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Article # 0008
UNDERGROUND LINE CUTTING SAFETY
by
R. L. Langley, P.E.
INTRODUCTION
An excavated area where more than one similar size underground steel pipe transports pressurized hazardous materials requires special precautions to avoid cutting into the wrong line during modifications. This paper describes measures to minimize potential hazards associated with this activity. All applicable federal, state and local safety and environmental laws, rules, regulations and company policies must be followed.
SAFETY CONSIDERATIONS
This describes safety considerations covering most typical situations. It’s impossible to anticipate each and every particular circumstance that might be encountered. Any deviations for special circumstances require proper risk assessment with designated authority approval. The following activities were developed primarily for flammable gas liquid pipelines, but could apply to other services:
A. Preliminary Activities
1. A designated company authority shall approve the line cutting and will agree to the detailed procedures to be used.
2. The line to be cut will be clearly marked and will be independently traced bi-directionally from the location of the line cut to all termination and interconnection points by at least two independent, knowledgeable persons. If any of the line is buried, it should be uncovered back to at least one identifiable above ground termination point. If this is not practical, refer to Step 4 of “Line Cutting Operations” below. In some cases, judgment by responsible authority may be exercised in assuring proper line identification.
3. Provide necessary safety equipment at the site, including vehicle/personnel traffic barriers, fire equipment, and personal protective equipment. Rather than cite a litany of specifics here, just ask the question “What could possibly go wrong and how would we to deal with it?”, and prepare accordingly.
NOTE: Regardless of procedures followed or precautions taken, it’s best to assume that transported materials will be discharged from the piping at the intrusion point and prepare accordingly.
4. Mark the exact cut location on the pipe. Observe the condition of the pipe at the marked point—if external corrosion is present or the material inside is corrosive, it is suggested that wall thickness be measured (ultrasonic or other accepted methods) to ascertain adequate wall thickness for planned activities.
5. Determine line cut method and procedures--i.e. torch cutting is used only after initial cold cutting (see “Line Cutting Operations”-Step 7) via non sparking equipment--i.e. pipe cutters, hydro cutter, air powered pipe saw etc. Evaluate and prepare for any special precautions associated with the selected cutting method bearing in mind the nature of the pipe’s contents.
6. Complete the attached “Line Cutting –Guideline Checklist” top portion, then the remainder of the form as work progresses.
7. Identify, assess and take precautions regarding any potential special circumstances such as the following:
· Hydrogen sulfide or other toxics presence
· Hydrates (ice type plug) or freeze-ups that could be blocking the line during bleed down—i.e. may give appearance of being depressured, but may not be
· Hazardous liquids--volatile, flammable, toxic etc. trapped in pockets, low points.
· Any connections to the line that could pocket materials or be inadvertently opened into the line during cutting operations
· Materials that can decompose exothermally during depressurization or exposure to air
· Nearby operations
B. Line Cutting Operations
1. The line is isolated and depressured.
2. After depressurization, skillet blinds are installed at each flanged termination and interconnection point with a gasket next to the shut block valve or flange, and spacers (for vent gap) such as welding rods between the skillet and flange connected to the line to be cut. All motive power (air, electricity, hydraulic, etc.) for actuated valves connected to the subject line should first be disconnected before blind installation. Disconnect all screwed connections from the line to be cut. (In some cases, a “double block and bleed” may be necessary or permissible with proper approval.)
3. Purge the line to be cut to safe limits of flammability, toxicity, or other specified parameters. Only if the line is totally exposed from at least one verified, depressured and purged termination point to the marked cut point, proceed to Step 7. If not, go to Step 4
NOTE: Drawings should not be relied upon as the primary source of valid information for situations where a line cannot be completely uncovered and traced to at least one above ground identifiable termination point. Actual physical verification of a depressured state is necessary before a line is cut. In this case, drawings are secondary information sources that can be either be affirmed or corrected by empirical findings.
4. If unequivocal identification and configuration of a (buried) line cannot be directly ascertained, a hot-tapping saddle will be clamped on the line at the marked cut location. Before hot-tapping is begun, inert gas pressure shall be applied through the valve on the hot-tapping saddle assembly to verify the saddle assembly is sealed to the pipe and would contain without leakage the highest conceivable pressure from any line in the area. The minimum size hot tap should be through a 1” valve. If necessary and with appropriate management/supervisory approval, alternately a 1” 6000 # forged steel coupling may be welded to the line for hot-tapping in the section to be cut, following safe hot tapping procedures.
5. After successful hot-tapping, verify depressurization; then test the line with appropriate instruments-combustible detectors, toxicity meters, etc.
NOTE: Pressure gauges are not primary indication of safe depressurization—they can malfunction showing incorrect readings. Physically verify the depressured state directly through the fully opened, unobstructed 1” tap valve before proceeding.
6. Depending on the results of (5), either continue depressuring or purging the line to safe levels, or proceed to the line cut.
7. Initially cut into the line using a “cold cut” device, such as an air powered port-a-lathe, air powered hacksaw, or a manual pipe cutter. Within the same excavation, other cuts and welds may be made on the subject line, providing the line can be completely visually traced from the first cut.
8. The attached “Line Cutting-Guideline Checklist” should be attached and/or incorporated with existing work safety permits were line cutting is part of the activity. This provides procedural accountability and documented checks/balances.
C. Other Considerations
1. Where lines containing (non toxic) flammables cannot be adequately purged for hot work, stopples may be installed and the gas vented to safe locations. If standard stopples cannot be used, then consider using manufactured in-line stopples with qualified personnel who can coordinate safe installation of the in-line stopples through a hot-tapped fitting.
NOTE: If the line contains toxics, atmospheric venting may not be possible and other evacuation means may need considered. Respiratory protection may be required.
2. There are rare situations where complete depressurization of a line may not be practical--i.e. continual “weathering off” of trapped flammable gas liquids, etc. in inaccessible low points. A residual pressure of 1-2 oz. may remain on the line after initial depressurization with assistance (steaming, inert sweep, etc.), and stopples may not be an option. Even in this situation, there are ways to accomplish successful cutting and welding operations with a delicate positive pressure “controlled burn” procedure, but it is not a recommended practice and if absolutely necessary, should be left to only the most skilled and experienced welding and safety professionals.
LINE CUTTING GUIDELINE CHECKLIST
Date: ___________________________ Time: ______________________
Facility ID/Name/Location: _________________________________________________
Name of Person Requesting Line Cut: _________________________________________
Project In-Charge Person___________________________________________________
Work to be performed by___________________________________________________
Line Diameter:___ Line Operating Pressure:_____ Material Inside Line:_____________
---------------------------------------------------------------------------------------------------------
1. Has the area where the line cutting will occur been properly excavated, cordoned off, and proper personnel notified? Yes No
2. Is the line to be cut and the cut location clearly & distinctly marked? Yes No
3. Has the line been completely traced out and all interconnections and termination points identified?
___________________________ Yes No
(Signature 1st qualified person)
___________________________ Yes No
(Signature 2nd qualified person)
4. Have power sources (air, electrical, hydraulic, etc) for actuated valves connected to the line been disconnected? Yes No
5. Has the line been depressured completely and physically verified? Yes No
6. Has the line been skillet blinded or disconnected at all termination and interconnection points? (Note below under “deviations” if double
block and bleed used in lieu of blinding or disconnection.) Yes No
7. Has the line been properly purged? Yes No
8. Was the line tested for combustibles or toxic content? Yes No
Readings______________Limits____________
9. Is the line totally and continually exposed from a depressured, safe above ground termination point to the designated cut point? Yes No
10. Will the line be hot tapped prior to cutting? Yes No
11. If the line was hot tapped, was communication verified between the tap location and the nearest identifiable opening? Yes No
12. If the line was hot tapped, was its interior tested through the tap? Yes No
Readings______________Limits____________
13. Is the area below and around the cut location free of flammable materials and are any potentially affected open drains plugged? Yes No
14. Is fire protection including a qualified firewatch, extinguishers, (pre-positioned) water fire suppression systems, etc. in place? Yes No
________________________________
Name of qualified firewatch)
15. Which type of non sparking “cold cut” device will be used? ______Port-A-Lathe
______Hacksaw
______Pipe cutter
_______________________Other (describe)
16. Describe deviations from procedure, reasons given and risk management measures: ______________________________________________________________________
______________________________________________________________________
______________________________________________________________________
______________________________________________________________________
______________________________________________________________________
______________________________________________________________________
______________________________________________________________________
Distribution:
_____________________________________name of copied
_____________________________________by (person furnishing copy)
Approvals:
_____________________________________Facility Manager
_____________________________________Project Person in Charge
_____________________________________Supervisor
Note: Progressive approvals and verification signoffs are required for accountability and proper checks/balances assurance.
BIOGRAPHY
R.L. (Bob) Langley, P.E. worked over 30 years in midstream (gas processing) staff and management positions in process engineering, operations, environmental, safety and health, training, and strategic sourcing. Bob holds a BS degree in Chemical Engineering from the University of Oklahoma, and currently is a consultant residing in The Woodlands, Texas.
Contact Information:
R.L. Langley, P.E.
19 Mistflower Place
The Woodlands, TX 77381
936-273-5965
Article # 0008 TEST QUESTIONS:
1. When preparing to cut into a buried line in an excavated area that contains multiple pipelines, it is most important to...
Note the wind direction
Physically verify with complete certainty the proper line and its configuration
Notify local law enforcement
All of the above
2. It’s important that the line to be cut be completely traced in both directions by at least…
One qualified person
Four qualified persons
Two qualified persons
Three qualified persons
3. The potential to cut into the wrong line exists ….
Where there is other piping in the same excavated area
When the workers get in a hurry
When one believes drawings are 100% correct
All of the above
4. In an excavation with multiple pipelines, the primary method of ascertaining a safe depressured condition of a line to be cut which cannot be visibly and completely traced from the cut point to at least one above grade termination point is…..
Direct physical verification through a valve tapped connection at cut point
Pressure gauge readings anywhere on the line as drawings indicate
Opening a vent valve anywhere on the line as drawings indicate
Changes in pipe temperature felt when depressuring
5. Purging a line is important primarily to
Clean the pipe walls before cutting
Remove any flammables or toxics to a safe level
Assure the correct line has been selected
Get it to a temperature that allows it to be worked on
6. Which of the following situations, if present, may indicate an apparent depressured state, but uncontrolled pressure increase potential could still exist?
A power operated valve not properly deactivated or skillet blinded
Pressure gauge on the line shows 0 psig
Hydrate (ice type solid) plug formation
All of the above
7. During initial intrusion on a depressured line, one should assume one of the following and prepare accordingly:
Everything’s OK-following all the precautions guarantees a safe situation
Flip a coin-head’s it’s OK, tails it’s not
Whatever is in the line will be leaking out under pressure at the first cut
All of the above
8. The initial cut into a depressured line should be made by a...
Cutting torch
Non sparking “cold cut” device
Chain Saw
Hammer & chisel
9. It’s important to pressure test the hot tapping saddle assembly clamped to the pipe to...
The highest conceivable pressure of any line within the same area
100 psig
200 psig
300 psig
10. Interconnection points to the subject line to be cut should normally be isolated by...
Disconnecting and/or skillet blinding from the subject line
Closing the valve(s)
Closing the valve and using lockout/tagout procedures
Being placed in a remote location without any other connections.
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