Welded Fin tube and NACE MR 0175/ISO 15156 1

[bmoorthy]

A heat Exchanger that uses Finned tubes (Finns welded to the tube).

Carbons steel tube (Tube condition normalized) hardness is less then 200 HV.Tube materila A 179 or A 106 gr b (yes A 106 is a pipe but used as tube in some cases like WHRU and some heat recovery and heater packages).

Finnes are Electric resistant welded to the tubes.

Finns are also carbon steel.

After finning no heat treatment.

1) Now, if the shell side fluid (External of the tube) is subject to Sour fluid ( containing H2S and the temperature is over 170 Deg C and the pressures are nothigher than 15 bars), does the Electric weld on the fin requires hardness examination?? if yes, where and what are the recommendations of NACE MR 0175/ISO 15156?

2) Does NACE MR 0175/ISO 15156 address welding process that employs welding without filler wires?

3) If the tube side fluid is containing H2s, (fins are not exposed to H2S fluid) then, does Fin and the welding come under the NACE MR 0175/ISO 15156 umberlaw?

 

[SJones]

1) Yes because hardness testing can only be waived for welds in tubular products from Table A.2 at the discretion of the user. Since the fin material is not a tubular material from Table A.2, it follows that the weld is to be hardness tested to comply with ISO 15156. The recommendations of ISO 15156 are that hardness testing, for joints other than those shown, has to be developed based on the figures and requirements within the standard. If you need an idea of how to do it, check

http://www.spiro-gills.com/downloads/pdf/spiro-gills-fin-tubing-brochure.pdf

2) Yes, because it does not exclude autogenous welding

3) Yes, because the failure mechanism is related to hydrogen which can permeate from the exposed surface. That's why one also tests weld cap hardness in a pipe to pipe butt weld for example. Since the fin is now contiguous with the tube, it is for all intents and purposes, the tube.

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[SJones]

I hasten to add that the above are my personal interpretations. It is advised to seek official interpretations through the correct channels:

http://isotc.iso.org/livelink/livelink?func=ll&objId=3340364&objAction=browse&sort=name

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[bmoorthy]

Thank you.

I had already written to NACE and since the reply could take as long as 6 months, i decided to check in these forums.

Also what is your view on whether PWHT after finning.