OTSG Tube Plugging

[eburrell]

I am at a simple-cycle power plant that uses a OTSG to provide steam for turbine steam injection. My history has always been with HRSGs and Coal Boilers, so I am used to higher pressures. This OTSG has a design pressure of 475 psig and temperature of 700 deg F.

The standard practice here is to cap leaking tubes with Swagelok fittings. I have a couple of questions:

1. Is this an acceptable practice? (I would have never done it in a HRSG or Fossil Boiler)
2. Where in the code (ASME) can I find the governing standard/section?

 

[davefitz]

I think you would need to review the nameplate of the OTSG to determine which part of the asme code the OTSG was build-to. It was probably section VIII div 2. Whicever code was used, review the first chapter of that code and that chapter will normally define which standards are to be used.

I have never heard of an OTSG that used swageloc fittings within the pressure vessel, normally those small tubes use an orbital welder to attach a repaired section to the failed section, providing there is enough clearance. I assume this OTSG is recieving hot gases from the exhaust of a CTG and that gas temperature is below 900F if it is an aeroderivative CTG. To prevent creep relief of the stresses in the threads one might need to specifiy the use of inconel or 304H or 316H fittings for an operating temp above 750F, if the code permits.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick

 

[davefitz]

I forgot to add that if the OTSG was built per asme sect I, then austenitic stainless steel ( eg, 304, 316 etc) cannot be used on water washed tubes ( evaporator, economizer) . Inconel or ferritic stainless steel may be options,as are the normal ferritic steels, but I do not think Swavgeloc provides ferritic options, so inconel may be the only swageloc choises is such a fitting is approved "within the setting". The issue is that of hydrogen cracking and chloride stress corrosion cracking.
Swageloc also supplies orbital welding machines, as does other manufacturers.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick