welding on live High pressure steam pipe

Date 03-09-2003 21:19

Joe, when you have your thickness readings you`ll see just how critical your hot tap weld will be. If you have access to API 2201 publication it gives requirements for preperation for welding of hot-taps.If I remember correctly any wall thickness over .500 wall is considered to be very low risk and minimal testing is required.UT thickness readings,engineering calculations due to the 750f operating temperature "to set the maximum amps"PT,UT flaw detection for lamination ,brinell hardness and a good exprienced welder at the helm. I did the inspection work on 4 full encirclement split tee`s recently that was 10"sch. 10 304ss and was under 3/16 thick ,it required the above nde a practice coupon to set the maximum amps and extensive engineering calculations before approval .We were a little worried, but it all came out just fine. In this case the temp, fluid and flow in the pipe was calculated and it was determined that rapid cooling of the weld area would protect the metal from burn through. I know what your going through,you can never be too safe when it comes to a hot-tap.If you are the inspector representing the contractor performing the welding ,refuse to make the weld untill they meet your requirements.A proceadure should be written for this weld and signed off by engineering due to the heat and age of that line.The reason for all this is to protect yourself from liabilities and the biggest of all is to protect that human life behind that hood.I know, I`ve been behind that hood sweating it out many times myself!!! Good luck and let us know how it turn out.

By jwright650 (*****)

Date 03-10-2003 13:41

I don't envy anyone who has to do a hot tap. It sounds like it could be very dangerous if the welder doesn't know what he's getting into. I agree with testing the areas well to be sure all the facts are known before starting. UT thickness guaging will help with determining how deteriated the wall thickness is or if it is laminated. Sounds like you are researching well and on the right track.
Good Luck with your project,
John Wright

By joe valdez (*)

Date 03-14-2003 15:57

Thanks old buddy, see my latest comments on the issue

By joe valdez (*)

Date 03-14-2003 15:56

Hi there:
Thanks for your comments you are correct in all aspects, and may I add these additional comments as an update status after raising key fundamental questions (taking API 579 fitness for servicecode&API 2201&API570) such as:
1)Above codes direct metallurgical engineer to perform PMI(possitive material ID) API 579
2)API 2201 suggest that hot tap machines be tested prior to utilization(common sense and required for field risk assesment)
3) Codes also suggest that PMI results are considered to match proper welding procedure.
Our design engineers didn't think this through properly(poor engineering)
as ussual they ignored qualified AWS inspector advises untill such a point when I refused to run with their program.E mail was circulated to all stakeholders including Lead Mechanical Engineer who then promptly called a meeting to discuss this potential hazardous issue . The outcome vindicated yours truly with the followin action plan to follow:
1) PMI to be conducted. results to be evaluated 2)tack test with 2 "bead on carrier line at 12 oclock and 5 clock 3)Dry MPI,if all is ok proceed welding stub (SA 106B) 4) Check with Hot tap contractor if they have proper machine that has 650 PSIG and 800deg F ratings(currently they will have to re tool in order to perform our hot taps)
5)Use clamp on sleeve with reinforcing bar ,this will provide an additional measure of safety( cantelever ) instead of split sleeve reinforcement pad that may split alon seams. 6) Prior to installing sleeve,metallurgist suggested buttering sleeve area with7018,,(debatable) .
Regards
Joe Valdez

By insp76

Date 03-16-2003 00:33

By insp76

Date 03-16-2003 00:51

Well Joe, I must say congradulations on sticking to your guns and getting that engineer up off his rear and openning up his eyes to a critical situation. All of your nde requirements are definately warrrented and should be adressed.Your welders will rest a little easier while making that weld. It`s a shame it takes drastic measures such as refusing to perform the welding to get the nde required to take on the job.In my opinion the cost of the nde is the main issue. I know myself because it`s a constant battle where I work.

By G.S.Crisi (****)

Date 03-11-2003 20:26

In first place I must say that, not being English my mother language and not living in an English speaking country, I didn't understand some of the initials and expressions Joe's used in his message. What do PMI, MPI, Hot Tap and UT Lam mean?
Second, I've checked into a couple of reputable metallurgy books here at Mackenzie U.'s library, and they agree that graphitization starts taking place at temperatures over 840 ºF (450 ºC), so Joe shouldn't bother about it.
What Joe should bother about is creep, which, according to the mentioned books, starts at 660 ºF (350 ºF). Also according to the books, carbon steel (and A-106 Gr B is a plain carbon steel) starts loosing its tensile strength at 700 ºF.
From these information we can deduct that the material was wrongly chosen since the beginning. They should have chosen a CrMo steel. Now, frankly speaking, we can also deduct that if the piping didn't bust nor showed any creep after 25 years, it won't do that in the future.
I agree with the metallurgist in using an E-7018 electrode to weld the coupon. The coupon should be of the same material than the pipe (carbon steel). So, why use a 0,5 Mo eletrode to weld together two pieces of carbon steel?
Giovanni S. Crisi
Sao Paulo - Brazil

By jwright650 (*****)

Date 03-11-2003 20:36

What do PMI, MPI, Hot Tap and UT Lam mean?

I'm going to take a stab at some of these.

PMI( he said was a "positive material identification")

MPI( I think he means "Magnetic Partical inspection" or MT as we call it.

Hot Tap ( I think refers to performing this repair with a live pipe or one that is still in service)

Ut Lam ( I think he's referring to Ultrasonic Inspection for laminations or UT as we call it.)

Well, How'd I do?
John Wright (a structural guy not a piping specialist)

By DGXL

Date 03-11-2003 21:27

Your hired, grab your hood and don't burn through the pipe.

By joe valdez (*)

Date 03-14-2003 16:02

Excellent you passed the exam

By colins

Date 03-13-2003 17:01

I agree with you Giovanni, graphization is not the main concern, creep is or at least should be. It may be a good idea to perform field metallography and have the microstructure looked at.
Joe, as you are the inspector, and the one who will be witnessing all of the work, it is critical that you are comfortable in performing this work and being witness to the welding.

I myself tend to error on the side of caution, all it takes is one missed step or a mistake to turn this operation deadly.

In regards to performing the UT lamination scan , i think it is a good idea.
However, a regular off the shelf transducer most likely will not work, you will need a high temp probe for any real accuracy.
If i was in your shoes i would sit down with your Engineer and work through this procedure and come to some kind of mutual agreement before any work starts.

Colin

By joe valdez (*)

Date 03-14-2003 16:00

Hi There old Pal,
You are doing ok,l API 579 points out that at 800 deg Fplus , is the point at wich graphitization is a concern.

By TimGary (****)

Date 03-12-2003 02:34

Please forgive my ignorance as I don't have experience with hot taps, but I was wondering about the mechanical taps I've heard about. Could you possibly use one of these instead of doing hot work?
I know that hot taps are performed every day, even on much more dangerous systems, but it still seems a bit crazy to me...
I have a friend in New Orleans that works as a welder for the gas utility department. He performs hot taps on live 200-PSI natural gas mains pretty often. He does them very primitively. No Lam Scan or other inspection work. He Just smacks the pipe with a hammer, and if it doesn't break through, he starts welding. He uses an oxy fuel torch (OAW) and fluxed filler metal. He said that the tricky part is that when he blows through, which seems to happen pretty often, the gas pressure blows out the torch, causing him to have to re-light the torch and close the hole by buttering it in with more filler metal, all before the ditch he is lying in fills with gas and blows up. His predecessor was killed in this manner. At first I didn't believe his wild stories, but as I got to know some of the people he works with, they all told me it was true.
As for me, I can think of lots of better ways to make a living.
Anyway, good luck with your project and please educate us all on this interesting subject by letting us know how it comes out.
Tim

By jwright650 (*****)

Date 03-12-2003 12:36

Looks like you would want to bolt on a saddle and drill when you are dealing with tapping gas lines, rather than welding. Tim, I agree that seems like a dangerous job for him and every living creature within miles of him.
I'll stick with welding on beams and columns,
John Wright

By DGXL

Date 03-13-2003 00:14

There were many responses to a similar post on hot-tapping. Try looking these up in the archives. Also looked up my old set of specs from Saudi ARAMCO regarding hot taps. Hardness testing was required unless an engineer deemed it not so. This had to be done in writing by the engineer, it was their responsibility at the point of deviation from the standard.

All of the requirements specified in the original post by Joe are part of a hot tap package. Ask the metallurgist if he/she does not mind being present during the operation. He/she may find that this is not required as well.

By the way, for anyone who has never seen a hot tap: Hot taps are performed regularly and safely when all the precautions are taken and the investigation is complete - prior to welding that fitting and punching that hole.

By joe valdez (*)

Date 03-14-2003 16:11

Hi There,Hardness can be conducted as a guide line.Our main concern is graphitization along grainboundaries and fusion lines.API 579.2201 & 570 points this out and also confirms your suggestion that Professional Engineers responsibility such as conducting PMI,risk assesment etc...
Another issue is actual hot tap macne packing ratings etc...
regards
joe Valdez

By G.S.Crisi (****)

Date 03-14-2003 16:29

I don't understand what you mean. If, as you've said above, API 579 points out that graphitization is a thing to bother about when the temperature is over 800 ºF and your's 750, then you shouldn't worry about graphitization, as I mentioned on my first post and Colin agreed.
Giovanni S. Crisi

By joe valdez (*)

Date 03-15-2003 06:21

Hi,
Well in our case,and I failed to mentioned this, operation wasn't sure if this line may have operated up to( or above?) the 800 deg F range,as a result we need to assume a worst case scenario don't you think? or should we trust that line was allways operating at the graphitization edge? and then the PMI issue,should we blindly trust that 20 to 25 years ago this pipe was indeed a SA 106B without proper chemical analysis?
That is the basis of my concerns taking all the above into consideration.

Regards
Joe Valdez

By G.S.Crisi (****)

Date 03-17-2003 19:45

The metallurgy books I've looked into say that for graphitization to occur the material should have worked at 850 °F or more (we can assume that the 800 °F mentioned by API includes a safety margin) CONTINUOUSLY and FOR EXTENDED PERIODS OF TIME.
"Continuously" means 24 hours per day.
"Extended periods of time" mean at least one year.
Is this your case?
As for the material being actually A-106 Gr. B, we can assume that the piping was designed by somebody and that the pipes were bought by somebody. The design documents (isometrics, bill of material etc.) and the purchase order should contain that information.
Giovanni S. Crisi