This article is part of a series about the typical stages and phases of complex engineering projects. Each article takes one stage and describes how Assai supports the requirements and common challenges of that stage – ultimately contributing to the efficient, timely, (cost-)effective and safe delivery of projects.

The Detailed Design phase is the 5th in complex engineering projects.

Detailed Design in a nutshell

The Detailed Design stage follows after the FEED stage (Front-End Engineering Design). The basic design (with typically 12 to 20% of engineering completed) will be refined to 100% – usually by a contractor (e.g. EPC, EPCM or PMC; see below for more) – to enable procurement and construction. This is an iterative process, as different design activities can influence each other; for example, equipment design by vendors or routing of pipes may cause changes to the plant layout design. Cost estimate accuracy in this stage has improved to around +/- 10%. The duration of this stage varies depending on the nature, location, size and complexity of the project.

In Detailed Design, larger equipment and long-lead items are already procured from vendors and suppliers, to allow integrating equipment dimensions and specifications into the design. Supplied equipment can come with all many kinds of vendor documentation, such as layouts, datasheets and manuals. In-time delivery of all vendor documentation by a (large) variety of equipment suppliers can be a major challenge and risk for engineering projects. It helps to have a clear, accessible, up-to-date Vendor Document Requirements list (VDR, VDRL or SDRL) with links to the related equipment and vendors/suppliers, and clear due dates to enable tracking & expediting of this documentation category.

The number of deliverables, stakeholders and activities is at its peak in the Detailed Design stage. Staying on top of things now demands a continuous, dedicated Document Control effort, and a suitable eDMS that meets the project requirements. This is crucial for achieving a timely completion and approval of all project deliverables, and prevent costly project delays or other (unplanned) deviations.

Key deliverables and outputs

A selection of typical deliverables of the Detailed Design stage:

  • Scope of Work
  • Project Schedule
  • Constructability Review
  • HAZOP report (hazard and operability study)
  • Process Flow Diagrams (PFD)
  • Pressure Safety Valve (PSV) study
  • 2D models
  • 3D models
  • Detailed designs that can be used for construction and installation
  • Detailed piping drawings such as isometrics
  • Pipe support details
  • Approved vendor drawings and P&ID’s
  • Vendor Data Sheets
  • (Equipment) Process data sheets
  • Equipment List
  • Valve List
  • Line List
  • Tie-in List
  • Instrument Index
  • Single-Line Diagrams (SLD)
  • Material Take Off (MTO; list of materials required for construction)
  • Start up, operating & commissioning procedures
  • Emergency shutdown (ESD) philosophy
  • Demolition drawings
Detailed Design results in highly detailed CAD drawings

EPC contract models

The previous article in this series (on the FEED stage) described that clients generally contract out at least the EPC work to EPC contractors. There are many more contact types than the well-known “EPC contract”, some of which extend the responsibilities or ownership of the contractor. The contract type chosen mainly depends on the amount of control desired by the client/owner, the amount of risk accepted/preferred, how clear and precise the Scope of Work is, and the expertise, experience, resources, time and budget available at the client.

Common EPC contract variants:

  • EPC: full outsourcing of all EPC work to the contractor; a single contract and single point of contact for the client; requires an extremely well-defined project brief, plans and specifications; takes longer to establish; fixed CAPEX (but extra cost for deviations from the Scope of Work); usually significant higher project cost than the EPCM model; less involvement and resources needed from the client; less suited for highly specialist or innovative projects with too many variables.
  • EPCM (with M for Management): the client is involved in management in all stages; more flexibility (to change the scope); all contracts with third parties (e.g. construction contractors, suppliers and vendors) are directly with the client; engineering (design) and procurement are handled by the EPC contractor; more control for the client; easier to establish; usually lower costs (less risk mitigation needed); more involvement and resources needed from the client; suited for less well-defined projects or with more variables.
  • PMC (Project Management Consultant): similar to EPCM but the PMC contractor only takes care of engineering management and also overall project management; the client has direct contracts with engineering contractors (besides construction contractors as in EPCM); this splits the responsibility for engineering and project management (PM) between two contractors; suited when the combination of required engineering and PM capabilities is difficult to find in the market.
  • EPCI (with I for Installation): similar to EPC and often related to offshore construction; the contractor takes care of the full installation on-site.
  • EPCC, EPCIC, or EPIC (with I for Installation and C for Commissioning): similar to EPC/EPCI but ‘turnkey’ (LSTK – Lump sum turnkey) for the client: the contractor is also responsible for commissioning.

In some sectors and industries the EPC model is no longer the dominant one, and new (public-private) models with more even risk distributions have become more regular. For instance the BOT (Build Operate Transfer) model which combines public and private resources, whereby the private party receives operating rights (a concession) for an extended period of time. Other variants seen include BOOT (Build Own Operate Transfer), DBOT (Design Build Operate Transfer), or ones where the asset does not get transferred eventually (e.g. BOO without the ‘T’ or DBFO: Design Build Finance Operate).

Detailed Design involves close collaboration between a wide variety of disciplines and companies.

Project control with Document Control

Document control – simply stated: being and staying in control of all project documentation – can make or break any engineering project, especially in the hectic Detailed Design stage. When actions are not clear or get missed, planning dates or due dates are exceeded, or information gets lost, that can easily cause a (costly) domino effect for a project, with one delay leading to another. Project milestones cannot be reached if project documentation is not progressing as planned, or if not correctly, timely and fully approved.

If on the other hand, document control is well-organized with an appropriate eDMS system – one that facilitates all stakeholders, allows finding the latest information fast, keeps everyone aware of actions and due dates, supports efficient and effective collaboration, covers risks and future liability, and gives comprehensive insight into progress and potential bottlenecks at all times – then this suddenly becomes an invaluable enabler for project control (and a cost-saver for the project too).

Many expensive software companies have promised to support our project requirements, and some tried long and hard, but failed to deliver. Assai have delivered everything they promised in sales presentations and are of great added value.

IM/DC department of a major project with ca. 600K documents

How Assai supports Detailed Design

Assai provides out-of-the-box support for all project stages (and operations), with over 30 years of experience. The following Assai features are key in supporting clients and contractors during Detailed Design and making sure everything is ‘AFC’ (Approved for Construction) in time:

  • Easy, unambiguous access to relevant information for all project roles
  • Highly efficient information exchange with external parties: Assai Portal
  • Never any doubt about the latest revision or latest information
  • Store any file type; integrated file viewer (with redline markup capability)
  • Out-of-the-box, flexible workflows for review & approval
  • Distribution matrix to simplify and automate document distribution
  • Full action tracking, with (proactive) automatic and manual reminders
  • High levels of automation for engineers and Document Controllers
  • Dedicated planning module; organize deliverables in a WBS
  • View progress and forecasts at any level: document, work package, project
  • Vendor document control features (easy VDRL tracking & expediting)
  • Store Purchase Orders (PO) and associate with documents
  • Assets module: associate documents with tags, equipment etc. for Operations
  • Technical query module to handle change requests and more (RFC, RFI)
  • Correspondence module to centrally store official letters
  • Easy preparation of construction work packages
  • Easy management of roles, responsibilities and user/group access
  • Detailed audit trails; coverage against liability
  • Many standard reports & dashboards, Power BI reporting
  • Extensive REST API integration options
  • Special offering: Assai for EPC’s

Plus as described in previous articles:

  • Assai offers a proven, specialised, user-friendly and secure eDMS for all project deliverables, no matter the project size or complexity. Everything is traceable and can be reported on.
  • Assai Cloud (or on-premises) is a flexible, turnkey solution with out-of-the-box support for engineering projects from start to end, plus operations, maintenance & modifications, and Digital Twin environments.
Assai supports Detailed Design by providing a topnotch eDMS.


We hope you found this article about the Detailed Design stage interesting and useful. Please let us know if you have any questions or feedback, or if you would like to explore with us how Assai could support your project(s).

A short summary of what was discussed in this article:

  • Based on the “FEED package” from the FEED stage, Detailed Design fills in all design and vendor details, which are required for proceeding with procurement, fabrication, construction and installation.
  • Clients or client-operators usually contract out the EPC stages of projects to a contractor, using one of the many possible contract models, such as EPC, EPCM, PMC or EPCI (as explained above).
  • The number of deliverables, stakeholders and activities is at its peak in the Detailed Design stage. Staying on top of things here demands a continuous, dedicated (Document Control) effort.
  • To prevent costly project delays, it is essential to manage the timely completion and approval of huge numbers of project deliverables from different sources (e.g. using an MDR and WBS/document planning).
  • Even more so than in the FEED stage, a specialized eDMS application and Document Control function are critical assets for completion of the Detailed Design stage – efficiently, safely, on time and within budget.
  • Many industry leaders worldwide trust Assai as their eDMS solution of choice, which is based on 30+ years of industry experience and best practices. Assai promises (and delivers) true out-of-the-box support for all project stages including Detailed Design and beyond; even for operations, maintenance & modifications, and Digital Twins.

Download the 50+ page PDF!

If you would like to read all articles in a 50+ page PDF which you can print or distribute in your organization, you can download them via the form below:

Previous stage: FEED

Next stage: Procurement & Fabrication

All articles in this series:

Feasibility Study
Conceptual Design
Detailed Design (current article)
Procurement & Fabrication
Construction & Installation

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