Process Safety Moments from CCPS

Date: June 2012Issue Number: 002AIChE © 2010. All rights reserved. Reproduction for non-commercial, educational purposes is encouraged. However, reproduction for the purpose of resale by anyone other than CCPS is strictly prohibited.

Mechanical Integrity of Tubing

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Mechanical Integrity of Tubing

Tubing, including metal tubing, and also tubing made of plastic, rubber, and other materials, is commonly used in process plants, for example: For instrument connections To flush pump and agitator seals For other applications with small flow requirements

Where do you use tubing in your plant?

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Incident 1

• A ½-inch stainless steel tube between a glycol pump and a process vessel failed at a fitting near the process vessel.

• The resulting leak sprayed onto a reboiler and ignited causing significant equipment damage.

• The tubing failure was concluded to be the result of vibration caused by the glycol pump.

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Incident 2

1-in SS tube to a gas scrubber failed at nut and ferrule compression fitting

Resulting gas leak ignited but self-extinguished without major damage

Exact cause not determined Pressure charts showed over-pressure before the incident Tubing possibly damaged or weakened during storms in previous hurricane season

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Incident 3

Gas leak from ½-in tubing for pump seal was detected during LNG plant startup

Repairs done by unqualified technician

When the plant re-started, tubing failed completely causing an LNG leak and fire

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Found during a plant inspection6

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Found during a plant inspection7

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Found during a plant inspection8

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What can you do?Review procedures for installation, inspection, and maintenance of

tubing.

Remember – tubing may not be as durable as pipe and may be more easily damaged. Avoid impacts to tubing and tubing connections.

Report damaged or leaking tubing observed in the plant and ensure it is repaired.

Use qualified personnel to install and repair tubing.

Use proper tools for installation and maintenance of tubing.

Use correct components – tubing, ferrules, nuts, and fittings - do not mix components from different manufacturers.

Ask your tubing supplier to provide information on proper installation and maintenance of their product.

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Safety precautions from a supplier*

• Do not bleed system by loosening a fitting nut or fitting plug.• Do not assemble and tighten fittings when the system is pressurized.

Always depressurize a system before adjusting the tightness of a tube fitting connection, or before disassembling tubing.

• Make sure that the tubing rests firmly on the shoulder of the tube fitting body before tightening the nut.

• Use the correct tool for gap inspection gauge to ensure sufficient pull-up upon initial installation.

• Always use proper thread sealants on tapered pipe threads.• Do not mix materials or fitting components from different

manufacturers – tubing, ferrules, nuts, and fitting bodies.• Never turn fitting body. Instead, hold fitting body and turn nut.• Avoid unnecessary disassembly of unused fittings.

* Ref.: Extracted from a compression tube fitting manufacturer installation guide – ask your tubing supplier for their recommendations.

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References

May 2012 CCPS Process Safety Beacon.

US Department of the Interior, Minerals Management Service, Gulf of Mexico OCS Region, Safety Alert No. 248, “Stainless Steel Tubing-Related Fires,” December 28, 2006.

Contact your tubing supplier for information.

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12CCPS Process Safety Moment No. 001

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Get more information:CCPS books and resources on mechanical integrity:

Guidelines for Mechanical Integrity Systems (2006)(available from CCPS/Wiley, or electronically from Knovel Corporation)

CCPS Member Companies: Volunteer to Serve on a CCPS Committee

Not a CCPS Member Company? Learn about the benefits

CCPS Web Site: www.aiche.org/ccps