Not logged inAmerican Welding Society Forum
Forum AWS Website Help Search Login
Up Topic Welding Industry / General Welding Discussion / Hot tapping of 10" API 5L pipe carrying Jet A1 fuel
- - By Saroj Date 07-27-2016 14:49
Dear all,
I am new here. I have query regarding WPS.
We are doing hot tapping calculation for a 10 inch line carrying jet A1 fuel.
We had based our heat input calculations on WPS provided by client. However pipe inner wall temperature comes to 375 deg celsius as per Appendix-C  in DEP 31.38.60.10-Gen.
Client is asking us to give our recommendations for welding parameters (Current Voltage & Travel speed) keeping in mind auto-ignition temperature of 210 deg celsius for fuel. Welding method is SMAW.
Kindly help at the earliest.

Best Regards,
Saroj
Parent - - By welderbrent (*****) Date 07-27-2016 22:13
Remember, the autoignition temp is calculated as- Definition. The flash point of a volatile liquid is the lowest temperature at which it can vaporise to form an ignitable mixture in air.

Thus,
1) you are not exposed to air while welding the tee member to the main line for a hot tap.  The vapors are the problem.
2) a 10" line has a fair amount of product which transfers heat temps and they don't build up quickly, especially if fuel is also flowing.
3) it takes fuel, heat and oxygen for combustion, fire, explosions to occur.  You are missing oxygen. 
4) this is done every year multiple times around the world and with few problems.  I have done it myself and am alive to tell you about it. 

There are others here with far more experience and knowledge than I in this area.  I'm sure they will be along.

He Is In Control, Have a Great Day,  Brent
Parent - - By Saroj Date 07-28-2016 07:56
Dear Mr. Brent,
Thank you for your clarification.
I would like to know from the members here what should be the recommended values of welding parameters viz. Current, Voltage & Travel speed for hot tapping a 10 inch (6.4 mm wall thickness) API 5L Gr. B Pipe carrying Jet A1 fuel considering a net factor of 0.57 for fillet welds.
Applicable standard is ASME section-IX or relevant AWS standard.

Regards,
Saroj
Parent - By js55 (*****) Date 07-28-2016 13:02
Welding parameters are not your problem. Whether there is available oxygen in the line to allow ignition, as brent said, is the problem. If there is oxygen then you will not be able to get the parameters low enough while still gaining good fusion, IMO. If there is no oxygen then the general Battelle calculation of around 1800F inner surface temp to prevent burn through should be acceptable.
- - By welderbrent (*****) Date 07-28-2016 21:39
I'm getting rather curious here, do you know what a hot tap is?  Have you ever performed the operation?  What part of the operation are you accountable for?  How will the tie in be accomplished? Drilling or torch or ??? 

Welding the branch in is not the actual 'hot tap'. 

Regardless of code and application all PQR/WPS's should be set up within the electrode manufacturer's recommended parameters.  Unless, of course, there is good reason to establish outside those boundaries and you can prove from the PQR that you are able to successfully accomplish that. 

If you, or the writer of the procedure, knows ANYTHING about welding you will know or be able to easily find those parameters and record them.  You don't want anyone else telling you, we could give you totally bogus info or at least what works for us may not be what will work correctly for your situation.  We know nothing about your equipment, personnel, electrode, weather, working conditions, other than you said it would be done with SMAW.  Not enough.

He Is In Control, Have a Great Day,  Brent
Parent - - By Trackergd (**) Date 07-29-2016 10:13
I wish I had some advice, but welding near anything flammable is not something I would ever do.  I would have the line shut down, drained, cleaned and purged.  Probably goes back to when my CH-47 crashed and I outran the crash truck crew trying to get away from the burning JP-4. :eek:
Parent - - By js55 (*****) Date 07-29-2016 12:42
Tracker,
Hot taps on live gas lines happen everyday without incident. But you need to know what you are doing.
Parent - By Trackergd (**) Date 07-29-2016 16:20
I'm sure they do kneed to know what they are doing.  Between the helicopter crash and my brother brazing up an empty gas tank, I am just going to say that is not in my skill set, and at 61, probably never will be. :lol:
- - By TRowe (*) Date 07-29-2016 20:35
Saroj,

Let me see if I can shed some light and direction.

In-service welding is a very safe process if, like it has been previously stated, "you know what you are doing". It seems your primary concern was the heat input of the welding on the pipe that is to remain in service.  The 2 main concerns should be, "avoiding burning through", which sounds like a concern of the yours based on the question related to the heat input and auto-ignition, and " hydrogen cracking".

API 1104 Appendix B (B.1 General) states :

Burning through - "Burning through is unlikely if the wall thickness is 0.250 in. (6.4 mm) or greater, provided that low-hydrogen electrodes (EXX18 type) and normal welding practices are used".

Burning through concern at this point of your query- greatly minimized.

Hydrogen Cracking: " For hydrogen cracking to occur, three conditions must be satisfied simultaneously. These conditions are: hydrogen in the weld, the development of a crack-susceptible weld micro-structure, and tensile stress acting on the weld".

This should be of great concern for future failure of the weld and should be addressed by a qualified individual.

I have welded on pipelines whose operating pressures were @ 1300 psi. For in-service welding the pressures/flow rates had to be lowered to
between 50-60% of the operating pressure before any welding would be allowed. While welding on this particular pipeline (LPG), I could be welding on a girth weld, "break arc", and before I could get my glove off and touch the pipe, where I had just finished welding, the pipe would be ice cold. "Perfect environment for cracking"

API 1107 Pipeline Welding Maintenance Practices is the most widely used recommended practice I have seen and used for in-service welding and the qualifying of welding procedures and welders. This is not to say that other codes or standards are not adequate, or that they do not address these concerns. This is what I am most familiar with.

Most of the welding procedures (API 1107) I have followed in the qualifying of a procedure or for welding on pipelines/piping that were in-service, have been thoroughly "worked over" from the top to the bottom by qualified individuals to address all welding concerns.

This is only the beginning to ensure the job is performed safely and everybody gets to go home.

A few other factors I would like to mention that must be addressed include, but are not limited to:

- prior to welding on the in-service pipe, the pipeline or pipe that is to be welded on (in-service) must be inspected visually where the actual welding is to occur for exterior/surface discontinuities (corrosion) that would suggest a loss of wall thickness. These must be identified and investigated by a qualified individual.

-Wall thicknesses must be determined (UT) where the actual welding is to occur for potential internal wall thickness loss. There should be within a procedure, a limited amount or percentage of pipe wall loss that is acceptable for welding, or not. If the pipe wall loss limits are exceeded, or the procedure does not allow any wall loss, welding in that location should not be performed and another location meeting the requirements should be used. These limits or percentages should be calculated by a qualified individual and known prior to welding.

-Flow rates and the associated pressures must be known and must be within the parameters set by the Company (Owner) or qualified individuals .

These are only a few, and there are many more factors that must be considered. Short cuts and a lack of knowledge are a perfect recipe for failure.

In-service welding is not something one must take lightly. However, if done properly and all the procedures are followed, I believe it to be safer than any other "tie-in" operation. I have safely completed, as have many others, countless in-service welds and hot-taps ranging in all sizes with varying wall thicknesses that included pipelines and piping that carried a variety of products that many would care not to even think about welding on for fear of catastrophe.

I would not hesitate to weld on any pipeline or pipe, regardless of the product it carries, provided all the "I's" were dotted and all the "T's" were crossed. If any thing were missing or something didn't feel right at any level, I would have to say "Spool me up, there's always tomorrow".

Hope this sheds some light.
Parent - - By Saroj Date 07-31-2016 12:15
All,
Thank you for your useful insights.I am learning still...
I have another query. The pipe to be hot tapped is internally coated with epoxy paint.
As per API RP 2207 it is not recommended to do hot tapping on internally lined/coated pipelines unless authorized by specialized procedures.
Kindly advise what is the way forward.
Parent - By kcd616 (***) Date 07-31-2016 13:29
this is just IMHO
run do not walk
get away from this
I see bad things coming:eek::sad:
I see an engineer thinking
this is almost as bad as marketing and IT people thinking
OXYMORON
those the 3 add in an inspector
you now have a 4 of a kind EPIC FAIL:sad::razz::evil::twisted::yell:
just my thoughts and experiences
sincerely,
Kent
P.S. : throw in an accountant now 5 of a kind
never beat for EPIC FAIL
Parent - - By welderbrent (*****) Date 07-31-2016 14:42
Sometimes you don't have a choice.  But that decision does not concern you, that is up to the Customer/owner and their engineers.  If they deem the hot tap a necessity and know the consequences of damaging the integrity of the coating thus shortening the life expectancy of the pipeline then that is their decision.  If you are part of that decision making process then obviously you are in way over your head and need to get someone else involved who knows what is going on and how to handle these things. 

The only other option is to totally shut down the line from further away in both directions, drain it, do the tie in (which then wouldn't really be a 'hot tap'), recoat the pipe and joint area effected by cutting and welding, and then open it back up to service.

Obviously, that totally disregards the advantages of doing a 'HOT TAP' but it all depends upon what is desirable in the finished product.

Note also, lines with this grade of fuel, will probably last longer without a lining than a lined pipe with water flowing through it.  And most of these lines don't have that long a life expectancy before being replaced because of system upgrades, modifications, remodeling, or total replacement due to relocation anyway. 

Again, the coating, since the system is sealed until tapped, won't bother the welding as it would in an open joint. And, with product keeping the area at a moderated temperature, the welding will have a minimal impact on the lining for much distance from the joint.  Having said that, once the lining is compromised in anyway it will continue to get worse with abrasive action of the product flow continually picking away at it.

Brent
Parent - - By Saroj Date 08-01-2016 09:55
All,
Our scope in this project is limited to providing design calculations to support hot tapping on this pipeline.
We had verified parameters like maximum allowable operating pressure during welding, allowable heat input based on WPS & allowable pr. differential with regards to run-pipe buckling.
Now client wants to know what is the minimum required flow to avoid brittle fracture due to too fast cooling of weld. Fluid velocity is 1.4 m/s.
Your inputs will be valuable.
Parent - - By Saroj Date 08-01-2016 10:23
I missed to add, line operating pressure is 305 psi
Parent - - By welderbrent (*****) Date 08-01-2016 14:10
Been a while, that pressure seems a little high for a 10" line.  Especially if it is normally flowing which stands to reason with jet fuel at a facility of any size. 

FAST cooling will not be a problem, it will be a steady heat and hard to get warm enough if not done properly.  But all this has been dealt with.  You really need to get a contractor on board with the proper experience and credentials to assist you with all the needed information.

There is a lot of info we don't have and are totally shooting in the dark to give you much of an answer.

Oh, been meaning to ask, we have some things going on with this forum and I would like to ask you a couple of other questions:
1) Are you an AWS member?
2) How did you hear about this forum?

Brent
Parent - - By Saroj Date 08-02-2016 09:21
Dear Brent,
I am not a AWS member.
AWS is a reputed organization which as a mechanical engineer i am supposed to be aware of...
I had query regarding welding, so while surfing internet for an answer i came across this forum.
Parent - By Lawrence (*****) Date 08-02-2016 11:15
Welcome to the forum Saroj !

We're glad you found us :)
Parent - By welderbrent (*****) Date 08-02-2016 21:40
As noted, the reason for asking is because of some upcoming proposed changes in who may access this forum.  Thank you for letting us know your membership status and how you found us.  This will not effect how, if, or content of answers to your query.

Brent
Parent - By TRowe (*) Date 08-01-2016 19:17
This might help with your design and cooling rate questions :

Pipeline Research Council International

PRCI Thermal analysis model for Hot-Tap welding, Version 4.2  / Catalog No. L51837;

PRCI Development of Simplified Weld Cooling Rate Models for In-Service Gas Pipelines / Catalog No. L51660.
Parent - - By Superflux (****) Date 07-31-2016 19:25
Sounds like a mock-up with ALL variables is in order.
Enough wall thickness and product flow gpm, it is do-able
Parent - By Saroj Date 08-03-2016 07:06 Edited 08-04-2016 14:03
All,

As per appendix C of DEP 31.38.60.10-Gen i am getting a pipe inner wall temperature of 550 deg celsius for fillet weld.
As per Battelle calculation there is no risk of burn through if temperature beneath the welding arc is less than 1800 F.
However, client wants us to do thermal analysis to verify the possibility of fast cooling of weld, brittle fracture and at the same time ensure service fluid does not reach its auto-ignition temperature.
Would like to know from the members here if there is a real need for such an analysis.
How is the output from thermal analysis going to be different from inference derived from above graphical method.
Are there alternative solutions like pre-heating, purging with hot nitrogen gas during welding to overcome fast cooling.
If in case we decide to go for analysis, is conjugate heat transfer analysis sufficient or the usual Battelle or PRCI model is necessary?
Your inputs will be valuable.
Up Topic Welding Industry / General Welding Discussion / Hot tapping of 10" API 5L pipe carrying Jet A1 fuel

Powered by mwForum 2.29.2 © 1999-2013 Markus Wichitill