Construction and Operations

Pipe for the Bluegrass and Tennessee Gas NGL Pipelines

Conclusion:Except in rare cases (Black Swans) our researchers think that “Welded Pipe” is likely acceptable for newly constructed NGL pipelines.  However, repurposing of existing NG pipelines to NGLs is much more dangerous their opinion because these pipes (Boardwalk and Tennessee Gas) were manufactured using low frequency electric-resistant welding (LF-ERW).  The Boardwalk and Tennessee Gas repurposed pipe would be inspected and hydrostatically tested in place prior to be put in service.  However, even if the pipe passes the hydrostatic test, the test can itself lead to pipe yielding that doesn’t fail until in use.  

Background:Studies have shown that pre1970’s LF-ERW pipe (welded @ 50-400Hz) carrying hydrocarbons fail in the field along the longitudinal welded seam. See references (1)-(4).  Three failures occurred between March – June 2013 (4).  The question has been asked, is this a systemic problem for ERW pipe for NGL pipelines?

In addressing this question one looks at the current pipe manufacturing processes used for constructing new pipelines.  There are four/five types: 1) High Frequency Electric Resistance Welded [HF-ERW] (welded @ 200-500kHz); 2) High Frequency Induction (HFI) Welded; 3) Straight Seam DSAW [double submerged arc welded] ie, inside and outside arc welded while submerged in flux; 4) Spirally Welded; and 5) Seamless. See references for descriptions ;
Mr. Fred Hagius, Williams Co. construction expert, told our researcher at the Open House in Frankfort that the 24-inch pipe planned for the Williams portion of the project would meet API 5L (American Petroleum Institute 5L) specifications.  I asked if the pipe would be seamless, and he said “no; the potential suppliers make welded pipe, and that is what everyone in the industry uses.”

A Corpac salesman that supplies seamless pipe told our researchers that seamless pipe costs twice as much as HF-ERW (frequency >400 kHz) pipe.  Also, spirally welded pipe is normally used for pipes greater than 24-inch diameter, where the pipe manufacturer buys steel coils that are cheaper as starting material instead of steel plates to make the pipe.  There should be no advantage for the pipeline using spirally welded pipe.  An Am. Steel Pipe salesman said that the ERW process greatly improved when pipe mills changed to high frequency electric-resistive heating welding (HF-ERW) many years ago (~1970).

Good supplier options for welded pipe seem to be American Steel Pipe (Birmingham), Stupp (Baton Rouge), Berg (Europe, Panama City & Mobile), and Corpac (Miami).  Pipe for Williams Co’s Gulfstream underwater project in 2003 was Berg Pipe, German-based, that used HFI welded pipe.  American Steel Pipe uses HF-ERW process; Stupp uses HFI & HF-ERW processes; and Berg uses the straight seam DSAW process.  Corpac is an international distributor that sells HFI longitudinal & spiral weld pipe as well as seamless pipe.  Seventy percent of Corpac’s pipe is foreign manufactured and 30% is domestic.

A paper by Greg Stark (5) explains how pipe manufacturers improved their process control so that Saudi Aramco could replace the more expensive pipe (seamless and SAW) used for sour crude production to the less expensive HF-ERW or HFI welded pipe.  The specs were changed from API 5L to include the ISO 3183 (International Organization for Standards) standard.  This forced the pipe manufacturers to meet more stringent requirements in controlling their manufacturing processes particularly the welding process so that the pipe could be used for liquids at pressures greater than 1,000 psi.

In the literature there is mention that the hydrostatic test can lead to failure in the field because the hydrostatic test can cause yield in the pipe without creating a catastrophic failure, which later fails in-service.  Both the Boardwalk and the Tennessee Gas Pipelines that are to be repurposed are LF-ERW pipe that will be hydrostatically tested in place. 

Also, inspection smart pigs aren't always smart either.   In our researcher's opinion, another potential risk is changing from NG to NGLs in the repurposed pipeline.  An incompressible fluid (NGL) is more susceptible to spikes in operating pressure than a gas (NG), making the pipe more susceptible to failure.  The reversal of flow direction suggests another pipeline concern.  If the existing NG compressor station locations are used for the NGL pump stations, the operating pressures in the pipeline will be highest where it used to be lowest and vice versa.    

(1) 1989 study shows the concern about old, LF-ERW pipe failures. ; 2011 PHMSA on pipe manufacturing processes shows concern about LF-ERW pipe. An article published in March 2008 including coauthors from Williams Co. examines a pre-1970 ERW Pipe Seam Weld Failure incident. June 2013 blog on “safe pipelines” discusses these same concerns about LF-ERW pipe.   A failure analysis report for a Canadian pipeline is referenced in the blog.p12h0105_ERW_Weld_Failure_Nig_Creek_Canada.pdf(4) July 2013 blog by the same author above on “safe pipelines” lists seven recent pipeline failures that are likely caused by LF-ERW seam failures: 1) Tallgrass, Torrington, WY-June2013; 2) Exxon Mobil, Mayflower, AR-March2013; 3) Chevron, Ogden, UT-March2013; 4) West Shore, Jackson, WI-July2012; 5) Enbridge, Deer River, MN-April 2010; 6) Philips, Denver City, TX-Jan2008; and 7) Dixie, Carmichael, MS-Nov2007.

Former TransCanada Corp. employee Evan Vokes’ impassioned testimony before a Canadian Senate committee last week painted “a very, very bleak picture of the pipeline industry in Canada, and probably by extension, the States” according to Sen. Betty Unger.

What Is a Pipeline System?
What is pigging?
How and Why Are Pipelines Cleaned?
What Are the Risks of Pigging?

Vokes’ allegations on Thursday against TransCanada, the Canadian company leading the controversial proposal to send tar sands oil from Alberta to the Gulf Coast via the Keystone XL pipeline, were sobering: a “culture of noncompliance” and “coercion,” with “deeply entrenched business practices that ignored legally required regulations and codes” and carries “significant public safety risks.”
Pipeline networks involve several components such as: 

1.  Initial Injection Station
Known also as supply or inlet station, is the beginning of the system, where the product is injected into the line. Storage facilities, pumps or compressors are usually located at these locations.  It is possible that any given pipeline could have multiple infection stations in various locations.
Example of an Initial Injection Station

2.  Compressor/Pump Stations
Pumps for liquid pipelines and Compressors for gas pipelines, are located along the line to move the product through the pipeline. The location of these stations is defined by the topography of the terrain, the type of product being transported, or operational conditions of the network.  While the Williams Company's representatives report there would be only one station in Ohio for the proposed Bluegrass Pipeline, other sources indicate that such stations are typically located every 10 - 20 lines across a route.
Example of a Compressor Station

3.  Partial Delivery Stations
Known also as intermediate stations, these facilities allow the pipeline operator to deliver part of the product being transported.  It is unknown whether any of these stations are planned for the proposed Bluegrass Pipeline.  For any company to use the products from this line, they would first need to be processed by a petrochemical plant such as this one:

4.  Block Valve Station
These are the first line of protection for pipelines. With these valves the operator can isolate any segment of the line for maintenance work or isolate a rupture or leak. Block valve stations are usually located every 20 to 30 miles (48 km), depending on the type of pipeline. There are no established rules on the positioning of these valves.  
Installation One Type of Block Valve System

5.  Regulator Station
This type of valve station, allows operators to release some of the pressure from the line. Regulators are usually located at the downhill side of a peak.
One Type of Regulator Station

6.  Final Delivery Station
Also called outlet stations or terminals, this is where the product will be distributed to the petrochemical plant for processing, such as the Geismar Plant in Louisiana which reportedly had a history of leaks and non-compliance prior to its explosion.

"Pigging" refers to the practice of using Pipeline Inspection Gauges or 'pigs' to perform various tasks such as cleaning, inspection, and maintenance operations on a pipeline. This is typically done without stopping the flow of the product in the pipeline. However, when pigs are removed from pipelines, there is typically a release of product into the environment. The pigging process also produces static electricity, which must be controlled to prevent fire.

An Example of one Type of Pig for a 28 inch Pipeline

Pigging is accomplished by inserting the pig into a 'pig launcher' (or 'launching station') - a funnel shaped Y section in the pipeline. The launcher / launching station is then closed and the pressure-driven flow of the product in the pipeline is used to push it along down the pipe until it reaches the receiving trap – the 'pig catcher' (or 'receiving station').

Pigging stations are placed along pipeline routes to enable maintenance procedures.  Learn more about pigging: 

Pipelines are cleaned to remove debris from the lines which collects during operations.  Pigs are used to clean the lines, and they may also be flushed with water or chemical solvents. Lines are sometimes flushed when the type of product being transported in the line is changed.  

Pigs must be pushed through pipelines with a high pressure using an inert gas or a liquid; if pushed by gas, some systems can be adapted in the gas inlet in order to ensure pig's constant speed, whatever the flow pressure is. The pigs must be removed, as many pigs are rented, pigs wear and must be replaced, and cleaning pigs push contaminants from the pipeline such as wax, foreign objects, hydrates, etc., which must be removed from the pipeline. There are inherent risks in opening the barrel to atmospheric pressure so care must be taken to ensure that the barrel is depressured prior to opening. If the barrel is not completely depressured, the pig can be ejected from the barrel and operators have been severely injured when standing in front of an open pig door. By accident, one pig was shot out of the end of a pipeline without a proper pig receiver and went through the side of a home 500 feet away.   See photos of the flying pig damage to a nearby home. 

When the gas product is sour, the barrel should be evacuated to a flare system where the sour gas is burnt. Operators should wear a self-contained breathing apparatus when working on sour systems.

Smart pigs contain sensitive electronics, and they must be fully sealed to prevent fluid from entering the pig, which otherwise could potentially cause fire or an explosion.

After pigging is complete, the data from the pig's sensors is used to evaluate the pipeline for corrosion, cracks, etc. to map defects.  This information is used to judge the severity of the defect and help repair crews locate and repair the defect quickly without having to dig up excessive amounts of pipeline. According to Wikipedia, in some cases, defects are monitored over a period of years so that plans can be made to repair the pipeline before any leakage or environmental damage occurs.