Q & A > Question Details
While working as an inspection engineer I faced some questions which answers are not clear to me. Please help me in this regard:
1. We are taking thickness record as per previous locations. I want to know how the locations are selected to record thickness on the pipe lines.
2. Sometimes we found higher thickness from the previous record. In this condition we recheck the thickness. Is there any alternative or tolerance limit?
3. How the retiring thickness of the pipe line is calculated?
4. Is there any suggestion while inspection of pipe line commenced?

12/12/2012 A: Ricardo Correia, Portugal, jrmc1977@gmail.com
1. You should create an inspection procedure, based in API 510. for example in a turn should have a TML, with 3 points to read thickness, 2 outside and one inside. Building and understanding the procedure is crucial.
2. If the difference is low consider the lowest, if the difference is large search around if you see any other low value, if not consider a mistake of reading.
3.see API 510. But you have to now your corrosion rate. I recommend you you create for example 3 levels of alarm.
4. start with the more predictive corrosion lines. Watch out for CUI, a inspection of a line with this problem is effective if you remove all the insulation.
21/07/2011 A: Sudhakara Babu Marpudi, Dangote Oil Refinery Company, m_sudhakarababu@yahoo.com
Loss of thickness in the piping / equipment is mainly caused by corrosion and erosion. One need to identify the Key corrosion loops tracing the P &IDs of MOC (material of Construction). Key corrosion loops helps in identifying the locations desirable for thickness monitoring. Generally good designs takes care of both corrosion and erosion by providing corrosion allowance and specifying errosion resistant material of construction. In case a unit decides to improve upon the profitability by moving away from the design window, a dedicated corrosion control program is advisable. We have used a TRIPOD team (members of Technical, Operations and reliability) guided by Corrosion experts towards this objective.
04/07/2011 A: Ashfaq Anwer, Engro Fertilizers Limited, ashfaqanwer@gmail.com
1. You must follow the guidelines as provided in API 570 for inspection of piping. There has been listed a criteria for selection of TMLs (Thickness Monitoring Locations). You must comply with those guidelines.
2. There is no such thing like tolerance limit. You need to fix the TMLs first and repeat your thickness on the same spots for correct data assessment and corrosion rate calculation.
3. Retiring thickness can be calculated by using the formula t = (P*D)/(S*E)
4. Inspection of pipelines must be performed in line with the applicable codes & standards. A complete integrity program has to be developed to monitor metal loss, health of cathodic protection, coating / wrapping etc.