ部の内圧クリープ中途止め試験により実績として蓄積しておき、許容の係数Ｋの一定値Ｋ０を実績として設定しておく。
そして、任意の試験鋼管１００の曲げ部の内圧クリープ試験を行い、この係数Ｋを、下記実施例に対応させ、許容の一定値Ｋ０よりも小さくなったとき、前記鋼管に異常が発生したものと判定することができる。 In this case, the coefficient K = T · S1 / U (1) is an equation that the tube thickness change rate T (thickness during use / thickness of unused material) × 100, outer diameter change rate U (during use) Of outer diameter / outer diameter of unused material)) × 100 and the flattening change rate: S1 is a function of (flatness S during use / flattening ratio S0 of unused material) × 100.
The actual data of the coefficient K = T · S1 / U is accumulated as an actual result by an internal pressure creep interruption test of the bent portion of the steel pipe 100 as shown in the following examples, and a constant value of the allowable coefficient K K0 is set as a record.
Then, an internal pressure creep test of a bent portion of an arbitrary test steel pipe 100 is performed, and when this coefficient K is made to correspond to the following example and becomes smaller than an allowable constant value K0, an abnormality occurs in the steel pipe. Can be determined.

以上の２つの方法により、鋼管１００の扁平変化率：Ｓ１あるいは係数Ｋ＝Ｔ・Ｓ１／Ｕを求めておき、この、鋼管１００の扁平変化率：Ｓ１あるいは係数Ｋ＝Ｔ・Ｓ１／Ｕの２つの値のいずれか又は双方が前記許容の一定値よりも小さくなったとき、鋼管１００に異常が発生したものと判定するので、抜管や精密研磨を必要としない非破壊方法であって、鋼管１００の曲げ部の外径Ｄ、管厚ｔ、扁平率Ｓを計測するだけの簡単な評価方法で以って、高精度の探傷評価が可能な鋼管１００の曲げ部の損傷評価方法を得ることができる。   By the above two methods, the flattening change rate of the steel pipe 100: S1 or the coefficient K = T · S1 / U is obtained, and the flattening change rate of the steel pipe 100: S1 or the coefficient K = T · S1 / U of 2 When one or both of the two values is smaller than the allowable constant value, it is determined that an abnormality has occurred in the steel pipe 100. Therefore, this is a non-destructive method that does not require extubation or precision polishing. It is possible to obtain a damage evaluation method for a bent portion of a steel pipe 100 capable of highly accurate flaw detection evaluation by a simple evaluation method by simply measuring the outer diameter D, the tube thickness t, and the flatness S of the bent portion. it can.

図２は、本発明の実施例を示すオーステナイト系耐熱鋼からなる鋼管の曲げ部の内圧クリープ中途止め試験の結果、つまり破断までに数回中途めして測定した評価成績表、図３は図２の評価成績評価表を示すグラフで、いずれもＴ（中途止め時間）／Ｔｒ（破断時間）をベースに示している。
図２〜図３において、Ｓ１が扁平変化率、Ｋが前記係数を示す。 FIG. 2 is a result of an internal pressure creep interruption test of a bent portion of a steel pipe made of austenitic heat resistant steel showing an embodiment of the present invention, that is, an evaluation result table measured several times before breaking, and FIG. These are graphs showing the evaluation result evaluation table, and all are based on T (interruption time) / Tr (break time).
In FIG. 2 to FIG. 3, S <b> 1 is a flat change rate, and K is the coefficient.

図２〜３において、オーステナイト系耐熱鋼からなる鋼管においては、Ｓ１及びＫは、クリープ初期ではＴ／Ｔｒに対して大きく減少し、Ｔ／Ｔｒの初期から中期に掛けては略一定で、Ｔ／Ｔｒの中期から後期にかけてまた減少する。
かかる図２〜３に示す、クリープ曲げ試験の結果に、前記のような鋼管１００の扁平変化率：Ｓ１あるいは係数Ｋ＝Ｔ・Ｓ１／Ｕを対応させてプロットする。 2 and 3, in a steel pipe made of austenitic heat-resistant steel, S1 and K greatly decrease with respect to T / Tr at the initial stage of creep, and are substantially constant from the initial stage to the middle stage of T / Tr. / Tr decreases again from mid to late.
The results of the creep bending test shown in FIGS. 2 to 3 are plotted in correspondence with the flattening change rate: S1 or coefficient K = T · S1 / U of the steel pipe 100 as described above.

そして、前記Ｓ１が許容の一定値ＳＩ０以下となったとき、前記鋼管１００に異常が発生したものと判定することができる。
また、前記Ｋが許容の一定値Ｋ０以下となったときにも前記鋼管１００に異常が発生したものと判定することができる。 When S1 becomes equal to or less than the allowable constant value SI0, it can be determined that an abnormality has occurred in the steel pipe 100.
Further, it can be determined that an abnormality has occurred in the steel pipe 100 even when the K is equal to or less than the allowable constant value K0.

本発明によれば、抜管や精密研磨を必要としない非破壊方法であって、鋼管の曲げ部の外径、管厚、扁平率を計測するだけの簡単な評価方法で以って、高精度の探傷評価が可能な鋼管の曲げ部の損傷評価方法を提供できる。   According to the present invention, it is a non-destructive method that does not require evacuation or precision polishing, and is a simple evaluation method that only measures the outer diameter, the tube thickness, and the flatness of the bent portion of a steel pipe, and provides high accuracy. It is possible to provide a damage evaluation method for a bent portion of a steel pipe capable of performing flaw detection evaluation.

（Ａ）は本発明の実施例にかかるオーステナイト系耐熱鋼からなる鋼管の曲げ試験時の部分図、（Ｂ）は（Ａ）のＡ―Ａ断面図である。(A) is the fragmentary figure at the time of the bending test of the steel pipe which consists of an austenitic heat-resistant steel concerning the Example of this invention, (B) is AA sectional drawing of (A). 前記実施例におけるオーステナイト系耐熱鋼からなる鋼管の曲げ試験データの一例である。It is an example of the bending test data of the steel pipe which consists of austenitic heat-resistant steel in the said Example. 前記オーステナイト系耐熱鋼からなる鋼管の曲げ部の内圧クリープ中途止め試験データの線図である。It is a diagram of the internal pressure creep stoppage test data of the bending part of the steel pipe which consists of said austenitic heat-resisting steel. 従来方法を示すブロック図である。It is a block diagram which shows a conventional method.

符号の説明Explanation of symbols

１００ 鋼管
１００ａ 曲げ後
１００ｂ 未使用時
Ｓ１ 扁平変化率
Ｋ 係数 100 Steel pipe 100a After bending 100b When not used S1 Flatness change rate K coefficient

Claims (2)

鋼管の曲げ加工を行うに際し、鋼管の曲げ後における扁平率：Ｓ０（（鋼管の最大外径−鋼管の最小外径）／（公称外径））×１００を設定し、さらに高温応力下で使用中の扁平変化率：Ｓ１（使用中途時の扁平率Ｓ／未使用材の扁平率Ｓ０）×１００を設定し、該扁平変化率Ｓ１が、予め設定された一定値よりも小さくなったとき、前記鋼管に異常が発生したものと判定することを特徴とする鋼管の曲げ部の損傷評価方法。   When bending a steel pipe, set the flatness after bending of the steel pipe: S0 ((maximum outer diameter of the steel pipe−minimum outer diameter of the steel pipe) / (nominal outer diameter)) × 100, and use under high temperature stress When the flat change rate is set to S1 (flat rate S during use / flat rate S0 of unused material) × 100, and the flat change rate S1 is smaller than a predetermined constant value, A method for evaluating damage of a bent portion of a steel pipe, wherein it is determined that an abnormality has occurred in the steel pipe. 鋼管の曲げ加工を行うに際し、鋼管の曲げ後における扁平率：Ｓ０を（（鋼管の最大外径−鋼管の最小外径）／（公称外径））×１００、扁平変化率：Ｓ１を（使用中途時の扁平率Ｓ／未使用材の扁平率Ｓ０）×１００とし、鋼管の曲げ後における外径変化率：Ｕを（使用中途時の外径／未使用材の外径））×１００に設定し、鋼管の曲げ後における管厚変化率：Ｔを（使用中途時の肉厚／未使用材の肉厚）×１００とし、Ｋ＝Ｔ・Ｓ１／Ｕが予め設定された一定値よりも小さくなったとき、前記鋼管に異常が発生したものと判定することを特徴とする鋼管の曲げ部の損傷評価方法。
When bending a steel pipe, flattening ratio after bending of the steel pipe: S0 ((maximum outer diameter of the steel pipe−minimum outer diameter of the steel pipe) / (nominal outer diameter)) × 100, flattening change rate: S1 (used) Midway flattening ratio S / unused material flattening ratio S0) × 100, and change rate of outer diameter after bending of steel pipe: U to (outside diameter during use / outer diameter of unused material)) × 100 Set, tube thickness change rate after bending of steel pipe: T is (thickness during use / thickness of unused material) × 100, and K = T · S1 / U is more than a preset constant value When it becomes small, it determines with the abnormality having generate | occur | produced in the said steel pipe, The damage evaluation method of the bending part of the steel pipe characterized by the above-mentioned.
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