In the State of Washington the usual time that a driver is required to maintain an SR-22 is 3 years. The reason that you are required to acquire the SR-22 may change the amount of time you are required to carry it though.
You can be mandated by this state to get a SR22 for a variety of reasons from a driver's license suspension reinstatement due to a DUI, accident without insurance or a second or subsequent offense of leaving a child unattended in a running vehicle, to name a few.
Typically in WA when you are eligible to reinstate your driver license, you must file future proof of financial responsibility, also known as an SR-22, for 3 years from the date you are eligible to reinstate your driver license for that incident.
If you are required by Washington State to file a SR-22 then contact the DMV to find out how long your specific situation requires you to carry this certificate of insurance as part of your policy.
Your can contact the Washington State Department of Licensing for more information. The phone line for SR22/26 insurance certificate information from the WA DOL is 360-570-7040.