GU-751 – HSE Precautions for NORM Contaminated Tanks, Vessels & Separators – PDO

Cleaning operations of tanks, vessels, and separators are periodically required to remove deposited sludge, sand, clay, and scales. Past experience has demonstrated that the level of sludge in the tanks can vary from several centimeters in height up to two meters. Prior planning by Maintenance Services to determine if tanks scheduled for cleaning/inspection are NORM contaminated is essential. These procedures shall only apply to tanks, vessels, or separators when monitored externally and internally records ≥ 0.5 μSv/hr.

Tanks are assumed to contain NORM sludge/silts until proven otherwise by monitoring and analysis. A NORM Radiological Survey must be performed at least two weeks prior to the commencement of works and is performed by a competent meter user. If the measurement is recorded ≥ 0.5 μSv/hr, a sample of the sludge must be collected for analysis prior to commencement of the cleaning. Note: If the tank is double lined, the radiation may not reach the exterior wall and direct monitoring of the sludge is required.

Once the oil is drained, a representative sample of the sludge shall be collected from the base of the tank. If a sample can be gathered without emptying the tank, this should be undertaken along with the NORM Survey. If the sludge does not exceed 0.5 μSv/hr, there is insufficient NORM to warrant implementing this procedure and the sludge or sands shall be treated as not NORM contaminated. It is necessary to collect a sludge sample for analysis as this will determine the disposal options.

The sample (> 100 grams) is analyzed for isotopic Radium-226,228 activity. If the activity of the Radium-226,228 is greater than 1 Bq/g of sludge, the sludge must be stored in a dedicated NORM facility for correct future disposal. If the activity is less than 1 Bq/g for Radium-226,228 according to current international standards, the sludge can be land farmed to remove the hydrocarbon content. At less than 1 Bq/g of Radium-226,228, the external dose from the gamma radiation is not of significant risk, however the inhalation risk to workers performing sludge removal from alpha and beta particles is exists and controls to prevent inhalation, ingestion, and absorption of NORM through open cuts is necessary.

This procedure is developed when the exterior NORM survey indicates the presence of NORM inside the tank. If NORM is not detected from exterior measurements of gas vessels, NORM may still be present in the interior (as Lead-210) and monitoring of the inside of the tank is required using an alpha/beta meter.
This document shall be read in conjunction with PR 1077 – Preparation of Tanks and Vessel for Internal Work – Procedure