Hydrocarbon Processing - February 2022 - 49

Plant Design,
Engineering,
Construction and
Commissioning
A. ALSUAYYID, Saudi Aramco, Dhahran,
Saudi Arabia; and N. JADAV, Saudi Aramco,
Reading, United Kingdom
Piping interface type selection
Most oil and gas process plant projects involve multiple
work packages executed by different lump sum turnkey
(LSTK) contractors executing work within their own package,
with a final piping interface connection at an agreed
boundary limit to accomplish the interface joint between two
parties and successfully close the piping interface.
An interface point (IP) is a physical location or boundary
where responsibility for the item passes from one contractor
to another contractor. Piping IPs are commonly located at or
near a geographical contract boundary, generally known as an
interface gate (IG). One of the contractors is assigned the role
of lead contractor, which has the responsibility for the delivery
of the IP for final closure while also determining the interface
type based on any limitations. The counter party to the
lead contractor is known as an interface contractor, which is
responsible to furnish necessary material and support details
up to the agreed IP.
For LSTK projects that do not have a predetermined set of
criteria for IP type selection, this article aims to establish the
best selection of above-ground piping interface type at the contractor
package boundary based on the following parameters:
* Advantages and disadvantages of different types,
with consideration to any effects on the integrity
of the interface point
* Impact on construction cost and schedule
* Seamless transfer of responsibility for a physical interface
connection from one party to another, and plant
reliability, availability and maintainability (RAM)
during its design life.
For LSTK projects, it is recommended to review relevant
project specifications and guidelines that show any technical
limitations for interface types. Two interface types-welded
interface and flanged interface-are further evaluated for
above-ground piping interfaces between two parties for any
process or utility service.
Other piping interface types, such as proprietary mechanical
piping joints for metallic pipes, and bell and spigot, lamination
or butt-fusion joints used in nonmetallic pipes, are outside
the scope of this article.
FIG. 1. Welded interface.
Hydrocarbon Processing | FEBRUARY 2022 49
INTERFACE TYPES
A brief overview of two interface types is provided here.
Welded interface. An interface connection between two contractors
at a predefined IP location is achieved via a welded joint
between two pipes, as depicted in FIG. 1.
An appointed lead contractor will be responsible for the final
closure weld and for testing in accordance with test procedures.
If remedial work is necessary, the appointed lead contractor
normally conducts this work as specified in the project contract.
A welded interface refers to a butt-welded joint between two
pipes following correct pipe end preparation by an individual
contractor within its own scope to make a proper final weld
joint. Contractors must exchange, agree on and finalize the relevant
details of the piping interface before executing the interface
work, such as:
* Pipe-pipe size, material, wall thickness, insulation,
end preparation, etc.
* Plant coordinates-Easting, Northing and Elevation
to specify exact location in 3D space within the IG.
* Stress and support-stress analysis results to confirm
allowable stress limits, support types and their locations
leading up to the IP.
* Fluid-fluid name or service and other properties such
as fluid phase, fluid temperature, pressure, flowrate,
flow regime, velocity, viscosity and all such relevant
operating, design and any upset conditions of the line in
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