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API 650 tank weld proximity and PWHT requirement in SOUR service

API 650 tank weld proximity and PWHT requirement in SOUR service

API 650 tank weld proximity and PWHT requirement in SOUR service

Hello All,

I need your insight.

We are building a process tank that is designed to API650.

By process, I mean it is not a simple storage API 650 tank and there is many internal plates (kick plates, deflectors etc.) inside tank that are welded to shell for a its process requirements.

Some of these internals welds are coming too close to other pressure retaining welds on the shell such as nozzles/shell weld joint or RF pads welds. API Code does not have any distance requirements for internals nozzles against other welds and is quiet on the subject.

Having said that, too close weld joints always are the root cause of heat affected zones and increase of local hardness. Our service is sour and the plates material is SA-516 Gr60 Normalized and NACE MR0175 compliant.

I am suggesting to the construction team to run PWHT on shell plates after completion of all the internal plates and external nozzle and RF Pad welds are complete to ensure local hardness is reduced and measures low (less than 248 HV or 22 HRC) where weld joints are too close (less than 1" some places).

Pls note, these are not COD plates where PWHT is mandatory. These are Other nozzles where internals seam welds are too close to external welds and I cannot relocate to open up space.

Do you agree with this approach? Am I doing something unnecessary? Please note that the shell plates thk is max 25-mm (1") where for this material group no PWHT is required as per code. I am doing this solely to reduce local harness in HAZ zones where the code is quiet about. Please advise.


RE: API 650 tank weld proximity and PWHT requirement in SOUR service

IMO, may have Material Engineer to suggesta low heat and /or low H2 electrode for the welding fabrication.

RE: API 650 tank weld proximity and PWHT requirement in SOUR service

Review the stipulated exclusions of Table 1 in ISO 15156-2, and see whether you can build a case to be less stringent.

Steve Jones
Corrosion Management Consultant


All answers are personal opinions only and are in no way connected with any employer.

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