求翻译：对屈服点小于或等于390Mpa的钢板，应抽取钢板总张数的20％进行超声检测，当发现有不合格的钢板时，应逐张检查。是什么意思？

On the yield point less than or equal to 390mpa steel plate should be taking 20% ​​of the total number of sheets of steel plate for ultrasonic testing, when the found unqualified plate, by Zhang to check.

The yield is less than or equal to 390 Mpa of sheet steel, should be the total number of sheets from the steel plate 20 per cent of the ultrasonic test, when you find a non-qualified sheet steel, should be one check.

Is smaller than to the yield point or was equal to 390Mpa the steel plate, should extract the steel plate total number of sheets 20% to carry on the supersonic examination, when discovered when has the unqualified steel plate, should chase opens the inspection.

Yield point steel less than or equal to 390Mpa, 20% of total plate count should be collected for ultrasonic test, when a plate is found not qualified, should be inspected one by one.

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