I'm on a mission to grow my passive income so that it can eventually cover my expenses. I'm making steady progress each month by reinvesting my passive income into buying more income streams.

Pipeline stocks are one of my top sources of passive income. I recently used about $280 of my dividend income to buy a few more shares of leading pipeline companies Enbridge (ENB 0.01%) and Kinder Morgan (KMI -0.24%). Here's why I continue adding to my positions in these premiere passive income producers.

A well-oiled dividend-paying machine

Enbridge currently yields 7.2%. That's several times higher than the S&P 500's 1.6% dividend yield. That prodigious payout is on a very sustainable foundation, which is why I recently spent about $145 to buy another four shares. That will add roughly $10.50 to my annual dividend income stream. 

The Canadian energy infrastructure giant generates very steady cash flow backed by long-term contracts and government-regulated rate structures supporting its pipeline and utility operations. Meanwhile, it pays out a reasonable percentage of that stable cash flow to shareholders in dividends (60% to 70%). That gives it a nice cushion while allowing it to retain billions of dollars in cash each year. 

Enbridge further supports its payout with a strong investment-grade balance sheet. It currently has a 4.6 leverage ratio, putting it at the low end of its 4.5-5.0 range. That gives it even more financial flexibility.

Enbridge has about 6 billion Canadian dollars ($4.5 billion) in annual funding capacity between post-dividend excess cash and balance sheet capacity. That gives it the funds to invest in new expansion projects, make selective acquisitions, and repurchase stock.

The company currently has CA$17 billion ($12.8 billion) of expansion projects in its backlog. Most of its expansions support lower carbon energy, including natural gas pipeline expansions, renewable natural gas projects, and offshore wind farms. Enbridge's extensive expansion project backlog gives it lots of visibility into its future growth. The pipeline giant anticipates it'll grow its cash flow per share at a 3% annual rate through 2025 and by around 5% per year over the medium term.

That should give Enbridge the fuel to continue growing its dividend. The company has increased its payout for 28 straight years. 

On an extremely solid foundation

Kinder Morgan's dividend currently yields 6.6%. That big-time payout is on a rock-solid foundation. That drove my decision to invest around $135 to purchase another eight shares, adding roughly $9 per year in dividend income.

Like Enbridge, Kinder Morgan generates very stable cash flow backed by long-term contracts and government-regulated rate structures. The natural gas infrastructure giant pays out a conservative portion of that steady cash to shareholders (its dividend payout ratio should be around 53% of its $4.8 billion in distributable cash flow this year). That allows Kinder Morgan to retain lots of cash to fund expansion projects, repurchase shares, and strengthen its balance sheet. 

Kinder Morgan expects to invest about $2.1 billion on expansion projects this year, which include natural gas pipeline expansions, renewable natural gas projects, and a carbon capture and sequestration project. These projects are part of a $3.7 billion backlog of primarily lower-carbon expansion investments. They should help grow its cash flow in the future, giving Kinder Morgan more money to pay dividends.

That spending level will enable the company to retain additional cash for debt reduction. Accordingly, Kinder Morgan currently expects its leverage ratio to end the year at 4.0, well below its 4.5 target. That gives it tremendous financial flexibility to capitalize on new investment opportunities as they arise.

The company's growing cash flow and strong financial profile also enable it to increase its dividend. Kinder Morgan delivered its sixth straight year of dividend growth earlier this year. That upward trend should continue. 

Excellent income stocks

Enbridge and Kinder Morgan pay high-yielding dividends that they back with rock-solid financial profiles. They produce more cash than they need to cover their big-time dividends, giving them the funds to continue expanding while maintaining strong balance sheets. That will give them the fuel to continue increasing their payouts. I want more of those growing dividend income streams in my portfolio, which is why I keep boosting my positions in these high-quality pipeline stocks.