7/25/2019 Corrosion en Plantas de Gas Natutal

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0033-1732/02/3803- $27.00 2002 MAIK Nauka/Interperiodica0284

Protection of Metals, Vol. 38, No. 3, 2002, pp. 284288. Translated from Zashchita Metallov, Vol. 38, No. 3, 2002, pp. 323327.Original Russian Text Copyright 2002 by Medvedeva, Guryanov.

The equipment failures in the units of purifying nat-ural gas from acid components, operating in the Astra-khan Gas Works (AGW), are mainly associated withcorrosion damage. Therefore, in this work, we aimed atanalyzing the corrosion condition of these units andsuggesting basic steps to enhance the efficiency of theequipment in use and newly added units.

The purifying plants operated at the AGW aredesigned for separating hydrogen sulfide and carbondioxide constituting ca. 25 and 15% of the raw gas,respectively. The acid components are separated with aselective solvent, by means of a regeneration cycle pro-cess. According to the process, upon the primaryremoval of deposit water and condensed gas the rawnatural gas is sent to absorber. Inside the absorber, thegas moves in a counterflow with the absorbent whichselectively dissolves H

2

S and CO

2

. The temperature inthe absorber is 110

C, the pressure is 6.5 MPa. Thepurified gas is removed from the absorber, whereas theabsorbent enriched in hydrogen-sulfide and carbon-dioxide is sent for regeneration. The absorbent firstpasses two separators (a high-pressure and a low-pres-sure ones) to separate hydrocarbons, then, it is heated inheat-exchangers, and finally moves to a desorber whereit looses the acid gases (at a temperature of 130

C anda pressure of 0.14 MPa). The regenerated absorbent isfurther cooled in the heat-exchangers, released of

mechanical impurities, and becomes ready for reuse.Four similar plants operate in parallel at the AGW

since the end of 1986early 1987. A 33%-diethanola-mine (imported) solution was first used as absorbent.Starting from November 1994, all plants were sequen-tially converted to a combined absorbent, that is, a35%-solution of mixture of alcanolamines (30% ofdiethanolamine, DEA and 70% of monoethanolamine,MEA) produced in Russia. However, with time, theidea of combined absorbent was given away, due to

adverse corrosion situation. Nonetheless, because sim-ilar combined absorbents are advantageously used inother works [1], we aimed at analyzing the current stateof affairs, in particular, assessing the above idea ofreplacing the absorbent.

The corrosion state of the equipment is monitoredsince the plants have been put into operation. The cor-rosion state of the equipment differs significantly fromthat of pipelines.

Based on the monitoring documentation, we con-cluded:

(1) The metal in the plants suffers both general and

pitting corrosion;

(2) No significant corrosion effect was observed inthe majority of the plants until 1994, except for thehigh- and low-pressure separators where corrosion pits,up to 2.8 mm deep, were detected at the inlet socketsand the adjacent sections of the shell. The correspond-ing corrosion rate was approximately 0.5 mm per year.Based on the results of inspecting the separators in1994, we found significant deviations from theirdesign, admitted during the manufacturing and puttinginto operation. Most probably it is these deviations thathave caused the above corrosion of inlet sockets;

(3) Starting from 1994, the corrosion grew dramati-cally severer. Almost all of the equipment became dam-aged by corrosion, and the heaviest was the damage tothe units that contacted the saturated absorbent, i.e.,separators and the desorber. As to the type of corrosion,it remained general and pitting, however, its ratebecame much higher (and mostly exceeded 1 mm peryear). Thus, the aggravation of the corrosion situationunambiguously synchronized with the transition to thecombined absorbent. Therefore, it is reasonable to con-

SHARINGOF EXPERIENCE

On the Corrosion State of Plants for Purifying Natural Gasfrom Acid Components

M. L. Medvedeva* and V. V. Guryanov**

*Gubkin Oil and Gas University, Moscow, Russia

**OAO Astrakhan gazprom, Astrakhan, Russia

Received March 16, 2001

Abstract

Corrosion state of the equipment of gas purifying units operated at the Astrakhan Gas Works forseparating acid components, from the raw product is analyzed. Corrosivity of the main technological media ofthese plants is analyzed. Methods for enhancing the efficiency of the equipment are recommended, includingthe optimization of the absorbent composition, computation of technological pipelines, etc.