Inerting and Purging Operations

1 Introduction to the course

1.1 Purpose of the Training Module
1.2 Summary of the classroom training session
1.3 Summary of the practical session both in the classroom and in the workplace

2 Types of purging and definitions

Types of purging: Direct purging: Displacement with fuel gas or air; vacuum techniques; application where high velocity purging is possible; implications of stratification - unsuitability for vessels and suitability for pipelines

Indirect Purging: Types of inert medium; Displacement purging; slug purging; pressure purging; dilution purging; Branch systems; simultaneous or sequential purging; loops.

Sources and quantity of inert gases: Carbon dioxide and nitrogen; use of single or multiple manifolds and high capacity regulators; need for adequate flow; choices of inert gas and freezing effects. Quantity expressed as multiples of space to be purged; quantities for slug displacement and dilution purging.

Definitions: Direct and indirect purging; stratification; dilution purging; slug purging; pressure purging; purge end point; purge pressure; purge velocity; purge volume; double block and bleed.

3 Sources and quantity of purge gas

Cylinders, 'skids', calculation of quantity of purge gas required

4 Precautions when purging

4.1 Static Hazards; bonding; purge gas velocity; stratification; colour coding of cylinders to ensure correct gas; asphyxiation by purge gases
4.2 Site notices: warning, prohibition, no smoking/naked light, and asphyxia hazard
4.3 Labelling of purged and un-purged plant
4.4 Equipment requirements: fire extinguishers, BA and personal O2 detectors

5 Purging proceedures, timing and purge end points

5.1 Use of triangular flammability diagrams as applied to natural gas/nitrogen/air purges; other purge gas scenarios; purge end points; effect of gas composition on triangle of flammability.
5.2 Achieving specified purge end point; use of end points as minimum standards
5.3 Flammability of gases in air; safety margins
5.4 Hazards of desorption from solid residues and vapours from liquid residues
5.5 Need for rechecking
5.6 Value of purge end points in purging pipelines and large volume vessels

6 Monitoring purge end points using gas detectors

6.1 Suitable and unsuitable gas detectors; recognising an appropriate detector; using catalytic, infra red and thermal conductivity gas detectors; switching-on procedure.
6.2 Calibration gas mixtures; calibrating and zeroing of detectors
6.3 Electrical safety certification of gas detectors and other electrical apparatus
6.4 Sampling techniques

7 Venting of purge gases

7.1 Minimising inventory to vent; diameter and flow in vent pipes; noise factors
7.2 Vent height and distance from buildings
7.3 Prevention of static charge build-up; use of flame traps

8 Post purging arrangements

8.1 Need for re-testing and frequency
8.2 Implications of confined space entry regulations when man entry planned

9 Planning a safe system of work

9.1 Preparation of method statement including plant description; isolation; use of physical lock-off; methods of purging and venting; permit-to-work and sign-off procedure
9.2 Purge: volume, velocity, pressure, end points and duration;
9.3 Risk assessment and notification of relevant bodies
9.4 Emergency and other contingency arrangements

10 Written multiple-choice question assessment test

Results of the MCQ assessment test and discussion

11 Practical exercises

Defining the practical exercise; preparing pipeline/vessel for purging; safety precautions; inert gas and purged gas interconnections/venting; choosing, inspecting and preparing the gas detector(s) for use. Undertaking the practical exercise. De-briefing from practical exercise.