求翻译：[0006] 目前，许多检测单位只能对防腐检测及钢管腐蚀环境评估的基础上用超声波法测量钢管腐蚀状况，该方法必须开挖并剥离防护层，再将仪器紧贴钢管进行检测量。是什么意思？

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[0006] At present, many examination units only can corrode the environment appraisal to the anticorrosion examination and the steel pipe in the foundation with the ultrasonic wave law survey steel pipe corrosion condition, this method must excavate and strip the protective layer, again carries on th

[0006] at present, many testing units can only be performed on anti-corrosion steel pipe corrosion detection and environmental assessment on the basis of the characterisation of steel tubes using ultrasonic corrosion condition, the method must be excavation and removal of protective layer, then inst