these are good threads:

http://www.passionatepm.com/blog/corrective-versus-preventive-actions-versus-defect-repairs-pmp-concept-38

Corrective versus Preventive Actions versus Defect Repairs

Other than scope changes, change requests may include corrective actions, preventive actions, and defect repairs.

While changes to the project scope, if significant, may update the project baselines (scope, schedule, and cost performance), corrective actions, preventive actions, and defect repairs should not be used to justify a baseline change.

It is important that any variances from the baselines are noted so as to understand the cause and impact of the variance and to contribute to lessons learned.

Corrective Actions

Corrective actions are taken when the project has deviated from the planned scope, schedule, cost, or quality requirements. Corrective actions are reactive in nature and are intended to bring the project’s performance back into alignment with the agreed-upon project baselines.

Preventive Actions

Preventive actions are taken when the project is trending away from the planned scope, schedule, cost, or quality requirements. Preventive actions are proactive in nature, based on a variance and trend analysis.

Preventive actions are intended to ensure the project is delivered in alignment with the agreed-upon project baselines.

Defect Repairs

Defect repairs are implemented when the product or deliverable does not meet the documented quality requirements.

Example

You are building a vacation log cabin for Mr. and Mrs. Johnson. You had originally planned to use a small backhoe for the excavation. Once excavation begins, you realize that the small backhoe is not sufficient and you are now behind schedule. Bringing in a larger backhoe would be a corrective action.

As you evaluate the costs to trim out the inside of the house, you determine that based on the cost trending, you could go over budget. As such, you substitute lower-cost interior doors to prevent exceeding the budget. This is a preventive action.

Upon preliminary inspection of the bathroom fixtures, you find that the hot and cold water are reversed. You ask your plumber to fix the plumbing. This is a defect repair.

The larger backhoe, substitute doors, and plumbing fix would not affect the project baselines as you will want to track the variances and document the causes. Generally speaking, the associated costs with these actions would be the responsibility of the performing project organization.

Now if Mr. and Mrs. Johnson opted to have a spa installed on the outside patio and that wasn’t in the original requirements, that would be a scope change and the baselines would need to be updated. Mr. and Mrs. Johnson would be responsible for the costs associated with the spa.

Summary

Change requests can include scope changes, corrective actions, preventive actions, and defect repairs.
Corrective actions are reactive in nature and are intended to bring the project back into alignment with the baselines.

Preventive actions are proactive in nature to ensure the project doesn’t deviate from the baselines.
Defect repairs are used to correct products or deliverables that do not meet the documented quality requirements.

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http://pmstudycircle.com/2012/09/defect-repair-vs-corrective-action-vs-preventive-action/#axzz2GEaAF52b

 http://projectmanagementsolutionsltd.com/main/?p=1143

 http://www.google.co.in/url?sa=t&rct=j&q=defects%20repair%2C%20corrective%20action%20and%20preventive%20action&source=web&cd=8&cad=rja&sqi=2&ved=0CF8QFjAH&url=http%3A%2F%2Fwww.bizphyx.com%2Fimages%2FSupport_Desk-Corrective_and_Preventive_Actions.pdf&ei=TfXbUNxbgvKtB4fIgegC&usg=AFQjCNFVUXCSfIKfy19SynsgdoSmaNLaPw&bvm=bv.1355534169,d.bmk

http://project-management-knowledge.com/definitions/p/preventive-action/

http://lmzr.perso.neuf.fr/notes/capa.html