Boiler water quality

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In accordance with the requirements of GB/T12145-2016, the allowable iron content levels for feedwater and steam at steam pressures of 3.8–5.8 are ≤50 ug/l and ≤20 ug/kg respectively; however, there are no specified limits for the iron content in boiler water. The water quality analysis results from our plant are shown in the figure below: the feedwater meets the standards, but the steam does not. The water supply sampling point is at the outlet of the boiler feed pump (before the economizer). To ensure that sampling by the sampler would be problem-free, the sampler was flushed for an extended period of time and the inner walls of the coil were cleaned, but none of these measures proved effective. My preliminary judgment is that it may be due to substandard dissolved oxygen, which has caused oxygen corrosion in the pipes, economizer, or boiler. I’m not sure if anyone knows about this; please help analyze it. Boiler feed water, furnace water saturated steam ≤50 ug/l; ug/l ≤20 ug/kg: 12.91, 132.26, 35.48; 19.35, 129.03, 29.03; 23.33, 146.67, 50.01