Hydrogen sulfide is considered corrosive, toxic, and lethal. As such, Ariel has specific recommendations as to the materials and compressor configuration options when compressing gas that contains H

2

S. Hydrogen Sulfide (H

2

S) can embrittle high strength, high hardness carbon steels, and most martensitic stainless steels (for a full and specific list of material compatibility with H

2

S refer to NACE MR-0175, ISO-15156).

Ariel's equipment configuration recommendations for sour gas service are based upon field experience and the NACE guidelines for the protection of the equipment.

It is the End Users responsibility to be aware of the level of H

2

S present, and to take all necessary precautions for the protection of personnel from harmful leakages of gas to the atmosphere.

Several considerations should be made when selecting compressors in sour gas service. As the gas is both corrosive and toxic, special safety requirements are necessary for the maintenance of the equipment. It may be suitable to provide a more conservative selection to lengthen the time between maintenance. This would include operating at slower piston speeds and allowing for lower discharge temperatures.

The toxic and lethal nature of the gas dictates the use of an appropriate purge and vent system to ensure the gas leakage at the packing case and distance pieces is not vented to the atmosphere. Please refer to the Packager Standards Section 8 Packing and Distance Piece Vent Systems for this topic..

With higher percentages of H

2

S in the gas stream, a review of the phase envelope and dew point of the gas constituents (not including water vapor) is recommended. At higher levels of H

2

S and higher pressures, the interstage cooling can easily reach the dew point for the H

2

S in the gas stream. Most often, condensation of the H

2

S is to be avoided.

Sour Gas service, Level 1, can be applied with non-lubricated cylinder construction. NACE SS Valves will be required along with the requirements and recommendations of Sour Level 1 trim below.

A two compartment distance piece, or a long single distance piece with wiper seal purge are required for sour gas service. These configurations offer the ability to create a purge and vent system which segregates the crankcase and operator atmosphere from the packing leakage.

Long two compartment distance piece, "L2C", is recommended above 2% H

2

S content as this provides better containment of the gas leakage. S2C distance piece and long single compartment distance piece with purged wiper seal can be used above 2% H

2

S content, but do not offer the same level of protection and flexibility for the vent / purge system design.

Two compartment distance pieces are available for all units except for the JGM:N:P:Q and KBE frames.

The long single compartment distance piece with wiper purge is available on the KBE:K:T, KBU:Z and KBB:V frames.

Refer to Packager Standards Section 8 Packing and Distance Piece Vent Systems for notes on a purge system for sour gas.

Ariel standard piston rod material is 4100 series carbon steel heat treated for strength. These are not suitable for sour gas service as defined by NACE MR-0175. For sour gas service with 100 ppm and greater H

2

S content stainless steel piston rods are required. Ariel stainless steel piston rod material is 17-4PH in the double H1150 condition, UNS S17400, (per NACE MR-0175), Rc 33 maximum, chromium-nitrided in the packing travel area for a surface hardness of 2500 Vickers. The chromium nitride process has a length limitation due to manufacturing constraints. Longer stainless steel piston rods will be tungsten carbide coated.

Ariel requires the use of "Purge packing" for sour gas services with 100 ppm and greater H

2

S content. The purpose of purge gas is to block and contain hazardous, toxic, flammable or corrosive gases, and to prevent such from entering the compressor frame where damage to the running gear, or personnel safety hazards can occur. The purge gas must be sweet natural gas or an inert gas, such as nitrogen. Purge packing refers to a packing case modified to accept an external purge pressure 15 to 20 psi above the primary packing vent/drain pressure with no more than 5 psi external system back pressure. Refer to Ariel's recommendations in Packager Standards Section 8 Packing and Distance Piece Vent Systems for a purge system for sour gas. See also "Packing Leakage".

When the purged packing option is selected on a long two compartment distance piece, the intermediate and wiper seal sets will be configured for purge along with the pressure packing case. When the purge packing option is selected on a long single compartment for the KBE:K:T, KBU:Z or KBB:V frames, the wiper seal will be configured for purge along with the pressure packing case.

Ariel recommends the use of cylinder flushing lube for first stage cylinders for sour gas services with 2% and greater H

2

S content. An atomizer for flushing lube injection can be constructed of tubing inserted into the gas stream at the suction pulsation cylinder nozzle with the end opened with a diagonal cut. The Packager would provide the lube lines from the end of the guide to the suction pulsation vessels cylinder nozzle. Flushing lube lines will be tubed to the end of the crosshead guide from the distribution block.  Flushing oil is used to ensure corrosion protection for the suction valves, both the valve bodies and springs. Flushing oil is available as an option on all units.  If the first stage flushing recommendation for Sour Level 2 is not taken, provisions for flushing on the pulsation vessel nozzle are recommended.

Some cylinders have two nozzles at the suction (dual nozzle and peanut flange).  Flushing lube for these two nozzle cylinders is configured for one flushing lube point per cylinder.  This is sufficient, considering the flushing lube connection is in the suction pulsation vessel nozzle.  If a client wants to apply flushing to both pulsation vessel nozzles, the packager can install a pipe tee to split the single line provided.

Ariel standard valve body material is 400 series stainless steel and 1040 carbon steel. These are not suitable for sour gas applications per NACE-MR0175. Ariel recommends the use of NACE compliant stainless steel valves for sour gas services with 2% and greater H

2

S content.Stainless steel valves generally consist of:

It could be prudent to start up a unit with standard valves and replace those with the stainless steel valves after any start up problems have been solved and piping debris has passed through the unit.

NACE Stainless Steel valves are required for Sour Level 1 service in non-lubricated cylinder construction.