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Cold Snap 2021 – Why Texas Froze

During the days before Valentine’s Day weekend, the 13th and 14th of February 2021, a severe winter storm came down across North America as the Polar Vortex slipped out of position and brought extremely cold air down from the Arctic and continued south over Texas and down into northern Mexico.
By Ron Merrick

This phenomenon occurs at least once during most winters, but this one was unusually cold and intense and traveled unusually far south. By Sunday morning the 14th, the temperatures were well below freezing across most of Texas. In Amarillo, closer to four other state capitals than to the Texas state capital in Austin, the high was +14°F (-10°C) and the low was +1°F (-17°C).

In Houston, the low was +35°F (+2°C), and was predicted to go below freezing and stay that way for two days. In some years, the temperature in Houston never gets to the freezing point, while in other years there may be a day or two all winter in freezing conditions.

Farther north, record-breaking cold and snow spread across the entire central portion of the U.S. It is a regular occurrence in parts of the upper Great Plains to have at least one snowstorm every year that shuts down interstate highways. In central Kansas the low temperature on that Monday was -11°F (-24°C), which broke a record that had stood since 1899.

While this storm was more intense than average and the temperatures hit record lows in some parts of the U.S., nowhere were the effects as relatively severe as central and southeast Texas. On Monday morning the 15th, the low in Houston was +17°F (-8°C). On Monday night in Houston, the low was +13°F (-10°C). The temperatures only rose above freezing briefly over the next couple days, including an afternoon of freezing rain on Wednesday the 17th. This contrasts with the historical average low temp in January for Houston of +43.2°F (+6.2°C).

For residents of northern and central Europe or of Alberta, these conditions sound like a typical winter’s day. But the effects of these temperatures were very much out of the ordinary for the Gulf Coast. At one point at least 4.5 million people in Texas were without electric power, out of a population of 29 million. At least 24 people are known to have died, with several dying from carbon monoxide poisoning. Some died because of faulty heaters or because of bringing a charcoal grill inside, others died because they ran their car engines in garages trying to stay warm. Several died in house fires. During previous cold snaps, I can remember looking out from a tall building and seeing two or three houses on fire across the Houston area, often due to people trying to keep warm using only a kitchen stove or a small portable gas heater.

Power Outages

The power in the Houston metropolitan area was off in some places for upwards of three days. In my home, the power was off for 20 hours, and a friend reported a power outage of 43 hours. Power supplies started failing on Sunday morning and the power outages reached their peak on Monday.

Fortunately, there was less need than usual for travel on Monday because it was the President’s Day holiday, in which government and banks were closed, although businesses and offices would have been open. A third to a half of the working population is working from home anyway, because of the pandemic.

As of Thursday evening, four days after the temperatures first fell, there were still about 315,000 customers without power out of about 12.4 million customers statewide. The complete restoration of normal power levels in Texas did not occur until Friday of that week.

A consequence of the freeze was that residential water lines began to freeze up. Many older homes and buildings in southeast Texas have galvanized steel piping, made from “furnace-welded” steel pipe with a very low maximum working pressure, and with class 150 malleable iron threaded fittings with no traceability. To avoid freezing, many homeowners learned years ago to maintain a small drip in a faucet on the theory that “running water doesn’t freeze”, and also that if an ice plug does form, the piping downstream of it will be de-pressured and thus the piping should be less likely to rupture.

Piping in most houses runs in the ceilings. When this frozen piping thaws, if there is a rupture in the line, water cascades down and collapses the ceilings onto all of your worldly goods, and sometimes onto the heads of the residents. While it’s possible to shut off the water supply to the house at the water meter, very few people have the skills or the tool needed to do that, nor do they know to store water in their bathtubs or buckets prior to shutting off the water. My house in Houston shows evidence, in the form of two or three repair couplings in the water piping and some scars in the ceilings, that this disaster must have happened to it in the years before we bought the house.

Electrical Service Island

As for electricity generation, Texas remained largely an ‘electrical service island’, as it was the only regional electric reliability organization (ERC, ed.) that roughly coincided with state lines.

Going back to the formation of the FPC, most Texas utility companies agreed with each other not to expand across state lines, only to be regulated by the state of Texas.

Most Texas electric power providers formed into two interconnections, one for north and one for south Texas. The exceptions are the far east and the western tip of Texas.

These interconnects proved useful during World War II, when large numbers of chemical plants and refineries were built in the Texas Gulf Coast, faster than power plants could be built to supply them. Since excess electricity was still available in north Texas, power was sold to these new plants by utilities in north and central Texas through the interconnections.


After the formation of the NERC “North American Electric Reliability Corporation”, (formerly the National Electric Reliability Council, ed.), the Texas interconnect structure was formalized by the foundation of the Electric Reliability Council of Texas (ERCOT) in 1970. The regulatory structure, which had previously been minimal in Texas, was formalized with the creation of the Texas Public Utility Commission (PUC) in 1975.

The PUC has authority over electric, water and telephone utilities in Texas, but not gas pipelines which are under the authority of the Texas Railroad Commission, which regulates oil and gas production, transmission and distribution.

Texas PUC deregulated the Texan electric power market, which was largely accomplished by 1999. The investor-owned utilities were separated into a deregulated power producer market, a regulated distribution market and an unregulated consumer market. The municipal-owned utilities and the rural electric co-ops (which by the 2000s often had significant urban populations) were allowed to continue their vertical integration but were nonetheless part of ERCOT and interconnected with other utilities, selling and buying power to other entities as directed by ERCOT, who actually managed the flow of electric power across Texas. Six of Texas’ largest cities were served by municipal power companies, and there were more than 300 electric co-ops.

Price Pressure

The power generating stations were spun off from their original owning companies and incorporated separately. Their mandate was to produce power for the lowest possible cost. A large number of independent power plants (IPP) were built, almost all with heat recovery steam generators (HRSGs) fueled with natural gas.

Older power plants in Texas had been fired by gas, coal from Wyoming, lignite from mines adjacent to the power plants, and two nuclear power plants, one near the Gulf Coast and one in central Texas, each with two units.
The effects of deregulation, and the downward pressure on prices as a long-term trend, had led over the years to closures of several coal-fired plants and some older, less efficient gas-fired plants.

The basis of power sales in Texas is “energy only”, where the power generator is paid only for power actually delivered to the grid. Another basis for payments to the generating entities is “energy plus capacity”, as used in some other markets. Under this basis, the power generator is also paid for maintaining or building a certain reserve capacity.

Peak Load Power Units Offline

Peak electric loads in Texas have always occurred in the summer, usually in the afternoons in July and August, because of air conditioning. This is the peak load (78,300 mw in 2020) that ERCOT and power generators plan for.
Because of this, power units that are primarily used for peaking rather than base load, are often shut down during the winter, and may be completely offline for maintenance purposes during fall, winter and early spring. In the fall of 2020, ERCOT released a forecast for 2020/2021 winter. Out of 82,300 mw “total resource capacity”, the peak demand forecast for winter was 57,700 mw.

The demand on the electric grid at the height of the freeze was nearly 70,000 megawatts, close to what the maximum demand on a typical summer afternoon is. At its worst, capacity off-line was about 45,000 mw (about 15,000 was from wind power and 30,000 was from conventional power plants).

Water Infiltration

Prof. Jesse Jenkins of Princeton University noted that, early Monday morning at the time the blackouts began, about 2/3 of the power in Texas was coming from gas, and about 40% of that was going offline. Wind power was actually making up much more of the shortfall than ERCOT had expected it to.

What actually happened to specific units will no doubt be thoroughly investigated. But one common theme is water infiltration. Water from rain and from condensation is notoriously hard to control. Condensation is a fact of life in the humid environments of much of the Gulf Coast.

After the 1989 freeze, it was found that one common cause was water in the instrument air lines. Despite that, close to half of the refining capacity on the Gulf Coast shut down because the water in the instrument air lines froze, effectively preventing operation of control valves and much instrumentation.

The effects of freezing in many process plants have been greatly reduced over the years, if nothing else because of the changes from 1989 to now from predominantly pneumatic instrumentation to predominantly electronic.

Fractured Components

The humid air in so many pieces of equipment, like electric motor actuators with poor seals, would have frozen. These items are routinely equipped with small heaters in colder climates but not in areas where the temperature never gets down to freezing. Some components in industrial plants may have actually fractured from the effects of water freezing inside them. Cast iron valves and piping, commonly used for water services, are especially vulnerable to fracturing from water freezing inside them.

Another major issue is lubrication of rotating equipment, as the viscosity of lubricants goes up as the temperature goes down. It’s possible that other causes may be found, including elastomer components and seals, that may have deformed, shrunk excessively or cracked under load because of the low temperatures.

Failure of heat tracing systems, sometimes because they were never tested or inspected before the cold weather hit, would be another root cause of some of these failures, as well as faulty or deteriorated or missing insulation.

Frozen Valves

Valves, especially, tend not to be insulated even though the adjacent piping is insulated. There are good reasons for this practice, but if the temperature in the line is borderline freezing, the valve may very well ice up.

Near the end of the 2011 freeze, an executive with the Lower Colorado River Authority, which operates coal-fired and gas-fired plants and gas transmission lines, along with another coal plant executive, both said that they suspected frozen valves in the gas lines played a role in the failures.

The exact methods of failure, and recommendations, to mitigate or prevent future failures, from the February 2011 freeze was documented by the NERC and the Federal Energy Regulatory Commission (FERC), the successor to the FPC, in a report which was presented to state legislatures for action.

A similar report was issued after the 1989 freeze, and as the actions recommended by that report were not mandatory, very little was done. As noted before, the federal government has no authority to compel ERCOT to take or not take any actions, since ERCOT operates entirely within the state of Texas and is thus only regulated by the Texas state government.

Winterizing Plants

The electric power recommendation portion of this report is as followed. Besides winterizing of plants, including better insulation and more heat tracing, other recommendations included starting of off-line reserve plants a few days before expected cold snaps, so that the unit’s own heat would protect it from the cold, rather than trying to cold-start it when the ambient temperature is already low. Other independent investigations were also conducted locally, with promises from the Texas state government and the Texas legislature that things would be better next time.

During the 2011 Texas legislature session, several bills were filed that would have directed ERCOT to order winterization of power plants, and other measures aimed at preventing the failures of the 2011 freeze from happening again. The final bill, SB 1133, was signed into law June 17, 2011. The recommendations for winterizing never had any enforcement mechanisms put in place.

Governor Demands Action

In 2014, the Texas PUC attempted to institute rules that would require power generators to identify all potential failures, including “weather design limits”. Stiff resistance from power companies caused the proposed rules to be weakened to “only address any failure points that were previously known”.

As of this writing, several members of the board of directors of ERCOT have resigned, mass indignation is processing through the Texas news media, Texas Governor Greg Abbott is demanding action and has presented recommendations to the Texas legislature for emergency consideration.

However, problems that are considered dire when they occur have a way of fading in importance with time, especially when their solutions involve spending actual corporate money, and especially when there is no legal path to reimbursement and no legal path to enforcement. 

Time will tell whether some future journalists will be reaching back in time to 2021 for yet more examples of “what could have been done”.


Several weeks after the freeze, during the hearings on why it happened, an additional reason for the failures was revealed. ERCOT, as the electricity manager, maintains a list of critical customers whose service has to be maintained if at all possible. This list includes hospitals, water treatment plants, and so forth. After the list of recommendations from the 2011 freeze was published, an ERCOT staffer prepared a form for the purpose of requesting this critical status, and sent it to all the natural gas providers (regulated by RRC, not ERCOT) for their compressor stations and related facilities. Only a small fraction of the gas providers ever returned that form, so when electric power was cut to an area containing an unrecorded compressor station, and the transmission of natural gas to an electric power station went down, the power plant went down too.






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Ron Merrick retired after forty-five years as a piping material engineer with Fluor. He remains active on standards committees. Ron resides in in Houston, Texas, and Wichita, Kansas.


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