HOW MANY TIMES REPAIR IS ALLOWED IN PIPE INDUSTRIES….?

 

HOW MANY TIMES REPAIR IS ALLOWED IN PIPE INDUSTRIES….?

·         In stainless steel, and primarily depending on the family of the stainless, the number of repairs should be kept to a minimum.

·         I, too, am not aware of any Code that specifically limits the number of repairs before the part is scrapped, but I could be wrong.

·         I think that should be decided beforehand by the Engineering Dept. of the fabricator.

·         For example, a 304 material would withstand more repairs than a 2205 Duplex.

·         A lot of the answer would be determined by the grade, and the extent of the repair.

·         The drawback of many repairs to stainless is the number of thermal cycles it is exposed to different families of stainless react to numerous thermal cycles differently.

·         Depending on the extent of the repair, the stainless can experience excessive grain growth, sensitization, and in some cases, sigma.

·         None of these are good. Numerous repairs in the same area can accelerate these problems if not careful.

·         Generally, carbon arc gouging of the area of the S.S. is not recommended due to the possibility of carbon impregnation in the base metal.

·         When speaking of repairs to S.S., one needs to consider if this a new fabrication or a piece that has been service for an extended time.

·         Too many circumstances need to be addressed before determining just exactly how many times it can be repaired without degrading the part.

·         Generally speaking, the number of repairs to a S.S. should be kept to a minimum and careful procedures should be observed.

·         In my opinion, each repair should be decided prior to any fabrication.

·         To just say that 3 weld repairs is acceptable is not always the best approach.

·         At FMC, Inc. it was the Engineering Dept. that set the number and it was incorporated in the QC Manual.

·         We also incorporated the applicable WRP (Weld Repair Procedure) in each weld package along with the PQR and WPS for each grade of steel.

·         Naturally, each WRP differed for each grade of steel, (stainless steel, low alloy steel, carbon steel, etc.)

·         We would use the same repair procedure and allowable number of repairs for new construction the same as for old weldments, which I never agreed with.

·         Like you mentioned, grade of steel, weld process, extent of repair, the service the weldment was exposed to, and the type of repair should all be considered independently.

·         In our metallurgical lab there was a number of analysis done on multiple repaired weldments.

·         We found that Duplex 2205 would not stand the multiple repairs that a 304/308 could stand, due to the possibility, or probability, of sigma formation.

·         There were many studies done, but the findings were not published, but kept "in-house" for the company welding dept.

·         In spite of the findings, the number of allowable repairs remained at 3.

·         3 sounds about right although I have worked several stainless steel jobs (both 304L & 316L) and never had I seen a weld repaired more than once thru radiographic examination.

·         I have noticed though that the repair areas certainly did not weld the "same" as a new weld so I would guess that there is some carbide precipitation going and multiple repairs of the same area would not be a good thing.

·         Even when a weld was cut-out and the same fitting re-used. The weld puddle seemed resistant and it was required to let the metal cool down (a lot more than a new joint) to produce a sound weld.

·         But you know, when an examiner determines a weld (to be good), he/she simply signs off: "Acceptable" and you never hear about it again.

·         For aerospace applications, it is not uncommon to have repairs prohibited. This typically applies to Class A and sometimes class B welds. When repairs are made, D17.1 denotes: "Repaired parts shall not be considered to fully meet engineering drawing requirements.