Wet H2S Guidelines

1. Purpose

This procedure describes when a process stream is to be designated by the Design Engineer as wet H2S service. This procedure applies to all technology centers across Inflection Point Engineering.

2. Guidelines

Inflection Point Engineering uses the NACE MR0103 definition to designate wet H2S service. When a process stream meets the requirements stated in this procedure to be designated as wet H2S service, the Design Engineer shall indicate such by placing a “Y” in the “WET H2S (Y/N)” box in the Stream Data Summary and Equipment box on the MSD. If the stream does not meet the definitions contained herein, the Design Engineer shall place an “N” in the appropriate boxes.

2.1 Wet H2S Service Definition

Inflection Point Engineering uses the definition contained in NACE MR0103 to determine if a process stream is in wet H2S service. NACE MR0103-2010 defines a process stream as wet H2S service when it contains an aqueous (liquid) water phase, AND one or more of the following:

(a) >50 ppmw total sulfide content in the aqueous phase; OR

(b) ≥1 ppmw total sulfide content in the aqueous phase and pH <4; OR

(c) ≥1 ppmw total sulfide content and ≥20 ppmw free cyanide in the aqueous phase, and pH >7.6; OR

(d) >0.3 kPa absolute (0.05 psia) partial pressure H2S in the gas phase associated with the aqueous phase of a processes.

Amine Piping and Equipment

All piping and equipment containing amine will be designed for wet H2S service. This applies for both lean and rich amine.

2.2 Process Conditions

When determining if a stream meets the definition of wet H2S service in 2.1, do not consider only steady-state operation, but also consider likely alternate scenarios. Examples of alternate scenarios include (but are not limited to) process upsets, loss of steam/heat tracing, startup/shutdown procedures, steam-out, etc.

2.3 Development of Standard Guidelines or Templates

Each is encouraged to develop, for each type of unit in its purview, detailed standard guidelines or templates to assist Design Engineers on when to designate wet H2S service. Some examples, taken from a guideline for hydrotreating units, are given below.

a. Recycle Gas

Killed carbon steel piping and equipment from the point of intermittent wash water injection up to and including the first recycle gas (or combined feed) exchanger in the discharge of the Recycle Gas Compressor. This includes, but is not limited to the following: Hot Separator Vapor Condenser (if KCS), Cold Separator, hydrocarbon and sour water piping from the Cold Separator to the Cold Flash Drum, Recycle Gas Scrubber, associated knockout drums, Recycle Gas Compressor, quench gas piping (up to the point where it changes to stainless piping material), recycle compressor spillback piping, and Recycle Gas Compressor discharge piping. This is to be applied regardless of whether a recycle gas scrubber is installed.

b. Cold Flash Drum

All piping and equipment around the Cold Flash Drum is to be designed for wet H2S service. This includes the flash gas piping (to and from the offgas scrubber, if installed), sour water piping, and hydrocarbon piping up to and including the first flash liquid heat exchanger.

c. Fractionation Equipment

Columns and overhead streams that contain H2S and water. This includes the receiver, sour water lines and hydrocarbon lines (reflux and net overhead liquid). The net overhead liquid would be specified for wet H2S service up to and including the first preheat exchanger of the subsequent column, if further fractionation is performed; otherwise, the piping to the battery limits will be specified for wet H2S service.