Oil & Gas Projects: Walkdown, Mechanical Completion, Pre-commissioning and Provisional Turnover

Oil & Gas Projects


Projects in oil and gas industry are generally quite complex. They have many stages/phases and processes. Among the important processes are Walkdown, Mechanical Completion (MC), Pre-commissioning and Provisional Turnover (PTO). MC and PTO are very important milestones in any project executed at site. These milestones are defined as follows:

MC is the milestone where it is verified at site that constructed/installed facility/plant/unit is in accordance with approved drawings and specifications, with exceptions of ‘B’ and ‘C’ Punch Items. The verification is done by means of site walkdown.

PTO is a milestone where it is confirmed that all pre-commissioning activities are completed along with all ‘B’ Punch Items.

The question arises, what path do the projects travel to achieve MC? What are the prerequisites to MC?

Similarly, what is the path to PTO? What are the prerequisites for PTO?

Following part of this article would explain the complete process until PTO through MC of projects. There may be variation but those would not be quite considerable.

Systemization of the Project Scope

In a project which is executed at site, the scope is divided into systems and subsystems, which may run into hundreds and even cross thousand, depending on size and complexities. Then the question arises: what are systems and subsystems?

To answer the question, the scope of project can be divided in various ways, viz., by discipline, by geographical locations, by systems, etc.

A system is a well-defined element of the scope that can be completed independently/separately. A system may be further divided into subsystems. Subsystems are the systems broken/split into manageable scopes for the purpose of measuring progress during the turnover process.

Following are the few examples of the systems:

  • Steam System
  • Plant Air System
  • HVAC System
  • Fire Fighting System
  • Chemical Injection System
  • HV System
  • Lighting System
  • Machine Monitoring System
  • Crude Heater System
  • Recycle Gas System
  • Condensate System

Examples of systems split into subsystems are Steam System into Low Pressure Steam Subsystem, Intermediate Pressure Steam Subsystem and High Pressure Steam System; Fire Fighting System into Fire Water Subsystem and Fire Detection Subsystems.

A system or subsystem may comprise of more than one discipline like electrical, mechanical, instrument, etc. Systemization of scope is generally done at the detail-engineering phase of the project.

Figure – 1: An example of systemization

Figure – 1: An example of systemization

Mechanical Completion (MC)

In order to achieve MC, walkdown is required for the whole scope or the part where it is required to be achieved. A convenient way of conducting the walkdown is going by system/subsystem to system/subsystem. Then the question arise; what are the prerequisites to start Walkdown? What path those prerequisites follow?

Let me explain in a simple way. The scope of the project comprises of ‘A’ & ‘B’ ITRs or QVDs. ITR means Inspection Test Record while QVD is Quality Verifying Document. They both are same thing called differently. While we will discuss ‘A’ ITR/QVD now, ‘B’ will be discussed later in this article. In order to start Walkdown, the condition is that all the ‘A’ ITRs/QVDs for that part/portion/scope is to be closed. What are these ‘A’ ITRs/QVDs? To understand them, we have to go into process of inspection/quality control.

When the quality control procedure is established for a project; it is followed by multiple Inspection and Test Plans (ITPs). These ITPs stipulate the inspection points for different works carried out at site or at vendor shops. These points may be Witness (W) or Hold (H) points, which will be discussed in another article. Based on each inspection point, Request For Inspection (RFI) is generated and based on successful inspection, they are closed, and the project execution moves on. These RFI’s form ‘A’ ITRs/QVDs. An ‘A’ ITR/QVD may comprise of one or more than one RFI. Similarly, one RFI may contain one or more ‘A’ ITRs/QVDs. When the RFI is closed, corresponding ITR(s)/QVD(s) also gets closed. Reiterating, when all ‘A’ ITRs/QVDs in the portion/part/scope is closed, it is ready for walkdown. Scope of the project generally comprises ‘A’ ITRs/QVDs which runs in multiple of ten thousand.

Generally, a multidisciplinary team carries out walkdown. During the walkdown, Punch Items are generated, which are classified as ‘A’, ‘B’ & ‘C’. These punch items are not to be confused with ‘A’ & ‘B’ ITRs/QVDs, as they are different. Punch items are deficient with respect to the approved drawings and/or specifications.

Once the walkdown is completed, all punch items are consolidated under categories ‘A’, ‘B’ and ‘C’. Thereafter, the process of punch closure starts. In order to close the punch, the deficiency is to be addressed followed by the acceptance and sign-off by the punch originator.

Figure – 2: QCP to ‘A’ ITR/QVD Closure

Figure – 2: QCP to ‘A’ ITR/QVD Closure

Upon closure of all associated ‘A’ Punch items, MC certificate is issued. There are certain documentation parts associated with these milestones and it varies from project to project, though majority of them are common.

Figure – 3: Walkdown to MC Certification

Figure – 3: Walkdown to MC Certification

Pre-commissioning to PTO

Upon issuance of MC Certificate, Pre-commissioning activities start. What is Precommissioning? Pre-commissioning activities are those which are required to bring a portion/part/scope into functional condition prior to Commissioning through PTO. It is worth to define Commissioning, which is are those activities required to bring the potion/part/scope into operational service in accordance with the specified design parameters contained in the technical specifications.

Returning to Pre-commissioning, few common examples are provided hereunder:

  • Pipe cleaning activities like water flushing, air blowing and steam blowing
  • Mechanical Run Test of Compressors and Pumps
  • Heater Refractory dryout
  • Leak test for flange integrity
  • Stroke Tests for Valves
  • Instrument Functional Test
  • Catalyst Loading of Reactors
  • Vacuum Leak Test of Reactor Section
  • Control Valve tuning
  • Interlocks check
  • Chemical cleaning
  • Chemical filling
  • Circuit breaker/isolator test
  • Vessel final box-up
  • Lifting equipment test
  • Damper functional test

Pre-commissioning activities have the corresponding ‘B’ ITRs/QVDs. A single pre-commissioning activity may comprise one or more ‘B’ ITR/QVD associate with it. A scope may comprise of many ‘B’ ITRs/QVDs which may run in multiple of thousands.

Once all ‘B’ ITRs/QVDs and ‘B’ Punch Items are closed, a portion/part/scope can be provisionally turned over, i.e. PTO is achieved.

It is to be noted that there are certain deliverables which also form part of prerequisites for achievement of PTO.

There may or may not be a Pre-startup Safety Review before PTO. However, it is quite essential before Commissioning.

Figure – 4: MC to PTO

Figure – 4: MC to PTO

Before closing, let me describe the Punch Items as follows:

‘A’ Punch item are those which has to be closed in order to start pre-commissioning activities.

‘B’ Punch items are those which has to be closed in order to start commissioning activities.

While ‘C’ punch items are minor in nature and can be closed before acceptance and they may include stenciling etc.

Figure – 5: Punch Closure Process

Figure – 5: Punch Closure Process

It is worth mentioning that the process of ITRs/QVDs, Walkdowns, Punchlisting require a proper tool to track and there are many completion suites available in the market.


Important Note

This article is intended to provide insight into Walkdown, MC, Pre-commissioning and PTO along-with Punch Items closure and processes in project, especially under oil & gas sector. Though it may be highly useful to a newcomer into this field, nevertheless, it would be useful for anyone in the field of Oil & Gas Projects.

Queries, comments and feedback are welcomed. You can reach out to the author on his email: [email protected].