HOT PASS

[srinivas rao]

Hi Gents,

I have  doubt reg HOT PASS.

1. what is the purpose of doing HOT PASS with more speed and high current?

2. Should the Welding Process used for Root be the same for HOT PASS? If not necessarily then how should we decide?

Thank you All

Regards,

Vasu

[yogesh]

** More current is required to melt the already solidified root + the
slag deposits if any lying on the root pass needs more current to melt
on

** not neccesarily ,welding process in hot pass need not be same


yogesh

[Sundaram Sundaram]

My dear Yogesh,

                           In my opinion the slag is high melting point compound and it will not melt during the hot pass(in a short span of time).But it will remain as a inclusion if it is present in the weld
With thanks & regards,

N.Shanmuga sundaram

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[M.Shankar]

Hi Mr. Rao

About & Purpose "HOT PASS"

The surface of a root pass may be irregular, have undercut, overlap, slag incl., or other defects, depending upon the type of weld and the condition of the root pass. The surface of a root can be cleaned by grinding or hot pass.

A hot pass can be used to correct some of the problems caused by a poor root pass. The hot pass may be a hotter than normal filler pass or it may be made without adding extra filler.

A hot pass can be used to correct incomplete root fusion or excessive concavity of the root surface, and improper penetration also.

Eg.1: Improper fusion generally is caused by insufficient heat and temperature for the joint. To correct this condition, a hot pass is used without adding more filler metal.

Eg.2: Concave root surface are generally caused by insufficient filler metal for the joint. To correct this condition, a “ hot filler pass” is used to add both the needed metal and heat.

The hot pass should be conducted the same as the first welding process, but depends on your situation. 

Eg. In piping if you use GTAW for root pass, then hot pass should be GTAW-it is preferable. If the welder grind the root to remove defects as stated above, he may remove root completely at any point (accidently), so in this case same welding process is preferred to cover root & your WPS.

The hot pass generally uses a higher than normal amperage setting (approx. 10% higher than root amps setting)  and a fast travel speed.

 

 

Rgds/shankar

---

From: srinivas rao <ksr...@gmail.com>
To: material...@googlegroups.com
Sent: Thu, 25 November, 2010 12:46:43 AM
Subject: [MW:8366] HOT PASS

[Majdi N Elyyan]

Dear All;

 

We have a hot tap on LPG line (Sour service) which require PWHT.

The run Pipe is 4”, the branch is also 4”, split tee will be used.

As per shell DEP-31.38.60.10 – for Hot tapping, clearly mention:

Hot-tap welding should not normally be performed on materials which require post-weld

heat treatment. However, if stress relieving or post-weld heat treatment is required, a

specialist shall be consulted to assess whether it is feasible to make the specific

hot-tapping operation with post-weld heat treatment.

Note: Stress-relieving may be required if a material is susceptible to stress corrosion cracking and post-weld

heat treatment may be specified by the design code if the wall thickness is greater than a certain limit.

 

& since we have no other options, we have to do the hot tap on the same, kindly advice WPS & PWHT procedures

 

Thank all in advance..

 

Regards

Majdi Elyyan

[manoj vernekar]

see here weldment is and HAZ is not coming in contact with process fluid.

 

 two buttweld you can weld with back strip in place,

 

 two fillet weld, as  we weld support where we are not performing any PWHT.

 

regards

 

manoj

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Manoj.Vernekar

[limesh M]

Dear Majdi,

 

You didn't mention the material designation(pipe and split tee material) and thickness of the pipe/split tee material.If you could provide it,it will be easy for experts to analyse your query.I also have interest in this matter.

 

 

Regards,

 

Limesh

On Sun, Nov 28, 2010 at 6:45 PM, Majdi N Elyyan <mel...@gmail.com> wrote:

--

[hemant solanki]

If thickness is coming out more than code requirement, you may have to do PWHT. For on line service welding, PWHT is not practically possible at site. You may have to choose compatible material, FEA analysis, ECA analysis..


Thanks,
H Solanki

On Mon, 29 Nov 2010 09:03:56 +0530 "Majdi N Elyyan" wrote

>

Dear All;

We have a hot tap on LPG line (Sour service) which require PWHT.

The run Pipe is 4”, the branch is also 4”, split tee will be used.

As per shell DEP-31.38.60.10 – for Hot tapping, clearly mention:

Hot-tap welding should not normally be performed on materials which require post-weld

heat treatment. However, if stress relieving or post-weld heat treatment is required, a

specialist shall be consulted to assess whether it is feasible to make the specific

hot-tapping operation with post-weld heat treatment.

Note: Stress-relieving may be required if a material is susceptible to stress corrosion cracking and post-weld

heat treatment may be specified by the design code if the wall thickness is greater than a certain limit.

& since we have no other options, we have to do the hot tap on the same, kindly advice WPS & PWHT procedures

Thank all in advance..

Regards

Majdi Elyyan

--
>To post to this group, send email to material...@googlegroups.com
>To unsubscribe from this group, send email to materials-weld...@googlegroups.com
>For more options, visit this group's bolg at http://materials-welding.blogspot.com/
>The views expressed/exchnaged in this group are members personel views and meant for educational purposes only, Users must take their own decisions w.r.t. applicable code/standard/contract documents.
>

[Shashank Vagal]

Hi Vasu, The main function of a hot pass is to provide feed to the shrinking root pass weld metal lest it shrink-cracks. The root pass has to penetrate and fill the root gap and initiate the joint. Once it gets a proper metal feed by way of a hot pass, it will do its job well. That is why HP is conducted immediately after the root cleaning operation is over and the root pass is still hot, hence maintaining the same welding set up as used for root pass (and welders) is highly recommended. It can be seen then why: The hot pass generally uses a higher than normal amperage setting (approx. 10% higher than root amps setting)  and a fast travel speed. The latter to reach all shrinking areas in time. No welding will stop before RP+HP are complete as a minimum. Shashank Vagal --- On Sun, 28/11/10, M.Shankar <mails_...@yahoo.co.in> wrote:

[Majdi N Elyyan]

Dear Limesh & All;

 

Thanx for your replies & advices.

 

The materials is A 106 Gr B, pipe Dia is 4” Sch 40, & we are using split tee 15 mm thick.

 

The same I had in my previous works, the issue were to qualified the welders for Temper Bead Procedure (Half bead). As per QW-290.

 

The surprise here for the client & client TPI, that, client TPI is asking to make a heating up to 300C for 30 to 60 min after completing the welding (which I search everywhere, I didn’t find such procedure in any relevant standards.)

The second surprising thing is my client, is asking to make preheating to 350C for 3 hours before starting the work plus hydrogen baking.

 

My point is, the life line is wet LPG, H2S present 2500 PPM, which is very high, plus if I keep heating the line up to this temperature, I need to ensure it will not imply any unwarranted impacts , thus jeopardizing the operational LPG unit itself.

 

 

Regards

Majdi Elyyan

[pgoswami]

Mr. Majdi,

 

Hot tap operation is a combination of many variables, welding is only one of them,though it's critical for any hot tapping operation. Note Hot Tap could lead to serious fatalities if not done properly. Since you mentioned about Shell's DEP, please note these DEP's are well respected in the industry. That does not mean what's written is absolutely unquestionable, but there're good rationale on what's written in the DEP's.

 

DEP 31.38.60.10-Gen, HOT-TAPPING ON PIPELINES, PIPING AND EQUIPMENT is quite detailed. Some important extracts are very relevant to your queries and would clear the doubts why the practice of hot tapping is not permitted as a general rule.

JUSTIFICATION FOR HOT-TAPPING:-Hot-tapping is potentially hazardous and therefore should only be undertaken when continuity of service is essential or shutdown of the system is impractical and when it is shown to be technically feasible and to offer a clear advantage over alternatives. The advantage may be economic and, in some situations, the safety and environmental risks may be less than those associated with more conventional methods.A decision on whether hot-tapping is to be applied shall be based on careful considerations including at least the following aspects:

• safety;
• condition of the pipe/equipment under consideration;
• configuration of the connection;
• code/statutory requirements;
• operating conditions;
• technical capabilities of the drilling equipment under the operating conditions (pressure, temperature, nature of product);
• related welding problems;
• economic aspects;
• environmental/pollution aspects.

If hot-tapping is to be applied under conditions approaching the technical or operational limits as defined in this DEP, specialist advice should be sought.

MATERIALS:-This DEP is relevant only to hot-tapping on carbon, carbon-manganese and high-strength low-alloy steels (e.g. ISO 3183 L245 to L485 or API 5L grades B to X70). Materials for pipelines and on-plot piping shall comply with the requirements of the piping classes DEP 31.38.01.12-Gen. and DEP 31.38.01.15 Gen. If it is proposed to hot-tap other materials, specialist materials/welding engineers shall be consulted and a specific procedure shall be developed. Current experience is limited to L450 (X65) materials (see also BS 6990) and therefore special attention should be given to procedures to be developed for higher grade materials.

It shall be ensured that during the welding operation the material in the region of the weld pool has sufficient strength to contain safely the internal pressure and avoid a blow-out.

The risk of blow-out is dependent upon a complex interaction of welding conditions, pipe material, pipe thickness, pipe temperature and hoop stress. For materials of yield strength not greater than 450 N/mm2, operating at temperatures of not greater than 350 °C and with a hoop stress of not greater than 72 % of the specified minimum yield stress, blow-out can be prevented during welding provided the minimum pipe thickness is not less than 5 mm.

The actual minimum wall thickness shall be determined by ultrasonic testing. For other materials or conditions, a minimum pipe thickness shall be determined, based on either specific previous experience and/or data from trials.

NOTE: For some products, due to chemical reaction, the safe pipe temperature might be much lower than350 °C (See also BS 6990).

Fitting and branch material shall be of a type and grade compatible with the material of the run-pipe to be hot-tapped, including sour service requirements where applicable.

Hot-tap welding should not normally be performed on materials which require post-weld heat treatment. However, if stress relieving or post-weld heat treatment is required, a specialist shall be consulted to assess whether it is feasible to make the specific hot-tapping operation with post-weld heat treatment.

Note: Stress-relieving may be required if a material is susceptible to stress corrosion cracking and post-weld heat treatment may be specified by the design code if the wall thickness is greater than a certain limit. Welding shall not be performed on lined, clad or internally coated pipe.

Hot-tap welding shall not be performed on the following materials:

- any material with a maximum allowable operating temperature greater than 370 °C;

- pipelines and on-plot piping where the minimum allowable operating temperature is less than -20 °C. For minimum allowable operating temperatures between -20 °C and 0 °C, additional attention shall be given to ensuring adequate material toughness

 PROCESS FLUIDS:- Hot tapping shall only be performed under the following conditions:

- the contained process fluids remain stable when subjected to the high metal temperatures (see 3.3) during welding;

- the process fluids remain stable when in contact with air during drilling and perforation operations;

- there shall be no decomposition or chemical reaction between components of the contained fluid (explosion, ignition, exothermic reaction);

- there shall be no chemical reaction between the fluid and the hot containment wall(burning, (stress) corrosion, embrittlement).

 These requirements lead to a number of situations in which welding operations are prohibited on equipment which contains:

- Mixtures of gases or vapours within their flammable range or which may become flammable as a result of heat input in welding operations.

- Substances which may undergo reaction or decomposition leading to a dangerous increase in pressure, explosion or attack on metal. In this context, attention is drawn to the possibility that under certain combinations of concentration, temperature and pressure, acetylene, ethylene and other unsaturated hydrocarbons may decompose   explosively, initiated by a welding hot spot.-- How about LPG- Does it fit into this category??

- Oxygen-enriched atmospheres in the presence of hydrocarbons which may be present   either in the atmosphere or deposited on the inside surface of the equipment or pipe.

- Compressed air in the presence of hydrocarbons which may be present either in the air   or deposited on the inside surfaces of the equipment or pipe.

- Gaseous mixtures in which the partial pressure of hydrogen exceeds 700 kPa (ga),except where evidence from tests has demonstrated that hot-tapping can be done  safely. 

Based on the above, welding on equipment or pipe which contains hazardous substances   or conditions as listed below (even in small quantities) shall not be performed unless   positive evidence has been obtained that welding/hot tapping can be applied safely.  

 Substances:   Acetylene;Acetonitrile;Butadiene;Caustic soda;*Chlorine;Compressed air at a pressure in excess of 3 000 kPa (ga);Ethylene;Ethylene oxide;Fat/lean DEA/MEA;HP steam (pressure in excess of 5 000 kPa (ga));Hydrogen (partial pressure in excess of 700 kPa (ga)); Hydrogen sulphide;*Hydrofluoric acid;Oxygen;Propene;Propene oxide;   Sulphuric acid;

 

I would think if the environment contains both LPG (which is flammable) and 2500 ppm of H2S which could be toxic in case of any leakage, a proper way would be to drain the line  purge and then perform hot tapping or weld followed by PWHT as required. Not only that wet H2S could cause typical issues related to wet H2S cracking. Hence you need to establish a welding procedure with controlled hardness.

 

The attached article is a good educative document on hot tapping in sour services.

 

Thanks.

 

Pradip Goswami,P.Eng.IWE

Welding & Metallurgical Specialist & Consultant

Email-pgoswami@sympatico.ca,

pgos...@quickclic.net

 

---

From: material...@googlegroups.com [mailto:material...@googlegroups.com] On Behalf Of Majdi N Elyyan
Sent: Tuesday, November 30, 2010 9:36 AM
To: material...@googlegroups.com
Subject: RE: [MW:8441] HOTTAP on SOUR LINE (PWHT Required)

[N VENKATESWARA PRASAD]

Dear Mr. Majdi,

Good Morning.

We are planning to do hop tapping of LPG pipe lines at Oman. Hope you
might have completed the hot tapping of LPG.

Can you please share your experience of the same. Please give details
of firm who has done this work.

Can you please give details ie. which country this hot tapping is
done, what are the problems faced and extra precautions followed. Can
you please give your contact no, so that i will contact you.

Regards

N.V. PRASAD

On 11/28/10, Majdi N Elyyan <mel...@gmail.com> wrote:
> Dear All;
>
>
>
> We have a hot tap on LPG line (Sour service) which require PWHT.
>
> The run Pipe is 4", the branch is also 4", split tee will be used.
>

> As per shell DEP-31.38.60.10 - for Hot tapping, clearly mention:

>
> Hot-tap welding should not normally be performed on materials which require
> post-weld
>
> heat treatment. However, if stress relieving or post-weld heat treatment is
> required, a
>
> specialist shall be consulted to assess whether it is feasible to make the
> specific
>
> hot-tapping operation with post-weld heat treatment.
>
> Note: Stress-relieving may be required if a material is susceptible to
> stress corrosion cracking and post-weld
>
> heat treatment may be specified by the design code if the wall thickness is
> greater than a certain limit.
>
>
>
> & since we have no other options, we have to do the hot tap on the same,
> kindly advice WPS & PWHT procedures
>
>
>
> Thank all in advance..
>
>
>
> Regards
>
> Majdi Elyyan
>