Repairs necessary to restore mechanical integrity to pressure retaining components and modifications made to pressure retaining components in heaters should follow the principles of the design and fabrication codes most applicable to the work. The following issues need to be considered when developing repair/modification plans and implementing them. This is not all-inclusive as other factors may need to be considered for specific situations.
a. Repairs and/or modifications are engineered to meet the requirements of the service including material selection.
b. Weld procedures qualified to ASME Section IX for the material and technique appropriate for the welding that needs to be performed.
c. Welders certified and qualified per ASME Section IX for the procedures to be used.
d. Weld details are defined including any surface preparation, joint preparation, weld joint design, and preheat temperature.
e. NDE techniques to be used and the acceptance criteria. Also, any intermediate inspection hold points need to be defined.
f. Heat treatment requirements for repair welds.
g. Any required pressure testing and the acceptance criteria of the test.
Repairs and alterations made to boilers should be performed to the applicable codes and jurisdictional requirements appropriate for the locality. As indicated earlier, jurisdictions typically define which types of boilers are legislated and the appropriate repair/alteration requirements. Most often, NB-23 will be the code to which repairs/alterations will be performed to for legislated boilers. Where there aren’t any governing codes or jurisdictional requirements, the repairs/alterations should follow the principles of the design and fabrication codes most applicable to the work. Any repairs and alterations need to be considered factors similar to those defined in 14.1 for heaters.
Materials used in repairs should be verified that they meet the materials specified for the repair. This includes, for example, tube materials and welding consumables. Alloy verification is critical to ensure the appropriate material is actually used and installed. Inadvertent substitution with another material can result in premature failure from corrosion, cracking, and stress rupture. Verifying materials often involves testing to show/indicate the proper chemistry. Testing can be accomplished with the use of suitable portable methods, such as chemical spot testing, optical spectrographic analyzers or x-ray fluorescent analyzers. Refer to API RP 578 for additional information on material verification programs.