Process Specification for Manual Hot Gas Welding of Non Structural
Thermoplastic Hardware

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| **Engineering Directorate**                                           |
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| **Structural Engineering Division**                                   |
|                                                                       |
| **November 2002**                                                     |
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| ![](media/image1.png){width="1.3944444444444444in" height="1.15in"}   |
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| National Aeronautics and                                              |
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| Space Administration                                                  |
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| **Lyndon B. Johnson Space Center**                                    |
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| Houston, Texas                                                        |
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**Process Specification for Manual Hot Gas Welding of Non Structural
Thermoplastic Hardware**

+---------------+-----------------------------+-----+------------------+
| **Prepared by | #### **Signature on File**  |     | 11/12/02         |
| :**           |                             |     |                  |
+---------------+-----------------------------+-----+------------------+
|               | Michael E. Fowler           |     | Date             |
|               |                             |     |                  |
|               | Manufacturing Engineering   |     |                  |
|               | and Integration Branch/ES6  |     |                  |
+---------------+-----------------------------+-----+------------------+
|               | ####                        |     | 11/18/02         |
|               |                             |     |                  |
|               | ###### Signature on File    |     |                  |
+---------------+-----------------------------+-----+------------------+
|               | Daniel J. Rybicki           |     | Date             |
|               |                             |     |                  |
|               | Materials and Processes     |     |                  |
|               |                             |     |                  |
|               | Technology Branch/ES4       |     |                  |
+---------------+-----------------------------+-----+------------------+

+---------------+----------------------------+-----+-----------------+
| **Approved    | #### **Signature on File** |     | 11/13/02        |
| by:**         |                            |     |                 |
+---------------+----------------------------+-----+-----------------+
|               | Gail K. Horiuchi, Chief    |     | Date            |
|               |                            |     |                 |
|               | Materials and Processes    |     |                 |
|               | Technology Branch/EM2      |     |                 |
+---------------+----------------------------+-----+-----------------+

  ----------- ---------------------------------------------- --------------
  REVISIONS                                                  

  VERSION     CHANGES                                        DATE

  Baseline    Original version                               10/29/99

  A           Reviewed per QMS requirement. Removed          11/25/02
              references to old division name.               
  ----------- ---------------------------------------------- --------------

# **1.0 SCOPE**

This process specification provides the minimum requirements that govern
the manual welding of non-structural, non-flight thermoplastic hardware.
Procedural and quality assurance requirements are given. All work
instructions used during welding shall satisfy the requirements of this
process specification and its applicable documents.

# **2.0 APPLICABILITY**

This process specification applies to manual arc welding of
non-structural, non-flight hardware that is fabricated on-site and under
the authority of NASA/Johnson Space Center (JSC) by manually applied Hot
Gas Welding process.

The term "non-structural hardware" refers to hardware that is
non-critical and is not flight related, man rated, load bearing, or
pressure retaining or shall not create a hazard to personnel or related
equipment in the event of failure.

# **3.0 USAGE**

This process specification shall be called out on the engineering sketch
or drawing by a drawing note with the following general format. Official
engineering drawings are not required for hardware fabricated under this
specification:

**WELD AND INSPECT PER NASA/JSC PRC-0012**

## 

1.  **[DESIGN REQUIREMENTS]{.underline}**

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a.  The design of welded joints shall conform to the applicable hardware
    design handbooks contained in the Engineering Standards Library.

b.  All engineering drawings shall depict welded joints using the
    applicable symbols described in AWS A2.4.

c.  Groove welded joints are preferred and shall be full penetration or
    shall have a reinforcement backing/splice plate attached to the side
    opposite the weld.

d.  Weld filler material shall be specified on the engineering drawing
    in the parts list or as a drawing note.

e.  Weld filler material shall be of the same polymer group as the base
    material.

## **4.0 [WORK INSTRUCTIONS]{.underline}**

Work instructions shall be generated for implementing this process
specification. The work instructions shall contain sufficient detail to
ensure that the manufacturing process produces consistent, repeatable
products that comply with this specification. At JSC, these work
instructions are approved as Detailed Process Instructions (DPIs) that
describe in a detailed, step-by-step format the required procedures,
equipment, and materials to be used for conducting a given process.

## 

# **5.0 REFERENCES**

The standards listed below shall be considered a part of this
specification.

**American Welding Society (AWS) Standards**

ANSI/AWS A2.4 Standard Symbols for Welding, Brazing and Nondestructive
Testing

ANSI/AWS A3.0 Standard Welding Terms and Definitions

**6.0 [MATERIAL REQUIREMENTS]{.underline}**

All materials used in the welding of hardware, including the base
materials, shall meet the requirements of an applicable JSC material
specification, commercial specification, or manufacturer's
specification.

Welding filler material shall be stored in clean, dry areas protected
from contamination and physical damage. Specific conditions of storage
and handling shall conform to the manufacturer's recommendations at a
minimum.

Inert gases shall be a standard welding grade or equivalent.

**7.0 [PROCESS REQUIREMENTS.]{.underline}**

All weldments fabricated in accordance with this process specification
shall meet the requirements of the applicable standards listed herein
based on the design and intended function of the hardware.

**7.1 WELDING PROCEDURES**

No specific Welding Procedure Specification (WPS) is required for
hardware fabricated to this specification.

**7.2 PROCESS VARIABLES**

**7.2.1 [Gases]{.underline}**

When compressed air is used as the process gas, it shall be dry and free
of oils and other contaminants harmful to the weld and welding
equipment.

Where excessive oxidation of the weld and adjacent surfaces are expected
to be a problem, an inert gas shall be used as the process gas during
welding. Pure argon or helium, or any mixture of these two gases may be
used.

Polyethylene (PE) shall only be welded with an inert gas. Compressed air
shall not be used for welding PE.

**7.2.2 [Cleaning]{.underline}**

Materials and agents that are selected to clean the material surfaces
prior to and after welding shall not be capable of softening or
decomposing (e.g., solvents) the base/weld material.

**7.2.3 [Tack Welding]{.underline}**

Tack welds shall be placed so that they will be completely consumed by
the finished weld.

##### 

##### 7.2.4 [Preweld Setup]{.underline}

The welder shall perform practice welds on scrap material prior to
beginning the production welding to ensure that the equipment setup
(e.g., gas pressure and flow, tip configuration, etc.) and technique
will produce sound welds and will not cause overheating (i.e.,
scorching, burning) or other deleterious condition to occur at the weld
joint area.

**8.0 [QUALIFICATION REQUIREMENTS]{.underline}**

No specific personnel or procedural certification is required to perform
the process to this specification however, welders shall be skilled and
proficient in the application of the process as determined by the
fabricating organization. To facilitate on-the-job training, personnel
in training may be allowed to weld on hardware fabricated under this
specification however, only under the supervision of a welder skilled
and proficient in the process.

# 

**9.0 [VISUAL EXAMINATION REQUIREMENTS]{.underline}**

The welder shall visually inspect all weld joints. The welds shall be
inspected in their finished condition as specified on the engineering
drawing. The welds shall conform to the following visual inspection
criteria:

a)  All welds shall reflect good shop practice and good workmanship
    pertinent to the material being joined.

b)  All welds shall be free of cracks, excessive oxidation and evidence
    of excessive heating (scorching, burning).

c)  The edges of all welds shall blend smoothly into the adjacent base
    material and shall be free of sharp notches or ridges.

d)  Butt welds shall show evidence of full penetration or shall be
    welded from both sides unless a backing/splice plate has been
    employed in the design.

e)  Welds shall exhibit a smooth surface contour that is flat, slightly
    convex, or slightly concave. Concavity and underfill of butt welds
    that do not employ backing or splice plates for reinforcement shall
    not exceed 20% of the base material thickness.

f)  Welds that have been dressed or have had the reinforcement removed
    shall exhibit a 125 *μ-*in or smoother finish.