Plant Revamp - Sweet Gas To Sour
Authors: Gardner Robert E. 
Published: December 2007

A used sweet gas products plant was converted to a plant consisting of a vapor recovery compression system, sweetening system, and gas stabilization-dehydration system. The plant was placed in service in a hydrogen sulfide oil-gas field. In a short time the plant required total disassembly, testing, and rebuilding to continue operating safely and in accordance with local, state, federal, and insurance companies requirements.

Introduction

The used sweet gas products plant was purchased by an oil and gas production company and purchased by an oil and gas production company and installed in a new oil-gas field with small quantities of hydrogen sulfide present. With this in mind, the plant was installed at a minimum cost by using as much of the original equipment as possible. The plant had operated only a short time before mechanical and process failures began to occur. In early 1975 R.E. Gardner Engineering, Inc. was contracted to study, test, design, purchase material and rebuild the plant as required. A chemical engineering consulting firm was also hired to study the process and furnish Gardner Engineering any process changes to be incorporated into the design process changes to be incorporated into the design and rebuild.

The preliminary study in the plant indicated the materials were primarily for a sweet gas operation. Also, due to age, the original equipment had to be tested and checked.

The major areas of testing, design, and rework will be discussed in this report. Also, the local, state, federal, and insurance requirements pertaining to this plant will be included. The pertaining to this plant will be included. The rebuilding process covered the tank farm area with the battery tanks, gas transmission system, scrubbers, lubrication systems, pumps, electrical systems, compressors, piping, and all pieces of equipment that were exposed to or came in contact with the sour gas atmosphere.

VALVES

One of the major areas of concern in the plant was the valves, particularly the hand valves. plant was the valves, particularly the hand valves. Some had leaked and caused major problems prior to the engineers being requested to review the plant. The National Association of Corrosion plant. The National Association of Corrosion Engineers standard (NACE) MR-01-75 on valve construction for hydrogen sulfide service required a Rockwell hardness of 22 or less for a valve to be acceptable in hydrogen sulfide service and not experience hydrogen embrittlement and stress cracking.

A portable Telebrineller tester was used to test the hardness of the valves including the automatic control valves. The test points on the metal were first cleaned to polished metal condition. The tester consisted of an anvil in a soft rubber molded head resting on a known Brinnel hardness metal test bar. Below the bar is an impression ball secured in a narrow aperture in the base of the head, maintained in direct contact with the bar and placed firmly against the metal to be tested. When the anvil was struck with a hammer, irrespective of the force of the blow, the impact was applied equally to the test bar and through the ball to the metal being tested. Since the impact is equal, the diameters of impressions are exactly relative, respectively, to the hardness of both the test bar and metal under test. A field microscope with a scale etched on the lens was used to read the diameter of the impression on both pieces of metal and ratioed by equation 1, or the ratio can be plotted on a graph as in figure 1 to determine the hardness. There are different methods of determining hardness but the NACE requirements are expressed in Rockwell. The conversion from Brinnel hardness to Rockwell hardness is found in table 1.