post weld heat treatment

[etrobal]

we need to install (asap!) a tee connection. however, the tee welds will require pwht but we don't have the time as the plant shutdown cannot be extended.

what we did is that we tapered the ends of the tee connection (three ends) to a thickness where pwht will not be needed and proceeded with the weld connection.

is the tapering of the thickness to forego the pwht allowed? is there a code or a standard that says so? is this good engineering practice? what might be the consequences of our action?

our design pressure is 6.6 mpag while design temperature is 282degC. the tee size is 30-inch diameter with a wall thickness of 25.4mm.

thank you.

 

[Cockroach]

Good luck with it. You are risking personnel safety and property damage, so make sure your insurance premiums are up to date.

Do the math: 6.6MPa on a 30 inch bore, what kind of force would you have? 1.0 inch wall thickness; ASME code calls for 0.75 inch and thicker requirement for PWHT. Look at the HAZ following weldament, how do the steel properties change in this localized area?

It's called due diligence.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[unclesyd]

Even though I've seen this done numerous times it was never at your pressures and temperature. This was mainly on CTW and low pressure steam so I would heed the advice from Cockroach along with getting your local jurisdiction on board.

Your OP was a little vague, can you comeback with more information like the pipe run thickness, taper description, tee schedule. etc.

 

[unclesyd]

Forgot to add, what is the material of costruction?

 

[etrobal]

thanks for the replies. really appreciate it.

our pipes came from manufacturers with current api-5L monograms.

the pipe run is a 30-inch schedule 30. i would like to revise my earlier design pressures and design temperatures to 2.14 mpag and 216degC. sorry, the earlier design parameters given to us are for a different pipeline.

tee schedule is 25.4mm thick. we have another connection-in-waiting, in a different line this time, an elbow of 0.875-inch (22mm) thick which is scheduled for tapering also.

is there a rule of thumb for tapering, say 25.4mm from the butt ends, something like that?

can you please quote a book, code (api, asme, ansi, din, jis) standard that i could use to inform management that we are not to use this kind of 'tying loose ends'?

thanks again.

 

[metengr]

etrobal;
First off, you should be using a recognized pressure pipe code like ASME B31.1. or B31.3, etc. Second, transitions need to be evaluated to assure adequate reinforcement (wall thickness) for pipe pressure and external pipe forces. Spend some time to review the suggested pipe codes and decide a course of action.

 

[Cockroach]

EtoBal....are you not the engineer? You need to show a lot more professionalism and do the research for the proper code, standardards and procedures regarding your installation. Is this not part of the design?

Management will push for a cost effective solution every time. As you put it, "schedule permitting". Don't get pushed into unprofessional practice or unseasoned judgement over economics!

Beside the weldament codes specifically state PWHT for 3/4 inch and larger. Your wall thickness is 1.0 inches. Pretty straight forward.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[Gymmeh]

Not to get off topic, I am young and trying to learn more about welding, and reading through this i got a little confused.

Is it common practice to mix English with Metric?

"the pipe run is a 30-inch"

"tee schedule is 25.4mm thick"

"2.14 mpag and 216degC"

Wouldn't it be best to select Metric since Mpa, Deg. C and, mm?

 

[jte]

Pipe sizes are often in inches, even in an otherwise metric system. If the diameters are provided as metric, then they are typically "metric" in name only, with a fairly rough diameter translation. Nobody orders up a 609.6mm diameter pipe.

Don't forget, Mr. Pascal was a real person, and the "P" in Pa is capitalized whether or not it is Pa or kPa or MPa.

jt

 

[etrobal]

thanks cockroach, unclesyd.

metengr, we do use the power pipng code b311 and asme section VIII div 1 for pressure vessels. b311 do not dwell on tapering, only the need for pwht. thanks too.

the stress analysis also do not show any high concentration of stresses, forces or moments at the tapered ends.

need to do some more reading since being the engineer does not necessarily mean i get to overrule my bosses. i need to prepare a memo regarding this practice.

for gymmeh, on metric or english, well, it is still convenience that rules. we are comfortable with this set up. try to find your comfort zone on parameters and you'll find it easy to do your work.

thanks again.

 

[metengr]

metengr, we do use the power pipng code b311 and asme section VIII div 1 for pressure vessels. b311 do not dwell on tapering, only the need for pwht. thanks too.

etrobal;
Here is some friendly advice despite my confusion of your entire situation. Please re-read your quote above and follow the rules in B31.1. You will be glad you did.

 

[etrobal]

metengr, thanks for the advice. appreciate it very much.
am doing just that, reading and rereading the b311 and other codes related to this.

 

[unclesyd]

One of them brain things, a random thought.

In the days of relatively cheap materials it was not uncommon for a supplier of fittings to furnish a fitting that was suitable for one schedule to have the ends turn down to fit a lower schedule, like a fitting with the thickness for Sch 80 and a Sch 40 weld prep or Sch 160 and a Sch 80 weld prep. In a few specific cases that I recall where the line thickness dictated PWHT it was carried out and others where the line size didn't require PWHT none was performed even thought the thickness of the fitting excluding the weld prep would require PWHT.

The expediter of a local fab shop just told me that he hasn't seen very much of this in several years and could recall only one case where there was any question raised about PWHT.

 

[Gymmeh]

jte, etrobal,
Thanks.