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Management of corrosion, scale formation, oxygen content and microbial populations, are essential in oil and gas production and processing systems. In addition, demulsifier chemical is used in the GOSPs to assist in water-oil emulsion breaking/separation. The injection of the inhibitor is a standard practice to control internal corrosion and scale build-up in carbon steel equipment and piping. This strategy has been shown to be very successful and cost effective.

13.1 Design Basis

Standard two-inch high pressure access fittings and injection quills are commonly used in GOSPs, oil & gas processing facility and gas plants for injecting typical oilfield treatment chemicals. High pressure access fittings are designed to permit safe, relatively easy insertion and retrieval of injection quills as well as other devices (such as coupons or monitoring equipment) while under full operating pressure.

This type of injection quill can be removed for cleaning while system is under pressure. The injection components, other than the access fitting body, shall be made out of 316L stainless steel or better and shall be suitable for sour service and meet the requirement of SAES-A-301, if injection is required into a sour service process.

Access fittings for injection must be installed in straight run pipe. The fitting must not be installed closer than a minimum of two pipe diameters downstream of a bend, valve or reducer and there must be a minimum run of 5D of straight

pipe downstream of the fitting before a bend, reducer, etc. When more than one access fitting is installed in one location, the fittings must be separated by a minimum three (3) feet. In order to operate the retriever, a minimum of twelve (12) inches clearance is required around the access fitting body and a minimum of eight (8) feet is required above or to the side of the pipe for top and side mounted fittings, respectively.

Check valves are required immediately upstream of the shut-off valve at the fitting. The shut-off valve should be 316L stainless steel and after installation onto the nipple must be seal welded in accordance to Saudi Aramco welding procedures. Positive shut-off valve required such as gate, needle or ball.

Short nipples and shutoff valves must be rated for sour service and they should be identifiable (grade and rating) as per SAES-L-105, Section 5. All valves installation and seal welding should be as per SAES-L-110, Section 8.

If a chemical injection fitting is not in service, the solid plug, injection nut and quill shall be extracted, the quill must be removed from the injection nut and a solid stainless steel pipe plug installed in its place. This prevents service fluid from migrating up the quill through the hollow injection nut and contacting and possible corroding the threaded nipple installed in the access fitting body tee.

Prior to re-installing the plugged injection assembly into the access fitting the upper and lower O rings shall be replaced.

13.2 Injection Locations

The following is a list of some of the chemical types and their typical injection locations in upstream facilities and Gas Plants:

♦ Corrosion Inhibitor

• GOSP production/test header

• Trunk lines/flow lines with high water cut

• GOSP Wasia wash water line

• GOSP LPPT/IPPT/HPPT gas compressor discharge lines

• GOSP dry gas line to NGL

• GOSP disposal water header

• GOSP wash water supply

• GOSP fire water supply

• Disposal water line in the 3-Phase Separators (Plant 429 of Abqaiq Plants)

• Gas out line from De-Ethanizer to Gas Plant (Plant R-57 of Abqaiq Plants)

• Suction line of the inter-stage/after coolers in NGL Plant (All NGL Plants in Abqaiq Plants)

• Off-gas from the De-Ethanizer reflux drum to Gas Plant (Plant 462 of Abqaiq Plants)

• Off-gas from the De-Ethanizer surge drum to condenser (Plant 462 of Abqaiq Plants)

• Off-gas from stripper feed drum to De-Ethanizer or Gas Plant (Plant 462 of Abqaiq Plants)

• NGL line (QA-10) to Ras Tanurah Refinery (Plant 462 of Abqaiq Plants)

• Total off-gas line to De-Ethanizer feed chiller (Plant 462 of Abqaiq Plants)

• Suction line of stripper overhead cooler (Plant 499 of Abqaiq Plants)

• Overhead gas line (Plant 334 of Abqaiq Plants)

• Discharge of condensate shipper pump (Gas Plants)

• Downstream of the gas wellhead christmas tree (Gas Plants)

• Ethane “C2”injection well

(only during the reproduction in some of the Gas Plants)

• Sour/Sweet wet gas flowlines

♦ Scale Inhibitor

• GOSP production/test header

• GOSP disposal water header

• IPPT/HPPT crude oil out stream in some GOSPs

• Disposal water line in the 3-Phase Separators (Plant 429 of Abqaiq Plants)

• Discharge of Condensate Shipper Pump (Gas Plants)

♦ Oxygen Scavenger

• Disposal water line in the 3-Phase Separators (Plant 429 of Abqaiq Plants)

♦ Biocide Injection

• Disposal water line in the 3-Phase Separators (Plant 429 of Abqaiq Plants)

♦ Demulsifier Injection

• Production Manifold

• GOSP test header

• Dehydrator/Desalter inlet

• Upstream of 3-Phase Separators (Plant 429 of Abqaiq Plants)

13.3 Requirements for Chemical Injection System in Upstream Facilities and Gas Plants

The typical design of the chemical injection point is shown in the library drawing DA-950035 “2-Inch high Pressure Access System Chemical Injection and Corrosion Monitoring”. The following table summarizes the chemical injection requirements in upstream facilities and Gas Plants.

Table 9 - Chemical Injection Requirements

Variable/Location Target or Limit Comments

Injection rate As communicated by the Area Corrosion Engineer

install in straight run pipe The fitting must not be installed closer than a minimum of two pipe diameters downstream of a bend, valve or reducer there must be a minimum run of 5D of straight pipe

downstream of the fitting before a bend, reducer, etc.

the fittings must be separated by a minimum three (3) feet

This is required when more than one access fitting is installed in one location

Access fitting design

A minimum of twelve (12) inches radial clearance is required around the access fitting body and a minimum of eight (8) feet is required above or to the side of the pipe for top and side mounted fittings, respectively.

This is required in order to operate the retriever

The style of the injection quill should have a scarf cut instead of a plain open end

Inject in center 1/3 of the stream

The recommended injection location is the center of the pipe to ensure even distribution away from pipe walls and for more homogeneous mix to take place in the pipe.

12 o’clock position Quill design

Injection quill length

Injection quills must be the correct length. Field verification of pipe diameter and quill length to be confirmed before installation by operations, process engineer, inspection and maintenance.

Variable/Location Target or Limit Comments

Quill orientation

For liquid-phase stream, the quill should be installed in the pipe so that the angled face of the quill faces the fluid downstream. While for mixed and vapor phase stream, the angled face of the quill should face the fluid upstream as shown in Figure 6 & 7.

To insure proper positioning of the quill cut in the pipe, the solid plug should be permanently marked to show orientation. One of the recommended field practices is to permanently mark the long side of the quill with a straight line using a file, small hacksaw cut or waterproof paint marker.

Quill metallurgy

The injection quill should be made out of 316L stainless material. Pipe and not tubing shall be used to fabricate the quill.

The quill material should be suitable for sour service and meet the requirement of SAES-A-301, if injection is required into a sour service process.