The evolution of offshore vessels and facilities that support the oil and gas industry has seen a transformation into large, complex feats of engineering. They’ve gone from wooden piers stretching off the coast of California in the 1940s to 25,000-ton semi-submersibles operating at depths of 4,400 feet in the Gulf of Mexico today. Because of this, adding large equipment to these facilities today requires a trained engineer to work through many different calculations and produce detailed engineering drawings before installation.

The process of adding accommodation or office modules to offshore facilities and vessels requires detailed engineering drawings to ensure the equipment will fit and operate properly. Armoda works closely with our customers to ensure that our package fits the physical space, intended use case, and regulatory requirements to be added to the vessel or facility. In this article, we will break down a typical set of design and engineering drawings.

When adding additional accommodations, offices, galleys, etc., to an offshore location, the building manufacturer will either work with the end user directly, if they have an in-house engineering team or through a third-party engineering firm hired by the end user. The manufacturer will then work closely with the engineering group to ensure that the units meet their requirements and any regulatory requirements. To make sure conditions are met, engineering drawings are supplied by the manufacturer. The drawings allow the engineers to determine where to position the units on the facility’s deck or vessel. The manufacturer’s drawings will vary, depending on various aspects of the project, such as what type of units are installed, where they are installed, etc.

To give an example of an engineering drawing package, we highlight a custom three-module package. This package is designed to add two private sleeping quarters, each with a bathroom and desk space. It also includes a galley/diner space connected to a recreation area outfitted with a TV and couch. Also, a utility room with a washer, dryer, and sink was included to allow for easy laundering. When a package of drawings is produced, it will have multiple drawings; each covering a specific aspect of the package. For this particular package, there is a cover sheet and thirteen sections. 

Engineering Drawings for Offshore Modules Sections: 

Cover Sheet

The cover sheet provides an overview of the sections contained within the drawing package. It also includes general information about the package (including design notes, loads, and codes), wind design data, construction notes, and seismic design data. In addition, on every page of the package at the bottom right is an information block. These blocks provide essential details about what the drawing is for, for whom, part number, description, and information about the material and finish. Finally, there is also a section that tracks the revision history of the drawings to ensure that as changes are made, people can easily identify that they are working from the same drawings.

1. General Arrangement Plan

The general arrangement plan gives a detailed drawing of how the inside of the modules will be laid out once completed. Each piece of equipment is given a number with an equipment schedule on the page that identifies it. Doors and windows are identified by letters with a schedule that offers additional information, including size and what side the hinges are on. The third schedule on the page is the outfitting schedule, which provides information on the exterior walls, floor, ceiling/roof, and corridor walls. Lastly, the drawings provide measurements of the various lengths throughout the interior and exterior.

2. Egress Plan

The egress plan uses arrows to show the escape pathways from all the various rooms within the modules.

3. Typical Building Section

This drawing shows two cross sections, one of the module and the other of a corridor. These show detailed information on what each is constructed of and the interior measurements.

4. Directional (NSEW) Elevations

This section is divided into each cardinal direction, north, south, east and west, providing the height and width of the modules at that side. Also included in these dimensions are any exterior additions such as securement arrangements, exhausts, vents, or lights that extend from the module, enlarging its overall size.

5. Electrical Plan

The electrical drawings use a legend to identify the electrical equipment placed throughout the modules: light switches, outlets, equipment connections, light fixtures, panel boards, emergency lights, vents, exits lights, three-way switches, receptacles, and data connections. It also contains a lighting schedule that uses letters to identify the location of lights and provide additional details such as quantity, type, manufacturer, mounting, and voltage. 

6. Panel Schedule

This section provides the details of the electrical panel located in the package, and it illustrates the voltage mains and the layout of the switches.  

7. Mechanical Plan

The mechanical plan shows the location and details of the HVAC system within the package. Its legend identifies the symbols that show supply grills, exhaust fans, balance dampers, airflow direction, thermostats, and flex ducts. The mechanical schedule uses letter/number combinations to identify equipment locations and provide electrical, heating, and cooling information. 

8. Plumbing

The plumbing plan details the dimensions and locations of the different pipes within the modules.

9. Riser Diagram

The riser diagram separates plumbing systems for the various types that are within the module. The plumbing legend uses different styled lines to denote the types of plumbing, such as potable water (cold and hot) and drain water. The drawings identify exactly where the pipes are located and what is attached to them (like appliances, drains, gates, and other modules).

10. Module(s) Framing Elevation

Like the other elevation drawings, the module(s) framing elevation drawing is broken into the four cardinal directions providing the frame’s dimensions. It shows where items, such as doors, vents, and other openings in the wall, are located.

11. Fire and Gas Detection

If required, the fire and gas plan will detail the number of safety systems within the modules. These can connect to an internal panel, or an existing panel, already located on the platform. Depending on the requirements and the application, this may include sprinkler and fire suppression systems. 

12. Structural Details

The structural details provide detailed information regarding the structure, member sizing, walls, roof, skid base, doors and how the structure will be fabricated. It will provide the lifting details.

13. Typical Lift Diagram

The typical lift diagram shows the module’s center of gravity (CoG) and its precise location. It also provides the location, number, and description of the lift lugs, shackles, slings, and D-rings.

The manufacturer supplies engineering drawings to give their customer’s engineers all the necessary information to determine where and how to position the unit or units on the deck of the facility or vessel. Then, they work together closely to ensure the modules will fit in the desired location and perform their intended duties. This article should give you a better understanding of the drawing and the purposes of each part.

For more information on how modules get installed on location, check out our article on site surveys and how they protect against costly complications once the units make it to their location.