Recently, an extensive gas piping repair project took place during a time-constrained shutdown/turn-around effort at a major industrial plant. The facility was looking to add a new plant main shut off valve, sectionalize the plant mains, and repair minor leaks in its natural gas distribution piping mains. They also wanted to install inline blinds/blanks to facilitate future repairs without having to purge major sections of the plant’s lines and risk an extended shut down.
Analyzing various gas piping repair issues, the piping repair process has been broken down into 10 main steps as are identified below:
TEN STEPS TO A SUCCESSFUL GAS PIPING REPAIR PROJECT
1. Logistical planning for securing purge materials, blinds, valves, gaskets, valve sealant, and trades labor.
2. Verification of existing connected equipment and installed piping/valves/purge points.
3. Gas utility communication and start-up/shut off planning.
4. Equipment shut off, pre-purge/bleed off, and purge.
5. Lockout/blanking planning including obtaining permits.
6. Piping/valve work (making the repairs).
7. Pressure testing/documentation.
8. Post purge/cancellation of lockout permits and removal of lockouts.
9. Utility removal of lockouts/service re-establishment.
10. Equipment light off.
A purge point is an area in the piping where a hose connection of some type can be made for removing natural gas from the system. In some cases, these are actual connections in the piping with valves expressly installed for this purpose. In other cases, this is a port on a valve installed for this purpose. A lack of purge points will make the job considerably more difficult as it will expand the scope of piping that needs to be taken out of service to conduct the job safely.
Relieving pressure or bleeding down a system is the process of removing gas in a piping network down to atmospheric pressure. This is usually done by attaching purge hoses to remote areas of the mains and then venting the gas off to a safe place.
Purge or bleed points should never be left unattended. Make sure that caution tape is installed to keep people/traffic away and that the end of the lines are attended and observed at a safe distance.
Another purge point issue is the purge point’s proximity to a safe place to discharge the pipe’s contents. The best places are considerable distances away from any ignition points, mechanical equipment (air handlers/exhaust fans), traffic, windows, and/or personnel. Consider the difficulty in trying to get purge point gas outside from the middle of the plant when no roof penetrations are near or available.
When are you done purging?
Two important issues to consider are when is purging complete and when is it safe to conduct a repair? Purging is complete when a non-detect (using a TIF type meter) occurs at the purge point indicating that no combustibles remain in the pipe. Most TIF type meters are sensitive to 5 ppm of natural gas. Make sure that purge gas, (nitrogen), continues to flow while the cuts are made. Make sure that prior to cutting, a welding or burning permit is obtained to reduce the probability that combustibles have accumulated, and/or that the area is free from combustibles and fire watches are posted.
Verify that all routings are as the drawings indicate. Confusion in blanking or shutting down a system can lead to disaster if lines are left energized. In some cases, equipment and/or facilities may have popped up near valves or purge points over the years that now make some areas relatively inaccessible. This isn’t something to discover when time is of the essence. Make sure the system is walked and field verify everything before proceeding.
Verify that each piece of equipment has a shut off that functions. Operate it and reseal all lubricated plug cock type valves related to equipment and system shut offs. Review the installation of regulators both in system mains and before equipment shut offs. These will be vulnerable to system test pressures later in the job and may need to be temporarily removed from service.
Pipe Spacing/Hanger Issues
The installation of blinds/blanks to remain in lines for future service considerations may require spreading pipes apart to gain the space thickness of the proposed blinds. In many cases, blinds need to be installed on both sides of the proposed valves. Spreading pipe for these purposes means that one needs to consider loosening hangers/friction clamps and/or installing come-alongs to pull pipe apart. Remember that if piping must be spread with come-alongs, to put blinds in; the blinds will not easily spin into position during their next intended use. It is better to plan and make space by cutting and re-welding for blinds if they are truly to be a useful part of your piping system.
Materials/Resources for Doing the Job:
Valves are heavy, in some cases several hundred pounds for 8” or 10” plug type valves with operators. This may require some type of rigging/support. Have extra valves on hand, or at least readily available from a supplier’s inventory, as valves get installed and issues can arise during or after installation. Consider what a dropped valve that gets broken would do to the planned project.
It is vital that the proper type of sealants for all valves in the system, including all distribution system valves, are available and used. All distribution system valves need to be exercised and validated to be sure they work and hold well prior to the actual system shut down. Valve sealants are specific to applications and valve manufacturers. You must have the right type and be knowledgeable on how to install them. Use an installation sealant gun that has a gauge to watch and identify when the valves are filled. Make sure they are operated frequently while installing the sealant. If a considerable number of valves are to be sealed, compressed air powered sealant injection tools are available.
Assume that this project will wear out many gaskets trying to get valves/blinds spread and installed. Ensure there is an adequate stock on hand.
It’s possible that blinds installed will not seal. Heat from welding can warp blinds or defect surfaces, allowing for leaks. Be certain that spare blinds of all anticipated sizes are available. Blinds are available for purchase in a number of different surface finishes. These include painted or RMS designations like RMS 150. RMS means root mean square, and it is a machining tolerance that relates to how rough the surface is. Typically, RMS 150 blinds work well with traditional gaskets.
When installing blinds consider the use of mechanical spreader tools, which are available in a variety of types used in the facilitation of spreading pipe for repairs and installing blinds. Remember that when installing a blind, to make sure that the side being opened up is completely purged with nitrogen. Make sure that the valve has been sealed and verified to not leak. Bleed the other side of the system/valve to reduce the probability of any gas being on the side of the valve to be blinded. Finally, use non-sparking tools to remove the bolts and complete the installation.
Being prepared for any circumstance or instance of delay is the best way to enter a gas piping repair project. Consider every avenue of the project and what can go wrong. Delay results in extended down time and potential for safety hazards to arise. However, rushing through a project and implementing incorrectly sized, surfaced or incorrect types of components will result in future complications that could have seriously negative consequences. Natural gas, nitrogen and fuel fired equipment all require extreme attention to detail. With careful consideration, a gas piping repair project can be long lasting and provide for safe operation and even production enhancements if upgraded and done well.
Honeywell Combustion Safety, formerly CEC Combustion Safety, LLC, has been in business since 1984. With engineers and staff members that sit on Code committees such as ASME CSD-1, NFPA 56, NFPA 85, NFPA 86, and NFPA 87, our inside expertise is integrated within all of our practices and our global reach ensures that customers around the world are kept safe. Contact us at +1 216.749.2992 or visit www.combustionsafety.com for additional information.