关于中国船舶工业无损检测标准与IACS Rec. 20标准的比较说明

船体结构焊缝进行无损检测（Non-destructive testing of ship hull steel welds）
中国船舶工业无损检测标准（CB/T）与IACS Rec. 20标准的比较说明
Brief introduction for comparing Chinese shipbuilding NDT standards (CB/T)
with IACS REC 20
几乎所有的中国船厂采用以下无损检测标准对船体结构焊缝进行无损检测：
CB/T3177-94（船舶钢焊缝射线照相和超声波检查规则）、CB/T3558-94（船舶钢焊缝射线照相工艺和质量分级）、CB/T3559-94（船舶钢焊缝手工超声波探伤工艺和质量分级）、CB/T3958-2004（船舶钢焊缝磁粉、渗透检测工艺和质量分级）
Almost all Chinese shipyards adopt following recognized NDT standards for non-destructive testing of ship hull steel welds：CB/T3177-94（Ship steel weld radiographic testing and UT testing standard，CB/T3558-94（Ship steel weld radiographic testing technology and quality classification），CB/T3559-94（Ship steel weld UT testing technology and quality classification）and CB/T3958-2004 （Ship steel weld magnetic particle & penetration testing technology and quality classification）
在IACS URZ23 和IACS Rec. 47中提及使用IACS Rec. 20对船体结构焊缝进行无损检测，为了便于验船师检查无损检测结果，现将上述标准与IACS Rec. 20标准的比较结果具体如下：In IACS URZ23 and IACS Rec. 47, IACS.20 is referred to be applied for non-destructive testing of ship hull steel welds. In order to convenience for surveyor checking NDT results, full comparison between above mentioned national NDT standards with IACS.20 are done, see the contrast tables and conclusions as follows:
一、射线照相检测radiographic testing:
表1 / Table 1：
表1/Table 1：
1. 比较CB普通级绿色数据与IACS REC 20的相应数据要求，在相同的透照范围内，透照灵敏度（发现金属丝指数）即像质计要求，CB/T3558-94标准的普通级严于IACS Rec. 20的要求；Regarding wire number visible on the film (nominal diameter) i.e. IQI, comparing green figures between CB/T3558-94 (normal class) and IACS REC 20, within the same nominal thickness range, found that IQI (normal class stipulated on CB/T3558-94) is much more stringent than that of REC 20.
2. 比较CB普通级红色IQI数据与IACS REC 20的IQI数据要求，在相同的透照范围内，透照灵敏度（发现金属丝指数）即像质计要求CB/T3558-94标准的普通级小于IACS Rec. 20的要求；Regarding wire number visible on the film (nominal diameter) i.e. IQI, comparing red figures between CB/T3558-94 (normal class) and IACS REC 20, within the same nominal thickness range, found that IQI (normal class stipulated on CB/T3558-94) is less stringent than that of REC 20.
3. 所以船厂或无损检测公司在射线照相透照灵敏度（发现金属丝指数）上，可以使用
CB/T3558-94标准的普通级要求，并注意在此情况下与IACS Rec. 20要求相一致，即在X 射线片子上看到相应要求的金属丝指数。

Hence, shipyard or NDT company may adopts CB/T3558-94 standard’s wire number visible on the film (nominal diameter), but shipyard has to pay attention to be in line with required IQI stipulated on IACS REC 20, i.e. required wire number visible on the film (nominal diameter), then it can meet IACS REC 20.
表2 / Table 2：
表2 / Table 2：
比较CB/T3558-94标准中，γ射线照相底片密度能够满足IACS Rec. 20标准；如船厂或无损检测公司在实际使用X射线照相时，操作人员应通过使用适当设备或增加曝光量等，使底片密度达到IACS REC 20的要求，这样就可以满足IACS Rec. 20标准对底片密度的要求。

Comparing CB/T3558-94, γ-ray can meet requirement of film density stipulated on IACS REC 20; in case shipyard or NDT company, are using of X-ray in normal practices, NDT operator should choose suitable X-ray equipment or increase exposal etc. to meet IACS Rec. 20 requirement on film density.
*注：根据IACS REC 20所述，黑度由船厂或无损检测公司根据ISO17636的表5进行选择：*Note：Acc. to requirement stipulated on IACS REC 20 (6.5.8), the optical density of the radiographs should be selected by the shipyard in accordance with table 5 of ISO17636 :
ISO17636表5 / ISO17636 table 5
Optical density of the radiographs 等级Class 黑度a / Density a
A（普通级）/（Normal class）≥2.0b
B（较高级）/（Upper class ≥2.3c
a：测量允许误差为±0.1 / Measuring tolerance of ±0.1 is permitted
b：经合同各方商定，可将为1.5 / May be reduced to 1.5 if specified, e.g. in an application standard. c：经合同各方商定，可将为2.0 / May be reduced to 2.0 if specified, e.g. in an application standard.
表3 / Table 3：
IACS Rec. 20标准射线照相质量分级
Acceptance criteria for radiographic testing - IACS REC 20
缺陷种类Discontinuity 接受标准
Acceptance criteria for radiographic testing¹)
裂纹Crack 不接受
Not accepted
未熔合
Lack of fusion 单个缺陷最大接受长度t/2或25mm，两者取小者；间断缺陷总计最大接受长度t或50mm，两者取小
Continuous²)maximum length t/2 or 25 mm whichever is the less intermittent cumulative³) length maximum t or 50 mm
未焊透Incomplete root penetration 位于十字接头的单面对接接头焊缝不接受
Not accepted in butt joint welded from one side
单个缺陷最大接受长度t/2或25mm，两者取小者；间断缺陷总计最大接受长度t或50mm，两者取小
Continuous²)maximum length t/2 or 25 mm whichever is the less intermittent cumulative³)length maximum t or 50 mm
夹渣
Slag inclusion 单个缺陷最大接受长度t或50mm，两者取小者；间断缺陷总计最大接受长度2t或100mm，两者取小
Continuous²)maximum length t or 50 mm whichever is the less intermittent cumulative³)’)length maximum 2t or 100 mm
注Note:
¹): “t”取焊接板材的最小厚度。

“t” is the plate thickness of the thinnest plate.
²): 两个相邻的单个间断缺陷长度L1和L2之间的直线距离L凡是小于其中最短的一个间断缺陷长度，均应视作一个连续的长形缺陷L1+L+L2。

Two adjacent individual discontinuities of length L1 and L2 situated on a line and where the distance L between them is shorter than the shortest discontinuity should be regards as a continuous discontinuity of length L1+L+L2.
³): 单个连续的间断缺陷长度的总和。

Sum of the length of individual continuous discontinuities.
): 如果从焊缝的横向上测量，平行夹渣之间的距离小于最大夹渣宽度的3倍，这些夹渣应被视作为同一条间断面。

Parallel inclusions not separated by more than 3 times the width of the largest inclusion should be regarded as one continuous discontinuity.
表4 / Table 4：
表3和表4比较Results after comparing Table 3 and Table 4：
1.裂纹、未焊透、未熔合等危害性缺陷在CB/T3558-94标准中是不接受的，在IACS Rec. 20
标准中可以接受一定长度的未熔合和未焊透缺陷；Crack, incomplete root penetration and
lack of fusion etc. is not accepted as per CB/T3558-94, but certain length of incomplete root
penetration and lack of fusion (specified on IACS REC 20) could be accepted as per IACS REC
20.
2.在两标准中夹渣的分级和评价，例如选取厚度为20mm的焊缝作缺陷评定，在IACS Rec. 20
标准中可以接受的单个夹渣长度为20mm，在CB/T3558-94标准中II级和III级合格的夹渣
的许可长度为10mm和13mm；间断的累计缺陷允许长度分别为: REC 20 为40mm、
CB/T3558-94为小于30mm、小于40mm；Regarding classifying slag flaws related to CB/T
3558-94 & IACS REC 20, for example, selected plate thickness as 20 mm for classifying, single
length of slag flaws as 20 mm could be accepted; but acc. to CB/T 3558-94, accepted length of
slag flaws for class II & III are 10mm, 13 mm; intermittent cumulative length are 40mm for
REC 20, less than 30mm and less than 40mm for CB/T3558-94
3.一般来讲，船厂或无损检测公司在实际评片中使用的合格等级至少为II级（III级合格为
船舯部0.6L之外等），所以CB/T3558-94标准的缺陷评价分级要严于IACS) Rec. 20标准
的要求。

General speaking, during normal classification practice, shipyard or NDT company
shall adopt lowest class as class II (Class III shall be accepted when out of 0.6 L area), so
classifying requirement of CB/T 3558-94 is much more stringent than that of REC 20.
二、超声波检测Ultrasonic testing:
表6 / Table 6：
表5、表6 / Table 5, Table 6：
1.在CB/T3559-94标准中，根据缺陷的波高和指示长度及分布状态，把焊缝质量分为Ⅰ~Ⅴ
级；高于ARL (判废线）的缺陷回波均评定为Ⅴ级；低于或等于MRL（测长线）的缺陷回波可评定为Ⅰ级；超过MRL（测长线）到ARL(判废线）之间的缺陷回波，据所测定的指示长度按分级表评级；As per CB/T3559-94, classifying welding seam quality as class I~V, the one higher than ARL shall be class V; the one less than or equal to MRL could be class I; the ones exceed MRL but below ARL shall be classified as per actual measured length.
2.在IACS Rec. 20标准中，规定了测长线和评定线的回波高度，测长线和评定线相当于ARL
(判废线）和DRL（测长区分线）；As per IACS REC 20, specified ECHO height of MRL and evaluation Line classifying welding seam quality as class I~V, the one higher than ARL shall be class V; the one less than or equal to MRL could be class I; the one exceed MRL but below ARL shall be classified as per actual measured length
3.对于缺陷的评定Acceptance criteria：
1）在IACS Rec. 20标准中，大于100%的DAC曲线的回波高度，单个缺陷最大接受长度t/2或25mm，两者取小者；在CB/T3559-94标准中，评定为判废不接受；As per IACS REC 20, greater than 100% of DAC curve, acceptance criteria is that Max. length t/2 or 25 mm whichever is the less; but it could not be accepted as per CB/T 3559-94.
2）在IACS Rec. 20标准中，回波高度在DAC缺陷50~100%之间，单个缺陷最大接受长度t或50mm，两者取小者；在CB/T3559-94标准中，据所测定长度评级；例如选取厚度为20mm的焊缝作缺陷评定，可以接受的单个夹渣长度为分别为20mm、10mm （II级合格）、15mm（III级合格）；As per IACS REC 20, greater than 50% but less than 100% of DAC curve, acceptance criteria is that Max. length t or 50 mm whichever is the less; but as per CB/T 3559-94, acceptance criteria is based on “indicated length for single flaw”, such as, selected thickness as 20 mm, accepted length for single slag is 20 mm, 10 mm (class II), 15 mm (class III).
3）在IACS Rec. 20标准中，低于33%的DAC曲线的波高（Φ3-10dB）评定为合格，在CB/T3559-94标准中，低于或等于MRL（测长线）的缺陷回波可评定为Ⅰ级；As per IACS REC 20, less than 33% of DAC curve (Φ3-10dB) could be accepted; as per CB/T 3559-94, ECHO height lower or equal to MRL could be accepted as Class I.
4）评估认为是裂纹、未焊透、未熔合的，两者都不接受；Both of IACS REC 20 and CB/T 3559-94 not accept that Indications evaluated to be cracks, lack of root penetration and lack of fusion regardless of ECHO height.
4.船厂或无损检测公司一般至少采用CB/T3559-94标准的II级为合格。

Shipyard or NDT
company at least to adopt “Class II” as accepted class ac. to CB/T 3559-94.
5.所以超声波标准即CB/T3559-94高于IACS Rec. 20标准的要求。

So UT requirement of CB/T
3558-94 is much more stringent than that of REC 20.
三、磁粉/渗透检测Magnetic particle & liquid penetration testing:
表7 / Table 7：
1.评估认为是裂纹、未焊透、未熔合的，两者都不接受；Both of IACS REC 20 and CB/T 3559-94
not accept that Indications evaluated to be cracks, lack of root penetration and lack of fusion. 2.在CB/T3958-2004标准中，任何长度大于3mm的线状缺陷、任何单个直径大于4mm的圆
形缺陷，不接受；As per CB/T 3958-2004, not accept any length over 3 mm for lined flaws and any dia. over 4 mm for rotundity flaws.
3.在IACS Rec. 20标准中，表面气孔可以接受的尺寸为在对接接头上的单个气孔直径≤0.25t
（角焊缝的单个气孔直径≤0.25a)，但最大直径3mm；相邻气孔最小间距为2.5倍的直径；
在CB/T3958-2004标准中，单个缺陷指示长度可接受的长度0.5~2.0（II级合格）和＞2~4（III级合格）；As per IACS REC 20, acceptance criteria for single pore diameter d≤0.25t¹)for butt welds (d≦0.25a¹)for fillet welds) with Max. diameter 3 mm; 2.5d as Min. distance to adjacent pore; As per CB/T 3958-2004, acceptance criteria for “Indicated length for single flaw” is 0.5~2.0 (Class II) and 2~4 (Class III).
4.船厂或无损检测公司一般至少采用CB/T3958-2004标准的II级为合格；Shipyard or NDT
company at least to adopt “Class II” as accepted class ac. to CB/T 3958-2004.
5.所以磁粉/渗透检测标准即CB/T3958-2004高于IACS Rec. 20标准的要求。

So MT/PT
requirement of CB/T3958-2004 is much more stringent than that of REC 20.
中国船舶工业无损检测标准（CB/T）与IACS Rec. 20标准的比较结(Conclusion):
1.射线探伤：接受标准采取中国船舶工业射线照相(CB/T3558-94) 标准是高于IACS Rec. 20
中相关要求的。

但在进行射线照相时应注意以下2个事项。

RT – the acceptance criteria in CB/T3558-94 is stringent then IACS Re. 20, however following 2 items should be taken into full consideration at the process of performing radiographic test:
a)关于射线照相透照灵敏度（发现金属丝指数）：船厂或无损检测公司可以使用
CB/T3558-94标准的普通级要求，但同时需充分考虑并满足IACS Rec. 20规定的要
求，即在X射线片子上看到相应要求（较高部分）的金属丝指数，详见下表。

Regarding
wire number visible on the film (nominal diameter): shipyard or NDT company may
adopts CB/T3558-94 with full consideration of IACS REC 20, viz. the required wire
number visible on the film (nominal diameter) should display the stringent ones as
required in CB/T3558-94 and IACS REC 20, details as mentioned in the Table in below:
b)关于黑度：比较CB/T3558-94标准中，γ射线照相底片密度能够满足IACS Rec. 20
标准；如船厂或无损检测公司没有γ射线源，在实际使用X射线照相时，操作人员
应通过使用适当设备或增加曝光量等，使底片密度达到IACS REC 20的要求(根据
ISO17636的表5的要求，经各方商定，黑度可以降低到1.5)，这样就可以满足IACS
Rec. 20标准对底片密度的要求。

即，使用X射线照相时RT底片黑度可接受范围为：
1.20~4.00。

Regarding density: comparing CB/T3558-94 with IACS REC 20, y-ray can meet
requirement of film density stipulated on IACS REC 20; in case shipyard or NDT
company don’t has γ-ray, during normal practice of X-ray, NDT operator should choose
suitable X-ray equipment or increase exposal etc. to meet IACS Rec. 20 requirement on
film density, (Acc. to table 5 of ISO17636, density may be reduced to 1.5 if specified, e.g.
in an application standard), then could meet requirement of film density stipulated on
IACS REC 20, viz, the acceptance range for the density of X-ray firm is 1.20~4.00.
2.超声波探伤：中国船舶工业超声波的标准(CB/T 3559-94)严于IACS Rec. 20标准的要求。

Chinese shipbuilding UT standard (CB/T 3559-94) is much more stringent than that of REC 20.
3.磁粉和着色探伤：中国船舶工业磁粉/渗透的标准(CB/T 3958-2004)严于IACS Rec. 20标准
的要求。

Chinese shipbuilding MT/PT standards (CB/T 3958-2004) is much more stringent than that of REC 20.。