DRYING AND NITROGEN PROCEDURE
CONTENT 1.0 Introduction 2.0 Purpose 3.0 Scope 4.0 Reference Documents 5.0 Abbreviations / Definitions 6.0 Organization / Responsibilities 7.0 Procedure 8.0 HSE Plan 9.0 Quality Plan
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1.0 Introduction In line with Standard Practices, drying and nitrogen purging activities shall be carried out on the newly installed Gas plant pipelines after successful hydro-testing of each completed pipeline section, in order to reduce the initial water content, preserve the pipeline from possible natural gas – air combustion or corrosion as a result of the test water. This is usually carried out parallel to dewatering with the aid of low density bare foam pigs and bi-directional sealing pigs driven with compressed dry air and dry nitrogen in a controlled process as to allow a continuous water and oxygen removal operation. 2.0 Purpose The purpose of this procedure is to ensure that all drying and nitrogen inerting operation for the gas plant Pipelines are carried out in accordance with the applicable Specifications and COMPANY’s requirements. 3.0 Scope This document shall apply to all the pipeline drying and nitrogen activities that will be carried out on the Soku – New Sanbarthelomew manifold pipelines Project by Contractor. Contractor shall adopt the drying and inerting method as specified in the scope of work. 4.0 Reference Document • • • • • 5.0
Specification for Pig Launcher and Pig Receiver – EKS-NST-MP-7737-00003 Pre-Commissioning and Commissioning Manual and Procedure – EKS-NST-BA6008-00001 Hydrostatic Pressure Testing Of New Pipeline – DEP 31.40.40.38 – Gen. Feb. 2011 Pipeline Engineering – DEP 31.40.00.10 – Gen. Feb. 2011 Pipeline pigging and cleaning procedure - EKS-NST-LA-8247-00001
Abbreviations / Definitions • • • • • •
HSE – Health Safety Environment. JHA – Job Hazard Analysis Pig launcher - A pig trap for launching pigs. Pig receiver - A pig trap for receiving pigs. Pig - A device which can be propelled through a pipeline by fluid flow and is normally used f o r various internal activities s uc h as separating fluids, cleaning and inspecting the pipeline. (A sphere is a spherically shaped pig).
6.0 Organization / Responsibilities `
The organization that shall be responsible for the execution of this document shall be as described below: • The Project Manager shall have overall responsibility for the successful and safe execution of all activities in the NCTL Project. • The Construction Manager shall be responsible for the successful and safe execution of this document. He shall delegate as may be necessary, all or part of this function to the Field Project Engineer. • The HSE Manager shall be responsible for the monitoring of the HSE aspects of this document and shall delegate all or part of this function to the Site HSE Officer. •
The Test Engineer shall in addition to undertaking as directed by the Construction Manager, have direct Site Management responsibility for a safe and successful execution of this document.
• The HSE Officer shall undertake as directed by the HSE Manager and shall carry out Site HSE surveillance and ensure HSE compliance. 7.0 Procedure 7.1 General Pipeline drying shall commence immediately after completion of the second dewatering pig run. Dewatering runs shall be repeated if drying does not commence within 48hr of the last dewatering pig run. Equipment sizing and calculations of the time required for drying shall be base on a film thickness of the residual water of not less than 0.1mm for the Gas Plant pipeline project. After drying the pipeline shall be purged with the drying medium at a minimum velocity of 3m/s in the pipeline at the discharge end. This shall continue until dew point at the discharge end remains below the specified dew point whilst replacing twice the content of the pipeline at purging pressure. Dry Nitrogen purging shall further be used to evacuate water vapor and oxygen from the pipeline using high sealing foam pigs. 7.2 Drying and Nitrogen purging methodology Different methods of determining the water vapor content of a gas are available. Secondary characteristics such as dew point, relative humidity shall be measured. For pre-commissioning operations, the Gas Plant AG pipelines shall be dried to a specific dew-point of -20oC at atmospheric pressure using a desiccant type air dryer with batches of absorbing foam pigs. All probe type dew point measuring devices shall be accompanied by calibration curves produced under controlled conditions so that true readings shall be ascertained. The dew point of air extracted from the pipeline shall be continuously monitored. Air pressure shall be as low as possible to absorb and therefore remove more moisture with the aid of the foam pigs. Once the desired dew-point is indicated for a period of 12hours or more, the drying shall be stopped. A check that the specified dryness limit has been met shall be effected by performing a soak test at the lowest possible pressure for a period of 12h and then `
passing an air volume equivalent to that of the pipe through the pipeline at the lowest possible pressure and monitoring the dew point of the air discharge. The out flowing air shall be at a dew point level well above -20 oC to ensure that a homogeneous -20oC dew point might be assured. Upon completion of the soak test, Dry Nitrogen is injected into the pipeline with either the cryogenic pumps or self extracting Nitrogen Membrane units. Nitrogen purging shall be performed at the same pressure level as the soak test or a bit higher but not to exceed the saturated vapor pressure at the prevailing temperature. During pressure increase at the beginning of a purge check, care shall be taken not to increase the dew-point in the pipeline due to compression effects. Prior to starting the Nitrogen Purge, the dew-point shall indicate well below -20 oC. The inlet and outlet readings could be 2oC different and yet be identical. The method is to therefore purge at as allow a pressure ensuring that inlet and outlet dew points remain steady below -20oC. Upon completion of purging, the pipeline shall be blocked in with Nitrogen gas for a period of at least 12 h and at a pressure of 3bar above the ambient pressure at all points along the pipeline. PRESSURE MONITORING SHALL BE CARRIED OUT BY MEANS OF PRESSURE GAUGES AND RECORDERS. After the soak test has been successfully completed, the pipeline shall be filled with dry Nitrogen to a pressure of 0.5bar above ambient pressure at any point along the pipeline, thereafter, gas filling can commence under low pressure. Warning Signs such as “PIPELINE UNDER NITROGEN PRESSURE” or “PIPELINE FILLED WITH DRY AIR” shall be placed at all affected pipe work including pig trap systems and block valve stations. 7.3
PROGRAM AND TESTING SCHEDULE The drying/purging program and schedule shall be submitted to COMPANY representative given at least 48hr notice for approval/comments before drying preparations are due to start. In addition, at least 48hr notice shall be given to COMPANY representative stating actual date and time such activity, checks and inspections are due to commence. The schedule shall be developed prior to any Drying and Nitrogen purging detailing the installations to be dried and purged, purge pressure and duration, preparing isometric for each section to be dried, construction of temporary works and test provision. The purge section shall clearly be identified by isometrics and P&I drawings. This is to ensure that each has sufficient vent and sampling points.
8.0 HSE Plan Appropriate HSE plan shall be put in place prior to and during the execution of this document. As a minimum, job hazard analysis (JHA) shall be developed; approved and be discussed on site during the execution of this procedure. The content of JHA shall be cascaded to the work crew via a daily tool box meeting in order to inform and reinforce on the c r i t i c a l HSE awareness of the work force regarding the activity at hand. The JHA shall be fully implemented; including the provision of all required PPE for a safe execution of this document. `
Good housekeeping shall be maintained at all times, to ensure proper control and management of resultant waste from the implementation of the document. Waste management shall be in accordance with the project management plan and the JHA document. Prior to dry air drying and Nitrogen purging/gassing up, the following safety measures covered in Contractor safety standards shall be addressed. These will include: 1. Ensuring communication links are satisfactory. 2. Notifying all relevant operators and personnel. 3. Erection of safety notices around relevant pipe work. 4. Safe monitoring of operations. 5. Safe venting and/or flaring of waste gases. 6. Transfer of cold work permits to hot work as relevant. 7. Establishment of operational safety zones per relevant regulations. 8. Correlation of all commissioning reports for plant and equipment to be exposed to the new operational status. 9.0 Quality Plan The quality plan for this work shall include as a minimum the proper recording and reporting of all auditable inspections and processes that shall be carried out during the implementation of this procedure. Quality inspection and reporting shall be in accordance with the ITP and in line with the Project Quality Plan.
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