×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Multiple structure fires sparked by suspected gas line failure in towns north of Boston
7

Multiple structure fires sparked by suspected gas line failure in towns north of Boston

Multiple structure fires sparked by suspected gas line failure in towns north of Boston

(OP)
Authorities ordered residents to leave their homes immediately after dozens of house fires broke out in a string of communities north of Boston Thursday evening.

The Massachusetts State Police were evacuating multiple neighborhoods and restricting access to the area.

"Residents in the affected towns of Lawrence/North Andover/Andover who have gas service from Columbia Gas should evacuate their homes immediately if they have not already done so," state police tweeted.

"Gas lines are currently being depressurized by the company it will take some time."

Link

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

From reports there's been numerous residential boiler explosions and subsequent fires. Something like 75 fires and 30,000 people being evacuated? What could cause a gas like to overpressurize?

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

Fsilure of a large pressure regulator...

Mike McCann, PE, SE (WA)


RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

If it was the failure of a regulator, shouldn't there have been a relief device to protect the piping downstream? The relief device could have failed as well. I know the HAZOPs I participate in at my current company would not have discussed multi source failures.

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

pressure regulating stations off pipelines do have PRVs.
from experience, if any work was done and involved cutting, welding, grinding, etc. of metal pipe and those metal shavings got to relief valve such that the sensing tube/pipe was plugged . . . use your imagination.
i saw a fuel pressure gauge "appear" to exceed 300-psig in a class 150 system design to 150-psig. PRV was not relieving and the good ole red button was depressed. weld slag was the culprit.
sand in newly installed fuel gas pipe was another situation.
this goes back to inspection during construction . . ., etc.

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

According to press reports:

"The Massachusetts Emergency Management Agency blamed the fires on gas lines that had become over-pressurised, but officials who responded to the area were still investigating the cause.
State officials said Columbia Gas was working to ease pressure on gas lines following the fires. Columbia had announced earlier in the day it would be upgrading gas lines in neighbourhoods across Massachusetts, including the area where the explosions happened.
It was not clear whether work was happening there on Thursday, and a spokeswoman did not immediately return calls."

http://www.abc.net.au/news/2018-09-14/boston-gas-e...

http://julianh72.blogspot.com

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

I know little about gas distribution, my area of interest is in T&D, but I think the gas company either did several things wrong, or we need to re-think how gas is distributed. Of course my opinion is worth nothing- but still scary and mystifying at the same time.

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

Scary. If I had gas piped into the house (which I do not, I live in a rural area with no gas distribution) I would install a PRV in the line well outside of the house and point the relief pipe away from any combustible materials. An elevated relief pipe similar to those at vehicle gas stations.

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

There is provision for HP relief at my meter, outside of my house.
I know because my failed once (not from HP but from age).
They continuously upgrade the regulators and meters. In WI they consider them to have a 20yr service life.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

I've seen systems where the PRV does not have enough flow area to limit the pressure in the case of something like a complete pressure regulator diaphram failure. The PRV is adequate for a small tear or a stuck regulator but not total regulator failure. In that case the pressure goes up very fast.

----------------------------------------

The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

(OP)
Gas distribution systems operate at lower pressure during off season. In the fall, the pressure in the system is increased to deal with the expected heating loads. Something must have gone wrong with the pressure increasing procedure.

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

If I was engaged in Homeland Security, I'd be paying close attention to this event and firing up an urgent gas infrastructure security review. No suggestion (yet) that this was an act of terrorism, but too many people will have had their eyes opened to new possibilities for creating "a spectacular".

A.

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

I am not normally one of those "I wish the media would stop saying..." guys. But I wish they would stop reporting that "authorities have stated that they believe this was caused by a gas leak."

It's not possible for dozens of fires, miles apart, to be caused by a singular gas leak. C'mon, guys =)

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

Oh, they're stupid enough to believe that work being done + gas explosions = gas leak.

It is scary though. It makes a point that having a gas backup generator isn't always the greatest idea.

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

We will have to wait for the failure analysis to be completed, but there are several possiblities. The interstate gas pipeline may be operating at 900 psig ( 60 bar g), but the pressure reducing station may reduce that to a consumer supply line ( AT CITY GATES)of less than 30 psig ( 2 bar g) and the household distribution line may be less than 0.7 psig. There typically are no releif valves to atmosphere, and the 900>>30 psig and the 30>>1 psig pressure reduction must be arranged as dual independent pressure regulators in series and with a fast acting shutoff valve that can close within 1 second when a hard wired pressure switch indicates an overpressure had occured. The pressure switches must be calibrated every 6 months, and the concept of "independent " pressure reduction must be interpreted strictly, implying that the power supply and the pressure sensing that operates the PRV must be completely independent from themselves.

Some possible errors might be: (1) possibly converted the PRV to a digital control sytem DCS operated control valve, and the DCS for each valve was common, which violates the independent requirement.

(2)Likewise a DCS control system can be hacked or malprogrammed. A similar error occurred in 1999 near seattle ( bellingham) and the failure was initiated when the the DCS hot-switched to a backup server, and such a "bumpless transfer" had failed the valves to a failed-closed position. The resulting "waterhammer" pressure-pulse burst the pipe.

(3) the pressure swich was not calibrated on schedule or it was plugged by particlulate condensation.

(4) the city gate PRV setpoint may have been incorrectly specced based on PSIG instead of inches water.

(5) the fast closing stop valve stem may have binded up due to corrosion as it might not have been stroked in over 20 yrs

(6) and a dozen other possibilities.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

My house service regulator (30>>1 psig pressure reduction) has a safety PRV built in.
The few that I have installed on propane service also had a built in PRV.
Are there jurisdictions that allow a final pressure reduction without a Pressure Relief Valve?

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

Is it possible that some condensable gas was introduced into the distribution system?
I remember a red-neck butane installation that use cheap undersized final pressure regulating valves without a PRV function.
Tank pressure butane was fed directly to the final PRVs. The tank was in the direct sunlight and the supply pipe ran in the shade. Butane condensed to a liquid in the common supply line.
When the appliances in the new commercial kitchen were started they worked well for a few minutes.
However the regulating valve acted as an expansion valve and got very cold. Then the low temperature caused the reducer to seize
In the full flow position. For several seconds the flame on the stove top would be 2 or 3 feet high. Then the flow of liquid butane would warm the valve and it would work normally for a minute or so.
That's when I was called in.
Three cook tops were doing this at random but frequent intervals.
The solution was twofold; Install an intermediate regulator at the butane supply tank and install a larger regulating valve at each appliance with a built in PRV vented outside.

Is it possible that the failure of an upstream regulator could supply enough volume to the homes that the individual PRVs were overwhelmed?

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

Yes, condensation of "heavy hydrocarbons" is possible ( C6+), espescially immediately downstream of the pressure reducing valve.For this reason the pressure switches should be protected from such condensibles. It may be a problem for those systems that are recieving "rich LNG" from western africa or facilities that recieve insufficiently processed frac gas.

The news reports are consistent with an issue with the City Gates pressure redcuing station, and an overpressure of the consumer supply piping would explain failures of the household pressure regulators, bursting their diaphrams. Other nes reports indicated that this system of consumer supply pipes are being upgraded and the field construction activities may have compromised the pressure control of the network.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

Thank you for your reply davefitz.
I have observed over the years that most systems have some inherent redundancy whether in regards to mechanical redundancy or in regards to redundancy in operating procedures or normal practice.

Quote (davefitz)

The news reports are consistent with an issue with the City Gates pressure redcuing station, and an overpressure of the consumer supply piping would explain failures of the household pressure regulators, bursting their diaphrams.
That makes sense. The first failure of an upstream regulator led to a second failure of local devices which in turn could overwhelm the local Pressure relief Valves and allow higher pressure gas to flow to the appliances.
I wonder if we will find that the system was originally designed with redundancy but repair work led to a back up pressure relief system being temporarily being disabled, leaving a single point of failure, the pressure regulator which failed.
That is probably more likely than a non-condensible gas issue.
If there was a single point of failure, could a similar failure happen on other systems, Continent wide?


Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

I wouldn't be surprised by more of this sort of problem in the future. No pressure reducing valve can be assured to be bubble tight in service, when shut hard some portion of them will leak. Historically this hasn't been a huge problem because we had pilot lights that created a non-zero minimum usage. Pilot lights are now considered "ecologically unsound" and new ranges, water heaters, gas fire place inserts, and HVAC units are pilotless. That means that a tiny leak-through of a regulator has no place to go and can put 30 psig from the street into homes rated for less than one psig. Most systems will not fail at 30 psig, but some will have components under pressure that really can't take 30 psig.

The failure in Boston will be described in the accident report, and we'll see how close the descriptions above are, but I don't think that this kind of failure actually requires much overpressure on the feeder trunks to happen as homes rush to zero minimum usage.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

I believe all gas service regulators for buildings are self-relieving, that is they will vent gas if the downstream side goes much above setpoint. I think here the problem was that the supply pressure went way above 30 psig.

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

(OP)
The only problem with that scenario is that the gas pressure never went to 30 psig.

"The senators noted that a federal regulator, the Pipeline and Hazardous Materials Safety Administration (PHMSA), reported that the pressure in the Columbia Gas system “should have been around 0.5 pounds per square inch (PSI), but readings in the area reached at least 6 PSI.”"

Link

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

More and more confusing. The statement linked by bimr says that the National Transportation Safety Board is leading the investigation. You would think they have enough on their hands with aircraft accidents and bridge collapses. Pipelines transport gas and liquids, but the NTSB just may be getting overloaded/overpressurized.

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

I heard recently that the Boston area nat gas distribution system is very old ( over 100 yrs old) and has old cast iron componetns that needed to be replaced. As a result the entire neighborhood supply piping will be operating at very low pressures ( <1.0 psig) and there will not be a pressure regulator at the external flow meter . The only diaphram pressure regulators are those at the individual household appliances. Those appliances cannot withstand a 6 psig gas pressure without failing. This is based on a recent statement by a gas utility spokesman for a more modern west coast location, and I cannot confirm its validity.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

Boston Globe:

"The construction work involved replacing aging pipes in the area with plastic lines. But the National Transportation Safety Board said the utility failed to tell the construction crew about disconnecting or relocating the sensor, allowing the device to detect a drop-off in pressure in the abandoned line and signal to a nearby control station to increase the flow of gas into the system."

Apparently the control system did not include safety checks, pre-commisioning checks.

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

Geesh! Obviously nobody-in-charge.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

Here's the official preliminary report. https://www.ntsb.gov/investigations/AccidentReport...

Seems almost inconceivable that the design of the modification didn't realize that the sensor line was big located nor that the regulators didn't have independent secondary pressure protection devices for the downstream sections. Nor that the monitoring centre had no executive commands available to it to remotely close the regulator station.

I had some issues before with this line of thinking which is different from an industrial design where the default is fail safe or fail close.

Distribution systems which shut off cause more hazards and disruption, but still need to prevent over pressure.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

Certainly a black-eye for Columbia Gas considering it was their own design and construction plan.

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

Yikes, A system that fails that catastrophically on the loss of a sensor is inconceivable. Surely there have to be backups, sensors fail all the time.

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

Somerville (a city only slightly north of Boston) has postponed some sewer work in my neighborhood because "[i]n response to the recent explosions in the Merrimack Valley, the Massachusetts Department of Public Utilities ordered all gas utilities to halt the tying in of new gas mains to the existing system".

I also saw some recent numbers on the repairs from channel 25.

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

2
An update courtesy of my alter ego BigInch:

There has been some further developments since. A criminal investigation that was opened as of Nov. Hard to believe that nobody looked at a PID before cutting in.

https://fox61.com/2018/11/01/feds-open-criminal-pr...

NTSB has also issued a Safety Recommendation in response to their initial investigations of the Lawrence disaster.
(https://www.ntsb.gov/investigations/AccidentReport...)

It advises that only registered professional engineers (PEs) be allowed to work on utility facilities.

There has long been exclusions for PE requirements to work on utility installations in many states. Massachusetts being one. Texas another.
This accident resulted in my opinion from extremely bad engineering practice, well almost none exactly, plus again in my opinion, a poor design.

It also prompted me to write to NTSB.

==========================================================
As a former Texas P.E, now retired, but having worked a lifetime in pipeline design engineering, construction and operations worldwide, I could not agree more with NTSB's recommendations as recently expressed in "Safety Recommendation Report: Natural Gas Distribution System Project Development and Review (Urgent)" [doc number PSR1802]. Specifically I could not agree more with the cautions that NTSB expressed therein, to use only qualified professionals and the recommendation that Massachusetts eliminate the exception requiring a competent registered professional engineer, authorized within the jurisdiction, to approve utility plans. Frankly, in my opinion, that accident was the result of complete incompetence. I would say engineering incompetence, however there appears to have been no engineer, even of minimal experience, involved at all. Alignment sheets at best show only the location of pipe and components. They do not typically show any control interrelations, as for example as would have a set of PFD and PID drawings. In fact, alignment sheets do not even show the direction of flow. Those facts alone should have been obvious even to a most inexperienced pipeline engineer and that is something I find of grave concern in itself.
I also believe the practice to which NTSB refers of Massachusetts making an exception for utility work in the face of their typical P.E. seal requirements for other types of work, and often on facilities that present a far lesser danger to the general public, is extremely common. I am sure it is not only Massachusetts that allows such serious exceptions to public safety to go unhindered. Take a look at TEXAS. Which brings me to my first question. Do you plan to advise all the state engineering license boards of the NTSB recommendation that PE seals be required for utility planning?

Furthermore I note that the resulting pressure in the pipeline damaged in the corresponding accident investigation was at some 12 X operating pressure. That makes me wonder how a pressure regulator, apparently designed to open more when downstream pressure goes low, thus increasing downstream pressure basically unhindered, came to be installed into a system where a change to plastic material and apparently a lower MAOP, would most certainly result in overpressure of that downstream piping. Such an installation would normally have to also provide at least one safety feature, if not both of the following,
1) A maximum pressure override, closing an immediately upstream block valve, set to the lowest of MAOP of the lower rated pipe, or MOP of the downstream system,
2) At least one relief valve set to the same
I would have insisted on providing both. Obviously a regulator set to open, potentially increasing pressure to mainline levels, would not have provided a safe design to supply a low pressure distribution system.
I am very much pleased to finally see movement towards actually requiring professionalism in utility design and planning. Long overdue. Thank You

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

It's truly incredible that they didn't realize the regulator sensing lines were located in the header they were abandoning.

Do we know if there was a relief valve located downstream the regulator (hopefully sized for the max flow of the regulator) that didn't work for some reason? Or was the low pressure distribution system really only protected by the pressure regulator?

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

I mostly agree with LittleInch, with some clarifications.

It is remotely possible that the physical / mechanical design of the revised piping system was reviewed by an engineer, but the procedure for upgrading the piping ( specifically the sequence of construction events) was not . The requirements for such upgrades that effect the public is that both the design AND construction procedures be reviewed by a PE.

The wording regarding utilies use a PE for all work might complicate the normal plant maintainance and repair procedures that occur daily 'within the fence" of a utilities' industrial facility is not likely to be accepted by the owners of large facilities that do not directly affect the public.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

What is MAOP? Sorry.

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

Maximum Allowable Operating Pressure.

Can be the same or lower than the design pressure but it the agreed limit of pressure that a pipe can sustain without risk of damage or permanent strain and to which protection devices should be present to prevent the operating pressure exceeding this pressure.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

From my inbox this morning from NSPE...

Quote:

I've got an exciting opportunity for you!

For more than 100 years, one of the most fundamental challenges faced by supporters of professional engineering licensure is the issue of state and territorial licensing exemptions in areas such as industry, government, and other areas of professional practice.

A pair of bills in the House and Senate (H.R. 2139 and S.1097) seek to the end the engineering license exemption for public utility pipelines. The bills are a federal response to the Merrimack Valley, Massachusetts incident that occurred in the fall of 2018, when over-pressurized gas pipelines exploded, destroying several homes and killing one person. This legislation is an important step in our fight towards ending licensing exemptions.

Express your support for H.R. 2139 and S. 1097.

NSPE's Government Relations staff has been hard at work to end engineering license exemptions, and we need your help to ensure this legislation goes through.

Ask your elected officials to support H.R. 2139 and S.1097.
In NSPE's conversations with congressional staffers, we have a lot more influence if we can show them their constituents care about and support this issue.

Contact your elected officials and ask them to cosponsor this legislation.

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

From the limited descriptions online it simply flabbergasts me that a system without a capable PRD at each residence and very limited shutoff capability was ever implemented in a major US city. Its easy to point fingers toward the first visible problem but ultimately the root cause of this disaster IMHO isn't lack of licensing or an incompetent employee as the NTSB reported but rather an unsafe design that likely was approved by multiple PEs in a corporation the size of Columbia as well as various regulatory agencies. Even more troubling is that Columbia's president also appears to have come up through their engineering dept and should've known better.

It appears that Mass has given oversight for the utility to a private engineering firm. Given the NTSB recommendations pushing bureaucracy rather than technical expertise and safety, it would be rather ironic if these PEs blessed a simple repair of the system without significant safety upgrades.

https://www.bostonherald.com/2018/12/18/massachusetts-dpu-puts-columbia-gas-under-engineering-firms-oversight/

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

I agree with CWB1. It should be common sense for any engineer, that knows what they are doing, to install positive protection in the form of a relief valve immediately downstream of a pressure control device, when such device is connected to a system of lower maximum allowed operating pressure. My guess is that the key words are "know what they are doing". I would say that means NOT simply installing a pressure control valves, or a shutoff valve, any of which can easily fail, be disconnected, or have it's pressure sensing lines disconnected, as what happened in this Lawrence accident.)

A lot of the regulations, codes and standards mention "protection" of downstream lower pressure systems, however the only regulation that I can find which specifies exactly how these (distribution) systems (or any higher pressure system) must be connected to a lower pressure system is Alberta, Canada's "Technical Standards and Specification Manual for Gas Distribution Systems". Relief valves discharging to atmosphere at a safe location are specifically required by that technical standard. I uploaded a copy of that standard here, in case the online document disappears some day. I pointed the red arrows to the Relief Valves in the diagrams, as shown on page 33-37.

Protecting low pressure systems from high inlet pressure by discharging any overpressure to atmosphere, or in the case of liquids, an atmospheric tank, at a safe location is the way to stop killing our clients and blowing up their homes and businesses. Alberta got it exactly right in their standard. We all can get this right, P.E. or not, now that you have access to this document. Why PHMSA hasn't managed to get it into the US regulations, or why it is not required by ASME B31.3,4 or 8, or all the rest of the codes and regulations that purport to govern design of similar systems, is inexcusable ... IMO. Anyway, now we all know exactly what we should do. Thank you Alberta.

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

ax1e, I haven't worked on the distribution end so cannot speak to regulation there, however I did design gas drilling and production equipment for a few years and can attest there are a number of regulations governing gaseous systems' safety in the American oilpatch. Unfortunately I cannot point to specifics thanks to a lousy memory and an excellent regulatory team translating the legal-eze and doublechecking our work, however I do recall the location, sizing, and redundancy of PRDs and shutoffs being critical requirements to prevent catastrophic failure. Granted, the oilpatch is heavily regulated between the EPA, OSHA, and other agencies but its still difficult for me to fathom this distribution system being approved and implemented as described online.

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

In my experience, US included, the existing regulations are not specific and it is common to see pressure reduction installations with the only form of safety being provided i.e. one, or more shut-in valves, i.e. no positive overpressure protection in the form of relief to atmosphere or tank. It is also routine for oversight agencies to approve a X2 shut-in valve system. I cannot explain it. The Lawrence disaster is the reason why I can't.

When designers are questioned on why, the typical responses are
1. Costs too much.
2. No room for a tank
3. No safe area nearby, no existing flare system
4. Its low pressure
5. I put in two dedundant shutoff valves

The first 4 are rather self-explicitory, however faulty they may be. As for the last, it appears to be a commonly held belief that redundancy somehow can increase the safety of an unsafe system to acceptable levels. Did you hear that right? Yes, similar to the "lightning never strikes twice in the same place" logic, that often comes with a lack of a deference to the Bayesian probabilities (formerly referred to as Murphy's Laws) that seem to be ever present in these types of "situations", but seldom, if ever, appear in supporting calculations documenting a system's ability to meet probabilistically acceptable safety levels. Here there were a number of factors that came together, poor original design, locating sensors far from protective device, no 100% positive pressure vent, lack of proper as-built drawings, insufficient experience of rework team, age of system and maybe a few others too, that increased the risk of this accident's probability.

Bayesian probability might be better suited to predict this, in that if one shutoff valve fails, it wouldn't be a great leap to expect that another one just like it would also fail, thus having two would not be providing much of any higher level protection at all. So the lesson is, if you do believe in the "two is better" philosophy, at least make the two different; use a shutoff valve and a relief valve, which points us back "common sense engineering experience" and the Alberta requirement.

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

I am surprised at the various comments that suggests that there are no fixed regulations of natural gas pipelines and their distribution to consmumer piping in the US. Each and every state has defined statutes that in turn reference federal regulaions, ASME codes, and NFPA codes that must be met, and in turn each of these codes rigorously define the required protection against overpressure . See US 49CFR part 192, or asme B31 series , or NFPA 54 nat'l fuel gas code, for example.

I did not read the Massachusetts final report, but it seems that there was inadequate supervision of the construction processes that led to the lack of overpressure relief during the system upgrade. Its possible that both the original system and the final upgraded system would have met code requirements, but that the process of trasnforming the system from the 100+ yr old legacy system to the modern higher pressure distribution system was flawed and not correctly managed.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

"the process of trasnforming the system from the 100+ yr old legacy system to the modern higher pressure distribution system was flawed and not correctly managed". Totally correct.

Nobody is saying that there are no applicable codes and regulations. There are regulations, but they are too inspecific on this topic.

CFR Title 49 Part 192 is the Federal regulation that governs "TRANSPORTATION OF NATURAL AND OTHER GAS BY PIPELINE: MINIMUM FEDERAL SAFETY STANDARDS". In 49 Part 192 Section 195 through 197 you can see exactly what they say about overpressure protection. https://ecfr.io/Title-49/pt49.3.192#se49.3.192_119...

Note that in SS 195 there is nothing more required than to provide suitable "pressure relieving or pressure limiting devices". SS 197 is slightly more specific, and in fact actually mention a redundancy requirement. If you are at less than 60 psi[g], all you need is a suitable regulator. If you are over 60 psi[g], you have some options, see Paragraph c1, where two regulators and a "safety device" inbetween, limiting pressure delivered by the upstream regulator, must be provided.
Now the rub there is ...
"This device [inbetween] may be either a relief valve or an automatic shutoff that shuts, if the pressure on the inlet of the service regulator exceeds the set pressure (60 p.s.i. (414 kPa) gage or less), and remains closed until manually reset."
In paragraph c2, a "service regulator and a monitoring regulator" are allowed. Two very similar devices.
Not until you get to paragraph c3 do you find the last option,
"A service regulator with a relief valve vented to the outside atmosphere,"
IMO, if you are going to require something, require the safest solution. Why is it the third option? Order of preference? Not mine!
The last two options in fact, IMO are the better ones of the 4 listed, but I still believe 3 can't be beat.

In the USA, there are only options. A man with two watches never knows the time. The relief valve venting to safe location is not even first on the option list. 1 and 2, not so safe. Option 4 might have worked, but still no venting possible if that valve didn't close. I believe that if the USA requlation was worded exactly as is the Alberta regulation, the Lawrence disaster would have been avoided.

If anyone knows of any specific laws, codes or regulations, international, country specific, US federal, state, city or otherwise, addressing this topic, I would be very pleased if they could post the reference here. Thanks.




RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

AX1E;
Each is entitled to their opinion, but providing a full capacity relief valve in the tens of thousands of applications of consumer gas pressure letdown stations would be distributing a massive fire risk . I think the vast majority of cases use the combination of a fast shut off valve + dual press red valves in series + a "leakage" relief valve + pressure switches to avoid the major fire risk, and that design has proven to be effective and prudent . Simply imagining the safe venting of such large relief valves in urban settings boggles the mind.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

"relief valves in urban settings boggles the mind". I'll add that to my list of excuses.

What is a "leakage" relief valve? Why would that not require a safe location?

Large meter stations delivering gas from interstate pipelines, especially those that feed Class 3 and 4 locations, are where they are most needed. I don't believe that there are so many of those stations that it would make the requirement prohibitive. Furthermore these stations are usually located on the fringes of the cities that they serve, because as you recognise, they do need to create a controlled space to have a safe vent location to atmosphere. As such they would be entirely feasible to install. The billion spent on repairs here would have bought a lot of them. It turned out to be a false economy, no doubt the result of the desire to please shareholders willing to risk somebody elses life, limb and property. Pipelines need to "change the chip". That is the reason why just about everyone is fighting pipelines these days. They just don't get it. The public does. They have had enough.

And this happened before Lawrence.
https://www.metrowestdailynews.com/news/20180228/e...

That link only works on my tablet. I'll upload a pdf.

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

After years of use, virtually every throttling valve eventually develops leakage, usually minute amounts. If the downsteam low pressure system does not have any relief valves, then even a small throttle valve leak will overpressure the downstream system under zero demand situations. Therefore a "leakage " relief valve may be used , perhaps sized for 1% casualty flow to address leakage thru the 2 press red valves (in series).The venting requirements of a 1% casualty flow releif valve is much easier to implement than a 100% casualty flow relief vent.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

OK. While it should work for small leakages across a damaged valve, it wouldn't be much help during a regulator, or snap action valve failure scenairo.

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

The code-required system design would imply that 3 simultaneous failures to occur in order to overpressure the downstream system, which is an unlikely scenario.. Once again:
-2 independent pressure regulators in series, plus a
-fast acting ( 1 sec stroke period) stop valve, hardwired to a
-pressure switch with required calibration schedule
-usually a leage relief valve is considered as well.

This avoids the fire hazard of a full capacity relief valve

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

Yes we can do the calculations. However today's experts recognise (Nissam Nicholas Taleb, author of "The Black Swan: The Impact of the Highly Improbable" and four other works on the subject) that there is a big problem with calculating the probability of "extremely low probability" events, stating that data on events which happen so infrequently are equally as rare, therefore we con't accurately describe how frequently they really can happen, unless you have managed to obtain infinite data. Apparent knowledge of probability is porportional to the number of times an event has appeared in the data. As its appearence decreases, error margins increase. That's how "extremely low probability events" still manage to happen. What to do? The experts warn that, even though it is acceptable to use the theoretical equations when consequences are limited to acceptable outcomes, there is extreme danger inherent in using them when predicting probability of high consequence events. Use the equations to justify one shut-off valve for a single connection to your house??? Use the equations for the $5 black jack table (and you'll still lose 5% on the average BTW). But do NOT use them when you've got a whole city of people to protect. Make a risk-consequence matrix. Redbox the unacceptble results. Pick the acceptable mitigating solution. Basically my take is, if you can do anything to avoid unacceptable events, DO IT!. Making it impossible is just .... so much safer. Unfortunately it is easy to see only in hindsight.

RE: Multiple structure fires sparked by suspected gas line failure in towns north of Boston

good luck with that.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Resources


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close