ABSTRACT

The numerous reasons for cleaning a transmission pipeline include increasing efficiency, preventing corrosion, increasing operational safety, complying with governmental regulations, and changing pipeline operations. As part of the pipeline cleaning procedure, a chemical cleaning agent is typically used to aid in the removal of various line deposits. With an emphasis on solids characterization, a series of six criteria based upon lab performance using line deposits have been designed to select the best cleaner in a particular application. Combining operational parameters and physical analysis of the line deposits, the choice between an oil soluble and a water soluble chemical treatment is based upon efficacy and operational considerations. The testing criteria then require the optimal agent to be dispersible in the solvent of choice, penetrate solids deposited on the pipeline walls, suspend the line deposits within the cleaning solution, retain solution flowability even with suspended solids, and settle for easier disposal. Each of the above criteria strongly correlate with desired field performance as demonstrated in several applications. Whether a particular deposit is black powder or a solid scale, the use of reasoned parametric design provides for a more efficient and cost effective chemical cleaning solution.

INTRODUCTION

With over one million miles of major oil and gas pipelines around the world and greater than 60 percent over 20 years old, many reasons exist to clean and maintain the operation integrity of this major infrastructure. ~ The major reasons to clean a pipeline can be broken into three general categories. First, clean to operate in a more efficient manner whether by lowering operating costs, lowering downtime, or simply obtaining a better in-line inspection. Second, clean to increase operating safety by removal of pyrophoric compounds such as iron sulfide. Third, clean to alter operational parameters either to comply with government regulation or change the product transported.

Why Clean?

The most common reason to clean a transmission pipeline is to increase

operational efficiency. Recently, a company reported savings in excess of 2 million dollars per year based upon removal of black powder from a gas transmission system. 2 Black powder is a ubiquitous problem in gas transmission systems with no group having a complete handle on the size of the problem. 3 Black powder typically consists of forms of iron oxide and iron sulfide mixed with small amount of oil or water contamination. As this is the most frequently encountered solids deposit, black powder will be the primary focus of the paper but the exact same parameters and reasoning applies to all solid deposits.

No matter how the calculation is performed, the loss of pipeline efficiency due to even a small solids build up is significant. Based upon a geometric model, if a 12 inch diameter pipeline has a smooth 5 percent deposit on the wall, the volumetric flow rate would decrease by over 10 percent at a fixed pressure. To restore the operating flow rate, the pressure of the pipeline would have to be increased by 30 percent. However, most deposits are not smooth and a much worse case ensues due to the introduction of turbulence by the deoposits.1 If this is the case, the same 5 percent deposit could reduce the throughput by 35 percent which would require a 140 percent increase in pressure to overcome. Another analysis by the Panhandle method shows that if the operating efficiency of a pipeline is increased from 90 to 95 percent in a 22 inch gas pipeline at the same operating pressure, the flow rate would increase by 22.5 mmcfd (2.83 x 10 4 m3/d). Assuming 10 cents per mcf (2.83 x 103 m3/d

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