An annulment erases a marriage and makes it as if you were never in the relationship. The state only allows this option in some limited cases.
The Washington Courts explain when you submit your application for an annulment, you must choose the reason for the request, and it must be something on the application list. If it is not, then you likely do not qualify for an annulment.
There are a few capacity issues that could make a marriage invalid in the state. If you were not mentally capable of entering into a marriage agreement, then you may qualify for an annulment. This could mean you were underage or you were unable to understand the situation. It also includes being under the influence of drugs or alcohol and intoxicated to the point where you did not know what you were doing.
In many of the reasons for annulment, there is the requirement to live together. This is living together by your own choice and not due to force. If you live together voluntarily after your marriage, then it is highly likely you will be unable to get a divorce in many situations.
The state requires that you enter marriage because it is what you want to do. Nobody should force you or coerce you into the arrangement. If your marriage only happened because you were under duress, then you may be able to get an annulment.
If your marriage took place in another state and is illegal in that state, then it becomes illegal in Washington, so you may seek an annulment.
Another situation that will make your marriage invalid is if one of you were already in a marriage with someone else. It is illegal in the country to marry more than one person, so subsequent marriages are not legal.
Lastly, you can seek an annulment on the grounds you and your spouse have a close blood relationship.
Keep in mind, these reasons allow you to apply for an annulment, but the judge makes the final decision in your case.