Serendip Associates Pvt Ltd. Have pioneered the manufacture of ‘All Welded Shelters’ in the country. This is the most advanced Shelter construction practice and is the best suited for Shelters operating under extreme conditions of Nuclear, Biological and Chemical Attack

Welded Shelters offer the following advantages over riveted Shelters

Riveted Shelters are assembled by riveting the Shelter Panels. Thousands of holes are drilled into the Shelter panels, for riveting during assembly. These holes offer leakage points for rain, dust, Nuclear, Biological and Chemical Agents etc. The sealing efficiency of the riveted holes, degrade with time in deployment.

Welded Shelters are assembled by welding the external and internal joints between the panels. The requirement of drilling numerous rivet holes for assembly is eliminated. The Shelters forms a hermetically sealed enclosure against rain, dust, Nuclear, Biological and Chemical agents. The sealing efficiency of the joints does not degrade with time in deployment. Welded Shelters have a longer performance life than riveted Shelters.

These numerous riveted holes in the Shelter are sealed against ingress of rain water, dust, B & C agents etc by application of a suitable sealant. The efficiency of this seal degrades with time and leads to problem of rain water leakage, dust entry, entry of B&C contaminations etc

Welded Shelters do not use sealant for sealing of joints. The welded joints provide environmental protection for longer durations of time, without degradation. The sealing against Biological & Chemical agents is perfect

The thousands of rivet holes in the Shelter offer points for leakage of Electromagnetic radiations. The impedance of the riveted joints is high. Riveted Shelters exhibit low and inconsistent levels of EMI Shielding, which degrade with time in deployment

Welded Shelters offer low joint impedance and higher, consistent levels of EMI attenuation. (See attached EMITR comparison). Both the inner and outer panel joints are welded, achieving the DEI (Double Electrically Isolated) concept of Shielding. In DEI, there are two EMI shielded enclosures, one floating within the other and electrically connected at one point, i.e. the EMI shielded door. (Practically connecting the two shields at a single point is not achievable due to the presence of cutouts, A/c cutouts, Doors etc) Welded Shelters exhibit high and consistent levels of EMI Shielding, which does not degrade with time.

The welded doors are manufactured by welding aluminum door and door post extrusions. The door post frame is welded into the aluminum grid structure of the Shelter panels. The facing of the panels, are welded continuously all around the edges of the door post. This ensures a perfect electrical continuity. The door post incorporates EMI / EMP gaskets.

The door panel is manufactured the same way as the door post. The facing of the door panel are welded into the door profiles all around the edges. The door profiles have knife edges that press into the EMI gaskets in door post. Also a weather gasket is provided in the door panel.

These doors provide better environmental sealing and EMI attenuation properties.

Welding of joints ensures a perfect hermetically sealed enclosure against ingress of Biological and           Chemical agents. The joints exhibit much better sealing than riveted joints, where there is possibility of leakage of B&C agents. Welded shelters fitted with Biological and Chemical        Ventilation system, offer the best protection against Biological and Chemical agents

The Welded Shelters are more efficient than riveted shelters in resisting the high pressure blast environments encountered during nuclear attacks.

During the nuclear blast, due to the wave of high pressure energy even tiny particles like stones, pebbles etc are converted into high velocity ballistic missiles that can damage the outer skin of the Shelter panels. Ballistic (Bullet Proof) panels of Aramide fibers can be provided on the outer surface of the panels to provide ballistic protection (say level II, NIJ stds).

When a Shelter passes through areas of N, B, & C contamination, it needs to be de-contaminated. The NBC agents collect over points like, the rivet heads, heads of fasteners, etc. As these collection points are minimized in welded Shelters, they are easier to decontaminate than riveted Shelters.

Page 7-10, para 7.4.2.1 Welding : which states that in terms of  electrical performance, welding is the ideal method of bonding.

Page 7-15 – 7-17, para 7.4.2.5 Rivets ; which states that riveting can cause bowing of the stock between the rivets. In the bowed or warped regions, metal to metal contact may be slight or non-existant, which allow RF energy to leak through and can be major cause of poor RF shield performance.

Table 7.2 Ratings of Selected Bonding Techniques, which rates gas welding as 10 in both electrical and mechanical properties.

Page 10-13 , para 10.4.1.1 shield : which states that for a HEMP (High altitude EMP) barrier, Shield assembly is typically accomplished by continuous welding, in order to minimize the number of discontinuities in the shield.

Page 1-173, para 1.10.2 EMP shield applications and para 1.10.3 EMP bonding practices which state that homogenous welding is to be used whenever possible because they offer the best protection against penetration of EMP signals.

2.0 An extract from Shelter catalogue from M/s Zeppelin, who are one of the few in the world having the technology of welding the structural sandwich panels to form Shelters.

Para 2 : Construction: This states that panels are internally joined by riveting and the external joints are welded to obtain a fully hermetic enclosure.

(We at Serendip Associates Pvt Ltd have developed the technology of continuous welding of both the internal and external joints between the panels, to result in the DEI or Double Electrically Isolated shelter construction for increased EMI/EMP attenuation levels).

Para 4.5 (N) EMP shielding, where the levels of EMI/EMP attenuation achieved are graphically represented.

Welded shelters provide better sealing against the ingress of Biological and Chemical agents. This is due to the bonding achieved by fusing the metal at the joints.

MIL-HDBK-784 – Guidelines – Design to minimize contamination and to facilitate decontamination of military vehicles and other equipments : Interiors and exteriors

Lapped surface, page 12 & 13, which indicates that welded joints are the most preferred for equipments that pass through NBC contaminated areas. Welded Shelters have all welded joints between the panels. There is no crevice between the sheets that can trap NBC Contaminants.

Riveted Joints: page 14, which states that rivets may loosen due to vibration, or faulty installation. NBC contaminants may be drawn into the capillary under the fastener head and even along the shank into the interior spaces. Decontamination by chemical means is impossible. NBC agents can leak into the enclosure.

Welded joints: page 15, which states that where ever feasible, permanent fasteners (rivets) should be eliminated by using welding. Welded shelters do not use rivets in the assembly of panels.

JSS : 5411 - 01 : 2004 - GENERAL REQUIREMENT OF RADAR SHELTERS

Page 8 : EMI / EMC Shelters : " The individual panels should be joined by welding on the outside .........."

Neither the NBC agents itself, nor the exposure can be controlled by design, but design can reduce the amount of agent remaining on the equipment. From the stand point of decontamination efficiency and effectiveness, the best design is the one that minimizes the effort or the need for decontamination. Welded shelters achieve these two design requirements by the elimination of surface configurations and crevices that may trap or retain NBC contaminants.