Decommissioning and abandonment of mains and services 63mm and above
This element covers the systematic decommissioning and abandonment of gas mains and services of diameter 63mm and above, ensuring safe disconnection from the live network. It involves conducting specified pressure and leak testing, interpreting technical drawings and method statements, selecting appropriate tools and isolation components, and physically decommissioning the asset while maintaining comprehensive records. The skills are critical for network alteration, replacement, and permanent removal of gas infrastructure, with a strong emphasis on compliance with health and safety legislation and industry standards such as IGEM/TD/13.
Assessment criteria
Quick Revision Summary (Key Takeaway)
The City & Guilds Level 2 Diploma in Network Construction Operations (Gas) – Main layer covers the skills and knowledge required to install, maintain, and repair gas distribution networks, focusing on main laying operations. It includes health and safety, excavation, pipe handling, jointing, and reinstatement, preparing learners for a career in the gas utility industry.
Topic Overview
The City & Guilds Level 2 Diploma in Network Construction Operations (Gas) – Main layer is a vocational qualification designed for individuals working in the gas distribution industry. It focuses on the construction and maintenance of gas mains, which are the large pipes that transport gas from the national transmission system to local distribution networks. This role is critical for ensuring a safe and reliable gas supply to homes and businesses.
The qualification covers a range of essential skills, including interpreting drawings and specifications, preparing and excavating trenches, laying and jointing pipes, and carrying out reinstatement of the ground. Health and safety is a major component, as working on gas mains involves significant risks such as excavation collapses, gas leaks, and traffic management. Learners also develop knowledge of different pipe materials, jointing techniques, and testing procedures.
This diploma is part of the wider Construction & Building Services sector, and it provides a pathway to further qualifications such as the Level 3 Diploma in Gas Network Operations or specialised roles in gas network maintenance. It is also recognised by employers in the utility industry, making it a valuable credential for career progression.
Key Concepts
Core ideas you must understand for this topic
- →Health and safety regulations: including the Health and Safety at Work Act, risk assessments, and safe excavation practices.
- →Pipe materials: understanding the properties and uses of polyethylene (PE), ductile iron, and steel pipes.
- →Jointing methods: butt fusion, electrofusion, and mechanical joints, and when to use each.
- →Excavation and reinstatement: trench preparation, support, backfilling, and surface restoration.
- →Testing and commissioning: soundness testing, purging, and pressure testing to ensure safety.
Learning Objectives
What you need to know and understand
- Be able to conduct specified testing of gas networks associated with decommissioning, Be able to interpret technical information for decommissioning, Be able to select components and resources for decommissioning, Be able to decommission the system, Be able to use and communicate data and information, Be able to resolve problems that arise from technical information and decommissioning work, Know health and safety guidance and legislation in utilities network construction operations, Understand how to decommission gas engineering products or assets
- Be able to conduct specified testing of gas networks associated with decommissioning, Be able to interpret technical information for decommissioning, Be able to select components and resources for decommissioning, Be able to decommission the system, Be able to use and communicate data and information, Be able to resolve problems that arise from technical information and decommissioning work, Know health and safety guidance and legislation in utilities network construction operations, Understand how to decommission gas engineering products or assets
Assessment Criteria
Key criteria assessors look for in your portfolio
- Award credit for demonstrating correct interpretation of technical plans and method statements, accurately identifying isolation points and abandonment requirements.
- Award credit for selecting the correct decommissioning components (e.g., squeeze-off tools, purge equipment, bagging systems) matched to pipe material, diameter, and pressure tier.
- Award credit for performing specified testing (e.g., pressure decay tests, tightness testing) in strict adherence to IGEM/UP/1 or IGEM/TD/13, and correctly recording results.
- Award credit for physical decommissioning sequence: isolating the section, venting or purging residual gas, cutting/capping, and permanently abandoning the asset without risk to live network.
- Award credit for thorough completion of decommissioning paperwork, including purge certificates, abandonment records, and as-laid-updated drawings, with clear communication to control and site teams.
- Award credit for correctly conducting pressure tests and interpreting results against criteria in relevant standards (e.g., IGEM/TD/13).
- Award credit for accurate interpretation of network diagrams and technical specifications to identify isolation points and decommissioning sequence.
- Award credit for selecting correct fittings and materials for capping and sealing, considering factors like pipe material and operating pressure.
- Award credit for methodical execution of decommissioning procedures, including purging, isolation, and verification of zero gas flow.
- Award credit for effective communication of decommissioning data, such as completing job records and updating asset logs.
Assessment Guidance
Guidance for achieving higher grades
- 💡Always structure your answers around the standard sequence: plan (interpret info), isolate, test, purge, decommission, reinstate, document. This demonstrates systematic understanding.
- 💡When describing practical tasks, explicitly name the relevant British Standard or IGEM recommendation (e.g., IGEM/TD/13, IGEM/UP/1) to show compliance knowledge.
- 💡In practical assessments, narrate your actions and decision-making, especially safety-critical steps like checking for gas presence with a calibrated CGI before any hot work.
- 💡For problem-solving questions, use the 'STOP' principle: Stop, Think, Observe, Plan—explain how you would address, for example, unexpected valve leakage during decommissioning by re-isolating and re-testing.
- 💡Familiarise yourself with key industry standards like IGEM/TD/13 for decommissioning and ensure your evidence references these where applicable.
- 💡When documenting decommissioning work, clearly show step-by-step processes with photographic evidence and signed-off checklists to meet assessment criteria.
- 💡Practice problem-solving scenarios, such as dealing with unexpected pipe conditions or valve failures, to demonstrate competency in resolving technical problems.
- 💡Always use the correct terminology, such as 'competent person', 'risk assessment', and 'permit to work'. This shows professional knowledge.
- 💡When answering questions about procedures, list steps in chronological order and include safety checks at each stage.
- 💡For calculations, show all your working and include units in every step to avoid losing marks for missing units.
Common Mistakes
Common errors to avoid in your coursework
- Misinterpreting technical diagrams, leading to incorrect identification of the pipe segment to be decommissioned or overlooking a connected service that remains live.
- Failing to check the material and pressure rating of the pipe, resulting in selection of inappropriate isolation equipment (e.g., using a squeeze-off tool rated for polyethylene on a steel main).
- Neglecting to purge the isolated section with inert gas before cutting or capping, creating a risk of explosive atmosphere.
- Inadequate testing—performing a pressure test without first isolating all potential sources of leakage or not accounting for temperature effects, leading to false pass results.
- Poor record-keeping: not updating asset records with precise abandonment details, causing future site safety hazards and non-compliance with network documentation standards.
- Confusing decommissioning procedures for different pipe materials (e.g., PE vs. steel), leading to inappropriate capping methods.
- Inadequate testing after isolation, assuming zero pressure without proper verification, risking gas leaks.
- Overlooking site-specific safety requirements such as permits to work or maintaining safe distances during excavation.
- Misconception: All gas pipes are made of steel. Correction: Modern gas mains are predominantly made of polyethylene (PE) due to its corrosion resistance and flexibility.
- Misconception: A trench does not need support if it is shallow. Correction: Even shallow trenches can collapse, and regulations require support if the depth exceeds 1.2 metres, but a risk assessment should always be done.
- Misconception: Soundness testing is only done after the main is backfilled. Correction: Testing is often done before backfilling to allow easy access for leak repairs.
Revision Plan
How to revise this topic in 1–2 weeks
- 1Week 1: Focus on health and safety regulations and risk assessment. Read the relevant sections of the HSE guidance and practice writing risk assessments.
- 2Week 2: Study pipe materials and jointing methods. Create flashcards for each material and its jointing technique. Watch videos of butt fusion and electrofusion.
- 3Week 3: Practice excavation and reinstatement procedures. Draw diagrams of trench support systems and label them.
- 4Week 4: Revise testing and commissioning. Work through past exam questions on soundness testing and pressure testing.
- 5Week 5: Take a full practice exam under timed conditions. Review your answers and focus on weak areas.
Exam Question Types
How this topic typically appears in the exam
- 📋Multiple-choice questions: Test knowledge of facts, such as pipe materials and safety regulations. Read each option carefully and eliminate obvious wrong answers.
- 📋Short-answer questions: Require brief explanations, e.g., 'State two purposes of a risk assessment.' Be concise but include key points.
- 📋Scenario-based questions: Present a real-life situation, e.g., 'A gas main has been damaged. Describe the steps you would take.' Use a structured approach: assess, isolate, repair, test.
- 📋Calculation questions: Involve volume, pressure, or depth calculations. Show all working and check units.
Command Word Expectations (CITY & GUILDS LIMITED)
What examiners look for when using specific command words in this specification
Provide a brief, factual answer without explanation. For example, 'State two types of pipe material used for gas mains.' Expect one mark per correct point.
Give a detailed account of a process or procedure. Include steps in order and key features. For example, 'Describe the procedure for jointing PE pipes using butt fusion.'
Give reasons or causes. For example, 'Explain why it is important to support trench sides.' Expect to link cause and effect, and use technical terms.
How Students Lose Marks (Examiner Pitfalls)
Common mark loss traps and how to write 100% full-mark answers
Step-by-Step Worked Solutions
Detailed solution breakdown for typical exam problems
Question: A gas main is to be laid at a depth of 900 mm in a public highway. The trench is 600 mm wide. Calculate the volume of spoil to be removed per metre length of trench, assuming the sides are vertical. Give your answer in cubic metres.
- 1.Step 1: Identify the given dimensions: depth = 900 mm = 0.9 m, width = 600 mm = 0.6 m, length = 1 m.
- 2.Step 2: Use the formula for volume of a rectangular prism: Volume = length × width × depth.
- 3.Step 3: Substitute the values: Volume = 1 m × 0.6 m × 0.9 m = 0.54 m³.
- 4.Step 4: State the final answer with units.
Question: Explain the procedure for carrying out a soundness test on a newly laid PE gas main using air, before it is put into service. (6 marks)
- 1.Step 1: Ensure the main is isolated and all connections are made.
- 2.Step 2: Introduce air into the main using a compressor, gradually increasing pressure to the test pressure (typically 1.5 times the working pressure, but not less than 100 mbar).
- 3.Step 3: Allow the pressure to stabilise for a period (e.g., 15 minutes) to equalise temperature.
- 4.Step 4: Record the pressure and hold it for a specified duration (e.g., 30 minutes).
- 5.Step 5: Monitor the pressure gauge for any drop. A drop indicates a leak.
- 6.Step 6: If a leak is found, locate it using leak detection fluid or electronic detectors, repair, and retest.
Active Recall Memory Test
Test your memory before revealing the key facts
Frequently Asked Questions
Common questions students ask about this topic
Pass / Merit / Distinction Evidence Checklist
How your portfolio evidence is graded for CITY & GUILDS LIMITED Decommissioning and abandonment of mains and services 63mm and above
Every vocational unit is marked against named criteria rather than an exam percentage. Your tutor's brief lists the exact codes for this unit — here is what each band is asking you to do.
Demonstrate baseline knowledge, accurate terminology, and core practical application.
Provide detailed analysis, structured explanations, and clear workplace reasoning.
Deliver thorough evaluation, original problem solving, and fully justified recommendations.
Before You Start
Prior knowledge that will help with this topic
- •Basic health and safety awareness, such as the CSCS card or equivalent.
- •Understanding of basic mathematics, including units and volume calculations.
- •Familiarity with hand tools and construction site practices.
Coursework AI Review
Paste your assignment brief and check your draft against its P/M/D criteria
Key Terminology
Essential terms to know
- Be able to conduct specified testing of gas networks associated with decommissioning, Be able to interpret technical information for decommissioning, Be able to select components and resources for decommissioning, Be able to decommission the system, Be able to use and communicate data and information, Be able to resolve problems that arise from technical information and decommissioning work, Know health and safety guidance and legislation in utilities network construction operations, Understand how to decommission gas engineering products or assets
- Be able to conduct specified testing of gas networks associated with decommissioning, Be able to interpret technical information for decommissioning, Be able to select components and resources for decommissioning, Be able to decommission the system, Be able to use and communicate data and information, Be able to resolve problems that arise from technical information and decommissioning work, Know health and safety guidance and legislation in utilities network construction operations, Understand how to decommission gas engineering products or assets
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