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
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
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
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.
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
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.