Derrick A. Jensen
Executive Vice President of Business Operations at Quanta Services
Thanks, Duke, and good morning, everyone. I'll start by saying that we've received so many phone calls and e-mails for an encore performance that I'm doing one more quarter call, but after this call, I'm dropping the mic. As Kip commentary, Jayshree is doing fine and though she is not joining the call today, she has been overseeing the quarter and will be signed in the certification for our filing. She will be delivering next quarter's call notes as I wander around backstage. With that, I'll turn to our earnings release where today, we announced record second quarter revenues of $4.2 billion. Net income attributable to common stock was $88 million or $0.59 per diluted share and adjusted diluted earnings per share, a non-GAAP measure, was a record for the second quarter at $1.54.
Our electric power revenues were $2.2 billion, a quarterly record and a 21% increase when compared to the second quarter of 2021. This increase was primarily due to growth in spending by our utility customers on grid modernization and hardening resulting in increased demand for our electric power services as well as approximately $80 million in revenues attributable to acquired businesses. Electric segment operating income margins in 2Q '22 were 10.6% compared to 11.4% in 2Q '21. The margin reduction is largely attributable to normal project variability. However, margins were pressured somewhat by inefficiencies attributable to supply chain disruptions impacting certain operations and elevated consumables costs.
Despite those headwinds, we were able to deliver double-digit margins in line with our expectations for the quarter. Also included within our Electric segment are our communications operations, which delivered improved sequential and quarter-over-quarter margins, putting us on pace for upper single-digit to double-digit margins for the year. Renewable Energy Infrastructure segment revenues for 2Q '22 were $924 million, a substantial increase from 2Q '21 primarily due to $490 million in revenues attributable to acquired businesses. Operating income margins in 2Q '22 were 8.8% comparable to the 9% in 2Q '21.
Underground Utility and Infrastructure segment revenues were a record $1.1 billion for the quarter 30% higher than 2Q '21, reflecting increased demand from our gas utility and industrial customers as well as an increased contribution from larger pipeline projects. Operating income margins for the segment were 8.1%, 530 basis points higher than 2Q '21. The margins reflect strong performance across the segment, most notably by our industrial operations, which had record quarterly revenues. One below the item -- going below the line item I want to mention is our other income and expense. As I discussed last quarter, we hold a common equity interest in the fixed wireless broadband technology provider, Starry Group Holdings, Inc.
As required, we remeasured the fair value of this investment based on the market price of the publicly traded company stock as of June 30, 2022, which resulted in the recognition of an unrealized loss of $41.7 million during the quarter. While the unrealized loss is significant, we remain confident in the Starry business as well as our scalable wireless platform and see a bright future for the deployment of Starry's fixed wireless technology. And we are not alone in this assessment. As a point of reference, the analyst community has an average price target for Starry above $9 per share. Our total backlog was $19.9 billion, a reduction of $0.6 billion compared to last quarter.
The reduction is primarily attributable to our multiyear MSAs, which saw a reduction in estimated value due to one quarter's worth of backlog turning into recognized revenues during the second quarter. Our 12-month backlog is a record $11.6 billion, a slight increase compared to last quarter, indicating consistent levels of committed work over the near term. With the continued demand for our services and robust activity across all of our segments, we fully expect backlog to remain strong and to report new record levels of backlog in subsequent quarters. For the second quarter of 2022, we had free cash flow, a non-GAAP measure at $14 million compared to $126 million of free cash flow in 2Q '21.
Free cash flow for the quarter was below our expectations, with the shortfall largely attributable to timing on certain renewable contract awards, which typically have favorable cash terms and continued elevated working capital requirements associated with the large ongoing Canadian renewable transmission project driving an increase in contract assets, which we've discussed in prior quarters. Regarding the Canadian renewable transmission project, we continue to work with the customer to address the growing contract asset balance. Expensive schedule delays, primarily due to COVID restrictions and its impact on remote locations of the project have extended production schedules through another build season.
This and other factors have negatively impacted our ability to meet contractual billing milestones and have also increased costs as a direct result. Discussions are ongoing with the customer with the revised build schedule agreed to by both parties. We've engaged in discussions regarding adjusting billing milestones and remain confident in our cost position, a resolution of certain of these amounts will likely extend beyond this year and have impacted free cash flow and will continue to impact DSO in the near term. The estimated impact of these dynamics is currently increasing DSOs by as much as five to six days.
On a positive note, another previously discussed large Canadian electric transmission project that dealt with similar challenges received customer approval for a significant portion of the contract assets associated with change orders during the quarter. The approved amounts were billed during the quarter, and we expect flex in 3Q '22, with resolution of the smaller remaining balance expected by the end of the year. Days sales outstanding, or DSO, measured 81 days for the second quarter of 2022, a decrease of two days compared to the second quarter of 2021 and an increase of one day compared to year-end. The decrease from 2Q '21, was primarily due to the favorable impact of the acquisition of Blattner, which historically operates with a lower DSO than certain of our other larger operating companies.
This positive impact was partially offset by the previously discussed working capital dynamics associated with the two large Canadian transmission projects. As of June 30, 2022, we had total liquidity of approximately $1.8 billion and a debt-to-EBITDA ratio of 2.4 times as calculated under our credit agreement. We expect continued earnings growth and cash generation to support our ability to efficiently delever over the following quarters while continuing to create stockholder value through our dividend and repurchase programs as well as strategic acquisitions. As of July 31, 2022, we've acquired approximately $104 million worth of stock since the beginning of the year as part of our repurchase program.
And in July, we acquired a utility contract in the West that specializes in underground construction. Turning to our guidance. We had a solid first half of the year, and we remain confident in our ability to deliver against the guidance we laid out on our last call. However, the composition of our earnings across our segments is slightly different than our initial expectations, which we believe reflects the benefit and strength of our portfolio of solutions. We continue to see strong demand for the services across our electric segment, and we now expect revenues to range between $8.5 billion and $8.6 billion, a $200 million increase from our previous range.
However, as Duke commented, portions of our transmission operations are being negatively impacted by customer-driven material delays. And accordingly, we're moving labor and equipment to address our customers' growing distribution needs. This shuffling of resources is creating inefficiencies as we also grow headcount, which we expect will slightly pressure margins in the back half of the year. As a result, we now expect margins for the segment to range between 10.6% and 10.8%, still a double-digit operating profile, but slightly below our previous expectations. Our Renewables segment was negatively impacted by the uncertainty on project timing attributable to potential supply chain disruptions.
However, we've seen some improvement in that regard over the last month. We currently see the opportunity for the back half of the year to be stronger with full year revenues now expected to range between $4 billion and $4.2 billion, a $200 million increase from our previous range and operating margins continuing to range between 8.5% and 9%. Our Underground segment has had a great start to the year. Given the solid performance to date and improved visibility into the remainder of the year, we are tightening our full year range of expectations. We now expect full year revenues for the segment to range between $4.1 billion and $4.2 billion, with margins expected to range between 7% and 7.5%, which puts our previous midpoint expectation as the new low end of the margin range.
With regard to free cash flow, we are lowering our full year expectations, primarily due to the Canadian transmission project dynamics we're working through, but also due to incremental revenue growth that will require additional working capital. Accordingly, we now expect free cash flow for the year to range between $550 million and $750 million. Due to the lower free cash flow, coupled with increased interest rates on our variable rate debt, we now expect full year interest expense to range between $120 million and $123 million. In the aggregate, our consolidated expectations for full year diluted earnings per share attributable to common stock are now expected to range between $3.32 and $3.65.
And full year adjusted diluted earnings per share attributable to common stock, a non-GAAP financial measure to range between $6.10 and $6.44. Additionally, we now expect adjusted EBITDA, a non-GAAP measure, to range between $1.64 billion and $1.71 billion for the year. For quarterly commentary and additional details on our financial expectations, please refer to our outlook summary, which can be found in the financial info section of our IR website at quantaservices.com. From a long-term perspective, the tailwinds behind our end markets remain robust. We believe our industry-leading solutions differentiate us from our peers and present management with the opportunity to deliver significant stockholder value through organic growth and strategic capital deployments through 2026 and beyond. I'll now turn it back over to our operator for Q&A. Operator?
